Comparative DNA binding ability and phosphatase-like activity of mono and dinuclear Ni (II) complexes: a structure-activity correlation

Two Ni(II) complexes [(Ni L1)(CH₃COO) (H₂O)₂](1) and [{(NiL2) (CH3COO)}₂ (µ-H₂O)] (2) having different coordination environments around metal centres have been selected to investigate structure-activity correlation for DNA binding and homogenous phosphatase-like activities. Complex 1 is a monomer in which the octahedral Ni(II) center is coordinated to phenolate oxygen along with two nitrogen atoms from imine and amine groups of the deprotonated ligand HL1. An oxygen atom of the acetate group is coordinated in monodentate mode, and two coordinated water molecules occupy the other two axial sites. Complex 2 is a dimer where each Ni(II) centre is coordinated in an octahedral environment through one imine nitrogen, one amine nitrogen, two bridging phenolate oxygens from two deprotonated ligands (HL2) molecules, a mono-dentate acetate group, and a bridging water molecule. The role of structural features of both the complexes has been studied in DNA binding activity and phosphate ester bond cleavage of bis(4-nitrophenyl) phosphate (BNPP) as a model substrate. Complex 2 showed higher DNA binding ability than complex 1 due to its stable bridging structure and high nuclearity. The catalytic phosphate ester bond hydrolysis of BNPP was explored with both complexes spectrophotometrically. The dinuclear complex 2 also exhibited a higher rate of acceleration in the BNPP hydrolysis than mononuclear complex 1. The active nucleophile from the coordinated water and cooperativity in two metal centres of complex 2 are the key features to cleave the phosphate ester bond of the substrate. Further, the first-order rate constants and various kinetic parameters based on the Michaelis-Menten equation were calculated for each complex. A significant phosphatase-like activity for complex 2 has been observed with a turnover number of 1.23 × 10⁻² s⁻¹.

A structure-activity relationship for phosphatase-like catalytic activities of two mono and di nuclear Ni(II) complexes has been studied. Dinuclear complex 2 exhibits higher phosphatase-like activity due to coordinated water molecules and cooperativity between two metal centres.