Synthesis,spectral, DFT,and antimicrobial studies of tin(II) and lead(II) complexes with semicarbazone and thiosemicarbazones derived from (2-hydroxyphenyl)(pyrrolidin-1-yl)methanone

A new series of metal complexes [M(L)₂] (where M = Sn(II), Pb(II), and HL = semicarbazone, thiosemicarbazone or phenylthiosemicarbazone) have been prepared and characterized by elemental analysis, conductance measurements, molecular weight determinations, UV–visible, infrared, and nuclear magnetic resonance (¹H-, ¹³C-, and ¹¹⁹Sn-NMR) spectral studies. Elemental analysis of the metal complexes suggested 1 : 2 (metal–ligand) stoichiometry. Infrared spectra of the complexes agree with coordination to the metal through the nitrogen of the azomethine (>C=N?) and the oxygen/sulfur of the ketonic/thiolic group. Electronic spectra suggest a distorted tetrahedral geometry for all Schiff base complexes. The bond lengths, bond angles, highest occupied molecular orbital, lowest unoccupied molecular orbital, Mulliken atomic charges, and the lowest energy model structure of the complexes have been determined with DFT calculations. Representative Schiff base and its metal chelates have been screened for their in vitro antibacterial activity against four bacteria, Gram-positive (Bacillus cereus, Staphylococcus aureus) and Gram-negative (Escherichia coli, Klebsiella pneumoniae) and four strains of fungus (Penicillium chrysogenum, Aspergillus niger, Rhizopus nigricans, and Alternaria alternata). The metal chelates possess higher antimicrobial activity than the free ligands.     

Use of microwave technology for the synthesis of organotitanium(IV) and organozirconium(IV) complexes with HPOH,HO<Superscript>∩</Superscript>N<Superscript>∩</Superscript>OH and HO<Superscript>∩</Superscript>N<Superscript>∩</Superscript>SH type of ligands

Synthesis and characterization of titanium(IV) and zirconium(IV) complexes of the types Cp₂M(Cl)(HPO), Cp₂M(HPO)₂, Cp₂M(O^∩N^∩O) and Cp₂M(O^∩N^∩S) (where M represents titanium or zirconium and HPO, O^∩N^∩O and O^∩N^∩S represent the donor sets of the ligands) have been reported. These new derivatives have been prepared by the reactions of titanocene dichloride or zirconocene dichloride with 2-hydroxy-N-phenyl benzamide(HPOH), 1-[(2-hydroxyphenyl)-1-N-phenylamino]hydrazine-carboxamide (HO^∩N^∩OH) and 2-hydroxy-N-phenyl benzamide benzothiazoline (HO^∩N^∩SH) in different molar ratios. The ligands and their complexes have been characterized by the elemental analyses, conductance measurement, molecular weight determinations and spectral studies. On the basis of electronic, I.r., ¹H.-n.m.r. and ¹³C.-n.m.r. spectral studies, trigonal bipyramidal and octahedral geometries have been proposed for the resulting complexes. All the ligands and their complexes have been screened for their biological activity on several pathogenic fungi and bacteria and were found positive in this respect.     

Ferrocenyl-substituted Schiff base complexes of boron: synthesis, structural, physico-chemical and biochemical aspects

Biological important complexes of boron(III) derived from 1-acetylferrocenehydrazinecarboxamide (L1H), 1-acetylferrocenehydrazinecarbothioamide (L2H) and 1-acetylferrocene carbodithioic acid (L3H) have been prepared and investigated using a combination of microanalytical analysis, melting point, electronic, IR, 1H NMR and 13C NMR spectral studies, cyclic voltammetry and X-ray powder diffraction studies. Boron isopropoxide interacts with the ligands in 1:1, 1:2 and 1:3 molar ratios (boron:ligand) resulting in the formation of coloured products. On the basis of conductance and spectral evidences, tetrahedral structures for boron(III) complexes have been assigned. The ligands are coordinated to the boron(III) via the azomethine nitrogen atom and the thiolic sulfur atom/enolic oxygen atom. On the basis of X-ray powder diffraction study one of the representative boron complex was found to have orthorhombic lattice, having lattice parameters: a=9.9700, b=15.0000 and c=7.0000. Both the ligands and their complexes have been screened for their biological activity on several pathogenic fungi and bacteria and were found to possess appreciable fungicidal and bactericidal properties. Plant growth regulating activity of one of the ligand and its complexes has also been recorded on gram plant, and results have been discussed.     

Effect of surface modification of indium tin oxide by nanoparticles on the electrochemical determination of tryptophan

The effect of surface modification of indium tin oxide (ITO) by multi wall carbon nanotube (MWNT) and gold nanoparticles attached multi wall carbon nanotube (AuNP-MWNT) has been studied to determine tryptophan, an important and essential amino acid for humans and herbivores. A detailed comparison has been made among the voltammetric response of bare ITO, MWNT/ITO and AuNP-MWNT/ITO in respects of several essential analytical parameters viz. sensitivity, detection limit, peak current and peak potential of tryptophan. The AuNP-MWNT/ITO exhibited a well defined anodic peak at pH 7.2 at a potential of ∼669 mV for the oxidation of tryptophan as compared to 760 mV at MWNT/ITO electrode. Under optimum conditions linear calibration curve was obtained over tryptophan concentration range 0.5-90.0 μM in phosphate buffer solution of pH 7.2 with detection limit and sensitivity of 0.025 μM and 0.12 μA μM⁻¹, respectively. The oxidation of tryptophan occurred in a pH dependent, 2e⁻ and 2H⁺ process and the electrode reaction followed adsorption controlled pathway. The method has been found selective and successfully implemented for the determination of tryptophan in human urine and plasma samples using standard addition method. The electrode exhibited an efficient catalytic response with good reproducibility and stability.     

Formation and characterization of non uniform long and ultralong period reversible optical fiber gratings

We report here for the first time to our knowledge the formation and characterization of non uniform long and ultralong period reversible optical fiber gratings. Study of the spectral response of LPFGs with periods exceeding one millimeter is scarce. The Non uniform LPFG with periods exceeding one millimeter is practically induced in communication grade single mode fiber, and then apodization and chirping effects are experimentally characterized. The spectral response is then compared with spectral response of uniform grating.     

Hydrogenase enzymes: Application in biofuel cells and inspiration for the design of noble-metal free catalysts for H2 oxidation

While hydrogen is often considered as a promising energy vector and an alternative to fossil fuels, the rise of the hydrogen economy is ever and ever postponed. This is mainly due to the high costs of the materials required for the elaboration of fuel cells, these wonderful systems that release the energy contained in the H₂ molecule in the form of electrical power. Indeed, scarce and precious platinum is required as a catalyst at both electrodes of fuel cells. A solution may be found in nature with metalloenzymes involved in hydrogen metabolism, called hydrogenases. These natural catalysts can be used directly in biofuel cells or serve as an inspiration to chemists for the elaboration of bio-inspired electrocatalytic materials.