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Ligand substitution; dipeptides; cis-[RuCl(Me₂SO)₃(H₂O)₂]⁺; kinetics.

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.

Arup Mandal¹ Parnajyoti Karmakar¹ Subhasis Mallick¹ Biplab K Bera¹ Subala Mondal¹ Sumon Ray¹ Alak K Ghosh¹

1. Department of Chemistry, The University of Burdwan, Burdwan 713 104, India

Published

July 2012

Manuscript received

29 November 2011

Manuscript revised

21 January 2012

Accepted

7 February 2012