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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
Author(s) -
Pepi Federico,
Barone Vincenzo,
Cimino Paola,
Ricci Andreina
Publication year - 2007
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200601093
Subject(s) - chemistry , enzyme , phosphate , gas phase , inorganic chemistry , organic chemistry
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.