SYNTHESIS OF NEW CATIONIC SCHIFF-BASE COMPLEXES OF COPPER(II) AND THEIR SELECTIVE BINDING WITH DNA

A series of cationic salen-type Schiff base complexes of copper(II), t he general formula of which is [Cu{R(3)N(+)-CH2-C6H3(O-)-CH=N-}(2)X]Br -2 (R: CH3, C2H5, C3H7, C4H9; X: C2H4, C3H6, C6H10, C6H4, C10H6), was newly prepared, and the molecular structure of complex 1 (R=CH3, X=C2H 4) 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 buff er, pH=7.2) using induced CD and the UV-vis spectra. Those complexes w ith aliphatic X group selectively bound to the groove of DNA, and the K-b's were in the range of 10(2)-10(3) mol dm(-3) (site size base pair s n=7.2-7.4). However, those with aromatic X group selectivity interca lated to the base pairs, and the K-b'S were in the range of 10(4)-10(5 ) 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) we re found to exhibit AT-sequence affinity from the induced CD spectra a nd K-b's for poly(dA-dT)-poly(dA-dT), poly(dG-dC)-poly(dG-dC), and pol y(dA-dC)-poly(dT-dG).