Michal Hušák

Bio: Michal Hušák is an academic researcher from Institute of Chemical Technology in Prague. The author has contributed to research in topics: Crystal structure & Powder diffraction. The author has an hindex of 12, co-authored 75 publications receiving 533 citations. Previous affiliations of Michal Hušák include Ivax Corporation & University of South Bohemia in České Budějovice.

MCE2005– a new version of a program for fast interactive visualization of electron and similar density maps optimized for small molecules

Abstract: A new version of MCE is described. This new version supports atom-position generation based on space groups and can display more unit cells around the basic unit cell. The display settings have been improved to allow the colors of the background, atoms and maps to be changed.

Simvastatin: structure solution of two new low-temperature phases from synchrotron powder diffraction and ss-NMR

Abstract: Simvastatin is a substance used for the treatment of hypercholesterolemia. In addition to the already known room temperature structure of simvastatin (Cejka et al. in Acta Cryst C59:o428, 2003) two new low-temperature polymorphs were found by X-ray powder diffraction with the phase transition at 261 and 223 K (later confirmed by DSC to be 272 and 232 K). The main differences among three polymorphs consist in the side-chains conformation only and the phase changes are fully reversible. The structures of the polymorphs were studied by the powder diffraction based on synchrotron radiation as well as by solid-state NMR spectroscopy.

Iron uptake system of some members of the genus tolypocladium: crystal structure of the ligand and its iron(III) complex

Abstract: A new type of fungal hydroxamic acid (1′S,2′R,4′S,6′R)-3-(2′,4′-dimethyl-6′-vinylcyclohexyl)-1,4-dihydroxy-2(1H)-pyridone (tolypocin, HL) has been isolated from the mycelium of the fungus Tolypocladium geodes. The acid (C15H21NO3) crystallized from methanol [monoclinic, space group P21, Z= 4, a= 12.28(1), b= 9.958(5), c= 12.737(4), A, β= 94.91(5)°]. The structure was solved by direct methods and refined to a final R value of 0.055 for 2393 unique observed reflections. The iron(III) trischelate complex of this ligand [FeL3] has been isolated from the mycelium of the fungus Tolypocladium terricola. Its methanol solvate (C45H60FeN3O9·2MeOH) was crystallized from methanol [orthorhombic, space group P212121, Z= 4, a= 20.27(3), b= 19.35(5), c= 13.43(4)A]. The structure was solved by direct methods and refined to a final R value of 0.062 for 5562 observed reflections. The absolute configuration of the complex as determined from CD spectra and anomalous X-ray dispersion has been shown to be Λ-cis both in solution and in the solid state.

Ergogaline, a new ergot alkaloid, produced by claviceps purpurea : isolation, identification, crystal structure and molecular conformation

Abstract: A new peptide ergot alkaloid containing L-homoisoleucine has been isolated from ergot sclerotia of the field-growing parasitic fungus Claviceps purpurea. The molecular and crystal structures have been studied by X-ray analysis [ergogaline monohydrate, monoclinic space group P21 with two molecules per unit cell of the dimensions a= 9.972(1), b= 10.902(1) and c= 14.761 (1)A, β= 94.05(1)°] and compared with the structures in solution as determined by 2D NMR spectroscopy.

Determining the Crystal Structures of Peptide Analogs of Boronic Acid in the Absence of Single Crystals: Intricate Motifs of Ixazomib Citrate Revealed by XRPD Guided by ss-NMR

Abstract: Uncertainties in the structure determination of peptide analogs of boronic acid, exacerbated by the many coordination modes of boron, represent an obstacle in understanding their role in living organisms and thus also in developing the next generation of anticancer drugs. For that reason, we present here a general experimental-computational strategy allowing structure determination of complex boronic acid derivatives with extensive conformational variability. We demonstrate successful solution of the crystal structures of two nonsolvated polymorphs of ixazomib citrate directly from synchrotron powder diffraction data, which is challenging because the two molecules in the asymmetric unit cell that exhibit 32 degrees of conformational freedom push the limits of current solution procedures. We used a novel two-step Rietveld refinement based on DFT-D restraints to improve information quality derived from powder diffraction data to be comparable with that of single-crystal solutions. NMR crystallography was ap...

Crystallographic Computing System JANA2006: General features

Abstract: Abstract JANA2006 is a freely available program for structure determination of standard, modulated and magnetic samples based on X-ray or neutron single crystal/ powder diffraction or on electron diffraction. The system has been developed for 30 years from specialized tool for refinement of modulated structures to a universal program covering standard as well as advanced crystallography. The aim of this article is to describe the basic features of JANA2006 and explain its scope and philosophy. It will also serve as a basis for future publications detailing tools and methods of JANA.

CRYSTALS enhancements: dealing with hydrogen atoms in refinement

Abstract: Because they scatter X-rays weakly, H atoms are often abused or neglected during structure refinement. The reasons why the H atoms should be included in the refinement and some of the consequences of mistreatment are discussed along with selected real examples demonstrating some of the features for hydrogen treatment that can be found in the software suite CRYSTALS.