Structure of anionic and protonated methyl ester of 2'-deoxyriboadenosine monophosphate has been calculated by the B3LYP/aug-cc-pvdz method. Protonation of the base results in significant strengthening of intramolecular C-H... 0 hydrogen bonds due to increase of electrostatic interactions between proton accepting and donating fragments and may be described as assistance to hydrogen bonding by the interaction of positively and negatively charged fragments of molecule. In the case of protonation of the N7 atom, those assistance results in formation of extra strong C8-H center dot center dot center dot O-P hydrogen bond with characteristics being close to strong conventional H-bonds. This leads to proton barrierless motion within the C8-H center dot center dot center dot O-P fragment. (c) 2007 Elsevier B.V. All rights reserved.