Articles written in Journal of Chemical Sciences

    • Displacement of aqua ligands from the hydroxopentaaquarhodium(III) ion by 1-hydroxybenzotriazole (HOBt): A kinetic and mechanistic approach

      Biplab K Bera Arup Mandal Biswarup Maity Sumon Ray Parnajyoti Karmakar Subala Mondal Subhasis Mallick Alak K Ghosh

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      The kinetics of the reaction of HOBt with [Rh(H2O)5(OH)]2+ has been studied spectrophotometrically in aqueous medium as a function of [Rh(H2O)5OH2+], [HOBt], pH and temperature. At pH 4.3, the reaction proceeds via a rapid outer sphere association complex formation step followed by two consecutive steps. The first of these involves ligand-assisted anation, while the second involves chelation as the second aqua ligand is displaced. The association equilibrium constant for the outer sphere complex formation has been evaluated together with the rate constants for the two subsequent steps. The activation parameters for both steps have been evaluated using Eyrings equation. Thermodynamic parameters calculated from the temperature dependence of the outer sphere association equilibrium constants are also consistent with an associative mode of activation. The product of the reaction has been characterized by IR and ESI-mass spectroscopic analysis.

    • Kinetic studies on substitution of cis-diaqua-chloro-tris-(dimethyl sulphoxide)-ruthenium(II) complex with some dipeptides in aqueous medium

      Arup Mandal Parnajyoti Karmakar Subhasis Mallick Biplab K Bera Subala Mondal Sumon Ray Alak K Ghosh

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      The kinetics of interaction between cis-[RuCl(Me2SO)3(H2O)2]+ and some selected dipeptides such as glycyl glycine(gly gly), glycyl alanine(Gly-L-ala) and glycyl-L-leucine(gly leu) has been studied spectrophotometrically as a function of [RuCl(Me2SO)3(H2O)$^+_2$], [dipeptide] and temperature at a particular pH(5.0), where the substrate complex exists predominantly as a diaqua species (in aqueous solution) and dipeptides as the zwitter ions. The reaction has been found to proceed via two distinct consecutive steps i.e., it shows a non-linear dependence on the concentration of dipeptide: first process is dependent and the second step is independent of ligand concentration respectively. The rate constants for the processes are: k$_1 \tilde 10^{−3}$s-1 and k$_2 \tilde 10^{−5}$ s-1. The activation parameters were calculated from Eyring plots suggests an associative mechanism for the interaction process. From the temperature dependence of the outer sphere association equilibrium constants, the thermodynamic parameters were also calculated, which gives a negative 𝛥G0 value at all temperatures studied, supporting the spontaneous formation of an outer sphere association complex.

    • Substitution reactions of [Pd(bipy)(malonate)] explored with a different set of ligands: Kinetic and mechanistic interpretation in aqueous medium and at pH 7.4


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      A brief overview of mechanistic studies of the reactions of Pd(II)-bipy-malonate complex with different set of ligands, viz., (N, S), (S, O) and (S) donor molecules is reported here. The kinetics of complex formation reactions of three sulphur containing bio-relevant ligands thioglycolic acid[L₁],thiourea[L₂] andthiosemicarbazide [L₃] were studied with innermetallic [Pd(bipy)(malonate)] complex at physiological condition. The effect of the nucleophilicity of the chosen nucleophiles was studied for the reactant complex under pseudo-first order conditions as a function of nucleophile concentration and temperature using stopped-flow technique. This article describes the results obtained for substitution reactions of bi-functional Pd(II) complex with different biomolecules, under varying experimental conditions. The kinetic studies showed that the malonate ring departs from the coordination zone of palladium centre via two-step mechanism. The first step depends on the concentration of the incoming ligand for all the ligands. But in the second step thiourea is ligand dependent where as other two are independent of the ligand concentration. Hence, it can be concluded that the second step is the chelation step for L₁ and L₃. The mechanism for the substitution of the coordinated malonate molecule is associative, as demonstrated by the negative values of ∆S=. Such type of complexes are less toxic than chloro-, which in turn hydrolyses to aqua or aqua complexes as they are prevented from oligomer formation at physiological pH.

    • Relative reactivity of N,N-donor ligands in substitution reactions of cis-diaqua(2-aminomethylpiperidine)platinum(II): a detailed kinetic and mechanistic study


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      The reactivity of cis-[Pt(pipen)(H2O)2]2+ (pipen=2-aminomethylpiperidine) was investigated by studying the interaction with some didentate N,N-donor ligands, namely, dimethylglyoxime (L1H), 1,2-cyclohexanedionedioxime (L2H) and α-furildioxime (L3H) in an aqueous medium. All the above substitutionreactions have been monitored spectrophotometrically at 320, 308 and 290 nm, respectively, where the spectral difference between the reactants and the products are appreciable. The kinetic study has been substantiated byproduct isolation, UV, IR and ESI-MS spectroscopic analysis. The rate parameters have been evaluated under different reaction conditions. The reactions were found to occur in two consecutive steps. The mechanism ofthe substitution reactions appears associative in nature as supported by the large and negative values of ΔS

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