X-ray Crystallographic Analysis of the Complexes of Enoyl Acyl Carrier Protein Reductase of Plasmodium falciparum with Triclosan Variants to Elucidate the Importance of Different Functional Groups in Enzyme Inhibition

Triclosan, a well-known inhibitor of Enoyl Acyl Carrier Protein Reductase (ENR) from several pathogenic organisms, is a promising lead compound to design effective drugs. We have solved the X-ray crystal structures of Plasmodium falciparum ENR in complex with triclosan variants having different substituted and unsubstituted groups at different key functional locations. The structures revealed that 4 and 2' substituted compounds have more interactions with the protein, cofactor, and solvents when compared with triclosan. New water molecules were found to interact with some of these inhibitors. Substitution at the 2' position of triclosan caused the relocation of a conserved water molecule, leading to an additional hydrogen bond with the inhibitor. This observation can help in conserved water-based inhibitor design. 2' and 4' unsubstituted compounds showed a movement away from the hydrophobic pocket to compensate for the interactions made by the halogen groups of triclosan. This compound also makes additional interactions with the protein and cofactor which compensate for the lost interactions due to the unsubstitution at 2' and 4'. In cell culture, this inhibitor shows less potency, which indicates that the chlorines at 2' and 4' positions increase the ability of the inhibitor to cross multilayered membranes. This knowledge helps us to modify the different functional groups of triclosan to get more potent inhibitors. (C) 2010 IUBMB IUBMB Life, 62(6): 467-476.

Electro-Oxidation of Borohydride on Rhodium, Iridium, and Rhodium-Iridium Bimetallic Nanoparticles with Implications to Direct Borohydride Fuel Cells

Electrochemical oxidation of borohydride is studied on nanosized rhodium, iridium, and bimetallic rhodium-iridium catalysts supported onto Vulcan XC72R carbon. The catalysts are characterized by X-ray diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy in conjunction with cyclic voltammetry and polarization studies. The studies reveal that a 20 wt % bimetallic Rh-Ir catalyst supported onto carbon (Rh-Ir/C) is quite effective for the oxidation of borohydride. Direct borohydride fuel cell with Rh-Ir/C as the anode catalyst and Pt/C as the cathode catalyst exhibits a peak power density of 270 mW/cm(2) at a load current density of 290 mA/cm(2) as against 200 mW/cm(2) at 225 mA/cm(2) for Rh/C and 140 mW/cm(2) at 165 mA/cm(2) for Ir/C while operating at 80 degrees C. The synergistic catalytic activity for the bimetallic Rh-Ir nanoparticles toward borohydride oxidation is corroborated by density-functional theory calculations using electron-localization function. (C) 2010 The Electrochemical Society. [DOI:10.1149/1.3442372] All rights reserved.

Photocatalytic degradation of phenol by base metal-substituted orthovanadates

Base metal (Cr, Mn, Fe, Ni, Cu) substituted CeVO4 compounds were synthesized by the solution combustion technique. These compounds were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, UV-vis spectroscopy, transmission electron microscopy and BET surface area analyzer. The characterization indicated that the base metals were substituted in the ionic state in all the compounds. These compounds were used for the photocatalytic degradation of phenol and the degradation rates obtained in the presence of these compounds werecompared against that obtained with the commercial Degussa P-25 TiO2 catalyst. Fe and Cr substituted CeVO4 showed photocatalytic activity that was comparable with that of Degussa P-25 TiO2. The concentration of toxic intermediates was high when the reaction was carried out in presence of Degussa P-25 TiO2 but it was found to be insignificant when the reaction was carried out in presence of base metal-substituted CeVO4. The effect of % Fe-substitution (varied from 1 to 5 at%) in CeVO4 on the photocatalytic activity was also investigated and it was observed that 1 at% Fe-substituted compound showed the highest activity. A mathematical model describing the kinetics of the photocatalytic degradation of phenol was developed on the basis of the catalyst structure and taking into account the formation of all the possible intermediates. The variation of the concentration of phenol and the intermediates was described by the model and the reaction rateconstants were determined. (C) 2010 Elsevier B.V. All rights reserved.

X-Ray structure of a ternary complex, copper(II)–lnosine 5-monophosphate–benzimidazole. The first example for the absence of direct metal–nucleotide interaction

The unprecedented absence of direct metal–nucleotide interaction has been observed in the X-ray structure of the ternary metal nucleotide system [Cu(bzim)(H2O)5]2+[IMP]2–·3H2O [IMP = inosine 5-monophosphate(2–), bzim = benzimidazole). The complex crystallizes in the space group P21 with a= 7.013(2), b= 13.179(9), c= 14.565(9)Å, = 94.82(4)°, and Z= 2. The structure was solved by the heavy-atom method and refined by full-matrix least squares on the basis of 1 761 observed (I? 3i) reflections to final R and R values of 0.034 and 0.036 respectively. The CuII has a distorted octahedral co-ordination with a nitrogen of the bzim ligand [Cu–N 1.947(5)Å] and three oxygens of water molecules in the basal plane [mean Cu–O 2.017(3)Å] and two more water oxygens at axial positions [Cu–O 2.194(6) and 2.732(5)Å]. The nucleotide base stacks with the bzim ligand at an average distance of 3.5 Å and an angle of 22°. In the lattice, N(7) of the base is linked to a lattice water through a hydrogen bond, while all the phosphate oxygens are involved in hydrogen bonds with co-ordinated as well as lattice water molecules. The co-ordination behaviour of IMP to CuII is compared in structures containing different -aromatic amines in order to assess the influence of the ternary ligand in complex formation. The present results indicate that, apart from the commonly observed phosphate binding, other modes of co-ordination are possible, these being influenced mainly by the -accepting properties of the ternary ligand.

Synthesis, X-ray structure and catalytic properties of a copper(II) Schiff base complex modeling the activity of the Cu-B site of dopamine beta-hydroxylase

The copper(II) complex [Cu(salgly) (bpy)] . 4H(2)O (1), where salgly is a tridentate glycinatosalicylaldimine Schiffbase Ligand, is prepared and structurally characterized. The complex is found to be catalytically active in the oxidation of ascorbic acid by dioxygen and the process is also effective in the presence of benzylamine giving benzaldehyde as a product, thus modeling the activity of the Cu-B site of dopamine beta-hydroxylase. (C) 2000 Elsevier Science S.A. All rights reserved.

Formation of crystalline diamond from amorphous diamond-like carbon films by pulsed laser irradiation

The formation of crystalline diamond films from amorphous diamond-like carbon films by pulsed laser irradiation with a 300 μs non-Q-switched Nd:YAG laser has been established by a combined study of transmission electron microscopy, x-ray photoelectron spectroscopy, and electrical resistivity. The films have been prepared by glow discharge decomposition of a mixture of propane, n-butane, and hydrogen in a rf plasma operating at a frequency of 13.56 MHz. Prior to laser irradiation, the films have been found to be amorphous by transmission electron microscope studies. After irradiation, the electron diffraction patterns clearly point out the formation of cubic diamond structure with a lattice spacing of 3.555 Å. However, the close similarity between diamond and graphite electron diffraction patterns could sometimes be misleading regarding the formation of a diamond structure, and hence, x-ray photoelectron spectroscopic studies have been carried out to confirm the results. A chemical shift in the C 1s core level binding energies towards higher values, viz., from 286.5 to 287.8 eV after laser irradiation, and a high electrical resistivity >1013 Ω cm are consistent with the growth of diamond structure. This novel "low-temperature, low-pressure" synthesis of diamond films offers enormous potential in terms of device compatibility with other solid-state devices.

Nature of Pb in superconducting cuprates containing lead: A Pb L3 x‐ray absorption near‐edge spectroscopy study

X‐ray absorption near‐edge spectroscopy studies show that Pb in superconducting Tl0.5Pb0.5CaSr2Cu2O7+δ is essentially in the 4+ state while it is in the 2+ state in Pb2Sr2Ca1−xLnxCu3O8+δ.

Crystallization and preliminary X-ray crystallographic analysis of a galactose-specific lectin from Dolichos lablab

The galactose-specific lectin from the seeds of Dolichos lablab has been crystallized using the hanging-drop vapour-diffusion technique. The crystals belong to space group P1, with unit-cell parameters a = 73.99, b = 84.13, c = 93.15 angstrom, alpha = 89.92, beta = 76.01, gamma = 76.99 degrees. X-ray diffraction data to a resolution of 3.0 angstrom have been collected under cryoconditions ( 100 K) using a MAR imaging-plate detector system mounted on a rotating-anode X-ray generator. Molecular-replacement calculations carried out using the available structures of legume lectins as search models revealed that the galactose-specific lectin from D. lablab forms a tetramer similar to soybean agglutinin; two such tetramers are present in the asymmetric unit.

Chemical-shift of the X-ray K-absorption edge of Co in some compounds, complexes and minerals

The chemical-shift of the X-ray K-absorption edge of Co was studied in a large number of compounds, complexes (spinels) and minerals of Co in its different oxidation states having widely different crystal structures and containing different types of bonding and various types of ligands, and were reported collectively, for the first time, in a single paper. A quadratic relationship was established on the basis of least-squares regression analysis to hold between the chemical-shift and the effective charge on the absorbing atom, but the dominance of the linear term was shown. This relation was utilized in evaluating the charge on the Co-ion in a number of minerals. The effect on chemical-shift of oxidation states of the absorbing atom, of the bond length, crystal structure and higher shell atoms of the molecule, and of electronegativity, atomic number and ionic radius of the ligand was discussed.

NO reduction, CO and hydrocarbon oxidation over combustion synthesized Ag/CeO2 catalyst

The combustion technique produces ionically dispersed Ag on a nano-crystalline CeO2 surface. The catalysts thus produced were characterized by X-ray diffraction, transmission electron microscopy and X-ray photoelectron spectroscopy. Catalytic properties towards NO reduction, CO and hydrocarbon oxidation have been investigated using the temperature programmed reaction technique in a packed bed tubular reactor. These results are compared with alpha-Al2O3 supported finely divided Ag metal particles synthesized by the same method. Both oxidation and reduction reactions over Ag/CeO2 have been observed to occur at lower temperatures compared to Ag/Al2O3. The rate and turnover frequency of the NO+CO reaction over 1% Ag/CeO2 are 56.3 mu mol g(-1) s(-1) and 0.97 s(-1) at 225 degrees C respectively. Activation energy (E-a) values are 71 and 67 kJ mol(-1) for CO+O-2 and NO+CO reactions, respectively, over 1% Ag/CeO2 catalyst.

High contrast laser writing in insitu textured germanium films via a novel chemical oxide formation

A high contrast laser writing technique based on laser induced efficient chemical oxidation in insitu textured Ge films is demonstrated. Free running Nd-YAG laser pulses are used for irradiating the films. The irradiation effects have been characterised using optical microscopy, electron spectroscopy and microdensitometry. The mechanism for the observed contrast has been identified as due to formation of GeO2 phase upon laser irradiation using X-ray initiated Auger spectroscopy (XAES) and X-ray photoelectron spectroscopy (XPS). The contrast in the present films is found to be nearly five times more than that known due to GeO phase formation in similar films.