Biomedical subjects

Lubomír Smrcok

Publications and source records attributed to Lubomír Smrcok.

5 recordsLinked to original sources

PubMed2006

On hydrogen bonding in 1,6-anhydro-beta-D-glucopyranose (levoglucosan): X-ray and neutron diffraction and DFT study.

The geometry of hydrogen bonds in 1,6-anhydro-beta-D-glucopyranose (levoglucosan) is accurately determined by refinement of time-of-flight neutron single-crystal diffraction data. Molecules of levoglucosan are held together by a hydrogen-bond array formed by a combination of strong O-H...O and supporting weaker C-H...O bonds. These are fully and accurately detailed by the neutron diffraction study. The strong hydrogen bonds link molecules in finite chains, with hydroxyl O atoms acting as both donors and acceptors of hydroxyl H atoms. A comparison of molecular and solid-state DFT calculations predicts red shifts of O-H and associated blue shifts of C-H stretching frequencies due to the formation of hydrogen bonds in this system.

Crystallography, X-Ray↗

PubMed2006

Gamma-alumina: a single-crystal X-ray diffraction study.

The structure of gamma-alumina (Al21+1/3square2+2/3O32) crystals obtained as a product of a corrosion reaction between beta-sialon and steel was refined in the space group Fd3m. The oxygen sublattice is fully occupied. The refined occupancy parameters are 0.83 (3), 0.818 (13), 0.066 (14) and 0.044 (18) for Al ions in 8a, 16d, 16c and 48f positions, respectively. The Al ions are distributed over octahedral and tetrahedral sites in a 63:37 ratio, with 6% of all Al ions occupying non-spinel positions.

Journal Article↗

PubMed2006

2-anilinomethylene-3-oxobutanenitrile: an X-ray and density functional theory study.

Molecules of the title compound, C11H10N2O, are effectively planar. In the crystal structure, they are stabilized primarily by electrostatic interactions, as the dipole moment of the molecule is 4.56 D. In addition, the molecules are linked by weak C-H...N and C-H...O hydrogen bonds. An analysis of bonding conditions in the molecule was carried out using natural bond orbital (NBO) formalism.

Journal Article↗

PubMed2005

Second-degree twinning and dynamic disorder in the crystal structure of deca-dodecasil 3R.

The structure of deca-dodecasil 3R (DD-3R), Si120O240, a very well suited material for the synthesis of inorganic/organic composites structured on a nanometer level, has been investigated in detail. So far, a highly complicated twinning has hampered its structure description at a desirable level of accuracy. This twinning has now been resolved and a new structure determination is presented. Structure refinement in the R\bar 3 space group revealed a large, unusually shaped atomic displacement ellipsoid for oxygen-bridging units (tetrahedra), bridging Si-O bonds shorter than expected and the linear Si-O-Si' bond angle dictated by special positions at a threefold axis. A structure model based on a statistically disordered bridging O atom improved the accuracy of the Si-O bonds of interest, but provided unacceptable O-O contacts. To solve this dilemma, ab initio NVT molecular dynamics calculations were performed to study the possible configurations. Wavelet analysis of the time variations of selected Si-O distances pointed to a synchronous shift of the whole building units (tetrahedra). Low-frequency features of the calculated phonon density of states agree well with the published INS (inelastic neutron scattering) spectra of several silica polymorphs, indicating that the nature of the disorder in DD-3R is dynamic rather than static.

Journal Article↗

PubMed2004

Pseudo-merohedrally twinned praseodymium hexacyanoferrate(III) tetrahydrate.

Crystals of the title compound, diaquahexa-mu-cyano-ferrate(III)praseodymium(III) dihydrate, Pr[Fe(CN)(6)].4H(2)O or [PrFe(CN)(6)(H(2)O)(2)].2H(2)O, are twinned with three components. The Pr atom is coordinated by eight atoms, viz. six N and two symmetry-related water O atoms. The Pr polyhedron (Pr has site symmetry m2m, Wyckoff position 4c) is linked to an FeC(6) octahedron (Fe located on a site with imposed 2/m symmetry, Wyckoff position 4b) through N atoms, forming an infinite array. The second (symmetry independent) water molecule lies on a mirror plane, is not included in coordination and is weakly hydrogen bonded to N atoms.

Journal Article↗