Alak K. Ghosh

Kinetics and mechanism of the interaction of DL-penicillamine with cis-diaqua(cis-1,2-diaminocyclohexane)platinum(II) perchlorate in aqueous medium

The kinetics of the interaction of DL-penicillamine with cis-[Pt(cis-dach)(OH2)2]2+ has been studied spectrophotometrically as a function of [cis-[Pt(cis-dach)(OH2)2]2+], [DL-penicillamine], and temperature at a particular pH (4.0), where the complex exists predominantly as the diaqua species and DL-penicillamine as a zwitterion. The substitution reaction proceeds via rapid outer sphere association, followed by two slow consecutive steps. The first is the conversion of title complex into an inner sphere complex and the second is the slower chelation step whereby another aqua ligand is replaced. The association equilibrium constant (K E) for the outer sphere complex formation has been evaluated together with rate constant for two subsequent steps. The activation parameters for both steps have been evaluated using the Eyring equation: ( = 36 ± 4 kJ mol−1, = −175 ± 12 JK−1 mol−1 and = 44 ± 1 kJ mol−1, = −189 ± 3 JK−1 mol−1). The low enthalpy of activation and large negative value of entropy of activation are consistent with an associative mode of activation for both consecutive steps. The kinetic study has been substantiated by conductivity measurement, product isolation, IR and ESI-MS spectroscopic analysis.

Kinetic Studies on Interaction of Platinum(II) Complexes with an ‘S’ Containing Ligand in Aqueous Medium

The kinetics of the substitution reactions of [Pt(dach)(H2O)2]2+ and [Pt(en)(H2O)2]2+ (where ‘dach’ and ‘en’ are cis-1,2-diaminocyclohexane and ethylenediamine, respectively) with excess N,N′-diethylthiourea have been studied in aqueous solution by UV–Vis spectrophotometry. The effect of different N–N spectator ligands on the reactivity of platinum(II) complexes was investigated by studying the water lability of the reactant complexes. The kinetic study has been substantiated by product isolation, IR, NMR and ESI-MS spectral analysis and DFT calculations. The reactions follow normal square-planar substitution mainly in an associative way. Rate parameters have been evaluated under different conditions. The substitution rates of the complexes studied can be tuned through the nature of the N–N chelates, which is important in the development of new active compounds for cancer therapy.

Kinetics and mechanism of reactions of some essential amino acids with cis-diaqua(1,3-diaminopropane)-platinum(II) ion: a potent anticancer agent

Abstract The substitution of both coordinated water molecules of cis-diaqua(1,3-diaminopropane)platinum(II) complex by a series of amino acids, viz. l-asparagine, l-glutamic acid, and glycine was investigated as a function of ligand concentration, temperature, and pH and found to occur in two consecutive reaction steps. The mechanism of the substitution reactions appears associative in nature as supported by the large and negative values of ΔS≠. The kinetic study has been substantiated by product isolation, UV, IR, and ESI-MS spectroscopic analysis and rate parameters have been evaluated under different reaction conditions.Graphical Abstract

Mechanistic and Kinetic Investigations on the Interaction of Model Platinum(II) Complex With Ligands of Biological Significance in Reference to the Antitumor Activity

The kinetics of interaction of cis-[Pt(cis-dach)(H2O)2]2+ (where dach is cis-1,2-diaminocyclohexane) with three different amino acids, namely L-Asparagine (L1H), L-Arginine (L2H), and L-Gluatmic acid (L3H) have been studied spectrophotometrically in the 40–60°C temperature range. The substitution was found to occur in two subsequent reaction steps: the first step is the ligand-assisted anation and the second one is the chelation step. The kinetic study has been substantiated by product isolation, IR, NMR, and ESI-MS spectroscopic analysis.

Kinetics and mechanism of the interaction of glycyl-L-leucine with [(H 2 O)(tap) 2 RuORu(tap) 2 (H 2 O)] 2+ ion at physiological pH

The interaction of glycyl-L-leucine (L-I/H) with [(H2O) (tap)2RuORu(tap)2(H2O)]2+ (tap=2-(m-tolylazo) pyridine) has been studied spectrophotometrically in aqueous medium as a function of [(H2O) (tap)2RuORu(tap)2(H2O)2+], [glycyl-L-leucine], pH and temperature. The reaction was monitored at 600 nm where the spectral difference between the reactant and product is a maximum. At pH 7.4, the interaction with glycyl-L-leucine shows two parallel steps, i.e. it shows a non-linear dependence on the concentration of glycyl-L-leucine; both processes are ligand dependent. The rate constants for the processes are: kl 10−3 s 1 and K2∼10−5 s−1. The activation parameters calculated from Eyring plots are: Δ H#1 = 15.8∓0.6kJ mol−1, ASf = −232 + 2J K 1 mol−1, AH2# =31.7∓3.5kJmol−1, AS* = −216∓ 10J K−1 mol−1. 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, which gave a negative AG° value for both the steps at all temperatures studied, supporting the spontaneous formation of an outer sphere association complex. The product of the reaction has been characterized from IR and ESI-mass spectroscopic analysis.

Kinetic Study of the Interaction of Three Glycine-Containing Dipeptides with Hydroxopentaaquarhodium(III) Ion in Aqueous Medium

The kinetics of the interaction of three glycine-containing dipeptides, namely, glycyl-L-valine (L1-L′H), glycyl-glycine (L2-L′H) and glycyl-L-glutamine (L3-L′H), with [Rh(H2O)5OH]2+ has been studied spectrophotometrically in aqueous medium as a function of the Rh(H2O)5OH2+ and dipeptide concentrations, pH and temperature, at constant ionic strength. At pH = 4.3, the substrate complex exists predominantly as the hydroxopentaaqua species and dipeptides as zwitterions. The reaction has been found to proceed via two parallel paths: both processes are ligand dependent. The rate constants for the processes are of the order: k1∼10−3 s−1 and k2∼10−5 s−1. The activation parameters for both steps were evaluated from Eyring plots. Based on the kinetic and activation parameters an associative interchange mechanism is proposed for both of the interaction processes. The low

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

\Delta H_{1}^{\neq}

Kinetics and mechanism of the reaction of thiocyanate ion with hexaaquo rhodium(III) ion

and

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

\Delta H_{2}^{\neq}

Kinetic and mechanistic aspects of ligand substitution on cis -diaqua ( cis -1,2-diaminocyclohexane)platinum(II) with three glycine-containing dipeptides

values and large negative values of