Synthesis of New Cationic Schiff Base Complexes of Copper(II) and Their Selective Binding with DNA

Abstract

Abstract A series of cationic salen-type Schiff base complexes of copper(II), the general formula of which is [Cu{R3N+–CH2–C6H3(O−)–CH=N–}2X]Br2 (R: CH3, C2H5, C3H7, C4H9; X: C2H4, C3H6, C6H10, C6H4, C10H6), was newly prepared, and the molecular structure of complex 1 (R = CH3, X = C2H4) was determined by an X-ray crystal structure analysis. The binding mode and binding constants (Kb) of all the complexes with calf thymus DNA were investigated at an ionic strength of I = 0.05(NaCl + HEPES buffer, pH = 7.2) using induced CD and the UV-vis spectra. Those complexes with aliphatic X group selectively bound to the groove of DNA, and the Kb’s were in the range of 102—103 mol dm−3 (site size base pairs n = 7.2—7.4). However, those with aromatic X group selectivity intercalated to the base pairs, and the Kb’s were in the range of 104—105mol dm−3 (n = 2.8—4.0). These binding modes were confirmed based on the salt dependence of Kb’s. In addition, 1 and 10 (R = CH3, X = C6H4) were found to exhibit AT-sequence affinity from the induced CD spectra and Kb’s for poly(dA-dT)–poly(dA-dT), poly(dG-dC)–poly(dG-dC), and poly(dA-dC)–poly(dT-dG).