Cationization of simple organic molecules by singly-charged Ag3+ cluster ions in matrix-assisted laser desorption/ionization mass spectrometry: metal cluster-molecule interactions

J Am Soc Mass Spectrom. 2004 Jun;15(6):879-83. doi: 10.1016/j.jasms.2004.03.002.

Abstract

It was found earlier that under matrix-assisted laser desorption/ionization (MALDI) conditions several organic compounds which produce adduct with silver ions, are also capable of forming adducts with Ag(3)(+) cluster ions under appropriate conditions. The Ag(3)(+) cluster ion can be in situ generated under the MALDI analysis conditions from silver trifluoroacetate cationization agent in the presence of organic MALDI matrices. In this article the fragmentation of a commercial plasticizer, a peracetylated isoflavone glycoside and a pyrazolylphenyl disulfide derivative cationized with silver ions and Ag(3)(+) cluster ions are compared. It was observed that the complexes of Ag(3)(+) are less fragmented than the corresponding adduct ions with Ag(+). The presumable fragmentation channel of [M + Ag(3)(+)] is the elimination of Ag(2) units from these complexes. No significant dissociation of [M + Ag(3)(+)], into M and Ag(3)(+) takes place, indicating a tight connection between the corresponding molecule and Ag(3)(+) cluster ion. However, with a compound carrying very labile groups, such as the pyrazolylphenyl disulfide derivative, intramolecular cleavages can occur prior to significant dissociation of the Ag(3)(+) cluster ion.