1:1 complexes of b-cyclodextrin (CD) with three amino acids (Gly, Phe and Trp) have been detected as ions in the gas phase using infusion positive and negative ion electrospray ionization mass spectrometry (ESI-MS). In contrast with the positive ion ESI mass spectra of simple aqueous solutions, the
Quantitative electrospray ionization mass spectrometric studies of ternary complexes of amino acids with Cu2+ and phenanthroline
✍ Scribed by Gatlin, Christine L.; Ture?ek, Franti?ek
- Publisher
- John Wiley and Sons
- Year
- 2000
- Tongue
- English
- Weight
- 102 KB
- Volume
- 35
- Category
- Article
- ISSN
- 1076-5174
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✦ Synopsis
Electrospray ionization (ESI) mass spectra of ternary complexes of Cu
2Y 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] Y type. Lysine (Lys) and arginine (Arg) formed doubly charged complexes of the [Cu(HAA -H)phen] 2Y 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] Y 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 (1F). A weak correlation was found between 1F and the ESI efficiencies for the formation of gaseous [Cu(AA -H)phen] Y [Cu(HAA -H]phen] 2Y and [AA Y H] Y 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] Y 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.
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