Ternary complexes of cobalt cysteinylglycine with histidylserine and histidylphenylalanine–stabilities and DNA cleavage properties

nteraction of cobalt cysteinylglycine with histidylserine and histidylphenylalanine was investigated in a 1 : 1 : 1 ratio at 35°C and 0⋅10 mol dm^ –3 ionic strength. Their stabilities and geometries were determined. Their DNA binding and cleavage properties were investigated. The intrinsic binding constants (Kb) for DNA bound 1 and 2 (3⋅03 × 10^ 3 M^ –1 for 1 and 3⋅87 × 10 ^3 M^ –1 for 2) were determined. Even though the negative charge on the complexes reduced their affinity for DNA, there was an enhancement of binding through specificity. The degradation of plasmid DNA was achieved by cobalt dipeptide complexes [Co II (CysGly)(HisSer)] (1) and [Co ^II (CysGly)(HisPhe)] (2). Cleavage experiments revealed that 1 and 2 cleave supercoiled DNA (form I) to nicked circular (form II) through hydrolytic pathway at physiological pH. The DNA hydrolytic cleavage rate constants for complexes 1 and 2 were determined to be 0⋅62 h ^–1 , for 1 and 0⋅38 h^ –1 for 2 respectively.