Oxidative radical driven cleavage of peptide backbone caused by matrix-assisted laser desorption/ionization-in-source decay with low matrix-to-peptide molar ratios

Complete and selective nitration of tyrosine residue in peptides caused by ultraviolet matrix-assisted laser desorption/ionization

“…In the peptide with Tyr and six Gly residues (Fig. 3), the spectrum with 3, 5-DNSA showed the definite mass shift at 45 Da in the intense a5 to a10 ions and A11 to A15 ions, suggesting Scheme 2 The specific cleavage at the Ca-C and N-Ca bond of the peptide backbone for the formation of a/x and c/z fragment pairs, through the site-specific hydrogen-bonding between matrix functional groups (-NO 2 and -NH 2 ) and the sites of amide region (NH and CO) of the peptide backbone occurs by attack of hydroxyl radicals (.OH) generated by the photolysis of 3, 5-DNSA molecules [19,20], as shown in Scheme 3. The generation of .OH radicals from nitroaromatic compounds can be strongly supported by the report of Nauser et al [21].…”