Theoretical studies on the DNA-intercalator properties of Co(III) polypyridyl complexes

Theoretical studies on the DNA-intercalator properties of Co(III) polypyridyl complexes 1 and 2 have been carried out. First, a sheared whole DNA-complex model to perform the study on DNA-interaction properties of Co(III) polypyridyl complexes was established, by using a combination method of the quantum-chemistry and the molecular mechanics as follows: The full geometric optimizations of these two complexes were carried out in aqueous solution using the restricted B3LYP method and LanL2DZ basis set, then the optimized complexes were docked into DNA-base-pairs using the docking program, and the obtained greater DNA-complex model was sheared to a simplified whole model, and finally the sheared DNA-complex model was exactly computed using the DFT/TDDFT method. Secondly, based on the computations of above-established models, via the analysis of the DNA-binding energies of complexes 1 and 2 as well as the intramolecular hydrogen bonds within the docking models, the trend in DNA-binding affinities, i.e., Kb(2) > Kb(1), can be reasonably explained. Thirdly, the electronic absorption spectra of docking models were also calculated and simulated using the TDDFT method. The simulated absorption spectra are in a satisfying agreement with experimental results, and the intense experimental absorption bands of these Co(Ш) complexes in the presence of DNA are theoretically explained in detail.