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

The kinetics of the interaction of adenosine with cis ‐[Pt( cis ‐dach)(OH 2 ) 2 ] 2+ (dach = diaminocyclohexane) was studied spectrophotometrically as a function of [ cis ‐[Pt( cis ‐dach)(OH 2 ) 2 ] 2+ ], [adenosine], and temperature at a particular pH (4.0), where the substrate complex exists predominantly as the diaqua species and the ligand adenosine exists as a neutral molecule. The substitution reaction shows two consecutive steps: the first is the ligand‐assisted anation followed by a chelation step. The activation parameters for both the steps have been evaluated using Eyring equation. The low negative value of Δ H ≠ 1 (43.1 ± 1.3 kJ mol −1 ) and the large negative value of Δ S ≠ 1 (−177 ± 4 J K −1 mol −1 ) along with Δ H ≠ 2 (47.9 ± 1.8 kJ mol −1 ) and Δ S ≠ 2 (−181 ± 6 J K −1 mol −1 ) indicate an associative mode of activation for both the aqua ligand substitution processes. The kinetic study was substantiated by infrared and electrospray ionization mass spectroscopic analysis. © 2011 Wiley Peiodicals, Inc. Int J Chem Kinet 43: 219–229, 2011