• Volume 119, Issue 6

November 2007,   pages  583-654

• Gallium(III) and indium(III) dithiolate complexes: Versatile precursors for metal sulfides

The chemistry of classical and organometallic complexes of gallium and indium with dithiolate ligands, i.e., dithiocarboxylates, xanthates, dithiocarbamates, dithiophosphates, dithiophophinates and dithioarsenates, has been reviewed. Synthesis, spectroscopic and structural aspects of these complexes are described. Their emerging role as single source molecular precursors for the preparation of metal sulfide thin films and nano-particles has been discussed.

• catena-Poly[[(pentaaqua)(4-nitrobenzoato-O,O')barium(II)] (𝜇-4-nitrobenzoato-O,O')]: A barium(II) coordination polymer showing O-H$\cdots$O and C-H$\cdots$O interactions

The reaction of barium carbonate with 4-nitrobenzoic acid (4-nbaH) results in the formation of a Ba(II) coordination polymer, catena-poly[[(pentaaqua)(4-nitrobenzoato-O,O')barium(II)](𝜇-4-nitrobenzoato-O,O')] 1. The polymeric compound [[Ba(H2O)5(4-nba-O,O')](𝜇-4-nba-O,O')]$_n$ 1 was characterized by elemental analysis, IR and UV-Vis spectra, weight loss studies, X-ray powder diffraction and its structure determined. In 1 five water molecules are coordinated to the central metal and one of the 4-nba ligands is bonded to Ba(II) in a bidentate manner (4-nba-O,O') through the carboxylate O atoms. The [(pentaaqua)(4-nitrobenzoato-O,O')barium(II)] units are linked into an infinite one-dimensional chain along 𝑏-axis with the aid of the second 4-nba anion, which functions as a bridging bidentate (𝜇-4-nba-O,O') ligand. This results in nine coordination around each Ba(II) ion in the coordination polymer. A long Ba$\cdots$Ba distance of 6.750(1) Å is observed between adjacent Ba(II) ions in the chain and the oxygen atoms of the carboxylate group and the nitro functionalities of the 4-nba ligand are involved in several O-H$\cdots$O and C-H$\cdots$O interactions.

• Ternary complexes of cobalt cysteinylglycine with histidylserine and histidylphenylalanine-stabilities and DNA cleavage properties

Interaction of cobalt cysteinylglycine with histidylserine and histidylphenylalanine was investigated in a 1 : 1 : 1 ratio at 35°C and 0.10 mol dm-3 ionic strength. Their stabilities and geometries were determined. Their DNA binding and cleavage properties were investigated. The intrinsic binding constants ($K_b$) for DNA bound 1 and 2 ($3.03 \times 10^3$ M-1 for 1 and $3.87 \times 10^3$ M-1 for 2) were determined. Even though the negative charge on the complexes reduced their affinity for DNA, there was an enhancement of binding through specificity. The degradation of plasmid DNA was achieved by cobalt dipeptide complexes [CoII(CysGly)(HisSer)] (1) and [CoII(CysGly)(HisPhe)] (2). Cleavage experiments revealed that 1 and 2 cleave supercoiled DNA (form I) to nicked circular (form II) through hydrolytic pathway at physiological 𝑝H. The DNA hydrolytic cleavage rate constants for complexes 1 and 2 were determined to be 0.62 h-1, for 1 and 0.38 h-1 for 2 respectively.

• Solvent effects in the reaction between piperazine and benzyl bromide

The reaction between piperazine and benzyl bromide was studied conductometrically and the second order rate constants were computed. These rate constants determined in 12 different protic and aprotic solvents indicate that the rate of the reaction is influenced by electrophilicity (𝐸), hydrogen bond donor ability (𝛼) and dipolarity/polarizability ($\pi^\ast$) of the solvent. The LSER derived from the statistical analysis indicates that the transition state is more solvated than the reactants due to hydrogen bond donation and polarizability of the solvent while the reactant is more solvated than the transition state due to electrophilicity of the solvent. Study of the reaction in methanol, dimethyl formamide mixtures suggests that the rate is maximum when dipolar interactions between the two solvents are maximum.

• Ab initio study of gas phase and water-assisted tautomerization of maleimide and formamide

Maleimide serves as an important starting material in the synthesis of drugs and enzyme inhibitors. In the present paper, knowing the importance of tautomerization in maleimide for its drug action, potential energy surface of maleimide is studied and its tautomerization has been discussed and compared with tautomerization of formamide. Gas phase tautomerization of maleimide requires large amount of energy (23.21 kcal/mol) in comparison to formamide (15.05 kcal/mol) at HF/$6-31+$G level. Thus making the proton transfer reaction a difficult process in gas phase. Water molecule lowers the energy barrier of tautomerization thus facilitating the tautomerization of maleimide to 5-hydroxy-pyrrol-2-one. Water assisted tautomerization of maleimide requires 19.60 kcal/mol energy at HF/$6-31+$G and 17.63 kcal/mol energy at B3LYP/6-31+G level, a decrease of 3.61 and 5.96 kcal/mol over gas phase tautomerization. Whereas, tautomerization of formamide requires 14.16 and 12.84 kcal/mol energy, a decrease of 0.89 and 2.01 kcal/mol energy over gas phase tautomerization at HF/6-31+G and B3LYP/6-31+G level, respectively. Water-assisted tautomerization in maleimide and formamide showed that difference in energy barrier reduces to 2.83 kcal/mol from 10.41 kcal/mol (in gas phase) at B3LYP level, which resulted that maleimide readily undergoes tautomerization in water molecule.

• Molecular modelling studies on 2-amino 6-aryl-sulphonylbenzonitriles as non-nucleoside reverse transcriptase inhibitors of HIV-1: A QSPR approach

Lipophilicity or hydrophobicity is a crucial physico-chemical property of an oral drug compound. In the present study, we have analysed the structural parameters responsible for enhancing the lipophilicity expressed in terms of Octanol-Water partition coefficient, log 𝑃, of 2-amino-6-arylsulfonylbenzonitrile (AASBN) derivatives used as NNRTIs in AIDS therapy. Connectivity based Randic (𝜒) and Balaban (𝐽) and atomistic Kier-Hall electrotopological state (𝐸-state) indices have been used to develop Quantitative Structure-Property Relationship (QSPR) and to predict the effect of substitution on the log 𝑃. Model has been developed using multiple linear regression analysis (MLR) for the training set (67 compounds) and the model was tested on a test set (7 compounds). Significant results were obtained for the training set ($R^2 = 0.948$, $R^2_{\text{adj}} = 0.939$, $SE = 0.177$, $F$-ratio = 101.22). The results of the test set too implicated a good fit ($R^2 = 0.941$, $R^2_{\text{adj}} = 0.929$, $SE = 0.157$, $F$-ratio = 80.05). Among the two connectivity based topological indices; Randic (𝜒) index showed better predictive ability than the Balaban (𝐽) index. Kier-Hall 𝐸-state indices indicated that among the functional groups, methyl, bromo, chloro groups on ring A, with their positive coefficients enhanced the lipophilicity. Amino, cyano group on ring B and the bridging S, SO, SO2 with their negative coefficients showed an adverse effect on the lipophilicity parameter. Thus, Kier-Hall 𝐸-state indices along with topological indices could be well applied for deriving QSPR models and analysing substitution effects of various functional groups. The training set, correlation matrix and observed and experimental log 𝑃 values are available as supplementary material for this article.

• Metal-organic deposition of YBa2Cu3O$_x$ and Bi2Sr2Ca1Cu2O$_x$ films on various substrates starting from different fluorine-free metallorganic compounds

YBa2Cu3O$_x$ (Y-123 ) and Bi2Sr2Ca1Cu2O$_x$ (Bi-2212) films on various substrates have been prepared by Metal-Organic Deposition starting from different metallorganic fluorine-free compounds and using a very simple instrumentation. The processing conditions include a rapid pyrolysis step in air and an annealing step in oxygen for Y-123 and in air for Bi-2212. The films obtained have been characterized by X-ray diffraction (XRD) and the formation of a superconducting phase of Y-123 or Bi-2212 was confirmed measuring the critical temperature ($T_c$) with Ac-susceptibility and resistive measurements. Microstructure and final cationic ratios have been studied by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS).

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• # Journal of Chemical Sciences

Volume 132, 2019
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