Gas-phase interactions of organotin compounds with glycine
Résumé
Gas-phase interactions of organotins with glycine have been studied by combining mass spectrometry experiments and quantum calculations. Positive-ion electrospray spectra show that the interaction of di- and tri-organotins with glycine results in the formation of [(R)2Sn(Gly)-H]+ and [(R)3Sn(Gly)]+ ions, respectively. Di-organotin complexes appear much more reactive than those involving tri-organotins. (MS/MS) spectra of the [(R)3Sn(Gly)]+ ions are indeed simple and only show elimination of intact glycine, generating the [(R)3Sn]+ carbocation. On the other hand, MS/MS spectra of [(R)2Sn(Gly)-H]+ complexes are characterized by numerous fragmentation processes. Six of them, associated with elimination of H2O, CO, H2O + CO and formation of [(R)2SnOH]+ (−57 u),[(R)2SnNH2]+( −58 u) and [(R)2SnH]+ (−73 u), are systematically observed. Use of labeled glycines notably concludes that the hydrogen atoms eliminated in water and H2O + CO are labile hydrogens. A similar conclusion can be made for hydrogens of [(R2)SnOH]+and [(R2)SnNH2]+ ions. Interestingly, formation [(R)2SnH+ ions is characterized by a migration of one the α hydrogen of glycine onto the metallic center. Finally, several dissociation routes are observed and are characteristic of a given organic substituent. Calculations indicated that the interaction between organotins and glycine is mostly electrostatic. For [(R)2Sn(Gly)-H]+ complexes, a preferable bidentate interaction of the type η2-O,NH2 is observed, similar to that encountered for other metal ions. [(R)3Sn]+ ions strongly stabilize the zwitterionic form of glycine, which is practically degenerate with respect to neutral glycine. In addition, the interconversion between both forms is almost barrierless. Suitable mechanisms are proposed in order to account for the most relevant fragmentation processes.
Mots clés
Quantum calculation
Amino acids
Atoms
Metal ions
Organometallics
Phase interfaces
Tin
hydrogen
organotin compound
water
article
chemical reaction
complex formation
dissociation
elimination reaction
gas
mass spectrometry
molecular interaction
molecular mechanics
positive ion electrospray
priority journal
quantum chemistry
static electricity
ab initio calculations
gas-phase reaction
organotins
Gases
Glycine
Ions
Models
Molecular
Organotin Compounds
Protons
Spectrometry
Mass
Electrospray Ionization
Tandem Mass Spectrometry
Electrospray spectra
Fragmentation process
Gas-phase reactions
Organic substituents
Domaines
Chimie-Physique [physics.chem-ph]
Origine : Fichiers produits par l'(les) auteur(s)
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