Quantum mechanical calculations for the misincorporation of nucleotides opposite mutagenic 3,N4-ethenocytosine.

The ubiquitous nature and persistence of exocyclic DNA adducts suggest their involvement as initiators of carcinogenesis. We have investigated the misincorporation properties of the exocyclic DNA adduct, 3,N(4)-ethenocytosine, using DFT and DFT-D methods. Computational investigations have been carried out by using the B3LYP, M062X, and wB97XD methods with the 6-31+G* basis set to determine the hydrogen bonding strengths, binding energy, and physical parameters. The single point energy calculations have been carried out at MP2/6-311++G** on corresponding optimized geometries. The energies were compared among the 3,N(4)-ethenocytosine adduct with DNA bases to find the most stable conformer. The solvent phase calculations have also been carried out using the CPCM model. The computed reaction enthalpy values provide computational insights to the earlier experimental observation in in vitro, E.coli, and mammalian cells of a high level of substitution mutation in which C → A transversion results from εC-T pairing [εC-T3 and εC-T4] in the adduct containing DNA sequence.