Perturbation of hydrogen bonds in the adenine . thymine base pair by Na+: A quantum chemical study.

Ab initio self-consistent field calculations with 4-31G and STO-3G basis sets show that Na+ are able to damage the H bonds in the formamidine . formamide complex, modeling the adenine . thymine base pair (both H bonds in the complex investigated are the same as in adenine . thymine). If a water molecule is placed between the complex and Na+, the H bonds of the model are fully protected. Covalent as well as noncovalent binding of polycyclic aromatic hydrocarbons to nucleic acids should decrease the local concentration of water as a result of the insertion of the hydrophobic hydrocarbon into the DNA and thereby increase the exposure of the DNA H bonds to Na+ attack. Thus, Na+ reaching the base pair could provoke or interfere with cell division.