The mechanism of matrix to analyte proton transfer in clusters of 2,5-dihydroxybenzoic acid and the tripeptide vpl

• Published in: Journal of the American Society for Mass Spectrometry Vol. 12; no. 6; pp. 726 - 731
• Main Authors: Land, C.Mark, Kinsel, Gary R
• Format: Journal Article Conference Proceeding
• Language: English
• Published: New York, NY Elsevier Inc 01.06.2001; Elsevier Science; Springer Nature B.V
• Subjects: Aminoacids, peptides. Hormones. Neuropeptides; Analytical, structural and metabolic biochemistry; Biological and medical sciences; Cations; Chemistry; Cluster analysis; Clusters; Desorption; Dihydroxybenzoic acid; Exact sciences and technology; Fundamental and applied biological sciences. Psychology; Gentisates; Hydroxybenzoates - analysis; Ionization potentials; Ions; Lasers; Leucine; Mass spectrometry; Oligopeptides - analysis; Organic chemistry; Peptides; Photon absorption; Photons; Proteins; Protonation; Protons; Reactivity and mechanisms; Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; Wavelengths; Peptides; Phenolic acid; Time of flight method; Proton transfer; Tripeptide; Reaction mechanism; Ionization potential; Matrix effect; Matrix assisted laser desorption ionization; Mass spectrometry; Wavelength
• ISSN: 1044-0305; 1879-1123
• DOI: 10.1016/S1044-0305(01)00239-2

Intracluster proton transfer from the matrix-assisted laser desorption/ionization matrix 2,5-dihydroxybenzoic acid (DHB) to the peptide valyl-prolyl-leucine has been investigated as a function of excitation laser wavelength and power. Ionization laser power studies at 308 nm indicate that cluster ionization occurs with a two-photon dependence, whereas matrix-to-analyte proton transfer and cluster dissociation requires an additional photon. At 266 nm, two-photon absorption leads to both cluster ionization and cluster dissociation/proton transfer. A consideration of these results clearly indicates that analyte protonation occurs following ionization of the cluster to produce a radical cation matrix/analyte cluster. Mass spectral features also indicate that mixed DHB/peptide cluster ionization can occur via two-photon ionization at wavelengths as long as 355 nm. These results suggest a reduction in the ionization potential of larger mixed DHB/peptide clusters of greater than 1 eV. The reduced ionization potential seen in these clusters suggests that radical cation initiated proton transfer remains a viable mechanism for analyte protonation in matrix-assisted laser desorption/ionization at these longer wavelengths.