Theoretical investigation of the conformation of 2'-deoxyriboadenosine monophosphate protonated at the N7 atom and stabilized by a very strong C8-H center dot center dot center dot O-P hydrogen bond indicates that this hydrogen bond may be disrupted by rotation of the adenine moiety around the glycosidic bond. A B3LYP/aug-cc-pVDZ scan of the relaxed potential energy surface demonstrates that this rotation is a multi-stage process, accompanying proton transfer from the N7 atom of adenine to the oxygen atom of the phosphate group with a change of conformation of the nucleotide from south/anti to north/syn conformation. Car-Parrinello molecular dynamics simulation indicates that rotation around the glycosidic bond is the preferred way for relaxation of the molecular geometry of this conformer. Both processes, i.e. conformational transition and proton transfer, are strongly coupled. However, the conformer containing a strong C-H center dot center dot center dot O hydrogen bond also corresponds to a local minimum on the Gibbs free energy surface. A specific property of this hydrogen bond is the large variation of the H center dot center dot center dot O distance (ranging from 1.3 to 2.2 angstrom), which is not caused by proton movement between the carbon and oxygen atoms, but rather by relative motions of the adenine and phosphate moieties. (C) 2010 Elsevier B.V. All rights reserved.