Coordination of Cu (II) with tripyridylamine and a tetradentate ligand and hydrolysis of 4-nitrophyenyl acetate catalyzed by these complexes

The complexation processes of Cu (II) with tripyridylamine(L-1) and N-(2'-hydroxybenzyl) -diethylenetriamine (HL2) have been studied by pH potentiometric titration at 25 +/- 0.1 degrees C, I = 0.1 (KNO3), The results indictate that, L-1 is a bidentate ligand and only forms stable Cu (II) complex with a ratio L:Cu (II) = 2:1, In the complex Cu (II) is able to combine a H2O molecule with a p Ka value of 7.54, which implies that the H2O bound to Cu (II) can readily deprotonate in the physiological pH range, Three nitrogen atoms of amino groups and one phenolic hydroxyl coordinate to Cu (II) for HL2. The coordinated hydroxyl can dissociate with a p Ka value of 4.44. The kinetics of p-nitrophenyl acetate (NA) hydrolysis catalyzed by the complexes was determined spectrophotometrically at 25 +/- 0.1 degrees C and I = 0.1 (KNO3) in 10% (V/V) CH3CN at pH 5.5 similar to 9.0 (50mmol.L-1 buffers), and the second-rate constants k(NP) for NA hydrolysis were obtained. The plot of k(NP) of Cu (II) (L-1)(2) vs pH has the characteristics of a Sigmoidal curve, with the maximum k(NP) value of 2.53 x 10(-2) L.mol(-1).s(-1). The results suggest that the Cu (II)-bound OH- acts as a good nucleophile and has good catalysis on NA ester hydrolysis.