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(Me 2 SO) 3 (H 2 O) 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(Me 2 SO) 3 (H 2 O) ], [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 s − 1 and k 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 ΔG 0 value at all temperatures studied, supporting the spontaneous formation of an outer sphere association complex. Graphical Abstract The kinetics of interaction between cis -[RuCl(Me 2 SO) 3 (H2O) 2 ] + and some glycyl-containing dipeptides such as glycyl glycine(gly gly), glycyl alanine(gly ala) and glycyl-L-leucine(gly leu) has been studied spectrophotometrically as a function of [RuCl(Me 2 SO) 3 (H 2 O) 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: first process is [ligand] dependent whereas the second step is [ligand] independent. The rate constants for the processes are: k 1 ~10 −3 s −1 and k 2 ~10 −5 s −1 .