| Abstract: | The lower‐energy stable structures of the A?T base pair are revealed under a search of its potential energy surface in the vicinity of its Watson–Crick configuration performed at the PM3 computational level. Their properties and the mutual position of the nucleic acid bases A and T in these structures allow to partition them into three classes: partially preopened, stretched, and fully preopened. The preferable monohydration sites of the preopened, stretched, and fully preopened pairs are also determined. It is demonstrated, first, that the monohydration of the A?T pair at particular sites favors a base pair preopeness and, second, that a binding of the water molecule to the preopened A?T base pair on the major groove side enhances its stabilization. It is also shown that water molecule placing in the vicinity of the central H bond of the A?T pair significantly facilitates its preopening. © 2001 John Wiley & Sons, Inc. Int J Quant Chem 82: 193–204, 2001 |
