Adenine nonplanarity

Choi Myong Yong et al., Nonplanarity of adenine Vibrational transition moment angle studies in helium nanodroplets. J. Phys. Chem. A 112, 7185-7190 (2008)... 

Theoretical and experimental methods are complementary to each other. For example, computational methods have suggested that the amino groups of nucleic acid bases in the ground state are nonplanar [58], However, experimental evidence for amino group nonplanarity was obtained only recently when Dong and Miller [59] measured the vibrational transition moment angles in adenine and three tautomers of cytosine in helium droplets. 

The examples of hydroxyl radical addition products identified in single crystals of adenine and guanine base derivatives confirm that water can play an important role in the radiation damage mechanism. It should be noted that the new mechanism has attracted some criticism [38]. The main objection is that nonplanar geometries were calculated for the gas phase radicals whereas planar structures are expected experimentally due to the hydrogen-bonding scheme... 

Nonplanarity of the guanine amino group is substantially more pronounced than the nonplanarity of adenine and cytosine. 

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