Gas‐phase interactions of organotin compounds with glycine

Abstract

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 η(2)-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.

Gas‐phase interactions of organotin compounds with cysteine

“…Consequently, in these two complexes, the interaction between S and Sn is predominantly electrostatic with a considerable covalent character. When involving nitrogen and oxygen, the interaction is still predominantly electrostatic with trends similar to those shown for [(CH 3 ) 2 Sn(Gly‐H)] + complexes …”

“…The N‐deprotonated form, DMT‐η 2 ‐SH‐NH , lies higher in energy (around 102 kJ mol −1 above the global minimum). Unlike what was found in the [(CH 3 ) 2 Sn(Gly‐H)] + complexes, the interaction of the metal with the carboxylic group appears clearly disfavored against the binding with the other reactive sites (N and S). This behavior could be associated with the particularly strong interaction taking place between the metal and the sulfur, as compared with the binding involving either nitrogen or oxygen.…”

“…These results suggest the formation of an intermediate in which NH 3 and C 3 H 4 O 2 S could interact with the metallic center. The fragmentation patterns observed with cysteine and glycine are therefore different, elimination of the amino acid being the unique process observed with the latter …”

“…Elimination of intact cysteine leading to the formation of the [(CH 3 ) 3 Sn] + carbocation ( m / z 165) is observed. Unlike what was observed with glycine, several additional fragmentation processes occur (Scheme ). Two other fragment ions are indeed detected, associated with the elimination of NH 3 ( m / z 269) and C 3 H 4 O 2 S ( m / z 182).…”

New diorganotin(IV) complexes of Schiff base derived from 4‐amino‐3‐hydrazino‐5‐mercapto‐4H‐1,2,4‐triazole: Synthesis, structural characterization, density functional theory studies, atoms‐in‐molecules analysis and antifungal activity

“…The ground state optimized geometries in the gas phase of diorganotin(IV) complexes 1 and 2 calculated at the B3LYP/6‐31G(d,p)/Def2‐SVP (Sn) level of theory are presented in Figure . The functional B3LYP has been credibly reported previously for electronic structure calculations of several organotin(IV) complexes with hetero donor atoms …”