• B Singh

      Articles written in Journal of Chemical Sciences

    • Magnetic and spectral studies of transition metal complexes of salicylaldehyde-2-aminoacetophenone-2-thenoylhydrazone

      B Singh A K Srivastav

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      Salicylaldehyde-2-aminoacetophenone-2-thenoylhydrazone (H2saath) has been found to react with the transition metal salts to form the complexes VO(H2saath)2SO4, M(H2saath)2Cl2 and M(H saath)2 [M=OV(IV), Mn(II), Co(II), Ni(II), Cu(II) and Zn(II)]. The complexes have been characterized by elemental analyses, molar conductance, magnetic susceptibility, electronic and photoacoustic, ESR, IR,1H and13C NMR studies. X-ray diffraction study suggests a tetragonal unit lattice for zinc(II) and an orthorhombic one for copper(II) complexes.

    • Studies on salicylaldehyde-2-aminobenzophenone-2-thenoylhydrazone complexes with 3d metal ions

      B Singh A K Srivastav

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      Salicylaldehyde-2-aminobenzophenone-2-thenoylhydrazone (Hsabth) complexes of OV(IV), Mn(II), Ni(II), Ni(II), Cu(II) and Zn(II) having 1∶2 metal-ligand stoichiometry have been prepared and characterized by elemental analyses, molar conductance, magnetic susceptibility, electronic, ESR, infrared, NMR (1H and13C) and X-ray powder diffraction studies. Square pyramidal geometry around oxovandium(IV) and octahedral geometry around the rest of the metal ions have been proposed on the basis of magnetic and spectral studies.

    • Studies on 4f-metal(III) complexes of N-thiophene-2-carboxamidosalicylaldimine

      B Singh P K Singh V P Tiwari

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      N-(thiophene-2-carboxamido) salicylaldimine (H2TCS) reacts with lanthanide chlorides in the presence of KOH to give complexes of the type K(Ln(TCS)2] [Ln=La(III), pr(III), Nd(III), Sm(III), Eu(III), Gd(III) and Dy(III)]. A tentative structure for these complexes has been suggested on the basis of molar conductance, TGA and DTA, magnetic susceptibility, electronic, infrared and1H and13C NMR data. The nephelauxetic ratio ($$\bar \beta $$), covalency (σ) and bonding parameter (b1/2) have been calculated from the electronic spectrum of the Nd(III) complex. A coordination number of six around the metal ion has been suggested.

    • Reaction of coordinated ligand-IV. Synthesis and characterization of some lanthanide complexes of 2,6-diacetylpyridine 2-thenoyl salicyl dihydrazone

      B Singh T B Singh

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      The complexes of the type [Ln(H2 dapthsh)Cl(H2O)2]Cl2 (Ln=La, Pr, Nd, Sm, Eu, Gd, Tb and Dy; H2 dapthsh=2,6-diacetylpyridine 2-thenoyl salicyl dihydrazone) have been prepared by reacting salicylhydrazone (sh) with [Ln(Hdapth)Cl2(H2O)3]Cl (Hdapth=2,6-diacetylpyridine mono (2-thenoylhydrazone) in ethanol. The condensation of coordinated acetyl C=O with — NH2 of salicylhydrazone occurs and the resulting azomethine nitrogen is found bonded to the Ln(III) ions. The compound has been found monomeric from FAB mass spectra. The bonding sites of the dihydrazone and coordination number and symmetry of the ligand field around Ln3+ ions have been deduced from IR, electronic and emission spectra.

    • Mono and trinuclear lanthanide complexes of 13-membered tetraaza macrocycle: Synthesis and characterization

      B Singh V L Singh

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      The reaction of 1,8-diamino-3,6-diazaoctane and diethyl malonate in dry methanol yielded a 13-membered macrocycle. Complexes of the type [Ln(tatd)Cl2 (H2O)3]Cl [LnIII=La, Pr, Nd, Sm, Eu, Gd, Tb, Dy; tatd=1, 5, 8, 11-tetra-azacyclotridecane-2,4-dione] have been synthesized by template condensation. The complex [La(tatd)Cl2 (H2O)3]Cl in methanol was reacted with lanthanide chlorides to yield the trinuclear complexes of type [2{La(tatd)Cl2(H2O)3}LnCl3]Cl2 [LnIII=La, Pr, Nd, Sm, Eu, Gd, Tb, Dy]. The chemical compositions of mono and trinuclear complexes have been established on the basis of analytical, molar conductance, electrospray (ES) and fast atom bombardment (FAB) mass data. In mononuclear complexes the Ln3+ ion is encapsulated by four ring nitrogens and in trimetallic complexes the exo-carbonyl oxygens of two mononuclear units coordinate to the Ln3+ ions resulting in a polyhedron around the lanthanide ions. Thus the macrocycle is bonded in a tetradentate fashion in the former complexes and hexadentate in the latter. The coordination number nine around the encapsulated Ln3+ and seven around the exo-oxygen bonded Ln3+ ions are established. The symmetry of the ligand field around the metal ions is indicated from the emission spectra.

    • Studies on syntheses and self-assembly behaviour of homoseleno-peptides


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      The development of straightforward synthetic and characterization methods for selenopeptides is essential to discovering hierarchical structured functional materials. Here, the synthesis of a series of homoselenopeptides1-4, having the benzyl (Bzl) group-protected selenocysteine [(Bzl)SeCH2CH(NH2)COOH] monomer units in the sequence, is reported. The homo-selenopeptides 1-4 are characterized by 1D (1H, 13C,and 77Se) and 2D (1H-1H COSY, 1H-1H NOESY, and 1H-1H TOCSY) NMR spectroscopy, and ESI-MS spectrometry. The triselenopeptide 1 shows a propensity for self-assembly into β-sheet amyloid-like fibril structure in acetonitrile (ACN) solution at room temperature. This has systematically been analyzed and established through the spectroscopic techniques; FT-IR, CD, and ThT-based fluorescence spectroscopy for secondary bonding analyses and microscopic techniques; SEM and TEM for the amyloid-like fibril structurein ACN solution. The amide I band vibrational stretching frequencies observed in the range 1600-1700 cm-1confirm that all peptides in the homologous series have a strong propensity to form amyloid-like fibril structures.

      Synthesis of a series of homo-selenopeptides 1-4 through the solid-phase peptide synthesis (SPPS), using Fmoc protected Sec(Bzl)-OH as a source of amino acid, has been described. Spectroscopic and morphological imaging studies revealed that the homo-selenopeptides have a high propensity to get self-organized into amyloid-like fibrillar structures.

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