Gas-phase hydrogen/deuterium exchange of positively charged mononucleotides by use of Fourier-transform ion cyclotron resonance mass spectrometry

The gas-phase structures of protonated (deoxy)nucleaside-5' and 3'-monophos phates (mono-nueleotides) have been examined by the use of gas-phase hydrog en/deuterium (H/D) exchange and high-field Fourier-transform ion cyclotron resonance mass spectrometry. These nucleotides were reacted with three diff erent deuterating reagents: ND3, D2O, and D2S, of which ND, was the most ef fective. All mononucleotides fully exchanged their labile hydrogen for deut erium with ND3 with the exception of deoxycytidine-3' monophosphate, deoxya denosined5'-monophosphate, adenosine-5'-monophosphate, and adenosine3'-mono phosphate. Semiempirical calculations demonstrate the presence of hydrogen bonding upon protonation of the purine mononucleotides which may lead to in complete H/D exchange. H/D exchange rates differed between the deoxymononuc leotides and the ribomononucleotides, suggesting that the 2'-OH group plays an important role in the exchange process. Reactions of nucleosides and mo nonucleotides with D2O demonstrate that a structure-specific long-lived ion -molecule complex between D2O and the mononucleotide involving the phosphat e group is necessary for exchange to overcome the high-energy activation ba rrier. in contrast, a structure-specific long-lived ion-molecule complex be tween the mononucleotides and ND3 is not required for exchange to occur. (C ) 2001 American Society for Mass Spectrometry.