Stannoxane capping derived from chiral tridentate NNO donor ligand for nickel and copper macrocycles: Comparative binding studies of stannoxane moiety and its modulated copper complex with CTDNA

Novel stannoxane type dinuclear tin complex C16H13N4O2Sn2Cl7 (1) and its modulated macrocyclic complexes [C24H36N10O3Sn2CuCl7] ClO4 (2) and [C24H34N10O2Sn2NiCl7] ClO4 (3) were synthesized and characterized by elemental analysis and various spectroscopic techniques (IR, 1H, 13C, 119Sn NMR, ESI-MS, EPR and UV-Vis). 119Sn NMR shows the presence of two tin metal centers in different environment. The proposed pseudo-octahedral geometry of copper in complex 2 and square pyramidal geometry of nickel in complex 3 were established by the analysis of spectroscopic data. Absorption and fluorescence spectral studies and viscosity measurements have been carried out to assess the comparative binding of dinuclear stannoxane complex 1 and its modulated copper complex 2 with calf thymus DNA. The intrinsic binding constants Kb of the complex 1 and 2 were determined as 4.4 × 104 M−1 and 7.5 × 104 M−1, respectively. Cyclic voltammetric studies have also been employed to ascertain the binding of complex 2 with CTDNA. The results suggest that the complex 2 binds to CTDNA twice in the order of magnitude compared to complex 1. Interaction studies of complex 2 with guanosine 5′-monophosphate further confirm the binding via N7 position of guanine and phosphate moiety.