Gas‐Phase Chemistry of Diphosphate Anions as a Tool To Investigate the Intrinsic Requirements of Phosphate Ester Enzymatic Reactions: The [M 1 M 2 HP 2 O 7 ] − Ions

Experimental studies on gaseous inorganic phosphate ions are practically nonexistent, yet they can prove helpful for a better understanding of the mechanisms of phosphate ester enzymatic processes. The present contribution extends our previous investigations on the gas‐phase ion chemistry of diphosphate species to the [M 1 M 2 HP 2 O 7 ] − ions where M 1 and M 2 are the same or different and correspond to the Li, Na, K, Cs, and Rb cations. The diphosphate ions are formed by electrospray ionization of 10 −4   M solutions of Na 5 P 3 O 10 in CH 3 CN/H 2 O (1/1) and MOH bases or M salts as a source of M + cations. The joint application of mass spectrometric techniques and quantum‐mechanical calculations makes it possible to characterize the gaseous [M 1 M 2 HP 2 O 7 ] − ions as a mixed ionic population formed by two isomeric species: linear diphosphate anion coordinated to two M + cations (group I ) and [PO 3 ⋅⋅⋅M 1 M 2 ⋅⋅⋅HPO 4 ] − clusters (group II ). The relative gas‐phase stabilities and activation barriers for the isomerization I → II , which depend on the nature of the M + cations, highlight the electronic susceptibility of P‐O‐P bond breaking in the active site of enzymes. The previously unexplored gas‐phase reactivity of [M 1 M 2 HP 2 O 7 ] − ions towards alcohols of different acidity was investigated by Fourier transform ion cyclotron resonance mass spectrometry (FT‐ICR/MS). The reaction proceeds by addition of the alcohol molecule followed by elimination of a water molecule.