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Eur. J. Mass Spectrom. 3, 390 - 395 (1997)

Letter: Formation and fragmentation reactions of platinum-terpyridine complexes of glycine and cysteine and their methyl derivatives via electrospray ionization mass spectrometry

Richard A.J. O'Hair
School of Chemistry, The University of Melbourne, Parkville, Victoria, Australia.

ABSTRACT:
Under electrospray ionization (ESI) conditions, several ions are observed from a 1.5 x 106 M solution of [Pt(terpy)Cl]Cl in water including: [Pt(terpy)Cl]+ (base peak), [Pt(terpy)HO]+ and [Pt(terpy)H2O]2+. When a 30- to 40-fold excess of glycine or its N- or O-methyl derivatives was added, the ESI mass spectrum was still dominated by the [Pt(terpy)Cl]+ ion, although a number of new ions were observed including [Pt(terpy)M]2+, [Pt(terpy)M H]+, [M + H]+ and [2M + H]+ ions (where M = the amino acid). In contrast, when a 10-fold excess of cysteine was used, the [Pt(terpy)Cl]+ ion virtually disappeared and the dominant ion became the [Pt(terpy)M H]+ ion. These results are consistent with the known solution chemistry of [Pt(terpy)Cl]Cl, which shows a preference for binding via the thiolate of cysteine residues. In addition, collision-induced dissociation was performed on both the [Pt(terpy)M]2+ and [Pt(terpy)M H]+ ions of glycine and cysteine. Isotopic labeling and methyl derivatives were used to elucidate the mechanisms of their fragmentation reactions.

Keywords: Electrospray ionization, tandem mass spectrometry, platinum terpyridine complexes, glycine, cysteine, ion trap mass spectrometer.


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