| Abstract
| - Complexes between ammonia, water, or hydrogen fluoride and adenine, guanine, or their 8-oxo derivativesare investigated using density-functional theory. The binding strengths of the neutral and (N9) anionic complexesare considered for a variety of purine binding sites. The effects of hydrogen-bonding interactions on the (N9)acidity of the purine derivatives are considered as a function of the molecule bound and the binding site. Itis found that hydrogen-bonding interactions with one molecule can increase the acidity of purine derivativesby up to 60 kJ mol-1. The (calculated) simultaneous effects of up to four molecules on the acidity of thepurine derivatives are also considered. Our data suggest that the effects of more than one molecule on theacidity of the purines are generally less than the sum of the individual (additive) effects, where the magnitudeof the deviation from additivity increases with the number, as well as the acidity, of molecules bound.Nevertheless, the increase in the acidity due to additional hydrogen-bonding interactions is significant, wherethe effect of two, three, or four hydrogen-bonding interactions can be as large as approximately 95, 115, and130 kJ mol-1, respectively. The present study provides a greater fundamental understanding of hydrogen-bonding interactions involving the natural purines, as well as those generated through oxidative DNA damage,which may aid the understanding of important biological processes.
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