Phosphate ester hydrolysis and DNA binding capacity of two new dinuclear Ni(II) complexes

Two new dinuclear Ni(II) complexes, [Ni2L1(OAc)2]ClO4 (1) and [Ni2L2(OAc)2] Br·0.5H2O (2) (where HL is the condensation product of 2,6-diformyl-4-X-phenol (X = CH3, Br) and N1-(2-aminoethyl)-N2-(4-nitrobenzyl)ethane-1,2-diamine), were synthesized and characterized. The coordination polyhedron of each metal ion in the complexes can be approximately described as a distorted octahedron. The Ni–Ni distances in 1 and 2 are 3.306 Å and 3.369 Å, respectively. The phosphate hydrolysis promoted by the complexes was examined using 4-nitrophenyl phosphate disodium salt hexahydrate (pNPP) as the substrate. The catalytic rate constants (kcat) are 1.29 × 10−5 s−1 for 1 and 0.47 × 10−5 s−1 for 2 at 25 °C in physiological pH condition. The binding activities of the complexes toward calf thymus (CT-DNA) were analyzed by spectroscopic and voltammetric methods, and the corresponding binding constants are 7.75 × 105 and 6.51 × 104 M−1 for 1 and 8.59 × 105 and 9.18 × 104 M−1 for 2, respectively. The linear Stern–Volmer quenching constants obtained in the fluorescent spectroscopic study of 1 and 2 are 0.7 × 103 and 1.5 × 103 M−1, respectively.