Gas-phase acidities of nucleosides combinedwith the knowledge of deprotonation sites, could improve our understanding ofchemical reactions basic to biological systems. In this paper, we mainly focusour attention on the influence of cation coordination on the acidities ofmultiple sites in cytosine nucleosides. The acidities of multiple sites in M+-L(Where L represents the cytosine nucleosidesand M+ is the particular metal ion such as Li+, Na+,and K+) complexes have been investigated theoretically employing theB3LYP and using 6-311++G (d,p). The geometrical characters, gas-phase acidities,sugar puckering and electronic property of nondeprotonated and/or deprotonatedcomplexes have been investigated. The results clearly indicate that theacidities of OH and NH groups in metal-nucleosides are significantly enhancedrelative to the neutral cytosine nucleosides. The calculated OH group's acidities of these molecules are inthe range ca. 341�352 kcal/mol. This is asurprising result, because it shows that hydrogen bonding can make the acidityof an alcohol as strong as an organic acid.

How acidity of Cytosine nucleosides change when bonded to a metal ion: Metal coordination and hydrogen bonding as
the sources strongly affected [Delta]H<sub>acidity</sub>

239th National Meeting (2010)

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