FREE-ENERGIES OF HYDRATION IN THE GAS-PHASE OF SOME PHOSPHATE SINGLY AND DOUBLY-CHARGED ANIONS - (HO)(2)PO2- (ORTHOPHOSPHATE), (HO)O2POPO2(OH)(2-)(DIPHOSPHATE), RIBOSE 5-PHOSPHATE, ADENOSINE 5'-PHOSPHATE, AND ADENOSINE 5'-DIPHOSPHATE

Singly and doubly charged anions, A(Z-), of phosphates, sugar phosphat es, and adenosine phosphates are obtained in the gas phase by electros pray. The ions are introduced into a reaction chamber where sequential hydration equilibria (n - 1,n) A(Z-)(H2O)(n-1) + H2O = A(Z-)(H2O)(n) occur. The equilibrium constants K-n-1,K-n are determined with a mass spectrometer. Free energies Delta G degrees(n-1,n) at room temperature were determined for (HO)(2)PO2-, orthophosphate, (HO)O2POPO2(OH)(2)(2 -), diphosphate, ribose 5-phosphate singly charged, adenosine 5'-phosp hate, and singly charged and doubly charged adenosine 5'-diphosphate. The magnitudes of the hydration energies provide information on the st ability of the ions. Unusually low hydration exoergicities indicate th e presence of intramolecular hydrogen bonding. Evidence is provided fo r the presence of intramolecular hydrogen bonding in ribose phosphate, adenosine monophosphate, and adenosine diphosphate.