Abstract
Experimental estimates of the premelting Adenine-Thymine base pair opening probability for some B-BNA sequences are two orders of magnitude smaller than those of other B-BNA sequences. The AT pairs in the sequence with smaller open probability seem to be those that have a well defined spine of hydration in the minor groove. We show that this spine of hydration can significantly enhance the thermal stability of the base pairs to which they are attached. The effect of this spine of hydration coupled with the possible stabilization effect contributed from neighboring GC pairs can explain the the differences in the observed AT pair opening probability for different AT containing sequences.