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Abstract: The noncovalent interactions between cytosine nucleobase with some biological anions such as F−, Cl−, CN−, , and OH− and cytosine nucleosides (i.e., cytidine and deoxycytidine molecules) with F−, Cl−, CN− anions have been demonstrated by DFT study. The molecular geometries, energy properties, H-bonding patterns, dipole moments and charge distribution of these complexes were investigated with the B3LYP method in conjunction with the 6-311++G(d,p) basis set. It has been found that anions can interact with cytosine nucleobase forming hydrogen bonds. In general, these interactions occur via N–H, O–H and C–H substituents of cytosine, cytidine and deoxycytidine. The presence of anions near these molecules strongly affects the electron distribution in the base structure. From this study, a greater understanding of hydrogen bonding interactions involving DNA and RNA molecules will be obtained. These interactions could provide insight to an unrecognized control element in biological processes, providing new and intriguing opportunities of exploring the electrostatic effects on biological processes. [Copyright &y& Elsevier]

Abstract: The coordination geometries, electronic features, absolute metal ion affinities, geometrical multiplicity and binding strength for the complexes formed by Mg2+, Ca2+, Zn2+ and Cu+ with cytidine and deoxycytidine have been determined theoretically employing the hybrid B3LYP exchange-correlation functional and using 6-311++G(d,p) orbital basis sets. Our study shows that the most stable coordination modes of cytosine nucleosides with these cations are rather similar. In the isolated state, the most stable form corresponds to a tridentate complex in which the cation interacts with three oxygen atoms: one from the carbonyl oxygen of cytosine moiety and two from the sugar unit (i.e., O5′ and O4′). The influences of metal cationization on the strength of the N-glycosidic bond, the values of the phase angle of pseudorotation P in the sugar unit and sugar ring conformation have been studied. In all cases, the N1; bond distance changes upon introducing positive charge in the nucleosides. [Copyright &y& Elsevier]