Hydration of DNA base pairs

Because of the limitation on the volume of our review, we have not reported here the details of geometrical structures of the hydrated DNA base pairs (for details see [140, 141]). However, as follows from the crystallographic data [143,144], the water molecules considered in [140,141] are located in the most probable area for the water - DNA base interaction. The following important conclusions are coming from the analysis of the geometry of the hydrated DNA 

The structure of cytosine - isoc5Tosine base pairs (iCC) deviates slightly from the gas phase geometry when the complex interacts with two and four water molecules. 

All complexes of cytosine - isocytosine base pairs dramatically change the geometry when they interact with six water molecules. They become strongly nonplanar and adopt a buckling structure. For example, the buckle angle amounts to 3.6 , 6.1 , 3.2 and 31.2 for isolated, two-, four- and six-hydrated iCCl complexes, respectively. The same effect has been observed for seven water molecules hydrating the AU complexes. 

There is a common feature in the influence of the hydration on iCC and AU base pairs. Both of them increase the degree of pyramidalization (the difference in the corresponding dihedral angles before and after hydration exceed 10 ) of the amino group upon increasing the number of hydrating water molecules. 

The predictions on the influence of hydration on the relative stability of different iCC and AU complexes are of importance because of the possible role of these complexes in replication fidelity. These data are shown in Tables 17 and 18. 

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