Organometallic chemistry of diphosphazanes. Part IX: Syntheses and spectroscopic studies of molybdenum and tungsten tetracarbonyl complexes of unsymmetrical diphosphazanes

The unsymmetrical diphosphazanes X2PN(Pr(i))PYY'(1a-1h) {X = Ph, YY' = O2 C6H4 (1a) or YY' = O2C12H8 (1b); X = Ph, Y = Ph, Y' = OC6H4Me-4 (1c), OC6H4Br-4 (1d), OC6H3Me2-3,5 (1e), OC5H4N-2 (1f), N2C3HMe2-3,5 (1g) or Cl (1h)} react with [M(CO)4(NHC5H10)2] (M = Mo, W) to yield the cis-chelate complexes [M(CO)4{X2PN(Pr(i)) PYY'}] {M = Mo (2a-2h); M = W (3-f,3-g)}. These complexes have been characterized by H-1, P-31 and C-13 NMR and IR spectroscopic studies.

Syntheses and studies on pyridinium pxofluorocomplexes of molybdenum, tungsten andiodine

(C5H5NH)2MO2F4 (M = Mo and W) and C5H5NHIO2F2 have been synthesized at room temperature by the reaction of molybdic, tungstic or iodic acid, respectively, with pyridinium poly(hydrogen fluoride). These complexes have been characterized by chemical analyses, H-1 nmr and infrared spectroscopy.

Crystal structures, dynamics and functional implications of molybdenum-cofactor biosynthesis protein MogA from two thermophilic organisms

Molybdenum-cofactor (Moco) biosynthesis is an evolutionarily conserved pathway in almost all kingdoms of life, including humans. Two proteins, MogA and MoeA, catalyze the last step of this pathway in bacteria, whereas a single two-domain protein carries out catalysis in eukaryotes. Here, three crystal structures of the Moco-biosynthesis protein MogA from the two thermophilic organisms Thermus thermophilus (TtMogA; 1.64 angstrom resolution, space group P2(1)) and Aquifex aeolicus (AaMogA; 1.70 angstrom resolution, space group P2(1) and 1.90 angstrom resolution, space group P1) have been determined. The functional roles and the residues involved in oligomerization of the protein molecules have been identified based on a comparative analysis of these structures with those of homologous proteins. Furthermore, functional roles have been proposed for the N- and C-terminal residues. In addition, a possible protein-protein complex of MogA and MoeA has been proposed and the residues involved in protein-protein interactions are discussed. Several invariant water molecules and those present at the subunit interfaces have been identified and their possible structural and/or functional roles are described in brief. In addition, molecular-dynamics and docking studies with several small molecules (including the substrate and the product) have been carried out in order to estimate their binding affinities towards AaMogA and TtMogA. The results obtained are further compared with those obtained for homologous eukaryotic proteins.

Synthesis and catalytic properties of cobalt- and molybdenum-containing mesoporous MCM-41 molecular sieves

Mesoporous MCM-41 type silicas containing molybdenum and cobalt have been prepared with pore sizes in the range 30-38 Angstrom and 54-59 Angstrom. Catalytic properties of these materials have been examined with respect to the oxidation of cyclooctene and aniline.

Enhanced sensitivity for the differential pulse polarographic determination of molybdenum(VI) based on adsorption catalytic current

A differential pulse polarographic (DPP) method based on the adsorption catalytic current in a medium containing chlorate and 8-hydroxyquinoline (oxine) is suggested for the determination of molybdenum(VI). Experimental conditions such as pH and the composition of supporting electrolyte have been optimized to get a linear calibration graph at trace levels of Mo(VI). The sensitivity for molybdenum can be considerably enhanced by this method. The influence of possible interferences on the catalytic current has been investigated. The sensitivity of the method is compared with those obtained for other DPP methods for molybdenum. A detection limit of 1.0 x 10(-8) mol/L has been found.

Thiol/disulphide exchange reaction: A key regulatory process in biological systems

Cysteine residues in proteins serve many important functions such as stabilizing and maintaining the three-dimensional conformation of many proteins(1), in enzyme catalysis, as a residue undergoing post-translational 2 and in the formation of DNA-binding modification domain of a class of transcriptional activators(3), It is also involved in biological redox coupling(4) and xenobiotic metabolism(5). Disulphide bonds formed by xenobiotic metabolism oxidation of cysteine residues have been used as a probe to study the structure/function relationships of proteins, Introducing novel disulphide bonds in proteins to increase their thermal stability and, therefore, the shelf life is an important goal of protein engineering(6,7), In addition, the thiol group of cysteine residue participates in a reaction termed as thiol/disulphide exchange reaction, the biological significance of this reaction being the theme of this review.

Molybdenum tetracarbonyl complexes of (aryloxy) lambda(3)-cyclotriphosphazanes; X-ray crystal structure of [Mo(CO)(4){EtNP(OC6H4Br-4)}(3)]

Treatment of the lambda(3)-cyclotriphosphazanes, cis-{EtNP(OR)}(3) [R = C6H4Br-4 (L-1) or C6H4Br-2 (L-2)] with [Mo(CO)(4)(NBD)] (NBD = norbornadiene) yields the mononuclear complexes [Mo(CO)(4)L-1] (1) and [Mo(CO)(4)L-2] (2). which have been characterised by IR, NMR (P-31 and H-1) and FAB mass spectral data. The structure of 1 has been confirmed by single crystal X-ray analysis. The structural and conformational changes brought about by complexation are discussed in terms of a bonding model based on "negative hyperconjugation". (C) 1998 Elsevier Science Ltd. All rights reserved.

Growth mechanism of phases by interdiffusion and atomic mechanism of diffusion in the molybdenum-silicon system

Tracer diffusion coefficients are calculated in different phases in the Mo-Si system from diffusion couple experiments using the data available on thermodynamic parameters. Following, possible atomic diffusion mechanism of the species is discussed based on the crystal structure. Unusual diffusion behaviour is found in the Mo(5)Si(3) and Mo(3)Si phases, which indicate the nature of defects present on different sublattices. Further the growth mechanism of the phases is discussed and morphological evolution during interdiffusion is explained. (C) 2011 Elsevier Ltd. All rights reserved.

Molybdenum trioxide catalyzed oxidative cross-dehydrogenative coupling of benzylic sp(3) C-H bonds: synthesis of alpha-aminophosphonates under aerobic conditions

Molybdenum trioxide (MoO3) catalyzed efficient oxidative cross-dehydrogenative-coupling (CDC) method for C-H functionalization of N-aryl tetrahydroisoquinolines has been explored. This user-friendly method of synthesizing alpha-aminophosphonates employs 1.1 equiv of dialkyl-H-phosphonate under aerobic condition. Formation of new C-P bonds from unfunctionalized starting materials under environmentally benign conditions provides an excellent avenue for the synthesis of biologically active alpha-aminophosphonates. (C) 2012 Elsevier Ltd. All rights reserved.

Mixed-ligand aroylhydrazone complexes of molybdenum: Synthesis, structure and biological activity

The reaction of the benzoylhydrazone of 2-hydroxybenzaldehyde (H2L) with MoO2(acac)(2)] proceeds smoothly in refluxing ethanol to afford an orange complex MoO2L(C2H5OH)] (1). The substrate binding capacity of 1 has been demonstrated by the formation and isolation of two mononuclear MoO2L(Q)] {where Q = imidazole (2a) and 1-methylimidazole (2b)} and one dinuclear (MoO2L)(2)(Q)] {Q = 4,4'-bipyridine (3)} mixed-ligand oxomolybdenum complex. All the complexes have been characterized by elemental analysis, magnetic and spectroscopic (IR, UV-Vis and NMR) measurements. The molecular structures of all the oxomolybdenum(VI) complexes (1, 2a, 2b and 3) have been determined by X-ray crystallography. In each complex, the dianionic planar ligand is coordinated to the metal centre via one enolate oxygen, one phenolate oxygen and an azomethine nitrogen atom. The complexes have been screened for their antibacterial activity against Escherichia coli, Bacillus and Pseudomonas aeruginosa. The minimum inhibitory concentration of these complexes and their antibacterial activity indicates that compounds 2a and 2b are potential lead molecules for drug designing. (C) 2012 Elsevier Ltd. All rights reserved.

Influence of nature of support on the catalytic activity of supported molybdenum-oxo species in benzyl alcohol conversion

Supported catalysts containing 15 wt.% of molybdenum have been prepared by the incipient wetness impregnation method. CaO, MgO, Al2O3, Zr(OH)4 and Al(OH)3 have been used as supports for the preparation of supported Mo catalysts. Characterisation of all the materials prepared has been carried out through BET surface area measurement, X-ray diffractometry and FT-IR spectroscopy. Catalytic activity measurements have been carried out with reference to structure-sensitive benzyl alcohol conversion in the liquid phase. The percentage conversion of benzyl alcohol to benzaldehyde and toluene varied over a large range depending on the support used for the preparation of catalysts, indicating the importance of the support on catalytic activity of Mo catalysts. Al(OH)3 has been found to be the best support for molybdenum among all the supports used. Support–metal interaction (SMI) has been found to play an important role in determining the catalytic activity of supported catalysts.

Pressure-Dependent Optical and Vibrational Properties of Mono layer Molybdenum Disulfide

Controlling the band gap by tuning the lattice structure through pressure engineering is a relatively new route for tailoring the optoelectronic properties of two-dimensional (2D) materials. Here, we investigate the electronic structure and lattice vibrational dynamics of the distorted monolayer 1T-MoS2 (1T') and the monolayer 2H-MoS2 via a diamond anvil cell (DAC) and density functional theory (DFT) calculations. The direct optical band gap of the monolayer 2H-MoS2 increases by 11.7% from 1.85 to 2.08 eV, which is the highest reported for a 2D transition metal dichalcogenide (TMD) material. DFT calculations reveal a subsequent decrease in the band gap with eventual metallization of the monolayer 2H-MoS2, an overall complex structureproperty relation due to the rich band structure of MoS2. Remarkably, the metastable 1T'-MoS2 metallic state remains invariant with pressure, with the J(2), A(1g), and E(2)g modes becoming dominant at high pressures. This substantial reversible tunability of the electronic and vibrational properties of the MoS2 family can be extended to other 2D TMDs. These results present an important advance toward controlling the band structure and optoelectronic properties of monolayer MoS2 via pressure, which has vital implications for enhanced device applications.

Spectrophotometric determination of molybdenum with Syzygium jambolanum DC leaf extracts

A new spectrophotometric method for the determination of molybdenum in industrial materials has been developed using the leaf extract of Syzygium jambolanum DC based on the reaction of Mo (VI) at pH 7.0 to produce an orange-yellow complex with an absorption maximum at 426 nm. The molar absorptivity of the complex is 4.27 x 10(4) l mol(-1) cm(-1) and the absorbance, is linear in the range 0.05-0.8 ppm. Sandell sensitivity coefficient was found to be 2.25 x 10(-3) mu g/cm(2). The method is ten times more sensitive than the aqueous thiocyanate system. It has been applied successfully in micronutrient fertilizer, artificial freshwater and sea-water analyses.