期刊
EUROPEAN JOURNAL OF MASS SPECTROMETRY
卷 12, 期 6, 页码 359-367出版社
IM PUBLICATIONS
DOI: 10.1255/ejms.821
关键词
MALDI mechanism; proton transfer; equilibrium thermodynamics; gas-phase basicity; gas-phase acidity
The equilibrium nature of a plume of laser desorbed material is explored through the application of a simple equilibrium model to the ion signals observed in 355 nm laser desorption/ionization mass spectra of mixtures of the NIALDI matrix alpha-cyano-4-hydroxycinnamic acid (alpha CHCA) with the amino acids glycine, alanine, valine, isoleucine, and phenylalanine. In these studies it is found that there are systematic and predictable increases in the relative yield of protonated amino acid with increases in amino acid gas-phase basicity. In addition, the thermodynamic values extracted from the equilibrium plot are shown to be in good agreement with values obtained from computational investigation of plausible alpha CHCA proton donor species. These results are supportive of a picture wherein the laser-desorbed material is viewed as a dense plume in which facile charge transfer occurs leading, ultimately, to a thermodynamically equilibrated distribution of proton donor and proton acceptor species.
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