Change search
Refine search result
1 - 44 of 44
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Rows per page
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sort
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
Select
The maximal number of hits you can export is 250. When you want to export more records please use the Create feeds function.
  • 1.
    Castro, Vasco
    et al.
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Stevensson, Baltzar
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Dvinskikh, Sergey V.
    Division of Physical Chemistry, Royal Institute of Technology, SE-10044 Stockholm, Sweden.
    Högberg, Carl-Johan
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Lyubartsev, Alexander P.
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Zimmermann, Herbert
    Department of Biophysics, Max-Planck-Institut für Medizinische Forschung, Jahnstrasse 29, D-69120 Heidelberg, Germany.
    Sandström, Dick
    Bruker BioSpin Scandinavia AB, Polygonvägen 79, SE-187 66 Täby, Sweden.
    Maliniak, Arnold
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    NMR investigations of interactions between anesthetics and lipid bilayers2008In: Biochimica et Biophysica Acta - Biomembranes, ISSN 0005-2736, E-ISSN 1879-2642, Vol. 1178, no 11, p. 2604-2611Article in journal (Refereed)
    Abstract [en]

    Interactions between anesthetics (lidocaine and short chain alcohols) and lipid membranes formed by dimyristoylphosphatidylcholine (DMPC) were studied using NMR spectroscopy. The orientational order of lidocaine was investigated using deuterium NMR on a selectively labelled compound whereas segmental ordering in the lipids was probed by two-dimensional 1H–13C separated local field experiments under magic-angle spinning conditions. In addition, trajectories generated in molecular dynamics (MD) computer simulations were used for interpretation of the experimental results. Separate simulations were carried out with charged and uncharged lidocaine molecules. Reasonable agreement between experimental dipolar interactions and the calculated counterparts was observed. Our results clearly show that charged lidocaine affects significantly the lipid headgroup. In particular the ordering of the lipids is increased accompanied by drastic changes in the orientation of the P–N vector in the choline group.

  • 2.
    Dvinskikh, Sergey V.
    et al.
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Thaning, Johan
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Stevensson, Baltzar
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Jansson, Kjell
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Kumar, Sandeep
    Raman Research Institute, C. V. Raman Avenue, Bangalore 560 080, India.
    Zimmermann, Herbert
    Department of Biomedical Optics, Max-Planck-Institut für Medizinische Forschung, Jahnstrasse 29, D-69120 Heidelberg, Germany.
    Maliniak, Arnold
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Mesomorphism in columnar phases studied by solid-state nuclear magnetic resonance2006In: Physical Review E. Statistical, Nonlinear, and Soft Matter Physics: Statistical Physics, Plasmas, Fluids, and Related Interdisciplinary Topics, ISSN 1063-651X, E-ISSN 1095-3787, Vol. 74, no 2, p. 021703-Article in journal (Refereed)
    Abstract [en]

    In this paper, we present 13C and 1H NMR investigations of 2, 3, 6, 7, 10, 11-hexahexyl-thiotriphenylene (HHTT). The measurements were carried out under both static and magic-angle spinning conditions. The phase diagram of HHTT is K↔H↔Dhd↔I, where H is a helical phase and Dhd is a columnar liquid crystal. The motivation was to characterize the molecular order and dynamics and to investigate differences at the molecular level between the two mesophases: H and Dhd. It is shown that Dhd is a conventional columnar liquid crystal, where the molecular core undergoes fast rotation about the symmetry axis. The orientational order in this mesophase is lower and the temperature dependence of the order parameter is steeper than in other triphenylene-based compounds. On the other hand, in the helical phase the core, similarly to the solid phase, is essentially rigid. The difference between the solid and helical phases is mainly manifested in an increased mobility of the aliphatic chains observed in the latter phase. In addition, the sample exhibits thermal history effects, which are observed in the different behavior upon cooling and heating.

    © 2006 The American Physical Society

  • 3.
    Gunawidjaja, Philips N.
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Lo, Andy Y.H.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Izquierdo-Barba, Isabel
    Garcia, Ana
    Arcos, Daniel
    Stevensson, Baltzar
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Grins, Jekabs
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Vallet-Regi, Maria
    Edén, Mattias
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Biomimetic Apatite Mineralization Mechanisms of Mesoporous Bioactive Glasses as Probed by Multinuclear ³¹P, ²⁹Si, ²³Na and ¹³C Solid State NMR2010In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 114, no 45, p. 19345-19356Article in journal (Refereed)
    Abstract [en]

    An array of magic-angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy experiments is applied to explore the surface reactions of a mesoporous bioactive glass (MBG) of composition Ca0.10Si0.85P0.04O1.90 when subjected to a simulated body fluid (SBF) for variable intervals. Powder X-ray diffraction and 31P NMR techniques are employed to quantitatively monitor the formation of an initially amorphous calcium phosphate surface layer and its subsequent crystallization into hydroxycarbonate apatite (HCA). Prior to the onset of HCA formation, 1H → 29Si cross-polarization (CP) NMR evidence dissolution of calcium ions; a slightly increased connectivity of the speciation of silicate ions is observed at the MBG surface over 1 week of SBF exposure. The incorporation of carbonate and sodium ions into the bioactive orthophosphate surface layer is explored by 1H → 13C CPMAS and 23Na NMR, respectively. We discuss similarities and distinctions in composition−bioactivity relationships established for traditional melt-prepared bioglasses compared to MBGs. The high bioactivity of phosphorus-bearing MBGs is rationalized to stem from an acceleration of their surface reactions due to presence of amorphous calcium orthophosphate clusters of the MBG pore wall.

  • 4.
    Iftekhar, Shahriar
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Physical Chemistry.
    Pahari, Bholanath
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Physical Chemistry.
    Okhotnikov, Kirill
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Physical Chemistry.
    Jaworski, Aleksander
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Physical Chemistry.
    Stevensson, Baltzar
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Physical Chemistry.
    Grins, Jekabs
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Inorganic and Structural Chemistry.
    Eden, Mattias
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Physical Chemistry.
    Properties and Structures of RE2O3-Al2O3-SiO2 (RE=Y, Lu) Glasses Probed by Molecular Dynamics Simulations and Solid-State NMR: The Roles of Aluminum and Rare-Earth Ions for Dictating the Microhardness2012In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 116, no 34, p. 18394-18406Article in journal (Refereed)
    Abstract [en]

    By combining molecular dynamics (MD) simulations with Si-29 and Al-27 magic-angle spinning nuclear magnetic resonance (NMR) spectroscopy, we present a comprehensive structural report on rare-earth (RE) aluminosilicate (AS) glasses of the RE2O3-Al2O3-SiO2 (RE = Y, Lu) systems, where the latter is studied for the first time. The structural variations stemming from changes in the glass composition within each RE system as well as the effects of the increased cation field-strength (CFS) of Lu3+ relative to Y3+-are explored and correlated to measured physical properties, such as density, molar volume, glass transition temperature, and Vickers hardness (H-V). Si-29 NMR reveals a pronounced network ordering for an increase in either the RE or Al content of the glass. Al mainly assumes tetrahedral coordination, but significant AlO5 and AlO6 populations are present in all structures, with elevated amounts in the Lu-bearing glasses compared to their Y analogues. The MD-derived oxygen speciation comprises up to 3% of free O2- ions, as well as non-negligible amounts (4-19%) of O-[3] coordinations (oxygen triclusters). While the SiO4 groups mainly accommodate the nonbridging oxygen ions, a significant fraction thereof is located at the AlO4 tetrahedra, in contrast to the scenario of analogous alkali- and alkaline-earth metal-based AS glasses. The average coordination numbers (CNs) of Al and RE progressively increase for decreasing Si content of the glass, with the average CN of the RE3+ ions depending linearly on both the amount of Si and the fraction of AlO5 groups in the structure. The Vickers hardness correlates strongly with the average CN of Al, in turn dictated by the CFS and content of the RE3+ ions. This is to our knowledge the first structural rationalization of the well-known compositional dependence of H-V in RE bearing AS glasses.

  • 5.
    Jaworski, Aleksander
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Charpentier, Thibault
    Stevensson, Baltzar
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Edén, Mattias
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Scandium and Yttrium Environments in Aluminosilicate Glasses Unveiled by Sc-45/Y-89 NMR Spectroscopy and DFT Calculations: What Structural Factors Dictate the Chemical Shifts?2017In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 121, no 34, p. 18815-18829Article in journal (Refereed)
    Abstract [en]

    Aluminosilicate (AS) glasses incorporating rare-earth (RE) elements exhibit favorable mechanical and (magneto)optical properties that reflect their unusual structural Organization. Yet, experimental reports on the local RE3+ environments in AS glasses are very sparse. We examine the Y3+ and Sc3+ cations in Y2O3-Al2O3-SiO2 and Sc2O3-Al2O3-SiO2 glasses of variable RE/Al/Si contents by utilizing magic-angle spinning (MAS) Y-89 and Sc-45 nuclear magnetic resonance (NMR) experiments coupled with density functional theory (DFT) calculations of Y-89/Sc-45 NMR chemical shifts. The DFT models reveal {Y-[p]} and {Sc-[p]} coordination numbers (p) spanning 5 <= p <= 8 and 4 <= p <= 7, respectively; with {Y-[6], Y-[7] and {Sc-[5], Sc-[6]} species dominating. Wide isotropic chemical shift ranges of 35-354 ppm (Y-89) and'48-208 ppm (Sc-45) are observed, as well as sizable shift'anisotropies up to approximate to 370 ppm and approximate to 250 ppm for Y-89 and Sc-45, respectively. Both the isotropic and anisotropic chemical shifts grow when the coordination number p is decreased for Y-89([p]) as well as Sc-45([p]). Second to the coordination number, we demonstrate that the Y-89/Sc-45 isotropic chemical shifts are mainly influenced by the RE/Al/Si constellation in the second coordination sphere of Y and Sc; where the shift tends to increase for emphasized contacts with neighboring RE and Al species at the expense of Si. These DFT-derived trends are corroborated by a progressive 89Y deshielding observed in MAS Y-89 NMR spectra for increasing Y and/or Al content of the glass. We also introduce heteronuclear MAS NMR experimentation involving the pairs of Y-89-Al-27 and Sc-45-Si-29 nuclides, utilized for probing the contacts between the Y3+/Sc3+ cations and the AS glass-network forming groups.

  • 6.
    Jaworski, Aleksander
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Physical Chemistry.
    Stevensson, Baltzar
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Physical Chemistry.
    Edén, Mattias
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Physical Chemistry.
    Direct O-17 NMR experimental evidence for Al-NBO bonds in Si-rich and highly polymerized aluminosilicate glasses2015In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 17, no 28, p. 18269-18272Article in journal (Refereed)
    Abstract [en]

    By using solid-state O-17 NMR spectroscopy, we provide the first direct experimental evidence for bonds between Al and non-bridging oxygen (NBO) ions in aluminosilicate glasses based on rare-earth (RE) elements, where RE = {Lu, Sc, Y}. The presence of similar to 10% Al-NBO moieties out of all NBO species holds regardless of the precise glass composition, at odds with the conventional structural view that Al-NBO bonds are absent in highly polymerized and Si-rich aluminosilicate glass networks.

  • 7.
    Jaworski, Aleksander
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Physical Chemistry.
    Stevensson, Baltzar
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Physical Chemistry.
    Edén, Mattias
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Physical Chemistry.
    Sc and Y Environments in Rare-Earth Aluminosilicate Glasses Unveiled by 45Sc and 89Y NMR Spectroscopy, MD Simulations, and DFT CalculationsManuscript (preprint) (Other academic)
  • 8.
    Jaworski, Aleksander
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Stevensson, Baltzar
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Edén, Mattias
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    The Bearings from Rare-Earth (RE = La, Lu, Sc, Y) Cations on the Oxygen Environments in Aluminosilicate Glasses: A Study by Solid State O-17 NMR, Molecular Dynamics Simulations, and DFT Calculations2016In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 120, no 24, p. 13181-13198Article in journal (Refereed)
    Abstract [en]

    Aluminosilicate (AS) glasses incorporating trivalent cations of rare-earth (RE) elements exhibit a significant structural disorder and manifest building blocks incommensurate with conventional glass structure models. We present a comprehensive experimental and computational study of the O speciations in RE2O3-Al2O3-SiO2 glasses with RE = {La3+, Y3+, Lu3+, Sc3+}, where the cations are ordered according to increasing field-strength. The coexisting O-17([p])-Sip-mAlm moieties were quantified by magic-angle-spinning (MAS) O-17 nuclear magnetic resonance (NMR) experiments and atomistic molecular dynamics (MD) simulations. Experimental O-17 quadrupolar products ((C) over bar (Qn)) and isotropic chemical shifts ((delta) over bar (iso)) agreed well with predictions from density functional theory with the projector augmented wave (PAW) and gauge including PAW approaches, respectively. We highlight an observed strong influence of both {(delta) over bar (iso), (C) over bar (Qn)} NMR parameters on the average number of O-17([p])-RE3+ contacts ((q) over bar) and establish simple correlations between g and each of Sisc, and CQ, that encompass mA.1, moieties with 1 < p < 3. The quadrupolar product of each O-[p]-Sip-mAlm motif depends linearly on the all fractional ionicity of,the bonds to the 170 site, which is readily calculated from the parameter set {m, p, (q) over bar} with (q) over bar extracted from the MD-generated glass models. We rationalize and discuss the stability of each O[p]-Sip-mAlm moiety using bond valence sums evaluated on the MD-derived RE AS glass models: all comprise non-negligible populations of unconventional 0 species, such as free O2- ions (O-[0] coordinations), and oxygen triclusters (O-[3]-SiAl2 and O-[3]-Al-3). The triclusters preferentially connect high-coordination Al-[5]/Al-[6] species via edge-sharing, where the participation in corner or edge shared polyhedra is reflected in the {(delta) over bar (iso), (C) over bar (Qn)} O-17 NMR parameters.

  • 9.
    Jaworski, Aleksander
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Physical Chemistry.
    Stevensson, Baltzar
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Physical Chemistry.
    Edén, Mattias
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Physical Chemistry.
    The Bearings from Rare-Earth (RE=La, Lu, Sc, Y) Cations on the Oxygen Environments in Aluminosilicate Glasses: A Study by Solid-State 17O NMR, Molecular Dynamics Simulations and DFT CalculationsManuscript (preprint) (Other academic)
  • 10.
    Jaworski, Aleksander
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Physical Chemistry.
    Stevensson, Baltzar
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Physical Chemistry.
    Pahari, Bholanath
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Physical Chemistry.
    Okhotnikov, Kirill
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Physical Chemistry.
    Eden, Mattias
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Physical Chemistry.
    Local structures and al/si ordering in lanthanum aluminosilicate glasses explored by advanced al 27 nmr experiments and molecular dynamics simulations2012In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 14, no 45, p. 15866-15878Article in journal (Refereed)
    Abstract [en]

    The structures of 15 La-Al-Si-O glasses, whose compositions span 11-28 mol% La2O3, 11-30 mol% Al2O3, and 45-78 mol% SiO2, are explored over both short and intermediate length-scales by using a combination of solid-state Al-27 magic-angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy and molecular dynamics (MD) simulations. MAS NMR reveals Al speciations dominated by AlO4 groups, with minor but significant fractions of AlO5 (5-10%) and AlO6 (less than or similar to 3%) polyhedra present in all La2O3-Al2O3-SiO2 glasses; the amounts of Al-[5] and Al-[6] coordinations increase for decreasing molar fraction of Si. The MD simulations reproduce this compositional trend, with the fractional populations of AlOp groups (p = 4, 5, 6) according well with the experimental results. The modeled La speciations mainly involve LaO6 and LaO7 polyhedra, giving a range of average La3+ coordination numbers between 6.0 and 6.6; the latter increases slightly for decreasing Si content of the sample. Besides the expected bridging and non-bridging O species, minor contributions of oxygen triclusters (<= 9%) and free O-2(-) ions (<= 4%) are observed in all MD data. The glass structures exhibit a pronounced Al/Si disorder; the MD simulations reveal essentially random SiO4-SiO4, SiO4-AlOp and AlOp-AlOq (p, q = 4, 5, 6) associations, including significant amounts of AlO4-AlO4 contacts, regardless of the n(Al)/n(Si) molar ratio of the glass. The strong violation of Al-[4]-Al-[4] avoidance is verified by 2D Al-27 NMR experimentation that correlates double-quantum and single-quantum coherences, here applied for the first time to aluminosilicate glasses, and evidencing AlOp-AlOq connectivities dominated by AlO4-AlO4 and AlO4-AlO5 pairs. The potential bearings from distinct fictive temperatures of the experimental and modeled glass structures are discussed.

  • 11.
    Kapla, Jon
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Engström, Olof
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Stevensson, Baltzar
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Wohlert, Jakob
    Widmalm, Göran
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Maliniak, Arnold
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Molecular dynamics simulations and NMR spectroscopy studies of trehalose-lipid bilayer systems2015In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 17, no 34, p. 22438-22447Article in journal (Refereed)
    Abstract [en]

    The disaccharide trehalose (TRH) strongly affects the physical properties of lipid bilayers. We investigate interactions between lipid membranes formed by 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) and TRH using NMR spectroscopy and molecular dynamics (MD) computer simulations. We compare dipolar couplings derived from DMPC/TRH trajectories with those determined (i) experimentally in TRH using conventional high-resolution NMR in a weakly ordered solvent (bicelles), and (ii) by solid-state NMR in multilamellar vesicles (MLV) formed by DMPC. Analysis of the experimental and MD-derived couplings in DMPC indicated that the force field used in the simulations reasonably well describes the experimental results with the exception for the glycerol fragment that exhibits significant deviations. The signs of dipolar couplings, not available from the experiments on highly ordered systems, were determined from the trajectory analysis. The crucial step in the analysis of residual dipolar couplings (RDCs) in TRH determined in a bicelle-environment was access to the conformational distributions derived from the MD trajectory. Furthermore, the conformational behavior of TRH, investigated by J-couplings, in the ordered and isotropic phases is essentially identical, indicating that the general assumptions in the analyses of RDCs are well founded.

  • 12.
    Kapla, Jon
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Stevensson, Baltzar
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Dahlberg, Martin
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Maliniak, Arnold
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Molecular Dynamics Simulations of Membranes Composed of Glycolipids and Phospholipids2012In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 116, no 1, p. 244-252Article in journal (Refereed)
    Abstract [en]

    Lipid membranes composed of 1,2-di-(9Z,12Z,15Z)-octade-catrienoyl-3-O-β-D-galactosyl-sn-glycerol or monogalactosyldiacylglycerol(MGDG) and 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) were studied by means of molecular dynamics (MD) computer simulations. Three lipid compositions were considered: 0%, 20%, and 45% MGDG (by mole) denoted as MG-0, MG-20, and MG-45, respectively. The article is focused on the calculation of NMR dipolar interactions, which were confronted with previously reported experimental couplings. Dynamical processes and orientational distributions relevant for the averaging of dipolar interactions were evaluated. Furthermore, several parameters important for characterization of the bilayer structure, molecular organization, and dynamics were investigated. In general, only a minor change in DMPC properties was observed upon the increased MGDG/DMPC ratio, whereas properties related to MGDG undergo a more pronounced change. This effect was ascribed to the fact that DMPC is a bilayer (Lα) forming lipid, whereas MGDG prefers a reverse hexagonal (HII) arrangement.

  • 13.
    Kapla, Jon
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Stevensson, Baltzar
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Maliniak, Arnold
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Coarse-Grained Molecular Dynamics Simulations of Membrane Trehalose Interactions2016In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 120, no 36, p. 9621-9631Article in journal (Refereed)
    Abstract [en]

    It is well established that trehalose (TRH) affects the physical properties of lipid bilayers and stabilizes biological membranes. We present molecular dynamics (MD) computer simulations to investigate the interactions between lipid membranes formed by 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) and TRH. Both atomistic and coarse-grained (CG) interaction models were employed, and the coarse graining of DMPC leads to a reduction in the acyl chain length corresponding to a 1,2-dilauroyl-sn-glycero-3-phosphocholine lipid (DLPC). Several modifications of the Martini interaction model, used for CG simulations, were implemented, resulting in different potentials of mean force (PMFs) for DMPC bilayer TRH interactions. These PMFs were subsequently used in a simple two-site analytical model for the description of sugar binding at the membrane interface. In contrast to that in atomistic MD simulations, the binding in the CG model was not in agreement with the two-site model. Our interpretation is that the interaction balance, involving water, TRH, and lipids, in the CG systems needs further tuning of the force-field parameters. The area per lipid is only weakly affected by TRH concentration, whereas the compressibility modulus related to the fluctuations of the membrane increases with an increase in TRH content. In agreement with experimental findings, the bending modulus is not affected by the inclusion of TRH. The important aspects of lipid bilayer interactions with biomolecules are membrane curvature generation and sensing. In the present investigation, membrane curvature is generated by artificial buckling of the bilayer in one dimension. It turns out that TRH prefers the regions with the highest curvature, which enables the most favorable situation for lipid sugar interactions.

  • 14.
    Kapla, Jon
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Wohlert, Jakob
    Stevensson, Baltzar
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Engström, Olof
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Widmalm, Göran
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Maliniak, Arnold
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Molecular Dynamics Simulations of Membrane-Sugar Interactions2013In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 117, no 22, p. 6667-6673Article in journal (Refereed)
    Abstract [en]

    It is well documented that disaccharides in general and trehalose (TRH) in particular strongly affect physical properties and functionality of lipid bilayers. We investigate interactions between lipid membranes formed by 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) and TRH by means of molecular dynamics (MD) computer simulations. Ten different TRH concentrations were studied in the range W-TRH = 0-0.20 (w/w). The potential of mean force (PMF) for DMPC bilayer TRH interactions was determined using two different force fields, and was subsequently used in a simple analytical model for description of sugar binding at the membrane interface. The MD results were in good agreement with the predictions of the model. The net affinities of TRH for the DMPC bilayer derived from the model and MD simulations were compared with experimental results. The area per lipid increases and the membrane becomes thinner with increased TRH concentration, which is interpreted as an intercalation effect of the TRH molecules into the polar part of the lipids, resulting in conformational changes in the chains. These results are consistent with recent experimental observations. The compressibility modulus related to the fluctuations of the membrane increases dramatically with increased TRH concentration, which indicates higher order and rigidity of the bilayer. This is also reflected in a decrease (by a factor of 15) of the lateral diffusion of the lipids. We interpret these observations as a formation of a glassy state at the interface of the membrane, which has been suggested in the literature as a hypothesis for the membrane sugar interactions.

  • 15.
    Landersjö, Clas
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Stevensson, Baltzar
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Eklund, Robert
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Östervall, Jennie
    Stockholm University, Faculty of Science, Department of Organic Chemistry. Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Widmalm, Göran
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Maliniak, Arnold
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Söderman, Peter
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Molecular conformations of a disaccharide investigated using NMR spectroscopy2006In: Journal of Biomolecular NMR, ISSN 0925-2738, E-ISSN 1573-5001, Vol. 35, p. 89-101Article in journal (Refereed)
    Abstract [en]

    The molecular structure of -l-Rhap-(1→ 2)--l-Rhap-OMe has been investigated using conformation sensitive NMR parameters: cross-relaxation rates, scalar 3 J CH couplings and residual dipolar couplings obtained in a dilute liquid crystalline phase. The order matrices of the two sugar residues are different, which indicates that the molecule cannot exist in a single conformation. The conformational distribution function, , related to the two glycosidic linkage torsion angles and was constructed using the APME method, valid in the low orientational order limit. The APME approach is based on the additive potential (AP) and maximum entropy (ME) models. The analyses of the trajectories generated in molecular dynamics and Langevin dynamics (LD) computer simulations gave support to the distribution functions constructed from the experimental NMR parameters. It is shown that at least two conformational regions are populated on the Ramachandran map and that these regions exhibit very different molecular order. Electronic Supplementary Material  Supplementary material is available for this article at http://www.dx.doi.org/10.1007/s10858-006-9006-0 and is accessible for authorized users.

  • 16.
    Leonova, Ekaterina
    et al.
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Hakeem, Abbas S.
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Jansson, Kjell
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Stevensson, Baltzar
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Shen, Zhijian
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Grins, Jekabs
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Esmaeilzadeh, Saeid
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Edén, Mattias
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Nitrogenrich La-Si-Al-O-N oxynitride glass structures probed by solid state NMR2008In: Journal of Non-Crystalline Solids, ISSN 0022-3093, E-ISSN 1873-4812, Vol. 354, no 1, p. 49-60Article in journal (Refereed)
    Abstract [en]

    We investigate the local structures of oxynitride La–Si–(Al)–O–N glasses by 29Si and 27Al magic-angle spinning (MAS) solid state Nuclear Magnetic Resonance (NMR). The glasses studied span an unprecedented range of compositions, up to >50 at.% lanthanum and nitrogen out of the cations and anions, respectively, and achievable through a recently introduced glass preparation route. Transmission as well as scanning electron microscopy verified homogeneous samples over length-scales down to 20 nm. As the nitrogen content of the glasses increased, 29Si NMR evidenced a progressive formation of Si–N bonds, with SiO2N2 tetrahedra dominating in the nitrogen-rich glass networks. In the oxygen-rich end of the series, aluminum is predominantly present in tetrahedral coordination as AlO4, whereas the glasses with highest nitrogen contents have a major fraction of AlO3N structural units. Trends in isotropic 29Si and 27Al chemical shifts and 27Al quadrupolar couplings are compared with results of La–Si–Al–O glasses and are discussed in relation to the glass compositions and their proposed structures.

  • 17.
    Mathew, Renny
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Physical Chemistry.
    Stevensson, Baltzar
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Physical Chemistry.
    Edén, Mattias
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Physical Chemistry.
    Na/Ca Intermixing around Silicate and Phosphate Groups in Bioactive Phosphosilicate Glasses Revealed by Heteronuclear Solid-State NMR and Molecular Dynamics Simulations2015In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 119, no 17, p. 5701-5715Article in journal (Refereed)
    Abstract [en]

    We characterize the intermixing of network-modifying Na+/Ca2+ ions around the silicate (QSin) and phosphate (QPn) tetrahedra in a series of 16 Na2O–CaO–SiO2–P2O5 glasses, whose P content and silicate network connectivity were varied independently. The set includes both bioactive and bioinactive compositions and also encompasses two soda-lime-silicate members devoid of P, as well as two CaO–SiO2 glasses and one Na2O–SiO2–P2O5 glass. The various Si/P↔Na/Ca contacts were probed by molecular dynamics (MD) simulations together with heteronuclear magic-angle-spinning (MAS) nuclear magnetic resonance (NMR) experimentation utilizing 23Na{31P} and 23Na{29Si} REDOR, as well as 31P{ 23Na} and 29Si{23Na} REAPDOR. We introduce an approach for quantifying the extent of Na+/Ca2+ ordering around a given QPn or QSin group, encoded by the preference factor 0⩽ PM ⩽ 1 conveying the relative weights of a random cation intermixing (PM = 0) and complete preference/ordering (PM = 1) for one of the species M, which represents either Na+ or Ca2+. The MD-derived preference factors reveal phosphate and silicate species surrounded by Na+/Ca2+ ions intermixed nearly randomly (PM ≲ 0.15), except for the QSi4 and QSi1 groups, which manifest more significant cation ordering with preference for Na+ and Ca2+, respectively. The overall weak preferences are essentially independent of the Si and P contents of the glass, whereas PM primarily correlates with the total amount of network modifiers: as the latter is increased, the Na/Ca distribution around the {QP0, QSi1, QSi2} groups with preference for Ca2+ tend to randomize (i.e., PCa decreases), while the PNa-values grow slightly for the {QP1, QSi3, QSi4} species already preferring coordination of Na. The set of experimental preference factors {PCa} for the orthophosphate (QP0) groups extracted from 31P{23Na} REAPDOR NMR-derived M2(P–Na) dipolar second moments agrees well with the MD-generated counterparts. Our results on the Na/Ca intermixing in soda-lime-silicate glasses are discussed in relation to previous reports, highlighting the dependence of the conclusion on the approach to data evaluation.

  • 18.
    Mathew, Renny
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Physical Chemistry.
    Stevensson, Baltzar
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Physical Chemistry.
    Tilocca, Antonio
    Eden, Mattias
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Physical Chemistry.
    Toward a Rational Design of Bioactive Glasses with Optimal Structural Features: Composition-Structure Correlations Unveiled by Solid-State NMR and MD Simulations2014In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 118, no 3, p. 833-844Article in journal (Refereed)
    Abstract [en]

    The physiological responses of silicate-based bioactive glasses (BGs) are known to depend critically on both the P content (np) of the glass and its silicate network connectivity ((N) over bar (SI)(BO)). However, while the bioactivity generally displays a nonmonotonic dependence on np itself, recent work suggest that it is merely the net orthophosphate content that directly links to the bioactivity. We exploit molecular dynamics (MD) simulations combined with P-31 and Si-29 solid-state nuclear magnetic resonance (NMR) spectroscopy to explore the quantitative relationships between (N) over bar (SI)(BO), npand the silicate and phosphate speciations in a series of Na2O-CaO-SiO2-P2O5 glasses spanning 2.1 <=(N) over bar (SI)(BO) <= 2.9 and variable P2O5 contents up to 6.0 mol %. The fractional population of the orthophosphate groups remains independent of np at a fixed (N) over bar (SI)(BO)-value, but is reduced slightly as (N) over bar (SI)(BO) increases. Nevertheless, P remains predominantly as readily released orthophosphate ions, whose content may be altered essentially independently of the network connectivity, thereby offering a route to optimize the glass bioactivity. We discuss the observed composition-structure links in relation to known composition-bioactivity correlations, and define how Na2O-CaO-SiO2-P2O5 compositions exhibiting an optimal bioactivity can be designed by simultaneously altering three key parameters: the silicate network connectivity, the (ortho)phosphate content, and the n(Na)/n(ca) molar ratio.

  • 19.
    Mathew, Renny
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Physical Chemistry.
    Turdean-Ionescu, Claudia
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Materials Chemistry.
    Stevensson, Baltzar
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Physical Chemistry.
    Izquierdo-Barba, Isabel
    Garcia, Ana
    Arcos, Daniel
    Vallet-Regi, Maria
    Eden, Mattias
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Physical Chemistry.
    Direct Probing of the Phosphate-Ion Distribution in Bioactive Silicate Glasses by Solid-State NMR: Evidence for Transitions between Random/Clustered Scenarios2013In: Chemistry of Materials, ISSN 0897-4756, E-ISSN 1520-5002, Vol. 25, no 9, p. 1877-1885Article in journal (Refereed)
    Abstract [en]

    By employing P-31 multiple-quantum coherence-based solid-state nuclear magnetic resonance spectroscopy, we present the first comprehensive experimental assessment of the nature of the orthophosphate ion distributions in silicate based bioactive glasses (BGs). Results are provided both from melt prepared BG and evaporation-induced self-assembly-derived mesoporous bioactive glass (MEBG) structures of distinct compositions. The phosphate species are randomly dispersed in melt-derived BGs (comprising 44-55 mol % SiO2) of the Na2O-CaO-SiO2-P2O5 system, whereas a Si-rich (86 mol % SiO2) and Ca-poor ordered MBG structure exhibits nanometer-sized amorphous calcium phosphate clusters, conservatively estimated to comprise at least nine orthophosphate groups. A Ca-richer MBG (58 mol % SiO2) reveals a less pronounced phosphate clustering. We rationalize the variable structural role of P in these amorphous biomatetials.

  • 20.
    Mathew, Renny
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Turdean-Ionescu, Claudia
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Yu, Yang
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Stevensson, Baltzar
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Izquierdo-Barba, Isabel
    Garcia, Ana
    Arcos, Daniel
    Vallet-Regi, Maria
    Edén, Mattias
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Proton Environments in Biomimetic Calcium Phosphates Formed from Mesoporous Bioactive CaO-SiO2-P2O5 Glasses in Vitro: Insights from Solid-State NMR2017In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 121, no 24, p. 13223-13238Article in journal (Refereed)
    Abstract [en]

    When exposed to body fluids, mesoporous bioactive glasses (MBGs) of the CaO-SiO2-P2O5 system develop a bone-bonding surface layer that initially consists of amorphous calcium phosphate (ACP), which transforms into hydroxy-carbonate apatite (HCA) with a very similar composition as bone/dentin mineral. Information from various H-1-based solid-state nuclear magnetic resonance (NMR) experiments was combined to elucidate the evolution of the proton speciations both at the MBG surface and within each ACP/HCA constituent of the biomimetic :phosphate layer a formed when each of three MBGs with distinct Ca, Si; and P contents was immersed in a simulated body fluid (SBF) for variable periods between 15 min and 30 days. Directly excited magic-angle-spinning (MAS) H-1 NMR spectra mainly reflect the MBG component, whose surface is rich in water and silanol (SiOH) moieties. Double-quantum-single-quantum correlation H-1 NMR experimentation At fast MAS revealed their interatomic proximities. The comparatively minor H species of each ACP and HCA component were probed selectively by heteronuclear H-1-P-31 NMR experimentation. The initially prevailing ACP phase comprises H2O and nonapatitic.HPO42-/PO43- groups, whereas for prolonged MBG soaking Over days, a well-progressed ACP -> HCA transformation was evidenced by a dominating (OH)-H-1 resonance from HCA. We show that H-1-detected H-1 -> P-31 cross polarization NMR is markedly more sensitive than utilizing powder X-ray diffraction or P-31 NMR for detecting the onset of HCA formation, notably so for P-bearing (M)BGs. In relation to the long-standing controversy as to whether bone mineral comprises ACP and/or forms via an ACP precursor, we discuss a recently accepted structural core-shell picture of both synthetic and biological HCA, highlighting the close relationship between the disordered surface layer and ACP.

  • 21.
    Okhotnikov, Kirill
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Stevensson, Baltzar
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Eden, Mattias
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    New interatomic potential parameters for molecular dynamics simulations of rare-earth (RE = La, Y, Lu, Sc) aluminosilicate glass structures: exploration of RE3+ field-strength effects2013In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 15, no 36, p. 15041-15055Article in journal (Refereed)
    Abstract [en]

    Sets of self-consistent oxygen-rare earth (RE = La, Y, Lu, Sc) interatomic potential parameters are derived using a force-matching procedure and utilized in molecular dynamics (MD) simulations for exploring the structures of RE2O3-Al2O3-SiO2 glasses that feature a fixed molar ratio n(Al)/n(Si) = 1 but variable RE contents. The structures of RE aluminosilicate (AS) glasses depend markedly on the RE3+ cation field strength (CFS) over both short and intermediate length-scales. We explore these dependencies for glasses incorporating the cations La3+, Y3+, Lu3+ and Sc3+, whose CFSs increase due to the concomitant shrinkage of the ionic radii: R-La > R-Y > R-Lu > R-Sc. This trend is mirrored in decreasing average RE3+ coordination numbers ((Z) over bar (RE)) from (Z) over bar (La) = 6.4 to (Z) over bar (Sc) = 5.4 in the MD-derived data. However, overall the effects from RE3+ CFS elevations on the local glass structures are most pronounced in the O and {Al-[4], Al-[5], Al-[6]} speciations. The former display minor but growing populations of O-[0] (free oxygen ion) and O-[3] (oxygen tricluster) moieties. The abundance of AlO5 polyhedra increases significantly from approximate to 10% in La-based glasses to approximate to 30% in their Sc counterparts at the expense of the overall dominating AlO4 tetrahedra, whereas the amounts of AlO6 groups remain <5% throughout. We also discuss the Si-[4]/Al-[p] (p = 4, 5, 6) intermixing and the nature of their oxygen bridges, where the degree of edge-sharing increases together with the RE3+ CFS.

  • 22.
    Pahari, Bholanath
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Iftekhar, Shahriar
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Jaworski, Aleksander
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Okhotnikov, Kirill
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Jansson, Kjell
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Stevensson, Baltzar
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Grins, Jekabs
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Edén, Mattias
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Composition-property-structure correlations of scandium aluminosilicate glasses revealed by multinuclear 45Sc, 27Al and 29Si solid-state NMR2012In: Journal of The American Ceramic Society, ISSN 0002-7820, E-ISSN 1551-2916, Vol. 95, no 8, p. 2545-1553Article in journal (Refereed)
    Abstract [en]

    Many features of aluminosilicate glasses incorporating a rare-earth (RE) ion are dictated by its mass and cation field strength (CFS). ScAlSiO glasses are interesting because Sc3+ exhibits the highest CFS but the lowest mass of all RE3+ ions. We explore relationships between the glass composition and several physical properties, such as density, glass-transition temperature (Tg), Vickers hardness, and refractive index, over the glass forming region of the ternary Sc2O3Al2O3SiO2 system. The glasses exhibit uniform and unexpectedly low Tg-values (similar to 875 degrees C), but a high microhardness (approximate to 9.3 GPa) that correlates with the Sc2O3 content. 29Si magic-angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy shows enhanced deshielding and a minor glass-network ordering as either the Al or Sc content of the glass increases. 27Al MAS NMR reveals that besides the expected AlO4 tetrahedra, substantial amounts of AlO5 (31%35%) and AlO6 (approximate to 5%) polyhedra are present in all ScAlSiO glass structures. 45Sc isotropic chemical shifts (similar to 92 ppm) derived from MAS and 3QMAS (triple-quantum MAS) NMR experiments are consistent with ScO6 environments.

  • 23.
    Stevensson, Baltzar
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Eden, Mattias
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Structural rationalization of the microhardness trends of rare-earth aluminosilicate glasses: Interplay between the RE3+ field-strength and the aluminum coordinations2013In: Journal of Non-Crystalline Solids, ISSN 0022-3093, E-ISSN 1873-4812, Vol. 378, p. 163-167Article in journal (Refereed)
    Abstract [en]

    Many studies have sought to rationalize property/structure relationships in rare-earth (RE) bearing aluminosilicate oxide or oxynitride glasses. In a set of 48 RE2O3-Al2O3-SiO2 (RE = La, Y, Lu, Sc) glasses of widely spanning compositions and RE3+ cation field-strengths (CFS), we observe strong correlations between the microhardness, glass compactness, and the average coordination number of Al. We argue that the well-known microhardness elevation for increasing RE3+ CFS stems not primarily from the RE3+ ions themselves, as hitherto believed, but merely from a structure-strengthening by AlO5/AlO6 polyhedra that cross-link different glass-network segments. The high-coordination Al populations grow together with the RE3+ CFS.

  • 24.
    Stevensson, Baltzar
    et al.
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Edén, Mattias
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Efficient orientational averaging by the extension of Lebedev grids via regularized octahedral symmetry expansion2006In: Journal of magnetic resonance, ISSN 1090-7807, E-ISSN 1096-0856, Vol. 181, no 1, p. 162-176Article in journal (Refereed)
    Abstract [en]

    Gaussian spherical quadrature methods in the guise of the Lebedev sampling grids are highly efficient for some orientational (“powder”) averaging problems in solid state NMR. However, their applicability is currently restricted, as the sets of orientations are derived analytically and because they are not well adapted to simulate the broad peakshapes encountered, for example, in the NMR on static powders or on half-integer quadrupolar spins subject to second order quadrupolar interactions under magic-angle spinning conditions. We remedy these problems by (i) introducing the recursive procedure regularized octahedral symmetry expansion (ROSE), to which any existing Lebedev set may be subjected. Each recursive step gives a 9-fold enlarged set of orientations. (ii) We demonstrate that ROSE-expanded grids, in conjunction with spectral interpolation, is well suited for calculating broad peakshapes. These advances combine into the apparently most efficient general-purpose two-angle orientational averaging technique proposed to date for solid state NMR applications.

  • 25.
    Stevensson, Baltzar
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Physical Chemistry.
    Edén, Mattias
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Physical Chemistry.
    Interpolation by fast Wigner transform for rapid calculations of magnetic resonance spectra from powders2011In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 134, no 12, p. 124104-Article in journal (Refereed)
    Abstract [en]

    We introduce a novel interpolation strategy, based on nonequispaced fast transforms involving spherical harmonics or Wigner functions, for efficient calculations of powder spectra in (nuclear) magnetic resonance spectroscopy. The fast Wigner transform (FWT) interpolation operates by minimizing the time-consuming calculation stages, by sampling over a small number of Gaussian spherical quadrature (GSQ) orientations that are exploited to determine the spectral frequencies and amplitudes from a 10-70 times larger GSQ set. This results in almost the same orientational averaging accuracy as if the expanded grid was utilized explicitly in an order of magnitude slower computation. FWT interpolation is applicable to spectral simulations involving any time-independent or time-dependent and noncommuting spin Hamiltonian. We further show that the merging of FWT interpolation with the well-established ASG procedure of Alderman, Solum and Grant [J. Chem. Phys. 134, 3717 (1986)] speeds up simulations by 2-7 times relative to using ASG alone (besides greatly extending its scope of application), and between 1-2 orders of magnitude compared to direct orientational averaging in the absence of interpolation. Demonstrations of efficient spectral simulations are given for several magic-angle spinning scenarios in NMR, encompassing half-integer quadrupolar spins and homonuclear dipolar-coupled (13)C systems.

  • 26.
    Stevensson, Baltzar
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Jaworski, Aleksander
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Edén, Mattias
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    The structural roles of Sc and Y in aluminosilicate glasses probed by molecular dynamics simulations2017In: Journal of Non-Crystalline Solids, ISSN 0022-3093, E-ISSN 1873-4812, Vol. 460, p. 36-46Article in journal (Refereed)
    Abstract [en]

    The incorporation of rare-earth (RE) elements into an aluminosilicate (AS) glass generally enhances its optical and mechanical properties. Atomistic molecular dynamics (MD) simulations were employed for probing the coordinations of Y3+ and Sc3+ in Y2O3-Al2O3-SiO2 and Sc2O3-Al2O3-SiO2 glasses of variable Si, Al, and RE contents. YO6 and ScO5 polyhedra are the most abundant RE species. We explore the trends in the distributions of the various (non)bridging oxygen species and Si/Al/RE cations in the first and second RE coordination spheres, respectively. The lowest REM and R051 coordinations of both Y and Sc exhibit a strong preference for coordinating non-bridging 0 species, which gradually relaxes for increasing coordination number p. Clear deviations from a statistical Si/AI/RE distribution around the REOp polyhedra is observed, with preferences for RE-RE contacts relative to RE-Al and (notably) RE-Si. The extents of RE-RE associations are similar for Y and Sc and grow slightly for increasing Si content and/or glass network polymerization. The propensity for RE-Al contacts becomes emphasized in the Sc AS glasses, mainly at the expense of Sc-Si. The YOp and ScOp polyhedra connect to their Si/Al/RE neighbors primarily by sharing corners, but a significant extent of edge-sharing is also observed, which increases both with the RE1PI coordination number, and along the series Si < Al-[4] < Al-[5]/Al-[6] approximate to RE of neighbors.

  • 27.
    Stevensson, Baltzar
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Physical Chemistry.
    Marini, Alberto
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Physical Chemistry.
    Zimmermann, Herbert
    Maliniak, Arnold
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Physical Chemistry.
    Carbon-13 NMR Chemical Shifts in Columnar Liquid Crystals2011In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 115, no 23, p. 7561-7567Article in journal (Refereed)
    Abstract [en]

    In this article, we present quantum chemical density functional theory (DFT) calculations of the NMR (13)C chemical shift (CS) tensors in 2,3,6,7,10,11-hexahexylthiotriphenylene (HHTT). The DFT calculations are performed on a smaller model molecule where the hexyl chains were reduced to methyl groups (HMTT). These tensors are compared with our previously reported experimental results carried out under magic-angle spinning (MAS) conditions. The phase diagram of HHTT is K <-> H <-> D(hd) <-> I, where H is a helical phase and D(hd) is a columnar liquid crystal. The motivation for the present study was to explain experimentally observed and puzzling thermal history effects, which resulted in different behavior in the helical phase upon cooling and heating. In particular, the CS tensors for the aromatic carbons measured in the helical phase upon heating from the solid phase were essentially unaffected, while the cooling from the columnar liquid crystal resulted in a significant averaging. We investigate the effect on the CS tensors of (i) conformational transitions, and (ii) relative molecular orientations within the columns for dimer and trimer configurations. Finally a motional wobbling (PIZZA) model for the dynamic averaging of the CS tensor in the helical phase is suggested.

  • 28.
    Stevensson, Baltzar
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Physical Chemistry.
    Mathew, Renny
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Physical Chemistry.
    Edén, Mattias
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Physical Chemistry.
    Assessing the Phosphate Distribution in Bioactive Phosphosilicate Glasses by P-31 Solid-State NMR and Molecular Dynamics Simulations2014In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 118, no 29, p. 8863-8876Article in journal (Refereed)
    Abstract [en]

    Melt-derived bioactive phosphosilicate glasses are widely utilized as bone-grafting materials for various surgical applications. However, the insight into their structural features over a medium-range scale up to similar to 1 nm remains limited. We present a comprehensive assessment of the spatial distribution of phosphate groups across the structures of 11 Na2O-CaO-SiO2-P2O5 glasses that encompass both bioactive and nonbioactive compositions, with the P contents and silicate network connectivities varied independently. Both parameters are known to strongly influence the bioactivity of the glass in vitro. The phosphate distribution was investigated by double-quantum 3113 nuclear magnetic resonance (NMR) experiments under magic-angle spinning (MAS) conditions and by molecular dynamics (MD) simulations. The details of the phosphate-ion dispersion were probed by evaluating the MD-derived glass models against various scenarios of randomly distributed, as well as clustered, phosphate groups. From comparisons of the P-P interatomic-distance spreads and the statistics of small phosphate clusters assessed for variable cutoff radii, we conclude that the spatial arrangement of the P atoms in phosphosilicate glasses is well-approximated by a statistical distribution, particularly across a short-range scale of <= 450 pm. The primary distinction is reflected in slightly closer P-P interatomic contacts in the MD-derived structures over the distance span of 450-600 pm relative to that of randomly distributed phosphate groups. The nature of the phosphate-ion dispersion remains independent of the silicate network polymerization and nearly independent of the P content of the glass throughout our explored parameter space of 1-6 mol % P2O5 and silicate network connectivities up to 2.9.

  • 29.
    Stevensson, Baltzar
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Mathew, Renny
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Yu, Yang
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Edén, Mattias
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Two heteronuclear dipolar results at the price of one: Quantifying Na/P contacts in phosphosilicate glasses and biomimetic hydroxy-apatite2015In: Journal of magnetic resonance, ISSN 1090-7807, E-ISSN 1096-0856, Vol. 251, p. 52-56Article in journal (Refereed)
    Abstract [en]

    The analysis of S{I} recoupling experiments applied to amorphous solids yields a heteronuclear second moment M-2(S-I) that represents the effective through-space dipolar interaction between the detected S spins and the neighboring I-spin species. We show that both M-2(S-I) and M-2(I-S) values are readily accessible from a sole S{I} or I{S} experiment, which may involve either S or I detection, and is naturally selected as the most favorable option under the given experimental conditions. For the common case where I has half-integer spin, an I{S} REDOR implementation is preferred to the S{I} REAPDOR counterpart. We verify the procedure by Na-23{P-31} REDOR and P-31{Na-23} REAPDOR NMR applied to Na2O-CaO-SiO2-P2O5 glasses and biomimetic hydroxyapatite, where the M-2(P-Na) values directly determined by REAPDOR agree very well with those derived from the corresponding M-2(Na-P) results measured by REDOR. Moreover, we show that dipolar second moments are readily extracted from the REAPDOR NMR protocol by a straightforward numerical fitting of the initial dephasing data, in direct analogy with the well-established procedure to determine M-2(S-I) values from REDOR NMR experiments applied to amorphous materials; this avoids the problems with time-consuming numerically exact simulations whose accuracy is limited for describing the dynamics of a priori unknown multi-spin systems in disordered structures.

  • 30.
    Stevensson, Baltzar
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Yu, Yang
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Edén, Mattias
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Structure-composition trends in multicomponent borosilicate-based glasses deduced from molecular dynamics simulations with improved B-O and P-O force fields2018In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 20, no 12, p. 8192-8209Article in journal (Refereed)
    Abstract [en]

    We present a comprehensive molecular dynamics (MD) simulation study of composition-structure trends in a set of 25 glasses of widely spanning compositions from the following four systems of increasing complexity: Na2O-B2O3, Na2O-B2O3-SiO2, Na2O-CaO-SiO2-P2O5, and Na2O-CaO-B2O3-SiO2-P2O5. The simulations involved new B-O and P-O potential parameters developed within the polarizable shell-model framework, thereby combining the beneficial features of an overall high accuracy and excellent transferability among different glass systems and compositions: this was confirmed by the good accordance with experimental data on the relative BO3/BO4 populations in borate and boro(phospho)silicate networks, as well as with the orthophosphate fractions in bioactive (boro)phosphosilicate glasses, which is believed to strongly influence their bone-bonding properties. The bearing of the simulated melt-cooling rate on the borate/phosphate speciations is discussed. Each local {BO3, BO4, SiO4, PO4} coordination environment remained independent of the precise set of co-existing network formers, while all trends observed in bond-lengths/angles mainly reflected the glass-network polymerization, i.e., the relative amounts of bridging oxygen (BO) and non-bridging oxygen (NBO) species. The structural roles of the Na+/Ca2+ cations were also probed, targeting their local coordination environments and their relative preferences to associate with the various borate, silicate, and phosphate moieties. We evaluate and discuss the common classification of alkali/alkaline-earth metal ions as charge-compensators of either BO4 tetrahedra or NBO anions in borosilicate glasses, also encompassing the less explored NBO-rich regime: the Na+/Ca2+ cations mainly associate with BO/NBO species of SiO4/BO3 groups, with significant relative Na-BO4 contacts only observed in B-rich glass networks devoid of NBO species, whereas NBO-rich glass networks also reveal substantial amounts of NBO-bearing BO4 tetrahedra.

  • 31.
    Säwén, Elin
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Stevensson, Baltzar
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Physical Chemistry.
    Östervall, Jennie
    Stockholm University, Faculty of Science, Department of Organic Chemistry. Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Physical Chemistry.
    Maliniak, Arnold
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Physical Chemistry.
    Widmalm, Göran
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Molecular conformations in the pentasaccharide LNF-1 derived from NMR spectroscopy and molecular dynamics simulations2011In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 115, no 21, p. 7109-7121Article in journal (Refereed)
    Abstract [en]

    The conformational dynamics of the human milk oligosaccharide lacto-N-fucopentaose (LNF-1), α-l-Fucp-(1 → 2)-β-d-Galp-(1 → 3)-β-d-GlcpNAc-(1 → 3)-β-d-Galp-(1 → 4)-d-Glcp, has been analyzed using NMR spectroscopy and molecular dynamics (MD) computer simulations. Employing the Hadamard 13C-excitation technique and the J-HMBC experiment, 1H,13C trans-glycosidic J coupling constants were obtained, and from one- and two-dimensional 1H,1H T-ROESY experiments, proton–proton cross-relaxation rates were determined in isotropic D2O solution. In the lyotropic liquid-crystalline medium consisting of ditetradecylphosphatidylcholine, dihexylphosphatidylcholine, N-cetyl-N,N,N-trimethylammonium bromide, and D2O, 1H, 1H and one-bond 1H, 13C residual dipolar couplings (RDCs), as well as relative sign information on homonuclear RDCs, were determined for the pentasaccharide. Molecular dynamics simulations with explicit water were carried out from which the internal isomerization relaxation time constant, τN, was calculated for transitions at the ψ torsion angle of the β-(1 → 3) linkage to the lactosyl group in LNF-1. Compared to the global reorientation time, τM, of 0.6 ns determined experimentally in D2O solution, the time constant for the isomerization relaxation process, τN(scaled), is about one-third as large. The NMR parameters derived from the isotropic solution show very good agreement with those calculated from the MD simulations. The only notable difference occurs at the reducing end, which should be more flexible than observed by the molecular simulation, a conclusion in complete agreement with previous 13C NMR relaxation data. A hydrogen-bond analysis of the MD simulation revealed that inter-residue hydrogen bonds on the order of 30% were present across the glycosidic linkages to sugar ring oxygens. This finding highlights that intramolecular hydrogen bonds might be important in preserving well-defined structures in otherwise flexible molecules. An analysis including generalized order parameters obtained from nuclear spin relaxation experiments was performed and successfully shown to limit the conformational space accessible to the molecule when the number of experimental data are too scarce for a complete conformational analysis.

  • 32.
    Teymoori, Gholamhasan
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Physical Chemistry.
    Pahari, Bholanath
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Physical Chemistry.
    Stevensson, Baltzar
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Physical Chemistry.
    Edén, Mattias
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Physical Chemistry.
    Low-power broadband homonuclear dipolar recoupling without decoupling: Double-quantum C-13 NMR correlations at very fast magic-angle spinning2012In: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 547, p. 103-109Article in journal (Refereed)
    Abstract [en]

    We report novel symmetry-based radio-frequency (rf) pulse sequences for efficient excitation of doublequantum (2Q) coherences under very fast (>60 kHz) magic-angle spinning (MAS) conditions. The recursively generated pulse-scheme series, R2(2p)(1)R2(2P)(-1) (p = 1; 2, 3,...), offers broadband C-13-C-13 recoupling in organic solids at a very low rf power. No proton decoupling is required. A high-order average Hamiltonian theory analysis reveals a progressively enhanced resonance-offset compensation for increasing p, as verified both by numerical simulations and 2Q filtration NMR experiments on C-13(2)-glycine, [2,3-C-13(2)] alanine, and [U-C-13] tyrosine at 14.1 T and 66 kHz MAS, where the pulse schemes with p >= 3 compare favorably to current state-of-the-art recoupling options.

  • 33.
    Thaning, Johan
    et al.
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Högberg, Carl-Johan
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Stevensson, Baltzar
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Lyubartsev, Alexander
    Stockholm University, Faculty of Humanities, Department of Baltic Languages, Finnish and German, Department of Dutch. Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Maliniak, Arnold
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Molecular Conformations in a Phospholipid Bilayer Extracted from Dipolar Couplings: A Computer Simulation Study2007In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 111, no 48, p. 13638-13644Article in journal (Refereed)
    Abstract [en]

    This paper describes an analysis of NMR dipolar couplings in a bilayer formed by dimyristoylphosphatidylcholine (DMPC). The couplings are calculated from a trajectory generated in a molecular dynamics (MD) simulation based on a realistic atom−atom interaction potential. The analysis is carried out employing a recently developed approach that focuses on the construction of the conformational distribution function. This approach is a combination of two models, the additive potential (AP) model and the maximum entropy (ME) method, and is therefore called APME. In contrast to the AP model, the APME procedure does not require an intuition-based choice of the functional form of the torsional potential and is, unlike the ME method, applicable to weakly ordered systems. The conformational distribution function for the glycerol moiety of the DMPC molecule derived from the APME analysis of the dipolar couplings is in reasonable agreement with the “true” distributions calculated from the trajectory. Analyses of dipolar couplings derived from MD trajectories can, in general, serve as guidelines for experimental investigations of bilayers and other complex biological systems.

  • 34.
    Thaning, Johan
    et al.
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Stevensson, Baltzar
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Maliniak, Arnold
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Molecular structure extracted from residual dipolar couplings: Diphenylmethane dissolved in a nematic liquid crystal2005In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 123, no 4, p. 044507-Article in journal (Refereed)
    Abstract [en]

    This paper describes an analysis of 1H–1H residual dipolar couplings (RDCs)in diphenylmethane (DPM) dissolved in a nematic liquid crystal, reportedby Celebre et al. [J. Chem. Phys. 118, 6417 (2003)]. Inthat article, the conformational distribution function for DPM was extractedfrom the RDCs, using the additive potential (AP) model whichis based on the molecular-field theory. The AP approach isa powerful, and frequently used, tool for analysis of thenuclear-magnetic-resonance (NMR) parameters in liquid crystals. It requires, however, apriori knowledge of the functional form of the torsional potential,which may even for a simple molecule, such as DPM,be complicated to determine. Here, we analyze the same setof the RDCs using our APME procedure, which is ahybrid model based on the AP approach and maximum entropy(ME) theory. The APME procedure does not require any assumptionsabout the functional form of the torsional potential and, incontrast with the ME method, is applicable to weakly orderedsystems. In the investigation reported in the present study, theresults from the APME analysis are in good agreement withthe AP interpretation, whereas the ME approach essentially fails inthe extraction of the conformational distribution function for DPM.

  • 35.
    Thaning, Johan
    et al.
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Stevensson, Baltzar
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Östervall, Jennie
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Naidoo, Kevin J.
    University of Cape Town. , CSIR Campus Rosebank..
    Widmalm, Göran
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Maliniak, Arnold
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    NMR Studies of Molecular Conformations in α-Cyclodextrin2008In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 112, no 29, p. 8434-8436Article in journal (Refereed)
    Abstract [en]

    A new approach for analysis of NMR parameters is proposed. The experimental data set includes scalar couplings, NOEs, and residual dipolar couplings. The method, which aims at construction of the conformational distribution function, is applied to α-cyclodextrin in isotropic solution and dissolved in a dilute liquid crystal. An attempt to analyze the experimental data using an average molecular conformation resulted in unacceptable errors. Our approach rests on the maximum entropy method (ME), which gives the flattest possible distribution, consistent with the experimental data. Very good agreement between experimental and calculated NMR parameters was observed. In fact, two conformational states were required in order to obtain a satisfactory agreement between calculated and experimental data. In addition, good agreement with Langevin dynamics computer simulations was obtained.

  • 36.
    Thiele, Christina M.
    et al.
    Clemens Schpf Institut fr Organische Chemie und Biochemie, Technische Universitt Darmstadt, Petersenstr. 22, D-64287 Darmstadt, Germany.
    Maliniak, Arnold
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Stevensson, Baltzar
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Use of Local Alignment Tensors for the Determination of Relative Configurations in Organic Compounds2009In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 131, no 36, p. 12878-12879Article in journal (Refereed)
    Abstract [en]

    In this proof of principle the use of local alignment tensors for the determination of relative configurations in moderately flexible molecules is demonstrated. These tensors are derived from residual dipolar couplings. Two methods for the analysis of partly linearly dependent RDCs in a rigid molecular fragment are also presented.

  • 37.
    Thiele, Christina M.
    et al.
    Clemens Schöpf Institut für Organische Chemie und Biochemie, Technische Universität Darmstadt, Petersenstrasse 22, 64287 Darmstadt (Germany).
    Schmidts, Volker
    Clemens Schöpf Institut für Organische Chemie und Biochemie, Technische Universität Darmstadt, Petersenstrasse 22, 64287 Darmstadt (Germany).
    Böttcher, Benjamin
    Clemens Schöpf Institut für Organische Chemie und Biochemie, Technische Universität Darmstadt, Petersenstrasse 22, 64287 Darmstadt (Germany).
    Louzao, Iria
    Clemens Schöpf Institut für Organische Chemie und Biochemie, Technische Universität Darmstadt, Petersenstrasse 22, 64287 Darmstadt (Germany). On leave from: Departamento de Química Orgánica, Facultad de Química, Universidad de Santiago de Compostela, 15782 Santiago de Compostela (Spain) .
    Berger, Robert
    Frankfurt Institute for Advanced Studies, Johann Wolfgang Goethe Universität, Ruth-Moufang-Strasse 1, 60438 Frankfurt (Germany).
    Maliniak, Arnold
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Stevensson, Baltzar
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    On the Treatment of Conformational Flexibility when Using Residual Dipolar Couplings for Structure Determination2009In: Angewandte Chemie International Edition, ISSN 1433-7851, E-ISSN 1521-3773, Vol. 48, no 36, p. 6708-6712Article in journal (Refereed)
    Abstract [en]

    Mission possible! The motional averaging of NMR spectroscopic data complicates the determination of conformation and relative configuration in flexible organic molecules. Two alternative routes are discussed for the treatment of conformational equilibrium in a moderately flexible compound (see the superposition of the two conformers of the butyrolactone studied) when residual dipolar couplings are used.

  • 38. Tosner, Zdenek
    et al.
    Andersen, Rasmus
    Stevensson, Baltzar
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Edén, Mattias
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Nielsen, Niels Chr.
    Vosegaard, Thomas
    Computer-intensive simulation of solid-state NMR experiments using SIMPSON2014In: Journal of magnetic resonance, ISSN 1090-7807, E-ISSN 1096-0856, Vol. 246, p. 79-93Article in journal (Refereed)
    Abstract [en]

    Conducting large-scale solid-state NMR simulations requires fast computer software potentially in combination with efficient computational resources to complete within a reasonable time frame. Such simulations may involve large spin systems, multiple-parameter fitting of experimental spectra, or multiple-pulse experiment design using parameter scan, non-linear optimization, or optimal control procedures. To efficiently accommodate such simulations, we here present an improved version of the widely distributed open-source SIMPSON NMR simulation software package adapted to contemporary high performance hardware setups. The software is optimized for fast performance on standard stand-alone computers, multi-core processors, and large clusters of identical nodes. We describe the novel features for fast computation including internal matrix manipulations, propagator setups and acquisition strategies. For efficient calculation of powder averages, we implemented interpolation method of Alderman, Solum, and Grant, as well as recently introduced fast Wigner transform interpolation technique. The potential of the optimal control toolbox is greatly enhanced by higher precision gradients in combination with the efficient optimization algorithm known as limited memory Broyden-Fletcher-Goldfarb-Shanno. In addition, advanced parallelization can be used in all types of calculations, providing significant time reductions. SIMPSON is thus reflecting current knowledge in the field of numerical simulations of solid-state NMR experiments. The efficiency and novel features are demonstrated on the representative simulations.

  • 39.
    Turdean-Ionescu, Claudia
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Stevensson, Baltzar
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Grins, Jekabs
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Izquierdo-Barba, Isabel
    Garcia, Ana
    Arcos, Daniel
    Vallet-Regi, Maria
    Edén, Mattias
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Composition-dependent in vitro apatite formation at mesoporous bioactive glass-surfaces quantified by solid-state NMR and powder XRD2015In: RSC Advances, ISSN 2046-2069, E-ISSN 2046-2069, Vol. 5, no 105, p. 86061-86071Article in journal (Refereed)
    Abstract [en]

    Silicate-based bioactive glasses exhibit bone-bonding properties due to the formation of a hydroxycarbonate apatite (HCA) layer at the glass surface on its contact with living tissues. This bone-healing process is triggered by ionic exchange between the glass and the surrounding fluids and thereby depends on the glass composition. In this work, the HCA formation from three mesoporous bioactive glasses (MBGs) of different compositions immersed in a simulated body fluid (SBF) was monitored for variable time intervals between 15 minutes to 30 days. By utilizing two independent assessment techniques, solid-state P-31 NMR spectroscopy and powder X-ray diffraction (PXRD), we report the first quantitative assessment of the HCA growth (i.e., in vitro bioactivity) from a bioactive glass: both techniques allow for monitoring the crystallization of the amorphous calcium phosphate (ACP) precursor into HCA, i.e., a profile of the relative ACP/HCA fractions of the biomimetic phosphate layer formed at each MBG surface and SBF-exposure period. The amount of HCA present in each solid specimen after the SBF treatment, as well as the composition of the remaining cation-depleted MBG phase, was determined from PXRD data in conjunction with measured concentrations of Ca, Si, and P in the solution. In contrast with previous findings from in vitro bioactivity assessments of the same MBG compositions, the HCA formation is herein observed to increase concurrently with the Ca and P contents of the MBG; these apparently different composition-bioactivity observations stem from a significantly lower MBG-loading in the SBF solution utilized herein. The results are discussed in relation to the general task of performing bioactivity testing in SBF, where we highlight the importance of adapting the concentration of the biomaterial to its composition to avoid perturbing the HCA crystallization and thereby altering the outcome of the test.

  • 40.
    Turdean-Ionescu, Claudia
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Stevensson, Baltzar
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Izquierdo-Barba, Isabel
    Garcia, Ana
    Arcos, Daniel
    Vallet-Regi, Maria
    Edén, Mattias
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Surface Reactions of Mesoporous Bioactive Glasses Monitored by Solid-State NMR: Concentration Effects in Simulated Body Fluid2016In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 120, no 9, p. 4961-4974Article in journal (Refereed)
    Abstract [en]

    A bone-mineral-mimicking layer of hydroxycarbonate apatite (HCA) forms at the surface of a bioactive glass on its contact with body fluids. We report a solid-state Si-29 nuclear magnetic resonance (NMR) spectroscopy study of the surface reactions preceding the HCA formation at three CaO-SiO2-(P2O5) mesoporous bioactive glasses (MBGs) with distinct compositions, surface areas, and mesoporous arrangements, during their immersion in simulated body fluid (SBF) out to 30 days. The evolution of the various populations of coexisting silicate species associated with the bulk-arid surface portions of the pore-walls were monitored. The MBGs revealed drastically different surface alterations between the scenarios of low (0.6 g/L) and high (20 g/L) MBG concentrations in the SBF: for the low MBG dose, which is expected to be more relevant for in vivo conditions, all MBGs follow a universal dissolution mechanism beyond approximate to 24 h of SBF soaking, regardless of their precise compositions and textural properties. The only essential difference among the specimens occurs during the first hour of soaking when their variable Ca2+ reservoirs are depleted. In contrast, for high MBG concentrations, the surface reactions and their associated silicate network degradation retard for Ca-poor MBGs, whereas the reactions are completely quenched for Ca-rich compositions. These findings rationalize previously reported discrepancies in the correlation between the HCA formation and the MBG composition for distinct concentrations during SBF testing, and simplify future MBG design by identifying which compositional and textural factors are relevant for a rapid and substantial HCA formation in vitro.

  • 41.
    Yu, Yang
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Guo, Hua
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Pujari-Palmer, Michael
    Stevensson, Baltzar
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Grins, Jekabs
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Engqvist, Håkan
    Edén, Mattias
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Advanced solid-state H-1/P-31 NMR characterization of pyrophosphate-doped calcium phosphate cements for biomedical applications: The structural role of pyrophosphate2019In: Ceramics International, ISSN 0272-8842, E-ISSN 1873-3956, Vol. 45, no 16, p. 20642-20655Article in journal (Refereed)
    Abstract [en]

    From a suite of advanced magic-angle spinning (MAS) NMR spectroscopy and powder X-ray diffraction (PXRD) experiments, we present a comprehensive structural analysis of pyrophosphate-bearing calcium phosphate cements that are investigated for bone-inductive biomedical implants. The cements consist mainly of poorly ordered monetite (CaHPO4), along with minor Ca orthophosphate phases, and two distinct pyrophosphate constituents: crystalline beta-Ca2P2O7 and amorphous calcium pyrophosphate (ACPP), the latter involving one water bearing portion and another anhydrous component. Independent 2D MAS NMR experiments evidenced close contacts between the amorphous pyrophosphates and the monetite phase, where ACPP is proposed to form a thin layer coating the monetite particles. Heteronuclear H-1-P-31 and homonuclear P-31-P-31 correlation NMR experimentation enabled us to detect, identify, and quantify even minor cement constituents (less than or similar to 2 mol%) that could not be ascertained by the Rietveld method. Quantitative phase analyses of the cements, as determined independently by P-31 NMR and PXRD, are contrasted and discussed.

  • 42.
    Yu, Yang
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Stevensson, Baltzar
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Edén, Mattias
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Direct Experimental Evidence for Abundant BO4–BO4 Motifs in Borosilicate Glasses From Double-Quantum 11B NMR Spectroscopy2018In: Journal of Physical Chemistry Letters, ISSN 1948-7185, E-ISSN 1948-7185, Vol. 9, no 21, p. 6372-6376Article in journal (Refereed)
    Abstract [en]

    By using double-quantum–single-quantum correlation 11B nuclear magnetic resonance (NMR) experiments and atomistic molecular dynamics (MD) simulations, we resolve the long-standing controversy of whether directly interlinked BO4–BO4 groups exist in the technologically ubiquitous class of alkali/alkaline-earth based borosilicate (BS) glasses. Most structural models of Na2O–B2O3–SiO2 glasses assume the absence of B[4]–O–B[4] linkages, whereas they have been suggested to exist in Ca-bearing BS analogs. Our results demonstrate that while B[4]–O–B[4] linkages are disfavored relative to their B[3]–O–B[3]/B[4] counterparts, they are nevertheless abundant motifs in Na2O–B2O3–SiO2 glasses over a large composition space, while the B[4]–O–B[4] contents are indeed elevated in Na2O–CaO–B2O3–SiO2 glasses. We discuss the compositional and structural parameters that control the degree of B[4]–O–B[4] bonding.

  • 43.
    Yu, Yang
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Stevensson, Baltzar
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Edén, Mattias
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Medium-Range Structural Organization of Phosphorus-Bearing Borosilicate Glasses Revealed by Advanced Solid-State NMR Experiments and MD Simulations: Consequences of B/Si Substitutions2017In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 121, no 41, p. 9737-9752Article in journal (Refereed)
    Abstract [en]

    The short and intermediate range structures of a large series of bioactive borophosphosilicate (BPS) glasses were probed by solid-state nuclear magnetic resonance (NMR) spectroscopy and atomistic molecular dynamics (MD) simulations. Two BPS glass series were designed by gradually substituting SiO2 by B2O3 in the respective phosphosilicate base compositions 24.1Na(2)O-23.3CaO-48.6SiO(2)-4.0P(2)O(5) (S49) and 24.6Na(2)O-26.7CaO-46.1SiO(2)-2.6P(2)O(5) (S46), the latter constituting the 45S5 Bioglass utilized for bone grafting applications. The BPS glass networks are built by interconnected SiO4, BO4, and BO3 moieties, whereas P exists mainly as orthophosphate anions, except for a minor network-associated portion involving P-O-Si and P-O-B-[4] motifs, whose populations were estimated by heteronuclear P-31{B-11} NMR experimentation. The high Na+/Ca2+ contents give fragmented glass networks with large amounts of nonbridging oxygen (NBO) anions. The MD-generated glass models reveal an increasing propensity for NBO accommodation among the network units according to BO4 < SiO4 < BO3 << PO4. The BO4/BO3 intermixing was examined by double-quantum-single-quantum correlation B-11 NMR experiments, which evidenced the presence of all three BO3-BO3, BO3-BO4, and BO4-BO4 connectivities, with B-[3]-O-B-[4] bridges dominating. Notwithstanding that B-[4]-O-B-[4] linkages are disfavored, both NMR spectroscopy and MD simulations established their presence in these modifier-rich BPS glasses, along with non-negligible B-[4]-NBO contacts, at odds with the conventional structural view of borosilicate glasses. We discuss the relative propensities for intermixing of the Si/B/P network formers. Despite the absence of pronounced preferences for Si-O-Si bond formation, the glass models manifest subtle subnanometer-sized structural inhomogeneities, where SiO4 tetrahedra tend to self-associate into small chain/ring motifs embedded in BO3/BO4-dominated domains.

  • 44.
    Yu, Yang
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Stevensson, Baltzar
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Edén, Mattias
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Structural Role of Sodium in Borosilicate, Phosphosilicate, and Borophosphosilicate Glasses Unveiled by Solid-State NMR and MD Simulations2019In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 123, no 42, p. 25816-25832Article in journal (Refereed)
    Abstract [en]

    We present a comprehensive study of the Na environments in a large ensemble of 32 silicate-based glass compositions from the borosilicate, phosphosilicate, and borophosphosilicate systems, which comprise either Na as the sole glass-network modifier or mixed with Ca. We examined the spatial distribution of Na in the glasses using Na-23 NMR The relative propensities of Na to associate with the BO3 and BO4 structural moieties in B-bearing glasses were probed by heteronuclear dipolar-based B-11{Na-23} magic-angle-spinning NMR experimentation, which yielded both dipolar second moments M-2(B-[p]-Na) and M-2(Na-B-[p] for each B-[3] and B-[(4]) coordination in a single experiment. These data agreed well with results from atomistic molecular dynamics simulations. Both the spatial distribution of Na and the relative preferences for B-[3] -Na and B-[4]-Na contacts depend primarily on the amount of nonbridging oxygen (NBO) anions in the glass network, and thereby on the modifier (Na-2(+) and Ca2+) concentrations, where two regimes were identified: (I) For low modifier contents, the Na+ cations are relatively uniformly dispersed across the structure, while there is a strong preference for B-[4]-Na associations. (II) For moderately high modifier contents, Na+ distributes randomly and with nonpreferential associations with the BO3 or BO4 species. However, when the Na+ and Ca2+ contents are increased further, the growing NBO populations of the glass network coupled with the strong preferential NBO accommodation at the BO3 moieties (relative to BO4) progressively elevate the propensity for B-[3]-Na contacts. We discuss the partitioning of the Na reservoir among the BO3 and BO4 groups for each regime I and II. We also rationalize the increased disorder of the Na dispersion and the concomitant shift from a preference for B-[4]-Na contacts to one for B-[3]-Na. Both the nature of the spatial distribution of Na and the relative preferences for B-[4]-Na and B-[3]-Na contacts in the glass are essentially independent of its precise combination of (B, Si, P) network formers.

1 - 44 of 44
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf