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

Article abstract of DOI:10.1246/bcsj.70.615

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 (K_b) 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 K_b'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 K_b's were in the range of 10⁴ - 10⁵ mol dm^-3 (n = 2.8 - 4.0). These binding modes were confirmed based on the salt dependence of K_b's. In addition, 1 and 10 (R = CH₃, X = C₆H₄) were found to exhibit AT-sequence affinity from the induced CD spectra and K_b's for poly(dA-dT)-poly(dA-dT), poly(dG-dC)-poly(dG-dC), and poly(dA-dC)-poly(dT-dG).