Ab initio study of alkylation of guanine-cytosine base pair by sulfur and nitrogen mustards.

Quantum modeling of the N7(G) alkylation of guanine-cytosine (G-C) base pair by sulfur (HD) and nitrogen mustard (HN2) was performed by using the Density Functional Theory (DFT) BPW91/6-31G++DP procedure. The vibrational IR and Raman spectra are discussed with regard to the N7 position of guanine when electrophilic HD+ episulfonium and HN2+ aziridinium attack the G-C base pair. Thermodynamic and polarizability considerations are also presented. The computed electronic chemical potential and the electrophilicity of the studied species indicate that an electronic transfer is produced from the nucleophile (G-C) base pair to the electrophile HD+ episulfonium or HN2+ aziridinium during the alkylation process.