Free Energies of Hydration in the Gas Phase of Some Phosphate Singly and Doubly Charged Anions:  (HO)₂PO₂⁻ (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 phosphates, and adenosine phosphates are obtained in the gas phase by electrospray. The ions are introduced into a reaction chamber where sequential hydration equilibria ( n − 1, n ) A Z - (H 2 O) n - 1 + H 2 O = A Z - (H 2 O) n occur. The equilibrium constants K n - 1, n are determined with a mass spectrometer. Free energies Δ G ° n - 1, n at room temperature were determined for (HO) 2 PO 2 -, orthophosphate, (HO)O 2 POPO 2 (OH) 2 2-, diphosphate, ribose 5-phosphate singly charged, adenosine 5‘-phosphate, and singly charged and doubly charged adenosine 5‘-diphosphate. The magnitudes of the hydration energies provide information on the stability of the ions. Unusually low hydration exoergicities indicate the presence of intramolecular hydrogen bonding. Evidence is provided for the presence of intramolecular hydrogen bonding in ribose phosphate, adenosine monophosphate, and adenosine diphosphate.