Interaction of psoralens with DNA-bases (II): An ab initio quantum chemical, density functional theory and second-order MØller-Plesset perturbational study

Intercalation complexes of psoralen and 8-methoxypsoralen with DNA-bases (G,C) and Watson-Crick (GC) base pair were studied using quantum chemical methods. The HOMO and LUMO energies, structures and properties of isolated psoralen and 8-methoxypsoralen have been computed. Their interactions with DNA-bases and base pair were studied aiming to shade more light on the nature of binding in DNA intercalation complexes. The geometry of adducts of psoralens with cytocine and guanine as well as Watson-Crick (GC) base pair have been optimized in two main orientations, planar and stacked, by means of HF, DFT and MP2 levels of computation employing different basis sets. The different computational methods have been compared and the effect of the basis set has been discussed. Interaction energy of the studied complexes were calculated and corrected for BSSE. Effect of vertical distance and rotational angle between the stacked molecules on the interaction energy were investigated by the above methods in gas phase and water media. Of the computational methods used, only higher correlated theories have been proven effective in describing these interactions. Ab initio methods which account for the electron correlation effects are the minimum level for studying the non-covalent interactions.