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

Eur. J. Mass Spectrom. 3, 390–395 (1997)
DOI: 10.1255/ejms.171

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 10^–6 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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