Investigation of the interaction between arsenic species and thiols via electrospray ionization tandem mass spectrometry

Arsenic species have been known to participate in a number of chemical and biological reactions, including oxidation–reduction reactions, acid–base reactions, covalent interactions, and methylation–demethylation reactions because of the element's multiple and interconvertible oxidation states. Little is known about the structure or bonding behavior between arsenic species and thiolcontaining biomolecules. Therefore, a better understanding of the bonding behavior and detailed information on the molecular structure for arsenic–thiol complexes is needed. As a result, we have investigated the interaction between arsenic species (arsenate (AsV), arsenite (AsIII), monomethylarsonic acid (MMAV), and dimethylarsinic acid (DMAV)) with biomolecules containing thiol groups (glutathione and cysteine) by electrospray ionization mass spectrometry (ESI-MS). These compounds were dissolved in methanol/water solution and introduced into the MS instrument in order to elucidate the direct bonding behavior of thiol group of biomolecules with arsenic species. In addition, further detailed structural information on this complex was obtained by collision-induced dissociation (CID) measurements.In each mass spectrum for mixture solutions between arsenic species and thiol compounds, various peaks such as protonated arsenic–thiol complexes, protonated noncomplexed thiol compounds, sodium bound cluster ions, and proton bound cluster ions were observed. In these mass spectra, the arsenic complexes were formed by interaction with thiol groups on the cysteine residues. These arsenic–thiol complexes produced a variety of fragment ions by cleavage of chemical bonds, and by interaction of other binding site on thiol compounds in tandem mass spectrometry experiments.