Gas‐phase interactions of organotin compounds with cysteine

The gas‐phase interactions of cysteine with di‐organotin and tri‐organotin compounds have been studied by mass spectrometry experiments and quantum calculations. Positive‐ion electrospray spectra show that the interaction of di‐ and tri‐organotins with cysteine results in the formation of (R)₂Sn(Cys‐H)]⁺ and (R)₃Sn(Cys)]⁺ ions, respectively. MS/MS spectra of (R)₂Sn(Cys‐H)]⁺ complexes are characterized by numerous fragmentation processes, notably associated with elimination of NH₃ and (C,H₂,O₂). Several dissociation routes are characteristic of each given organic species. Upon collision, both the (R)₃Sn(Gly)]⁺ and (R)₃Sn(Cys)]⁺ complexes are associated with elimination of the intact amino acid, leading to the formation of (R)₃Sn]⁺ cation. But for the latter complex, two additional fragmentation processes are observed, associated with the elimination of NH₃ and C₃H₄O₂S. Calculations indicate that the interaction between organotins and cysteine is predominantly electrostatic but also exhibits a considerable covalent character, which is slightly more pronounced in tri‐organotin complexes. A preferred bidentate interaction of the type ‐η²‐S‐NH₂, with sulfur and the amino group, is observed. As for the (R)₃Sn(Cys)]⁺ complexes, their stability is due to the combination of the hydrogen bond taking place between the amino group and the sulfur lone pair and the interaction between the carboxylic oxygen atom and the metal. Copyright © 2016 John Wiley & Sons, Ltd.