Density functional study of the binding of the cyclen-coordinated M(II) (M = Zn, Cu, Ni) complexes to the DNA base. Why is Zn better to bind?

摘要

The interaction of the macrocyclic tetraamines (1,4,7,10-tetraazacyclododecane; cyclen)-coordinated divalent metals M(II) (M = Zn, Cu, Ni); M(II)-cyclen complex 1 with DNA bases has been theoretically examined by means of density functional method (B3LYP) using the model DNA bases, hypoxanthine for guanine and uracil for thymine. Both bases are bound to 1 by the charge transfer and electrostatic interactions, i.e. (i) the donation of the lone pair electron on the base-N to the metal, and (ii) the H-bond of the C=O oxygen of the base with the N-H unit of the cyclen ligand. The stabilization energy of both M(II)(hypoxanthine)-cyclen 3 and M(II)(uracil)-cyclen 4 complexes gave the sequence Zn > Cu > Ni, reflecting the strength of the interaction of the base-N with the metal (i) although the H-bonding (ii) is stronger with the opposite order. It was revealed that the strength of the charge transfer (i) is determined by the energy level of the unoccupied s + p hybridized σ orbital of the metal which appears by the coordination of the cyclen ligand. These results were verified by the electron flow estimated from the change in the charge distribution by binding on the cyclen ligand and on the coordinated bases. The calculations also showed that the Zn(II)-cyclen complex 1 binds more strongly to uracil in agreement with the experimental finding.