Pseudo-first-order reaction kinetics and binding studies of trans-[Co(en) 2 (Et)H 2 O] complex with 1H-imidazole, substituted 1H-imidazoles, histidine, histamine, glycine and glycine ethyl ester were investigated by means of spectrophotometric techniques. Equilibrium constants were determined as a function of pH at 258. Binding and kinetic studies were correlated to basicity and steric hindrance. From the equilibrium data, it was found that the entering nucleophile is participating in the transition state, an I d mechanism is proposed. The effect of the incoming ligands on the complex was studied by molecular mechanics. The interaction of trans-[Co(en) 2 (Et)H 2 O] with CT DNA was studied spectrophotometrically.Introduction. -To understand the mechanistic aspect of coenzyme B 12 , which actively carries many enzymatic reactions, model complexes of the coenzyme are widely studied. Much of the study with model complexes reveals that the active part of the coenzyme is the CoÀC bond cleavage, which initiates the enzymatic reaction. The pentammine(methyl)cobalt(III) complex is the simplest model for coenzyme B 12 [1], where four ammine ligands are bound to the Co-center in equatorial positions and one ammine and the methyl ligand are in axial positions trans to each other. Later, cobalamins and cobaloximes were extensively studied.The carbanion ligand coordinated to the Co III center is influenced by the presence of other ligands in cis or trans position with respect to the carbanion ligand. A cis and trans effect on the CoÀC bond was reported for naturally occurring methylcobalamin [2] and various synthetic complexes such as those with tetrapyrrole, imine, oxime, mixed imine-oxime or ammine ligands [3 -7]. The data for the trans-[Co(DH) 2 (Me)L] (DH ¼ dmg ¼ dimethylglyoximato) revealed that the 13 C-NMR chemical shift, the

In view of the growing interest for the synthesis of metal complexes and their interaction with DNA, we have synthesized and characterized two complexes containing ruthenium as metal center. The complexes are of the type [Ru(dppz)L 4 ](ClO 4 ) 2 where L are biologically important ligands such as pyrazole and dimethylpyrazole. The characterization of these complexes is done by 1 H NMR, 13 C NMR, elemental analysis and mass spectroscopy. The interaction of these complexes with CT DNA was monitored and binding constants were determined using absorption and fluorescence spectroscopy. The mode of binding was found to be intercalative for both complexes and was determined using hydrodynamic viscosity studies. The complexes were further studied for photocleavage studies with supercoiled plasmid pBR322 DNA.