Novel method for [M + Cu]+ ion formation by matrix-assisted laser desorption ionization |
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| Institution: | 1. The Laboratory for Biological Mass Spectrometry, Department of Chemistry, Texas A&M University, P.O. Box 30012, College Station, TX 77842-3012, USA;1. Institute of Electronics, Bulgarian Academy of Sciences, 72 Tsaridradsko shose Boul., Sofia 1784, Bulgaria;2. International Center for Materials for NanoArchitectonics (MANA), National Institute for Materials Science (NIMS), 1-1 Namiki, Tsukuba 305-0044, Japan;3. Rostislaw Kaischew Institute of Physical Chemistry, Bulgarian Academy of Sciences, Acad. G. Bonchev Str., Block 11, Sofia 1113, Bulgaria;1. Research and Early Development, Genentech Inc., 1 DNA Way, South San Francisco, CA, 94080, USA;2. Pharma Technical Development Europe Analytics, F. Hoffmann-La Roche Ltd, Grenzacherstrasse 124, 4070, Basel, Switzerland |
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| Abstract: | Direct deposition of a MALDI sample onto a copper sample stage and irradiation with UV light (337 nm) produces copper adduct ions of both the matrix and analyte molecules. This technique for introducing Cu+ into the gas-phase avoids suppression of ion signal that accompanies addition of metal salts to the sample solution. We observe good correlation between the number of basic residues in peptides and the number of Cu+ ions that add to the peptide. For example, the peptide KRQHPG contains three basic residues and forms ions with up to three Cu+ adducts. Postsource decay experiments demonstrate that for arginine containing peptides, arginine anchors the Cu+ ion. That is, all metastable ions contain the arginine complexed to Cu+ and the only immonium ion observed is that of arginine–Cu+. In addition, preliminary calculations indicate that guanidine has the highest Cu+ ion affinity followed by histidine. |
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