• Subala Mondal

Articles written in Journal of Chemical Sciences

• Kinetics and mechanism of the ligand substitution reaction of di-𝜇-hydroxobis(bipyridyl)dipalladium(II) ion with diethyldithiocarbamate anion in aqueous solution

The kinetics of the interaction between diethyldithiocarbamate (Et2DTC) and the title complex has been studied spectrophotometrically in aqueous medium as a function of nucleophile concentration, temperature and pH at constant ionic strength. The reaction is a two-step process in which the first step is liganddependent, but the second step is ligand-independent and is assigned to ring closure. The rate and activation parameters, conductivity studies and IR data were used to deduce a plausible mechanism.

• Mechanistic aspects of ligand substitution on [(H2O)(tap)2RuORu(tap)2(H2O)]2+ {tap=2-(m-tolylazo)pyridine} ion by three glycine-containing dipeptides in aqueous medium at physiological pH

The interaction of the title complex with selected glycine-containing dipeptides(L-L'H) such as glycyl-glycine(L-L1H), glycyl-L-alanine (L-L2H) and glycyl-L-leucine(L-L3H) has been studied spectrophotometrically in aqueous medium as a function of [substrate complex], [ligand] and temperature. The reaction has been monitored at 600 nm where the spectral difference between the reactant and product is a maximum. At pH 7.4, the interaction with studied dipeptides shows two parallel steps. i.e., it shows a non-linear dependence on the concentration of dipeptides; both processes are ligand-dependent. 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. Based on the kinetic and activation parameters an associative interchange mechanism is proposed for the interaction processes. From the temperature dependence of the outer sphere association equilibrium constant, the thermodynamic parameters were also calculated. The product of the reaction has been characterized by IR and ESI-mass spectroscopic analysis.

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

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

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.

• # Journal of Chemical Sciences

Volume 134, 2022
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Posted on July 25, 2019

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