A DFT Study of Reactions of Methyldiazonium Ion with DNA/RNA Nucleosides: Investigating Effect of Sugar Moiety on Methylation Pattern of Bases

摘要

Methyldiazonium ion (CH_3N_2~+) is an ultimate carcinogen that can methylate multiple sites in DNA/RNA. In present contribution, density functional theory calculations using the B3LYP and M06-2X functionals and the 6-31G(d,p) and aug-cc-pVDZ basis sets are carried out to study methylation reactions of CH_3N_2~+ at the different nucleophilic sites of DNA/RNA bases and their nucleosides. Total 12 nucleophilic sites, that is, the N2, N3, N7, and O6 sites of guanine; the N1, N3, N6, and N7 sites of adenine; O2 and N3 sites of cytosine and the O2 and O4 sites of thymine and uracil have been considered for study. Thus, a total of 30 reactions have been studied here. The polarizable continuum model is used for solvation calculations. The N7 site of guanine, N7(G), is found to be most reactive in all the reactions studied here, which is in agreement with experiment. However, the calculated reactivity of CH_3N_2~+ toward the N7(G) site in aqueous media follows the order: guanine>deoxyguanosine>guanosine. The reactivities of many other sites including the O6(G), O2(C), and N3(A) sites are also modified in going from DNA/RNA bases to their nucleosides and from DNA to RNA nucleosides. Thus, we note that the presence of sugar moiety significantly modifies the methylation pattern of bases caused by CH_3N_2~+. VC 2014 Wiley Periodicals, Inc.