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  • 101. Choi, Minkee
    et al.
    Na, Kyungsu
    Kim, Jeongnam
    Sakamoto, Yasuhiro
    Terasaki, Osamu
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Ryoo, Ryong
    Stable single-unit-cell nanosheets of zeolite MFI as active and long-lived catalysts2009In: Nature, ISSN 0028-0836, E-ISSN 1476-4687, Vol. 461, no 7261, p. 246-249Article in journal (Refereed)
    Abstract [en]

    Zeolites-microporous crystalline aluminosilicates-are widely used in petrochemistry and fine-chemical synthesis(1-3) because strong acid sites within their uniform micropores enable size- and shape-selective catalysis. But the very presence of the micropores, with aperture diameters below 1 nm, often goes hand-in-hand with diffusion limitations(3-5) that adversely affect catalytic activity. The problem can be overcome by reducing the thickness of the zeolite crystals, which reduces diffusion path lengths and thus improves molecular diffusion(4,5). This has been realized by synthesizing zeolite nanocrystals(6), by exfoliating layered zeolites(7-9), and by introducing mesopores in the microporous material through templating strategies(10-17) or demetallation processes(18-22). But except for the exfoliation, none of these strategies has produced 'ultrathin' zeolites with thicknesses below 5 nm. Here we show that appropriately designed bifunctional surfactants can direct the formation of zeolite structures on themesoporous and microporous length scales simultaneously and thus yield MFI (ZSM-5, one of the most important catalysts in the petrochemical industry) zeolite nanosheets that are only 2 nm thick, which corresponds to the b-axis dimension of a single MFI unit cell. The large number of acid sites on the external surface of these zeolites renders them highly active for the catalytic conversion of large organic molecules, and the reduced crystal thickness facilitates diffusion and thereby dramatically suppresses catalyst deactivation through coke deposition during methanol-to-gasoline conversion. We expect that our synthesis approach could be applied to other zeolites to improve their performance in a range of important catalytic applications.

     

  • 102.
    Christensen, J.
    et al.
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Oleynikov, P.
    Hovmöller, S.
    Zou, X.D.
    Solving Approximant Structures Using a 'Strong Reflections' Approach2004In: Ferroelectrics, ISSN 0015-0193, Vol. 305, no 1, p. 273-277Article in journal (Refereed)
  • 103.
    Christensen, Jeppe
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Non-Standard Crystallography: Examples in 3- and 3+1 Dimensional Space2007Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Crystallography today is by many seen as merely a tool for determining the structure of a material on the atomic level. It is expected that whatever comes out of the tool is the indisputable truth, a fact. This thesis is based on five publications illustrating that this is very far from the real world of materials research. The experiences drawn from the structural work in the papers are put together to illustrate when to be alert, and how to proceed with a structural investigation using non-standard crystallography. The focus is on interpreting the signs of additional order being present in a structure. The signs may be weak, such as extreme thermal vibration, or unit cell deformation. Or the signs can be strong, with superstructure reflections indicating the presence of either commensurate or incommensurate superstructures.

  • 104.
    Christensen, Jeppe
    et al.
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Lidin, Sven
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Malaman, Bernard
    Venturini, Gerard
    Vacancy Ordering Effects in AlB2-type ErGe2-x(0.4 < x < or = 0.5)2008In: Acta Crystallographica Section B: Structural Science, ISSN 0108-7681, E-ISSN 1600-5740, Vol. 64, no 3, p. 272-280Article in journal (Refereed)
    Abstract [en]

    In the Er-Ge system, the compostion range ErGe2 to Er2Ge3 has been investigated. Eight samples were produced by arc melting of the elements, and analyzed using X-ray powder diffraction. Nine crystal structures were found to be present in the samples. The structures are described as a homologous series and presented within the superspace formalism using the superspace group X2/m(0)0s, X representing the centring vector (½, ½, 0, ½). In this description the modulation vector q = (a* + c*) is shown to be a direct measure of the Ge content as ErGe2 -  ( falls in the range to ½). The large composition range is achieved by extended vacancy ordering in the planar 63 net of Ge with subsequent relaxation.

  • 105.
    Christensen, Kirsten E.
    et al.
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Bonneau, Charlotte
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Gustafsson, Mikaela
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Shi, Lei
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Sun, Junliang
    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.
    Jansson, Kjell
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Sbille, Isabelle
    Su, Bao-Lian
    Zou, Xiaodong
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    An open-framework silicogermanate with 26-ring channels built from seven-coordinated (Ge,Si)10(O, OH)28 clusters2008In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 130, no 12, p. 3758-3759Article in journal (Refereed)
    Abstract [en]

    We report a new open-framework silicogermanate SU-61 containing 26-ring channels with a low framework density. It can be seen as a crystalline analogue to the mesoporous silica MCM-41. The structure is built from the assembly of (Ge,Si)10(O,OH)28 clusters. It is the first time that silicon has been successfully introduced in the Ge10 cluster in significant amounts (21% of the tetrahedral sites). Five- and six-coordinated Ge10 clusters have previously been observed in other germanate compounds leading to either dense or open structures. In SU-61, the seven-coordinated clusters fall onto yet another underlying net, the osf net. SU-61, along with other Ge10 based frameworks, shows the versatility of the germanate system to adopt defined topologies playing on the connectivity of the clusters following the principles of net decoration and scale chemistry.

  • 106.
    Christensen, Kirsten E.
    et al.
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Bonneau, Charlotte
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Shi, Lei
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Gustafsson, Mikaela
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Zou, Xiaodong
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Open-framework germanates formed by the flexible Ge10 cluster2008In: Zeolites and related materials: Trends, targets and challenges: Proceedings of the 4th International FEZA Conference, Vol. 174, Part A / [ed] Antoine Gédéon, Pascale Massiani and Florence Babonneau, Amsterdam: Elsevier, 2008, p. 317-320Conference paper (Refereed)
    Abstract [en]

    Open-framework germanates have shown promising results in achieving extra-large pores and channels. Pores that extend to the mesoporous range (>20Å) were reported in SU-M. The structure of SU-M is built by the Ge10X28 (Ge10, X = O, OH, F) clusters. This cluster is also found in Ge-pharmacosiderite, Na4Ge9O20, ICMM-7 and SU-61. The Ge10 cluster has a flexibility to form compounds with both high and very low framework densities.

  • 107.
    Christensen, Kirsten E
    et al.
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Xu, Ruren
    Yu, Jihong
    Li, Guanghua
    Zou, Xiaodong
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Pan, Qinhe
    Li, Jiyang
    Shi, Lei
    Ren, Xiaoyan
    Bonneau, Charlotte
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Sun, Junliang
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    A germanate built from 68126 cavity co-templated by a (H2O)16 water cluster and 2-methylpiperazine2008In: Angewandte Chemie International Edition, ISSN 1433-7851, E-ISSN 1521-3773, Vol. 47, no 41, p. 7868-7871Article in journal (Refereed)
    Abstract [en]

    Totally tubular: A new tubular germanate is cotemplated by 2-methylpiperazine and an (H2O)16 cluster in a hydro(solvo)thermal synthesis. The germanate features a large, highly symmetric 68126 cavity (see picture; yellow sphere) built from 12 Ge7X19 (X=O, OH, F) clusters (GeX6 red, GeX5 yellow, GeX4 green).

  • 108.
    Christensen, Kirsten Elvira
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Open-Framework Germanates: Crystallography, structures and cluster building units2008Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis is focussing on the crystallographic challenges and what knowledge we can gain from studying the different open-framework germanates. Five new open-framework germanates have been synthesized and the structures have been determined by single crystal X-ray diffraction. A thorough description is made of the different problems raised with the different compounds, whether it is choice of crystal system in SU-61, twinning and possible ordering in SU-46, superstructure and variation in elemental content in SU-57, template disorder in JLG-5 or framework disorder in SU-44.

    Open-framework germanates are often built from one type of cluster, such as the Ge7 [Ge7X19], Ge8 [Ge8X20], Ge9 [Ge9Xn, n =25-26] and Ge10 [Ge10X28], (X =O, OH, F) clusters. The structures built by clusters containing different kinds of polyhedra are discussed, with a focus on the 4-coordinated Ge7 clusters, the larger cluster aggregate found in SU-8 and SU-44 and the structures built by the Ge10 clusters.

  • 109.
    Christensen, Kirsten Elvira
    et al.
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Shi, Lei
    Conradsson, Tony
    Ren, Tie-zhen
    Dadachov, Mike S.
    Zou, Xiaodong
    Design of Open-Framework Germanates by Combining Different Building Units2006In: Journal of American Chemical Society, ISSN 0002-7863, Vol. 128, no 44, p. 14238-14239Article in journal (Refereed)
  • 110.
    Christensen, Kirsten Elvira
    et al.
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Shi, Lei
    Tang, Liqiu
    Conradsson, Tony
    Dadachov, Mike S.
    Zou, Xiaodong
    Design of three-dimensional open-framework structures from inorganic clusters2007In: From Zeolites to Porous MOF Materials - the 40th Anniversary of International Zeolite Conference, 170: Proceedings of the 15th International Zeolite Conference, Beijing, P. R. China, 12-17th August 2007, Elsevier , 2007, p. 682-689Chapter in book (Other academic)
  • 111.
    Christensen, Kirsten Elvira
    et al.
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Shi, Lei
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Tang, L.Q.
    Conradsson, T.
    Dadachov, M.S.
    Zou, Xiaodong
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Design of three-dimensional open-framework structures from inorganic clusters2007In: Studies in Surface Science and Catalysis. Elsevier BV, Vol. 170, p. 682-689Article in journal (Refereed)
  • 112. Colmont, M.
    et al.
    Terasaki, Osamu
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    TEM investigation of the microporous compound VSB-1: building units and crystal growth mechanisms2007In: Journal Solid State Chemistry, Vol. 180, p. 885-893Article in journal (Refereed)
  • 113. Cong, D. Y.
    et al.
    Wang, Y. D.
    Xu, J. Z.
    Zuo, L.
    Zetterström, P.
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry, Structural Chemistry.
    Delaplane, R.
    Neutron diffraction study on crystal structure and phase transformation in Ni-Mn-Ga ferromagnetic shape memory alloys2007In: Powder Diffraction, ISSN 0885-7156, E-ISSN 1945-7413, Vol. 22, no 4, p. 307-311Article in journal (Refereed)
    Abstract [en]

    Crystal structure and phase transformation behaviors in two Ni-Mn-Ga ferromagnetic shape memory alloys (FSMAs) with compositions of Ni48Mn30Ga22 and Ni53Mn25Ga22 (at. %) as a function of temperature were investigated by in situ neutron diffraction experiments. Neutron diffraction technique proves to be highly efficient in characterizing structural transformation in Ni-Mn-Ga FSMAs, which consist of nearby elements in the periodic table. Our neutron results show that Ni48Mn30Ga22 has a cubic, L-21 Heusler structure from 373 to 293 K. Its crystal structure changes into a seven-layered orthorhombic martensitic structure when cooled to 243 K, and no further transformation is observed upon cooling to 19 K. Neutron diffraction results also show that Ni53Mn25Ga22 has a tetragonal 14/mmm martensitic structure from 20 to 403 K. A pre-transformation around room temperature is observed from an abrupt jump in unit-cell volume of Ni53Mn25Ga22, which corresponds with an endothermic peak detected in a heated DSC curve.

  • 114. Corma, Averlino
    et al.
    Zou, Xiaodong
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Hovmöller, Sven
    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.
    Sun, Junliang
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Zhang, Daliang
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Jordá, José L.
    Díaz Cabañas, María J.
    Cantín, Ángel
    Moliner, Manuel
    Synthesis and structure of polymorph B of zeolite Beta2008In: Chemistry of Materials, ISSN 0897-4756, E-ISSN 1520-5002, Vol. 20, no 9, p. 3218-3223Article in journal (Refereed)
    Abstract [en]

    It was found that either polymorph B or polymorph C of zeolite beta can be obtained from the same structure directing agent: 4,4-dimethyl-4-azonia-tricyclo[5.2.2.02,6]undec-8-ene hydroxide. The synthesis occurs through a consecutive process where polymorph B is first formed and then transformed into polymorph C. It is possible to produce a zeolite highly enriched in polymorph B, provided that the transformation of this phase into polymorph C is slowed down up to the point where polymorph C is only detected at trace levels. The structure of polymorph B was determined for the first time by electron crystallography with SAED and HRTEM from areas of unfaulted polymorph B crystals.

  • 115.
    Csöregh, Ingeborg
    et al.
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Toda, Fumio
    1,1,1,3,3,3-Hexafluoro-2,2-bis(4-hydroxyphenyl)propane-benzene (2/3)2007In: Acta Crystallographica Section E, Vol. E63, p. 1796-1771Article in journal (Refereed)
  • 116.
    Cumpstey, Ian
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Eriksson, Lars
    Department of Physical, Inorganic and Structural Chemistry.
    Bis(methyl 2,4,6-tri-O-acetyl-beta-D-allofuranosid-3-yl)sulfane2007In: Acta Crystallographica Section E, ISSN 1600-5368, Vol. E63, p. o4197-Article in journal (Refereed)
  • 117. Dadachov, Mike. S.
    et al.
    Tang, Liqiu
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Zou, Xiaodong
    Crystal structure of 1,4-diazabicyclo[2,2,2]octane hexafluorotitanium hydrate, (C6H14N2)[TiF6]·H2O2000In: Z. Kristallogr, Vol. NCS215, p. 607-608Article in journal (Refereed)
  • 118. Dadachov, Mike. S.
    et al.
    Tang, Liqiu
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Zou, Xiaodong
    Crystal structure of dipiperazine decafluorodititanate dihydrate, (C4H11N2)2[Ti2F10]·2H2O2000In: Z. Kristallogr, Vol. NCS215, p. 605-606Article in journal (Refereed)
  • 119. Dadachov, Mike. S.
    et al.
    Tang, Liqiu
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Zou, Xiaodong
    Crystal structure of dipiperazine decafluorooxodititanate dihydrate, (C4H12N2)2[Ti2F10O)]·2H2O2001In: Z. Kristallogr, Vol. NCS216, p. 141-142Article in journal (Refereed)
  • 120.
    Dahl, Leif
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Preparation and characterisation of perovskite and noble metal promoted oxide based catalysts1997Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This work concerns efforts to improve or replace noble-metal based catalysts used for car exhaust purification.

    Various oxide based catalysts have been prepared by impregnating washcoats such as (-Al2O3 and SiO2 with appropriate metal ions, and assemblies calcinated at elevated temperatures have been tested for catalytic activity in the oxidation of CO and C3H6 and reduction of NO. SEM-EDS, ATEM-EDS and XRD have been used for phase analysis and for studies of the morphology of catalysts prepared in situ. The perovskite compounds La1-xSrxMe1-2yCuyRuyO3 with Me = Al and Ga have been prepared, in situ and ex situ [SGIW1]respectively, and tested for catalytic activity. Changes in cell parameters and catalytic activity of in-situ LaAl1-xCuxO3 when exposed alternatingly to oxidising and reducing car exhaust atmospheres have been studied. The catalytic activity of various transition metal oxides with and without addition of Pt/Rh or Pd have also been tested.

  • 121. Dahl, P.
    et al.
    Kaus, I.
    Zhao, Z.
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry, Inorganic Chemistry.
    Johnsson, Mats
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry, Inorganic Chemistry.
    Nygren, M.
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry, Inorganic Chemistry.
    Wiik, K.
    Grande, T.
    Einarsrud, M. -A
    Densification and properties of zirconia prepared by three different sintering techniques2007In: Ceramics International, ISSN 0272-8842, E-ISSN 1873-3956, Vol. 33, no 8, p. 1603-1610Article in journal (Refereed)
    Abstract [en]

    Densification of nanocrystalline yttria stabilized zirconia (YSZ) powder with 8 mol% Y2O3, prepared by a glycine/nitrate smoldering combustion method, was investigated by spark plasma sintering, hot pressing and conventional sintering. The spark plasma sintering technique was shown to be superior to the other methods giving dense materials (>= 96%) with uniform morphology at lower temperatures and shorter sintering time. The grain size of the materials was 0.21, 0.37 and 12 mu m after spark plasma sintering, hot pressing and conventional sintering, respectively. Total electrical conductivity of the materials showed no clear correlation with the grain size, but the activation energy for spark plasma sintered materials was slightly higher than for materials prepared by the two other densification methods. The hardness, measured by the Vickers indentation method, was found to be independent on grain size while fracture toughness, derived by the indentation method, was slightly decreasing with increasing grain size.

  • 122.
    Dahlberg, Martin
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Polymorphic phase behavior of cardiolipin derivatives studied by coarse-grained molecular dynamics2007In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 111, no 25, p. 7194-7200Article in journal (Refereed)
    Abstract [en]

    Cardiolipin (CL) is a negatively charged four acyl chain lipid, associated with energy production in bacterial and mitochondrial membranes. Due to the shape of CL, negative curvatures of aggregates are favorable if the charges in the head group can be reduced. The phase polymorphism of CL, and of associated derivatives with 2, 3, 4, or 5 chains, has been determined previously and offers a model system in which micellar, lamellar, and inverse hexagonal phases can be observed. We present an extension to a previously established coarse-grained molecular dynamics model with the aim of reproducing the different CL phases with two adjustable parameters: the number of acyl chains and the effective head group charge. With molecular dynamics simulations of large lipid systems, we observed transitions between different phases on the nanosecond to microsecond time scale. Charge screening by high salt or low pH was successfully modeled by a reduction of phosphate charge, which led to the adoption of aggregates with more negative curvature. Although specific ion binding at the interface and other atomistic details are sacrificed in the coarse-grained model, we found that it captures general phase features over a large range of aggregate geometries.

  • 123. Damian, E.
    et al.
    Eriksson, Lars
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Sandström, Magnus
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Sodium trichloromethanesulfonate monohydrate2006In: Acta Crystallographica, Vol. C62, p. m419-m420Article in journal (Other academic)
  • 124.
    Damian, Emiliana
    et al.
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Eriksson, Lars
    Sandström, Magnus
    Sodium trichloromethanesulfonate monohydrate2006In: Acta Crystallographica, Vol. C62, p. m419-m420Article in journal (Refereed)
  • 125.
    Damian, Emiliana
    et al.
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Jalilehvand, Farideh
    Abbasi, Alireza
    Pettersson, Lars G. M.
    Sandström, Magnus
    Sulfur K-edge X-ray Absorption Spectra for Dimethyl Sulfoxide in the Solvated Thallium(III), Indium(III), Gallium(III) and Aluminum(III) Ions2005In: Physica Scripta, Vol. T115, p. 1077-1079Article in journal (Refereed)
  • 126.
    Damian, Emiliana
    et al.
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Jalilehvand, Farideh
    Leung, Bonnie
    Pettersson, Lars G. M.
    Stockholm University, Faculty of Science, Department of Physics.
    Sandström, Magnus
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Theoretical and experimental sulfur K-edge X-ray absorption spectroscopic (XANES) study of cysteine, cystine, methionine and methionine sulfoxide2009In: Dalton Transactions, ISSN 1477-9226, E-ISSN 1477-9234, Vol. 18, p. 3542-3558Article in journal (Refereed)
    Abstract [en]

    The experimental sulfur K-edge x-ray absorption near edge structure (XANES) spectra of the amino acids cysteine, homocysteine, penicillamine, methionine, the oxidation products methionine sulfoxide and the disulfide cystine, have been analyzed by transition potential DFT calculations. The absolute energies and intensities of the main pre-edge sulfur 1s electron transitions have been computed to determine the character of the receiving low energy unoccupied molecular orbitals (MO), and to investigate the influence of external interactions, especially by introducing water molecules hydrogen bonded to the ionic species present in different pH ranges. When the thiol group deprotonates for the three amino acids cysteine, homocysteine and penicillamine the energy of the main transition, to an MO with antibonding σ*(S-H) character, reduces by ~1.1 eV and the receiving MO obtains σ*(S-C) character. The energy shifts due to hydrogen bonding were in most cases found to be relatively small, although the transition intensities could vary significantly due to the changes induced in the molecular charge distribution, thereby affecting the shapes of the spectral features. For the cysteine and penicillamine zwitterions deconvolution of the experimental spectra allowed the microscopic acid dissociation constants to be extracted separately for the thiol and the protonated amine groups, pKaT = 8.5 ± 0.1 and 8.2 ± 0.1, and pKaN = 8.9 ± 0.1 and 8.8 ± 0.1, respectively, in both cases with the thiol group the more acidic. Coordination of cysteine to nickel(II) or mercury(II) introduced a new low energy transition involving metal ion orbitals in the receiving LUMO. The small experimentally observed energy differences between the similar main absorption features of the cysteine and methionine zwitterions, 0.2-0.3 eV in comparable surrounding, as well as a minor difference in their intensity ratio, are reflected in the calculated transitions. The S K-edge XANES spectrum of the disulfide cystine displays a characteristic double peak with the lower energy transition (2469.9 eV) into the antibonding σ*(S-S) MO. The second peak, at 2471.5 eV in aqueous solution, contains several transitions into MO:s with σ*(S-C) character involving also charge transfer to the water molecules hydrating the protonated amine groups (NH3+) of cystine. The experimental energy difference between the two peaks increases by 0.2 eV for solid cystine, while no such increase occurs for the –S-S- bond between the cysteine residues in the oxidized disulfide of glutathione, where the amine groups are engaged in peptide bonds. This study shows that externally induced changes in the intramolecular bonding, e.g. by coordination, conformation geometry or hydrogen bonding, can significantly influence the S K-edge spectra, and emphasizes the importance of a similar chemical surrounding of the model compounds for standard spectra of sulfur functional groups, used to deconvolute composite experimental spectra.

  • 127.
    Damian Risberg, Emiliana
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Structure and bonding of sulfur-containing molecules and complexes2007Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Synchrotron-based spectroscopic techniques enable investigations of the many important biological and environmental functions of the ubiquitous element sulfur. In this thesis the methods for interpreting sulfur K-edge X-ray absorption near edge structure (XANES) spectra are developed and applied for analyses of functional sulfur groups. The influence of coordination, pH, hydrogen bonding, etc., on the sulfur 1s electronic excitations is evaluated by transition potential density functional theory. Analyses have been performed of reduced sulfur compounds in marine-archaeological wood from historical shipwrecks, including the Vasa, Stockholm, Sweden and the Mary Rose, Portsmouth, U.K.. The accumulation of sulfur as thiols in lignin-rich parts of the wood on the seabed is also a probable pathway in the natural sulfur cycle for how reduced sulfur enters fossil fuels via humic matter in anaerobic marine sediments. Sulfur K-edge XANES spectra for several biochemical model compounds and for coexisting isomeric sulfur species in cysteine and sulfite(IV) aqueous solutions have been analyzed with the aid of theoretical calculations. Cysteine derivatives are important for biochemical detoxification, and mercury(II) cysteine complexes in solution have been structurally characterized by means of Extended X-ray Absorption Fine Structure (EXAFS), Raman and 199Hg NMR spectroscopy. Lanthanoid(III) ions were found to coordinate eight dimethyl sulfoxide oxygen atoms in a distorted square antiprism in the solid state and in solution, by combining crystallography, EXAFS, XANES and vibrational spectroscopy. The mean M-O bond distances for the disordered crystal structures are in good agreement with those from the lattice-independent EXAFS studies. The different sulfur K-edge XANES spectra for the dimethyl sulfoxide ligands in the hexasolvated complexes of the trivalent group 13 metal ions, Tl(III), In(III), Ga(III) and Al(III), were interpreted by theoretical calculations.

  • 128.
    Damian Risberg, Emiliana
    et al.
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Mink, János
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Abbasi, Alireza
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Skripkin, Mikhail Yu.
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Hajba, Laszló
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Lindqvist-Reis, Patric
    Bencze, Éva
    Sandström, Magnus
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Ambidentate dimethyl sulfoxide coordination in protonated dimethyl sulfoxide, (CH3)2SO-H+, and in dichlorobis(dimethyl sulfoxide) palladium(II) and platinum(II) solid solvates, by vibrational and sulfur K-edge X-ray absorption spectroscopy2008In: Dalton TransactionsArticle in journal (Refereed)
    Abstract [en]

    The protonated dimethyl sulfoxide cation (CH3)2SO-H+ formed in concentrated hydrochloric acid displays a new low energy feature in its sulfur K-edge X-ray absorption near edge structure (XANES) spectrum. Density Functional Theory – Transition Potential (DFT-TP) calculations reveal that the energy of the transition S(1s)  LUMO, which has antibonding *(S-O) character, has decreased about 0.8 eV. Normal coordinate force field analyses of the vibrational spectra show that the SO stretching force constant of the oxygen-coordinated (CH3)2SO-H+ species has decreased to 3.73 N cm-1 from 4.72 N cm-1 in neat liquid dimethyl sulfoxide. The effects of sulfur coordination on the ambidentate dimethyl sulfoxide molecule were investigated for the trans-Pd((CH3)2SO)2Cl2 and cis-Pt((CH3)2SO)2Cl2 complexes with square planar coordination of the chlorine and sulfur atoms. The XANES spectra again showed shifts toward low energy of the transition S(1s)  LUMO, now with antibonding *(M-Cl, M-S) character, with a larger shift for M = Pt than Pd. DFT-TP calculations indicated that the differences between the XANES spectra of the geometrical isomers of the M((CH3)2SO)2Cl2 complexes are expected to be too small to allow experimental distinction. The vibrational spectra of the palladium(II) and platinum(II) complexes were recorded and complete assignments of the fundamentals were achieved. Even though the M-S bond distances are quite similar the high covalency especially of the Pt-S bonds induces significant increases in the S-O stretching force constants, 6.79 and 7.18 N cm-1, respectively.

  • 129.
    Danielsson, Jonas
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Computational chemistry studies of UV induced processes in human skin2004Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis presents and uses the techniques of computational chemistry to explore two different processes induced in human skin by ultraviolet light. The first is the transformation of urocanic acid into a immunosuppressing agent, and the other is the enzymatic action of the 8-oxoguanine glycosylase enzyme.

    The photochemistry of urocanic acid is investigated by time-dependent density functional theory. Vertical absorption spectra of the molecule in different forms and environments is assigned and candidate states for the photochemistry at different wavelengths are identified.

    Molecular dynamics simulations of urocanic acid in gas phase and aqueous solution reveals considerable flexibility under experimental conditions, particularly for for the cis isomer where competition between intra- and inter-molecular interactions increases flexibility.

    A model to explain the observed gas phase photochemistry of urocanic acid is developed and it is shown that a reinterpretation in terms of a mixture between isomers significantly enhances the agreement between theory and experiment , and resolves several peculiarities in the spectrum.

    A model for the photochemistry in the aqueous phase of urocanic acid is then developed, in which two excited states governs the efficiency of photoisomerization. The point of entrance into a conical intersection seam is shown to explain the wavelength dependence of photoisomerization quantum yield.

    Finally some mechanistic aspects of the DNA repair enzyme 8-oxoguanine glycosylase is investigated with density functional theory. It is found that the critical amino acid of the active site can provide catalytic power in several different manners, and that a recent proposal involving a SN1 type of mechanism seems the most efficient one.

  • 130.
    Danielsson, Jonas
    et al.
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Laaksonen, Aatto
    A theoretical study of the photoisomerization of anionic urocanic acidArticle in journal (Refereed)
  • 131.
    Danielsson, Jonas
    et al.
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Laaksonen, Aatto
    Gas phase photoisomerization of urocanic acid - a theoretical study2003In: Chemical Physics Letters, ISSN 0009-2614, Vol. 370, no 5-6, p. 625-Article in journal (Refereed)
  • 132.
    Danielsson, Jonas
    et al.
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Söderhäll, J. Arvid
    Laaksonen, Aatto
    Hydration structure and conformational dynamics of urocanic acid: a computer simulation study2002In: Molecular Physics, ISSN 0026-8976, Vol. 100, no 12, p. 1873-Article in journal (Refereed)
  • 133.
    Danielsson, Jonas
    et al.
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Ulicny, Jozef
    Laaksonen, Aatto
    A TD-DFT study of the photochemistry of urocanic acid in biologically relevant forms and solvent - influence of ionic, rotameric and protomeric state2001In: Journal of the American Chemical Society, ISSN 0002-7863, Vol. 123, no 40, p. 9817-Article in journal (Refereed)
  • 134.
    Deiana, Luca
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Dziedzic, Pawel
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Zhao, Gui-Ling
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Vesely, Jan
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Ibrahem, Ismail
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Rios, Ramón
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Sun, Junliang
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry, Structural Chemistry.
    Córdova, Armando
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Catalytic asymmetric aziridination of α,β-unsaturated aldehydes2011In: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 17, no 28, p. 7904-7917Article in journal (Refereed)
    Abstract [en]

    The development, scope, and application of the highly enantioselective organocatalytic aziridination of α,β-unsaturated aldehydes is presented. The aminocatalytic azirdination of α,β-unsaturated aldehydes enables the asymmetric formation of β-formyl aziridines with up to >19:1 d.r. and 99% ee. The aminocatalytic aziridination of α-monosubstituted enals gives access to terminal α-substituted-α-formyl aziridines in high yields and upto 99% ee. In the case of the organocatalytic aziridination of disubstituted α,β-unsaturated aldehydes, the transformations were highly diastereo- and enantioselective and give nearly enantiomerically pure β-formyl-functionalized aziridine products (99% ee). A highly enantioselective one-pot cascade sequence based on the combination of asymmetric amine and N-heterocycliccarbene catalysis (AHCC) is also disclosed. This one-pot three-component co-catalytic transformation between α,β-unsaturated aldehydes, hydroxylamine derivatives, and alcohols gives the corresponding N-tert-butoxycarbonyl and N-carbobenzyloxy-protected β-amino acid esters with ee values ranging from 92–99%. The mechanisms and stereochemistry of all these catalytic transformations are also discussed.

  • 135.
    Deiana, Luca
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Zhao, Gui-Ling
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Leijonmarck, Hans
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Lehmann, Christian
    Sun, Junliang
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry, Structural Chemistry.
    Lehmann, Christian W.
    Córdova, Armando
    Stockholm University, Faculty of Science, Department of Organic Chemistry. Mid Sweden University.
    Direct Catalytic Asymmetric Synthesis of Pyrazolidine Derivatives2012In: ChemistryOpen, ISSN 2191-1363, Vol. 1, no 3, p. 134-139Article in journal (Refereed)
    Abstract [en]

    A highly enantioselective, metal-free cascade reaction between di-1,2-N-protected hydrazine and α,β-unsaturated aldehydes is disclosed. The catalytic, asymmetric cascade transformation is a direct entry to 3-hydroxypyrazolidine and 3-allylpyrazolidine derivatives in one step and two steps, respectively, with >19:1 d.r. and 98–99 % ee using simple chiral pyrrolidines as catalysts.

  • 136. Dekov, Vesselin M.
    et al.
    Hålenius, Ulf
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Eriksson, Lars
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Native Sn–Pb droplets in a zeolitic amygdale (Isle of Mull, Inner Hebrides)2009In: Geochimica et Cosmochimica Acta, ISSN 0016-7037, E-ISSN 1872-9533, Vol. 73, no 10, p. 2907-2919Article in journal (Refereed)
    Abstract [en]

    Despite the particular scientific interest in the elements with high affinity to S and O2, but found in zero-valence state in nature, the origin of these native minerals has been little explored and remains obscure. Here we describe unique Sn–Pb droplets found in a closed analcime–calcite amygdale collected from a basaltic unit cropping out at Carsaig Bay (Isle of Mull, Inner Hebrides). The droplets consist of intimate intergrowths of nearly pure Sn0 and Pb0 domains in proportion 88:12 and are enveloped in a thin, brownish film of organic composition. The occurrence of the Sn–Pb droplets in a closed amygdale, their relationship with the host analcime + calcite and their Pb isotope composition (which does not match any known anthropogenic Pb source) rule out the possibility of anthropogenic contamination and support the natural origin of the Sn–Pb alloy.

    The variable isotope (Pb, Sr, Nd) compositions in different members of the host basaltic sequence suggest that a parent basaltic magma was modified by crustal assimilation and post-emplacement alteration processes. Considering all possible explanations, it appears that the most likely source of Pb for the Sn–Pb alloy is a discrete basaltic unit with an isotopic composition comparable to the Antrim basalts (Northern Ireland). The amygdale phases, on the other hand, show isotopic evidence for incorporation of elements from both local basaltic and sedimentary units. The apparent isotopic disequilibrium between Sn–Pb droplets and amygdale phases indicates a complex, multi-stage fluid evolution. The occurrence of Sn–Pb droplets in organic capsules suggests that the droplets and the enveloping organic substances are co-precipitates. This implies that the transportation and deposition of Sn and Pb might have occurred through organometallic compounds. We assume interaction of seawater fluids carrying metals leached from basaltic rocks with hydrocarbons from sedimentary units as a prerequisite for the formation of the organometallic complexes. The zeolites lining the basaltic vesicles might have destabilized the migrating organo-Sn and Pb compounds causing their breakdown and precipitation of Sn–Pb alloy.

  • 137. Dominguez-Rodriguez, Arturo
    et al.
    Gomez-Garcia, Diego
    Zapata-Solvas, Eugenio
    Shen, James Z.
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry, Inorganic Chemistry.
    Chaim, Rachman
    Making ceramics ductile at low homologous temperatures2007In: Scripta Materialia, ISSN 1359-6462, E-ISSN 1872-8456, Vol. 56, no 2, p. 89-91Article in journal (Refereed)
    Abstract [en]

    Polycrystalline ceramics are brittle at room temperature but may deform by dislocation slip processes at higher temperatures, where T >= 0.5 T-M (T-M, the melting temperature), leading to strain hardening, i.e. the total strain to rupture is limited. We show that mutual sliding of nanometer grains and atomic transport along their boundaries enables low-temperature metal-like plasticity in nanocrystalline ceramics. Compression of fully dense MgO nanoceramics at temperatures as low as 700 degrees C (0.31 T-M) exhibited stress-strain curves with no strain hardening.

  • 138.
    Dong, Kun
    et al.
    Institute of Process Engineering, Chinese Academy of Sciences, 100190 Beijing, China.
    Zhou, Guohui
    Institute of Process Engineering, Chinese Academy of Sciences, 100190 Beijing, China.
    Liu, Xiaomin
    Institute of Process Engineering, Chinese Academy of Sciences, 100190 Beijing, China.
    Yao, Xiaoguian
    Institute of Process Engineering, Chinese Academy of Sciences, 100190 Beijing, China.
    Zhang, Suojiang
    Institute of Process Engineering, Chinese Academy of Sciences, 100190 Beijing, China.
    Lyubartsev, Alexander
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Structural Evidence for the Ordered Crystallites of Ionic Liquid in Confined Carbon Nanotubes2009In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 113, no 23, p. 10013-10020Article in journal (Refereed)
    Abstract [en]

    Ionic liquids (ILs) are a class of new green materials that have attracted extensive attention in recent decades. Many novel properties not evident under normal conditions may appear when ionic liquids are confined to a nanometer scale. As was observed in the experiment, an anomalous phase behavior from liquid to high melting point perfect crystal occurred when 1-n-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF6]) ionic liquid was confined in a carbon nanotube. In this work, we performed molecular dynamics (MD) simulations for [bmim][PF6] ionic liquid and provided direct structural evidence that the ionic crystallizes in a carbon nanotube. The ordered ionic arrangement in both the radial and the axial directions can be observed inside the channels of the CNTs to induce the form of crystallites. The ionic stacking and distributing can be determined by the sizes of the CNTs. Hydrogen bonds remain the dominant interactions between cations and anions when the ionic liquid enters into the CNT from the bulk phase. The free energies as the thermal driven forces were calculated, and it is found that it is very difficult for a single anion to enter into the channel of the CNT spontaneously. A more favorable way is through an ion-pair in which a cation “pulls” an anion to enter into the channel of the CNT together. It is predicted that other ionic liquids that possess similar structures, even including the pyridinium-based ionic liquids, can show higher melting points when confined in CNTs.

  • 139.
    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

  • 140. Dvinskikh, S.V.
    et al.
    Castro, Vasco
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Sandström, D.
    Heating caused by radiofrequency irradiation and sample rotation in 13C magic angle spinning NMR studies of lipid membranes2004In: Magn. Reson. Chem., Vol. 42, p. 875-881Article in journal (Refereed)
  • 141. Dvinskikh, S.V.
    et al.
    Castro, Vasco
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Sandström, D.
    Probing segmental order in lipid bilayers at variable hydration levels by amplitude- and phase-modulated cross-polarization NMR2005In: Phys. Chem. Chem. Phys., Vol. 7, p. 3255-3257Article in journal (Refereed)
  • 142.
    Dziedzic, Pawel
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Schyman, Patric
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry, Department of Physical Chemistry.
    Kullberg, Martin
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Córdova, Armando
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Highly enantioselective organocatalytic addition of aldehydes to N-(phenylmethylene)benzamides: Asymmetric synthesis of the paclitaxel side chain and its analogues2009In: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 15, no 16, p. 4044-4048Article in journal (Refereed)
  • 143.
    Eden, Mattias
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Determination of absolute quadrupolar tensor orientations by double-quantum NMR on powders2009In: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 470, no 4-6, p. 318-324Article in journal (Refereed)
    Abstract [en]

    We introduce a new nuclear magnetic resonance (NMR) approach for determining electric field gradient (‘quadrupolar’) tensor orientations directly from polycrystalline powders. It involves a homonuclear 2D experiment that correlates (two-spin) double-quantum and single-quantum coherences of half-integer quadrupolar spin nuclei undergoing magic-angle-spinning. The 2D NMR spectrum is sensitive both to the relative orientations between the correlated quadrupolar tensors and to their orientations relative to the dipolar vector of the spin-pair. A novel strategy to calculate 2D spectra from multi-spin systems is used to extract the tensor orientations. We demonstrate the method by estimating the three 23Na quadrupolar tensor orientations in Na2SO3

  • 144.
    Eden, Mattias
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Homonuclear dipolar recoupling of half-integer spin quadrupolar nuclei: techniques and applications2009In: Solid State Nuclear Magnetic Resonance, ISSN 0926-2040, E-ISSN 1527-3326, Vol. 36, no 1, p. 1-10Article in journal (Refereed)
    Abstract [en]

    We review recent advances in solid state NMR methodology for recovering homonuclear dipolar interactions among half-integer quadrupolar spins undergoing sample rotation. Existing dipolar recoupling techniques are contrasted, based on (i) the form of their associated dipolar Hamiltonian, (ii) the different experimental conditions necessitating their realization and (iii) their roles as components in multi-dimensional NMR correlation spectroscopy. Various types of structural information accessible from such solid state NMR experimentation is reviewed. Promises and limitations of methodologies targeting homonuclear dipolar couplings between half-integer spins under high-resolution conditions are discussed, with particular focus on the demands set for structural investigations of crystalline as well as structurally disordered (amorphous) inorganic network materials

  • 145.
    Eden, Mattias
    et al.
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry, Physical Chemistry.
    Grins, Jekabs
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry, Inorganic Chemistry.
    Jansson, Kjell
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Inorganic and Structural Chemistry.
    Shen, Zhijian
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Materials Chemistry.
    Al and O substitutions in BaS-phases, Ba2AlxSi12-xN16-xO2+x: A TEM, XRD and solid-state NMR study2008In: Solid State Sciences, ISSN 1293-2558, E-ISSN 1873-3085, Vol. 10, no 1, p. 50-60Article in journal (Refereed)
    Abstract [en]

    In a series of Ba-based oxonitrido-silicate S-phases (Ba2AlxSi12-xN16-xO2+x) spanning a compositional range up to x approximate to 3, we examine the incorporation of Al and O by Si-29 and Al-27 magic-angle spinning (MAS) solid state nuclear magnetic resonance (NMR) and Al-27 triple-quantum MAS (3QMAS). The 3QMAS spectra reveal Al-27 signals from two distinct structural environments, assigned to AlN4 or AlN3O tetrahedra, respectively, and with their relative amounts depending on the S-phase substitution parameter x. Si-29 NMR show variable fractions of SiN4 and SiN3O environments. The NMR results accord overall with a structural substitution model for which O enters at one crystallographic position (occupied according to N4-xOx), in conjunction with a random Al for Si substitution at two distinct crystallographic positions. This leads to S-phase frameworks built from SiN4, SiN3O, AlN4 and AlN3O tetrahedra.

  • 146.
    Eden, Mattias
    et al.
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Lo, Andy
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Supercycled symmetry-based double-quantum dipolar recoupling of quadrupolar spins in MAS NMR2009In: Journal of Magnetic Resonance, Vol. 200, no 2, p. 267-279Article in journal (Refereed)
    Abstract [en]

    Using average Hamiltonian (AH) theory, we analyze recently introduced homonuclear dipolar recoupling pulse sequences for exciting central-transition double-quantum coherences (2QC) between half-integer spin quadrupolar nuclei undergoing magic-angle-spinning. Several previously observed differences among the recoupling schemes concerning their compensation to resonance offsets and radio-frequency (rf) inhomogeneity may qualitatively be rationalized by an AH analysis up to third perturbation order, despite its omission of first-order quadrupolar interactions. General aspects of the engineering of 2Q-recoupling pulse sequences applicable to half-integer spins are discussed, emphasizing the improvements offered from a diversity of supercycles providing enhanced suppression of undesirable AH cross-terms between resonance offsets and rf amplitude errors.

  • 147. Egorov, Andrei V.
    et al.
    Brodskaya, Elena N.
    Laaksonen, Aatto
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Molecular Dynamics Simulation Study of Solid-Liquid Phase Transition in Water Clusters. The Effect of Cluster Size2007In: Synthesis and Reactivity in Inorganic, Metal-Organic and Nano-Metal ChemistryArticle in journal (Refereed)
  • 148. Egorov, Andrei V
    et al.
    Laaksonen, Aatto
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Brodskaya, Elena N
    Computer Simulations Studies of Solid–Liquid Phase Transitions in Solid Water Nano Particles2008In: Journal of Computational and Theoretical Nanoscience, Vol. 5, p. 1–9-Article in journal (Refereed)
  • 149. Egorov, AV
    et al.
    Laaksonen, Aatto
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Brodskaya, EN
    Molecular dynamics simulation study of solid-liquid phase transition in water clusters. The effect of cluster size2008In: Journal of Synthesis and Reactivity in Inorganic, Metal-Organic, and Nano-Metal Chemistry, Vol. 38, no 1, p. 62-67Article in journal (Refereed)
  • 150.
    Elenius, Måns
    et al.
    Stockholm University, Faculty of Science, Numerical Analysis and Computer Science (NADA) (together with KTH).
    Zetterling, Fredrik
    Dzugutov, Mikhail
    KTH, MSE.
    Fredrickson, Daniel
    Department of Chemistry, University of Wisconsin.
    Lidin, Sven
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry, Department of Inorganic Chemistry.
    Structural model for octagonal quasicrystals derived from octagonal symmetry elements arising in beta-Mn crystallization of a simple monatomic liquid2009In: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 79, no 14, p. 144201-1-144201-10Article in journal (Refereed)
    Abstract [en]

    While performing molecular-dynamics simulations of a simple monatomic liquid, we observed the crystallization of a material displaying octagonal symmetry in its simulated diffraction pattern. Inspection of the atomic arrangements in the crystallization product reveals large grains of the beta-Mn structure aligned along a common fourfold axis, with 45° rotations between neighboring grains. These 45° rotations can be traced to the intercession of a second crystalline structure fused epitaxially to the beta-Mn domain surfaces, whose primitive cell has lattice parameters a=b=c=a_{beta-Mn}, alpha =beta =90°, and gamma =45°. This secondary phase adopts a structure which appears to have no known counterpart in the experimental literature, but can be simply derived from the Cr3Si and Al3Zr4 structure types. We used these observations as the basis for an atomistic structural model for octagonal quasicrystals, in which the beta-Mn and the secondary phase structure unit cells serve as square and rhombic tiles (in projection), respectively. Its diffraction pattern down the octagonal axis resembles those experimentally measured. The model is unique in being consistent with high-resolution electron microscopy images showing square and rhombic units with edge-lengths equal to that of the beta-Mn unit cell. Energy minimization of this configuration, using the same pair potential as above, results in an alternative octagonal quasiperiodic structure with the same tiling but a different atomic decoration and diffraction pattern.

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