Change search
Refine search result
12 51 - 74 of 74
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.
  • 51.
    Samain, Louise
    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).
    Ladd, Danielle M.
    Seo, Dong-Kyun
    Javier Garcia-Garcia, F.
    Häussermann, Ulrich
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Structural analysis of highly porous gamma-Al2O32014In: Journal of Solid State Chemistry, ISSN 0022-4596, E-ISSN 1095-726X, Vol. 217, p. 1-8Article in journal (Refereed)
    Abstract [en]

    Two highly porous gamma-aluminas, a commercial catalyst obtained from the calcination of boehmite and a highly mesoporous product obtained from amorphous aluminum (oxy)hydroxide via a sol-gel-based process were investigated by Al-27 nuclear magnetic resonance (NMR), transmission electron microscopy (TEM), and atomic pair distribution function (PDF) analysis of synchrotron powder diffraction data. NMR data showed for both materials a distribution of tetrahedrally and octahedrally coordinated Al at a 0.30:0.70 ratio, which is typical for gamma-aluminas. TEM studies revealed that rod-shaped particles with about 5 nm in thickness are the building blocks of the porous structure in both materials. These particles often extend to a length of 50 nm in the commercial catalyst and are considerably shorter in the sol-gel-based material, which has a higher surface area. Refinement of PDFs revealed the presence of a similar to 1 nm scale local structure and the validity of a tetragonal average structure for both materials. This tetragonal average structure contains a substantial fraction of non-spinel octahedral Al atoms. It is argued that the presence of local structure is a general feature of gamma-alumina, independent of precursor and synthesis conditions. The concentration of non-spinel Al atoms seems to correlate with surface properties, and increases with increasing pore size/surface area. This should have implications to the catalytic properties of porous gamma-alumina.

  • 52. Schitco, Cristina
    et al.
    Turdean-Ionescu, Claudia
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Bazarjani, Mahdi Seifollahi
    Tai, Cheuk-Wai
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Li, Duan
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Fasel, Claudia
    Donner, Wolfgang
    Shen, James
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Riedel, Ralf
    Gurlo, Aleksander
    Edén, Mattias
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Silicon oxycarbonitrides synthesized by ammonia-assisted thermolysis route from polymers: A total X-ray scattering, solid-state NMR, and TEM structural study2016In: Journal of the European Ceramic Society, ISSN 0955-2219, E-ISSN 1873-619X, Vol. 35, no 4, p. 979-989Article in journal (Refereed)
    Abstract [en]

    Solid-state nuclear magnetic resonance (NMR) spectroscopy, total X-ray scattering with a pair distribution function (PDF) analysis, and transmission electron microscopy (TEM) were employed to explore the structures of microporous and non-porous ceramics synthesized by an NH3-assisted thermolysis from polymers. Polysiloxane (SPR-212a, Starfire® Systems) and polysilazane (HTT-1800, KiON Speciality Polymers) polymers form microporous silicon oxycarbonitride ceramics with accessible and tailored micropores. 29Si magic-angle-spinning NMR showed that the introduction of nitrogen leads to structures incorporating considerable amounts of SiN4 and SiO2N2 building blocks. The samples derived from a polycarbosilane (SMP-10, Starfire® Systems) remained non-porous: for such a C-rich and N-bearing phase, the NMR, TEM, and PDF results suggested a Si network exhibiting domains dominated by either SiN or SiC bonds. 13C NMR revealed primarily “carbidic” CSi4 environments in the C-rich phases, as well as the formation of an amorphous sp2-hybridized carbon phase; both are believed to be detrimental for the micropore formation.

  • 53.
    Spektor, Kristina
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). European Synchrotron Radiation Facility (ESRF), France.
    Nylen, Johanna
    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).
    Edén, Mattias
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Stoyanov, Emil
    Navrotsky, Alexandra
    Leinenweber, Kurt
    Häussermann, Ulrich
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Formation of hydrous stishovite from coesite in high-pressure hydrothermal environments2016In: American Mineralogist, ISSN 0003-004X, E-ISSN 1945-3027, Vol. 101, no 11, p. 2514-2524Article in journal (Refereed)
    Abstract [en]

    In low-temperature, high-pressure hydrothermal environments coesite transforms into hydrous forms of stishovite. We studied hydrous stishovite produced from hydrothermal treatment of silica glass as initial SiO2 source at temperatures of 350-550 degrees C and pressures around 10 GPa. The P-T quenched samples were analyzed by powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), thermal analysis, and IR and magic-angle spinning (MAS) NMR spectroscopy. The presence of significant amounts of H2O (ranging from 0.5 to 3 wt%) is shown from thermogravimetric measurements. PXRD reveals that at temperatures below 400 degrees C, hydrous stishovite is obtained as two distinct phases that may relate to the solid ice-VII environment present at prevailing P-T conditions. Initially formed hydrous stishovite is metastable and dehydrates over time in the low-temperature, high-pressure hydrothermal environment. The primary mechanism of H incorporation in stishovite is a direct substitution of 4H(+) for Si4+ yielding unique octahedral hydrogarnet defects. In IR spectra this defect manifests itself by two broad but distinct bands at 2650 and 2900 cm(-1), indicating strong hydrogen bonding. These bands are shifted in the deuteride to 2029 and 2163 cm(-1), respectively. Protons of the octahedral hydrogarnet defect produce H-1 MAS NMR signals in the 9-12 ppm region. The presence of multiple resonances suggests that the octahedral defect is associated with various proton arrangements. At elevated temperatures, the NMR signals narrow considerably because of proton dynamics.

  • 54.
    Spektor, Kristina
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Inorganic and Structural Chemistry.
    Nylén, Johanna
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Inorganic and Structural 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.
    Stoyanov, Emil
    Navrotsky, Alexandra
    Leinenweber, Kurt
    Häussermann, Ulrich
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Inorganic and Structural Chemistry.
    Formation of hydrous stishovite from coesite in high pressure hydrothermal environmentsManuscript (preprint) (Other academic)
  • 55.
    Steiner, Emilie
    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).
    Zimmermann, Iwan
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Brotin, Thierry
    Edén, Mattias
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Kowalewski, Jozef
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Investigation of chloromethane complexes of cryptophane-A analogue with butoxy groups using C-13 NMR in the solid state and solution along with single crystal X-ray diffraction2015In: Magnetic Resonance in Chemistry, ISSN 0749-1581, E-ISSN 1097-458X, Vol. 53, no 8, p. 596-602Article in journal (Refereed)
    Abstract [en]

    Host-guest complexes between cryptophane-A analogue with butoxy groups (cryptophane-But) and chloromethanes (chloroform, dichloromethane) were investigated in the solid state by means of magic-angle spinning C-13 NMR spectroscopy. The separated local fields method with C-13-H-1 dipolar recoupling was used to determine the residual dipolar coupling for the guest molecules encaged in the host cavity. In the case of chloroform guest, the residual dipolar interaction was estimated to be about 19kHz, consistent with a strongly restricted mobility of the guest in the cavity, while no residual interaction was observed for encaged dichloromethane. In order to rationalize this unexpected result, we performed single crystal X-ray diffraction studies, which confirmed that both guest molecules indeed were present inside the cryptophane cavity, with a certain level of disorder. To improve the insight in the dynamics, we performed a C-13 NMR spin-lattice relaxation study for the dichloromethane guest in solution. The system was characterized by chemical exchange, which was slow on the chemical shift time scale but fast with respect to the relaxation rates. Despite these disadvantageous conditions, we demonstrated that the data could be analyzed and that the results were consistent with an isotropic reorientation of dichloromethane within the cryptophane cavity.

  • 56.
    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.

  • 57.
    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.

  • 58.
    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.

  • 59.
    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.

  • 60.
    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.

  • 61.
    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.

  • 62.
    Teymoori, Gholamhasan
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Pahari, Bholanath
    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).
    Low-power broadband homonuclear dipolar recoupling in MAS NMR by two-fold symmetry pulse schemes for magnetization transfers and double-quantum excitation2015In: Journal of magnetic resonance, ISSN 1090-7807, E-ISSN 1096-0856, Vol. 261, p. 205-220Article in journal (Refereed)
    Abstract [en]

    We provide an experimental, numerical, and high-order average Hamiltonian evaluation of an open-ended series of homonuclear dipolar recoupling sequences, SR2(2p)(1), with p = 1, 2,3, .... While operating at a very low radio-frequency (rf) power, corresponding to a nutation frequency of 1/2 of the magic-angle spinning (MAS) rate (omega(nut) = omega(r)/2), these recursively generated double-quantum (2Q) dipolar recoupling schemes offer a progressively improved compensation to resonance offsets and rf inhomogeneity for increasing pulse-sequence order p. The excellent recoupling robustness to these experimental obstacles, as well as to CSA, is demonstrated for 2Q filtering (2QF) experiments and for driving magnetization transfers in 2D NMR correlation spectroscopy, where the sequences may provide either double or zero quantum dipolar Hamiltonians during mixing. Experimental and numerical demonstrations, which mostly target conditions of ultra-fast MAS (greater than or similar to 50 kHz) and high magnetic fields, are provided for recoupling of C-13 across a wide range of isotropic and anisotropic chemical shifts, as well as dipolar coupling constants, encompassing [2,3-C-13(2)]alanine, [1,3-C-13(2)]alanine, diammonium [1,4-C-13(2)]fumarate, and [U-C-13]tyrosine. When compared at equal power levels, a superior performance is observed for the SR2(2p)(1) sequences with p >= 3 relative to existing and well-established 2Q recoupling techniques. At ultra-fast MAS, proton decoupling is redundant during the homonuclear dipolar recoupling of dilute spins in organic solids, which renders the family of SR2(2p)(1) schemes the first efficient 2Q recoupling option for general applications, such as 2Q-1Q correlation NMR and high-order multiple-quantum excitation, under truly low-power rf conditions.

  • 63.
    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.

  • 64.
    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.
    Viswanathan, Elumalai
    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.
    Multiple-quantum spin counting in magic-angle-spinning NMR via low-power symmetry-based dipolar recoupling2013In: Journal of magnetic resonance, ISSN 1090-7807, E-ISSN 1096-0856, Vol. 236, p. 31-40Article in journal (Refereed)
    Abstract [en]

    By using a symmetry-based R2(8)(1)S2(8)(-1) double-quantum (2Q dipolar recoupling sequence, we demonstrate high-order multiple-quantum coherence (MQC) excitation at fast magic-angle spinning (MAS) frequencies up to 34 kHz. This scheme combines several attractive features, such as a relatively high dipolar scaling factor, good compensation to rf-errors, isotropic and anisotropic chemical shifts, as well as an ultra-low radio-frequency (rf) power requirement. The latter translates into nutation frequencies below 30 kHz for MAS rates up to 60 kHz, thereby permitting rf application for very long excitation periods without risk of damaging the NMR probehead or sample, while the compensation to chemical shifts improves as the MAS rate increases. 31P MQC spin counting is demonstrated on powders of calcium hydroxyapatite (Ca-5(PO4)(3)OH) and anhydrous sodium diphosphate (Na4P2O7), from which all even coherence orders up to 30 and 14 were detected, respectively, over the respective MAS ranges of 15-24 kHz and 20-34 kHz. The amplitude distributions among the P-31 MQC orders depend on the precise nutation frequency during recoupling, despite that the highest detected order was relatively insensitive to this parameter. An observed gradual transition from a Gaussian to exponential functionality of the MQC amplitude-profile is discussed in relation to the prevailing approach to derive spin-cluster sizes by fitting the MQC amplitude-distribution to a Gaussian decay, where minor systematic deviations between the model and experimental data are frequently reported.

  • 65. 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.

  • 66.
    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.

  • 67.
    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.

  • 68. Weber, Florian
    et al.
    Liao, Wei-Chih
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Barrantes, Alejandro
    Edén, Mattias
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Tiainen, Hanna
    Silicate-Phenolic Networks: Coordination-Mediated Deposition of Bioinspired Tannic Acid Coatings2019In: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 25, no 42, p. 9870-9874Article in journal (Refereed)
    Abstract [en]

    Surface modification with polyphenolic molecules has been pursued in biomedical materials owing to their antioxidant, anti-inflammatory, and antimicrobial characteristics. Recently, the use of silicic acid (Si-aq) as a mediator for efficient surface deposition of tannic acid (TA) was reported, but the postulated Si-TA polymeric networks were not characterized. Herein, we present unambiguous evidence for silicate-TA networks that involve Si-O-C motifs by using solid-state NMR spectroscopy, further supported by XPS and ToF-SIMS. By using QCM-D we demonstrate the advantages of Si-aq, compared to using transition-metal ions, to improve the coating efficiency under mildly acidic conditions. The presented homogenous coating buildup and validated applicability in inorganic buffers broadens the use of TA for surface modifications in technological and biomedical applications.

  • 69.
    Yu, Yang
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Bacsik, Zoltán
    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).
    Contrasting In Vitro Apatite Growth from Bioactive Glass Surfaces with that of Spontaneous Precipitation2018In: Materials, ISSN 1996-1944, E-ISSN 1996-1944, Vol. 11, no 9, article id 1690Article in journal (Refereed)
    Abstract [en]

    Body-fluid-exposed bioactive glasses (BGs) integrate with living tissues due to the formation of a biomimetic surface layer of calcium hydroxy-carbonate apatite (HCA) with a close composition to bone mineral. Vast efforts have been spent to understand the mechanisms underlying in vitro apatite mineralization, as either formed by direct precipitation from supersaturated solutions, or from BG substrates in a simulated body fluid (SBF). Formally, these two scenarios are distinct and have hitherto been discussed as such. Herein, we contrast them and identify several shared features. We monitored the formation of amorphous calcium phosphate (ACP) and its crystallization into HCA from a Na2O–CaO–SiO2–P2O5 glass exposed to SBF for variable periods out to 28 days. The HCA growth was assessed semi-quantitatively by Fourier transform infrared spectroscopy and powder X-ray diffraction, with the evolution of the relative apatite content for increasing SBF-exposure periods evaluated against trends in Ca and P concentrations in the accompanying solutions. This revealed a sigmoidal apatite growth behavior, well-known to apply to spontaneously precipitated apatite. The results are discussed in relation to the prevailing mechanism proposed for in vitro HCA formation from silicate-based BGs, where we highlight largely simultaneous growth processes of ACP and HCA.

  • 70.
    Yu, Yang
    et al.
    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 relationships of bioactive borophosphosilicate glasses probed by multinuclear B-11, Si-29, and P-31 solid state NMR2016In: RSC Advances, ISSN 2046-2069, E-ISSN 2046-2069, Vol. 6, no 103, p. 101288-101303Article in journal (Refereed)
    Abstract [en]

    By combining B-11, Si-29, and P-31 nuclear magnetic resonance (NMR) experimental results, we present a comprehensive structural investigation of 15 borophosphosilicate (BPS) glasses of the Na2O-CaOB2O3- SiO2-P2O5 system: in two base compositions comprising 46 mol% (S46) and 49 mol% (S49) SiO2, progressive replacements of SiO2 by B2O3 were performed at a constant total Na2O and CaO content. The S46 glass members constitute B-bearing analogs of 45S5 Bioglass that is utilized extensively for bone grafting in periodontal and orthopedic surgery. Orthophosphate ions prevail throughout all structures, while the silicate network polymerization increases slightly with a growing amount of B2O3 in the glass. B-11 NMR revealed continuous BO3 -> BO4 conversions for increasing B2O3 content, with asymptotic fractions of 34% and 43% of B-[4] coordinations out of the borate speciation observed for the series of S46 and S49 glasses, respectively. While all BPS glasses are homogeneous across a mm-scale, strong preferences for B-[3]-O-B-[3] and B-[4]-O-Si-[4] bond formation lead to structures comprising (sub) nm-sized domains of BO3 groups in boroxol rings and borosilicate networks built by SiO4 and BO4 tetrahedra. These borate/ borosilicate networks are merged mainly by B-[4](3Si) and B-[3](1Si) moieties in Si-rich BPS glasses (where each value in parentheses specifies the number of bonds to Si atoms), while B-[4](3Si) and B-[4](2Si) groups are the dominant network contact points in the B-rich glasses. We discuss the partitioning of non-bridging oxygen ions between the BO3 and SiO4 groups, the relative propensities for B-[4]-O-Si-[4] and B-[4]-O-B-[3] bond formation, as well as the expected bearings of our proposed BPS structural model for the glass degradation in aqueous media, where we identify the fractional population of B-[4] coordinations and the silicate network connectivity to constitute the dissolution-controlling parameters.

  • 71.
    Yu, Yang
    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).
    Edén, Mattias
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Quantitative composition–bioactivity relationships of phosphosilicate glasses: Bearings from the phosphorus content and network polymerization2018In: Journal of Non-Crystalline Solids, ISSN 0022-3093, E-ISSN 1873-4812, Vol. 502, p. 106-117Article in journal (Refereed)
    Abstract [en]

    Bioactive phosphosilicate glasses integrate with bone/tooth tissues by forming a bone-mineral mimicking surface layer of calcium hydroxyapatite (HA). The HA formation (“in vitrobioactivity”) in a simulated body fluid (SBF) solution is known to depend both on the P content (nP) and silicate network connectivity () of the glass, but the precise bioactivity–composition relationships remain poorly understood. We present a comprehensive study that clarifies the dependence of the in vitro bioactivity on the {nP, } parameters for Na2O–CaO–SiO2–P2O5 glass powders (2.6–6.0 mol% P2O5) exposed to SBF for 24 h, using infrared (IR) and solid-state 31P nuclear magnetic resonance (NMR) spectroscopy in conjunction with measured Ca and P concentrations in the solution. IR-derived relative apatite amounts reveal that an increase in the P content of the pristine glass promotes apatite formation by gradually reducing its dependence on the silicate network polymerization: increasing nP widens the  range that provides a high and nearly constant amount of HA, which scales roughly linearly with nP; these properties assist future design of P-rich bioactive glasses. All glasses provide significant HA formation for increasing  values up to ≈2.6, above which the in vitro bioactivity is lost due to insufficient glass dissolution. We also discuss the complex dependence of the SBF-testing outcome on the mass concentration and composition of the glass powder, as well as on its particle sizes, highlighting critical concerns that may guide developments of improved in vitro bioactivity-testing protocols. A strong dependence of the HA formation on the particle sizes is observed for glass powders with low P2O5 content (2.6 mol%), as opposed to their P-richer counterparts that reveal no pronounced particle-size effects.

  • 72.
    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.

  • 73.
    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.

  • 74. Zazzi, A
    et al.
    Hirsch, TK
    Leonova, E
    Stockholm University.
    Kaikkonen, A
    Grins, J
    Stockholm University.
    Annersten, H
    Edén, M
    Stockholm University.
    Structural investigations of natural and synthetic chlorite minerals by X-ray diffraction, Mossbauer spectroscopy and solid-state nuclear magnetic resonance2006In: Clays and Clay Minerals, Vol. 54, p. 252-265Article in journal (Refereed)
12 51 - 74 of 74
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