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Quantitative electrospray ionization mass spectrometric studies of ternary complexes of amino acids with Cu 2+ and phenanthroline
Author(s) -
Gatlin Christine L.,
Tureček František
Publication year - 2000
Publication title -
journal of mass spectrometry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.475
H-Index - 121
eISSN - 1096-9888
pISSN - 1076-5174
DOI - 10.1002/(sici)1096-9888(200002)35:2<172::aid-jms926>3.0.co;2-c
Subject(s) - chemistry , amino acid , electrospray ionization , stability constants of complexes , ternary operation , ternary complex , phenylalanine , side chain , mass spectrometry , electrospray , stereochemistry , crystallography , chromatography , organic chemistry , ion , biochemistry , enzyme , computer science , programming language , polymer
Electrospray ionization (ESI) mass spectra of ternary complexes of Cu 2+ and 1,10‐phenanthroline with the 20 essential amino acids (AA) were investigated quantitatively. Non‐basic amino acids formed singly charged complexes of the [Cu(AA − H)phen] + type. Lysine (Lys) and arginine (Arg) formed doubly charged complexes of the [Cu(HAA − H)phen] 2+ type. Detection limits were determined for the complexes of phenylalanine (Phe), glutamic acid (Glu) and Arg, which were at low micromolar or submicromolar concentrations under routine conditions. Detection limits of low nanomolar concentrations are possible for amino acids with hydrophobic side‐chains (Phe, Tyr, Trp, Leu, Ile) as determined for Phe. The efficiencies for the formation by ESI of gaseous [Cu(AA − H)phen] + ions were determined and correlated with the acid–base properties of the amino acids, ternary complex stability constants and amino acid hydrophobicities expressed as the Bull–Breese indices (Δ F ). A weak correlation was found between Δ F and the ESI efficiencies for the formation of gaseous [Cu(AA − H)phen] + [Cu(HAA − H]phen] 2+ and [AA + H] + ions that showed that amino acids with hydrophobic side‐chains were ionized more efficiently. In the ESI of binary and ternary amino acid mixtures, the formation of gas‐phase Cu–phen complexes of amino acids with hydrophobic side‐chains was enhanced in the presence of complexes of amino acids with polar or basic side‐chains. An interesting enhancement of the ESI formation of [Cu(Glu − H)phen] + was observed in mixtures. The effect is explained by ion‐cluster formation at the droplet interface that results in enhanced desorption of the glutamic acid complex. Copyright © 2000 John Wiley & Sons, Ltd.