Vratislav Langer

Synthesis, a case of isostructural packing, and antimicrobial activity of silver(I)quinoxaline nitrate, silver(I)(2,5-dimethylpyrazine) nitrate and two related silver aminopyridine compounds

The synthesis and low temperature crystal structures of [Ag(quinoxaline)]n(NO3)n, 1, [Ag(2,5-dimethylpyrazine)(NO3)]n, 2 and [Ag4(3-aminopyridine)4(NO3)4]n 3 are presented. The quinoxaline compound forms a 1D coordination polymer with the characteristic linear 2-coordination figure of silver(I), the N-Ag-N angle being 164.2(1) degrees, and only weak silver-nitrate interactions. In addition there is an interaction giving pairs of parallel chains as the main structural theme. The 2,5-dimethylpyrazine compound has approximately trigonal-planar coordination, also binding one nitrate at the relatively short Ag-O distances 2.444(3) angstroms and 2.484(3) angstroms, respectively, for the two crystallographically different silver atoms. This also results in a 1D coordination polymer that, despite the large differences in the Ag(I) coordination environment, is isostructural with 1. [Ag4(3-aminopyridine)4(NO3)4]n 3 forms a 2D coordination polymer by bridging nitrate ions. The antimicrobial activity of 1-3, and also of [Ag3(2-aminopyridine)4](NO3)3, 4 was screened for 13 different pathogens and substantial activity was shown for 1 against Escherichia coli and Pseudomonas aeruginosa (MIC 4 microg cm(-3)) and somewhat lower activity was registered against Sarcina lutea and Salmonella typhi for 1, Bordetella bronchiseptica for 2, Salmonella typhi and Pseudomonas aeruginosa for 3, and Escherichia coli and Shigella sonnie for 3 (MIC 8 microg cm(-3)). Only low activity was shown against the yeast Candida albicans for 1, 2 and 4 whereas no activity against this pathogen was registered for 3.

Phenylphosphonic acid as a building block for two-dimensional hydrogen-bonded supramolecular arrays

Abstract The potential use of organic phosphorus acids for the architecture of supramolecular hydrogen-bonded assemblies has been demonstrated by the structural determination of phenylphosphonic acid (1), anilinium phenylphosphonate (2), p-phenylazoanilinium phenylphosphonate (3), ethylenediammonium phenylphosphonate hydrate (4) and hexamethylenediammonium phenylphosphonate hydrate (5). Compounds 1, 2, 4 and 5 exhibit layered structures with two-dimensional networks of hydrogen bonds from which the organic tails point out. Compound 3 crystallizes as two concomitant polymorphs showing supramolecular isomerism: a monoclinic phase (3a) with a layered structure and a triclinic phase (3b) in which hydrogen bonds form columns. In these assemblies, there are supramolecular motifs such as chains and rings of hydrogen-bonded moieties. Water molecules are involved in the formation of hydrogen-bonding networks for compounds 4 and 5. For compound 5, hexamethylenediammonium ions link the adjacent sheets, forming a pillared-layered structure. It has been shown that the phosphonate groups can act as both donor and acceptor of hydrogen bonds. Analysis of the hydrogen bonds of the types (P–)O–H⋯O(–P) and N–H⋯O(–P) reveals that they can be regarded as medium to strong hydrogen bonds.

Synthesis, Crystal Structure, Quantum Chemical Calculations, DNA Interactions, and Antimicrobial Activity of [Ag(2-amino-3-methylpyridine)2]NO3 and [Ag(pyridine-2-carboxaldoxime)NO3]

[Ag(2-amino-3-methylpyridine)(2)]NO(3) (1) and [Ag(pyridine-2-carboxaldoxime)NO(3)] (2) were prepared from corresponding ligands and AgNO(3) in water/ethanol solutions, and the products were characterized by IR, elemental analysis, NMR, and TGA. The X-ray crystal structures of the two compounds show that the geometry around the silver(I) ion is bent for complex 1 with nitrate as an anion and trigonal planar for complex 2 with nitrate coordinated. ESI-MS results of solutions of 2 indicate the independent existence in solution of the [Ag(pyridine-2-carboxaldoxime)](+) ion. The geometries of the complexes are well described by DFT calculations using the ZORA relativistic approach. The compounds were tested against 14 different clinically isolated and four ATCC standard bacteria and yeasts and also compared with 17 commonly used antibiotics. Both 1 and 2 exhibited considerable activity against S. lutea , M. lutea , and S. aureus and against the yeast Candida albicans , while 2-amino-3-methylpyridine is slightly active and pyridine-2-carboxaldoxime shows no antimicrobial activity. In addition, the interaction of these metal complexes with DNA was investigated. Both 1 and 2 bind to DNA and reduce its electrophoretic mobility with different patterns of migration, while the ligands themselves induce no change.

Stereochemical assignment of the enantiomers of omeprazole from X-ray analysis of a fenchyloxymethyl derivative of (+)-(R)-omeprazole

Abstract The absolute configurations of the enantiomers of the H+, K+-ATPase inhibitor omeprazole 1 have been determined by an X-ray crystallographic study of a derivative of (+)-(R)-1. The examined compound 6-methoxy-2-[[(4-methoxy-3,5-dimethyl-2-pyridinyl)methyl]-(R)-sulfinyl]-1-[[[(1R-endo)-1,3,3-trimethylbicyclo[2.2.1]hept-2-yl]- oxy]methyl]-1H-benzimidazole4 was synthesized from enantiomerically pure (1R-endo)-2-(chloromethoxy)-1,3,3-trimethylbicyclo[2.2.1]heptane2 and enantiomerically pure (+)-(R)-1. Finally, enantiomerically, diastereomerically and regioisomerically pure 4 was converted back to (+)-(R)-1 in order to verify that no stereomutation had occurred on sulfur during the synthesis of 4.

Oxidation of Simple and Pt-Modified Aluminide Diffusion Coatings on Ni-Base Superalloys—I. Oxide Scale Microstructure

The isothermal oxidation at 1050°C of one simple (PWA73) and three Pt-modified (RT22, SS82A and MDC150L) aluminide diffusion coatings, deposited on the same single crystalline Ni-base superalloy, CMSX-4, was investigated. The oxidation was studied by gravimetry, scanning-electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray spectrometry (EDS) and grazing angle X-ray diffraction (XRD). TEM samples were prepared by focused ion beam (FIB) milling. It was found that the oxide on the simple-aluminide coating grew much faster and started to spall much earlier than those on the Pt-modified coatings. This was related to the higher amount of other phases than α-Al2O3 in the oxide scale on the simple-aluminide coating. It was shown that the presence of Pt in the coating suppressed the formation of deleterious phases such as spinels in the oxide scale, but also that the surface morphology of the coating prior to oxidation plays an important role.

Ash sintering and deposit formation in PFBC

Agglomerated bed material and deposits from various surfaces in the bed area and in the flue gas duct of pressurized fluidized bed combustion (PFBC) plants were examined by chemical and X-ray diffraction methods. Crystalline compounds present in the deposits were identified and possible mechanisms leading to the formation of bed material agglomerates, deposits and fouling on surfaces in the flue gas duct are discussed. The results show that all of the chemical systems CaS-CaSO4-alkali species, silicate-alkali-chlorine and silicate systems containing iron-rich oxides are important in the sintering and fouling process.

Synthesis of new series of quinoxaline based MAO-inhibitors and docking studies

A series of 2-benzyl-3-(2-arylidenehydrazinyl)quinoxalines 3, 4-benzyl-1-aryl-[1,2,4]triazolo[4,3-a]quinoxalines 4 and phenyl(1-aryl-[1,2,4]triazolo[4,3-a]quinoxalin-4-yl)methanones 5 analogues were synthesized and investigated for their monoamine oxidase (MAO) inhibitory property. The inhibition profile was found to be competitive for compounds 3k, 3m, 5f and 5n with MAO-A selectivity. Observation of the docked positions of these compounds revealed interactions with many residues previously reported to have an effect on the inhibition of the enzyme. The structural features of the new compounds have been determined from the microanalytical, IR, (1)H, (13)C NMR spectral studies and X-ray crystalography.

The metal site of Pseudomonas aeruginosa azurin, revealed by a crystal structure determination of the Co(II) derivative and Co-EPR spectroscopy.

The crystal structure of cobalt‐substituted azurin from Pseudomonas aeruginosa has been determined to final crystallographic R value of 0.175 at 1.9 Å resolution. There are four molecules in the asymmetric unit in the structure, and these four molecules are packed as a dimer of dimers. The dimer packing is very similar to that of the wild‐type Pseudomonas aeruginosa azurin dimer. Replacement of the native copper by the cobalt ion has only small effects on the metal binding site presumably because of the existence of an extensive network of hydrogen bonds in its immediate neighborhood. Some differences are obvious, however. In wild‐type azurin the copper atom occupies a distorted trigonal bipyramidal site, while cobalt similar to zinc and nickel occupy a distorted tetrahedral site, in which the distance to the Met121,Sδ atom is increased to 3.3–3.5 Å and the distance to the carbonyl oxygen of Gly45 has decreased to 2.1–2.4 Å. The X‐band EPR spectrum of the high‐spin Co(II) in azurin is well resolved (apparent g values gx′ = 5.23; gy′ = 3.83; gz′ = 1.995, and hyperfine splittings Ax′ = 31; Ay′ = 20–30; Az′ = 53 G) and indicates that the ligand field is close to axial. Proteins 27:385–394, 1997.

Effects of Different Substituents on the Crystal Structures and Antimicrobial Activities of Six Ag(I) Quinoline Compounds

The syntheses and single crystal X-ray structures of [Ag(5-nitroquinoline)2]NO3 (1), [Ag(8-nitroquinoline)2]NO3·H2O (2), [Ag(6-methoxy-8-nitroquinoline)(NO3)]n (3), [Ag(3-quinolinecarbonitrile)(NO3)]n (4), [Ag(3-quinolinecarbonitrile)2]NO3 (5), and [Ag(6-quinolinecarboxylic acid)2]NO3 (6) are described. As an alternative to solution chemistry, solid-state grinding could be used to prepare compounds 1 and 3, but the preparation of 4 and 5 in this way failed. The Ag(I) ions in the monomeric compounds 1, 2, 5, and 6 are coordinated to two ligands via the nitrogen atoms of the quinoline rings, thereby forming a distorted linear coordination geometry with Ag-N bond distances of 2.142(2)-2.336(2) Å and N-Ag-N bond angles of 163.62(13)°-172.25(13)°. The 1D coordination polymers 3 and 4 contain Ag(I) centers coordinating one ligand and two bridging nitrate groups, thereby forming a distorted trigonal planar coordination geometry with Ag-N bond distances of 2.2700(14) and 2.224(5) Å, Ag-O bond distances of 2.261(4)-2.536(5) Å, and N-Ag-O bond angles of 115.23(5)°-155.56(5)°. Hirshfeld surface analyses of compounds 1-6 are presented as d(norm) and curvedness maps. The d(norm) maps show different interaction sites around the Ag(I) ions, i.e., Ag···Ag interactions and possible O-H···O, C-H···O, C-H···N, and C-H···C hydrogen bonds. Curvedness maps are a good way of visualizing π-π stacking interactions between molecules. The antimicrobial activities of compounds 1, 2, and 6 were screened against 15 different multidrug-resistant strains of bacteria isolated from diabetic foot ulcers and compared to the antimicrobial activities of the clinically used silver sulfadiazine (SS). Compound 2 showed activity similar to SS against this set of test organisms, being active against all strains and having slightly better average silver efficiency than SS (5 vs 6 μg Ag/mL). Against the standard nonresistant bacterial strains of Staphylococcus aureus , Pseudomonas aeruginosa , Proteus mirabilis , and Streptococcus pyogenes , compound 1 performed better than silver nitrate, with an average MIC of 6 μg Ag/mL versus 18 μg Ag/mL for the reference AgNO3. Electrospray ionization mass spectrometry (ESI-MS) analyses of compounds 3 and 6 in DMSO/MeOH confirm the two-coordinated Ag(+) complexes in solution, and the results of the (1)H NMR titrations of DMSO solutions of 5-nitroquinoline and 8-nitroquinoline with AgNO3 in DMSO suggest that 5-nitroquinoline is more strongly coordinated to the silver ion.

Determination of the thermal expansion of κ-Al2O3 by high temperature XRD

Abstract In this work, the thermal expansion of κ -Al 2 O 3 has been characterised using high temperature X-ray diffraction of κ -Al 2 O 3 powder obtained from crushed chemical vapour deposited κ -Al 2 O 3 coatings. The lattice parameters, volume, thermal linear and volume expansion coefficients have been determined in the range 23 to 840 °C. It was found that κ -Al 2 O 3 expands anisotropically, the expansion being about equal along the b - and c -axis, while it is significantly lower along the a -axis. Compared with α -Al 2 O 3 , the expansion is slightly lower along c κ than along c α , similar along b κ and a α , while it is significantly lower along a κ than along a α . The expansion data imply that all aluminium ions in κ-Al 2 O 3 are not ordered in a hexagonal mesh as in α -Al 2 O 3 , but are ordered in lines along the a -axis.