Tuning the Adsorption Interactions of Imidazole Derivatives with Specific Metal Cations

Gold as a coordinator of an imidazole conjugated dye of BODIPY derivatives for the identification of simple mercaptans

Rapid detection of mercaptans in materials and the environment is of great help to material analysis and pollutant monitoring. Gold (Au) shows a high affinity to mercaptans. The coordination and steric effect of mercaptans to Au may be used for the development of new fluorescent sensors. It is possible to distinguish simple mercaptans (such as, HS^-, thioglycolic acid) from glutathione (GSH) using Au as a coordinator of dye. Herein, a water-soluble fluorescent sensor of an imidazole conjugated 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) derivative (BIM) was characterized by spectroscopic methods. BIM showed a large Stokes shift and high affinity to metals. Especially, Au-combined BIM produced a new complex BIMAu showing improved fluorescence emission, which can be quenched by thioglycolic acid and sodium hydrosulfide, but less affected by GSH. The detection limit of thioglycolic acid was 0.014 µM. Both NaSH and thioglycolic acid coordinated with BIMAu, while GSH took Au³⁺ away from BIMAu. These results indicate that the gold coordination competition between imidazole-substituted dyes and mercaptans is a good method for the development of new fluorescence chemosensors.

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)₂ Sn(Cys-H)]⁺ and [(R)₃ Sn(Cys)]⁺ ions, respectively. MS/MS spectra of [(R)₂ Sn(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)₃ Sn(Gly)]⁺ and [(R)₃ Sn(Cys)]⁺ complexes are associated with elimination of the intact amino acid, leading to the formation of [(R)₃ Sn]⁺ cation. But for the latter complex, two additional fragmentation processes are observed, associated with the elimination of NH₃ and C₃ H₄ O₂ S. 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)₃ Sn(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.