Structures of H-bonded DNA base pairs

A very interesting result is revealed by an inharmonic vibrational analysis of the AT WC base pair [9]. The effective geometry of this pair is nonplanar despite that the planar structure is a minimum on the potential energy surface. The difference between equilibrium and effective geometries is because the molecular vibrations shift the nuclear positions from their equilibrium positions. This might be the case of many other base pairs which are currently assumed as planar complexes. Thus spectroscopic experiments in the gas phase should reveal a nonplanar, double-minimum structure for base pairs. 

a rather large conformational flexibility of the pyrimidine rings of the bases could to some extent contribute to the flexibility of pairs [62], 

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