Département de chimie moléculaire

Non-covalent complexes (NCC) between hexose monophosphates (HexP) and arginine (R) were analyzed using ESI MS and MS/MS in neg. mode under different (hard, HC and soft, SC) desolvation conditions. High resoln. mass spectrometry (HRMS) revealed the presence of different ionic species, namely, homo- and heteromultimers of R and HexP. Deprotonated heterodimers and corresponding sodiated species were enhanced under HC likely due to a decrease in available charge no. assocd. with the redn. of H⁺/Na⁺ exchange. The quantum calcns. showed that the formation of covalent systems is very little exothermic, therefore, such systems are disfavored. Desolvation dependent CID spectra of deprotonated [(HexP+R)-H]^- complexes demonstrated that they can exist within the hydrogen bond (HB) and salt bridge (SB) forms, yielding either NCC sepn. or covalent bond cleavages, resp. Although HB forms are the main species, they cannot survive under HC; therefore, the minor SB forms became detectable. Energy-resolved mass spectrometry (ERMS) expts. revealed diagnostic fragment ions from both SB and HB forms, providing evidence that these isomeric forms are inconvertible. SB formation should result from the ionic interactions of highly acidic group of HexP with strongly basic guanidine group of arginine and thus requires an arginine zwitterion (ZW) form. This was confirmed by quantum calcns. Ion-ion interactions are significantly affected by the presence of sodium cation as demonstrated by the fragmentation patterns of sodiated complex species. Regarding CID data, only SB between protonated amino group of R and deprotonated phosphate group of HexP could be suggested, but the primary amine is not enough basic then, the SB must be fleeting. Nevertheless, the observation of the covalent bond cleavages suggests the presence of structures with a free neg. charge able to induce fragmentations. Indeed, according to quantum calcns., solvated salt (SS) systems involving Na⁺/COO^- salt solvated by neutral phosphate and neg. charge on sugar ring are preferentially formed.