Hydration of cytidine, 2'-deoxycytidine and their phosphate salts in the aqueous solutions. A molecular dynamics computer simulation study.

To compare the hydration pattern of the cytidine (Cyd) and 2'-deoxycytidine (dCyd) in the aqueous solutions at the level of microscopic interactions. Molecular Dynamics (MD) computer simulations have been undertaken. The results indicate that the hydration of the heterocyclic base moiety in cytidine and 2'-deoxycytidine has a hydrophobic character. None of the three potential Watson-Crick base pair centres hydrogen bonds with the water molecules and the formation of something akin to a clathrate cage structure of water around base moieties of nucleosides in the aqueous solution is suggested. In contrast, the hydration of Cyd and dCyd sugar moieties shows a hydrophilic character and the three-dimensional networks of H-bonds involving all hydrophilic centres are formed differently around the ribose and 2'-deoxyribose. The sugar hydroxyl groups participate in the hydrogen bonding with water both as H-donor and as H-acceptor. Their donor-acceptor abilities have been evaluated and compared. The coordination numbers, the geometrical data of the first hydration shell, and the number of hydrogen bonds have been calculated. The changes in the pattern of hydration with the increased concentration of nucleosides and upon nucleoside protonation are discussed. The analysis of the pairwise interaction energies are also presented.