Gas‐phase intramolecular hydroxyl‐amino exchange of protonated arginine and verified by the synthetic intermediate compound

Abstract

A new fragmentation process was proposed to interpret the characteristic product ion at m/z 130 of protonated arginine. The α-amino group was dissociated from protonated arginine and then combined with the (M + H-NH ) fragment to form an ion-neutral complex which further generated a hydroxyl-amino exchange intermediate compound through an ion-molecule reaction. This intermediate compound was synthesized from argininamide through a diazo reaction, and then the reaction mixture was analyzed using liquid chromatography combined with mass spectrometry (LC-MS). The collision-induced dissociation experiments under the same conditions revealed that this intermediate compound produced the characteristic product ion at m/z 130 as well as protonated arginine, and in addition, density functional theory calculations were performed to confirm simultaneous loss of NH and CO from this intermediate to give the m/z 130 ion.

Aqueous microdroplets enable abiotic synthesis and chain extension of unique peptide isomers from free amino acids

“…Two ion-neutral complexes 2 and 3 ( 83 , 84 ) are accessible from fully covalent oxazolidinone ion 1. The coexistence of covalent and ion-neutral forms of an ion has been implicated in gas-phase reactions of Gly ( 85 ), as well as the hydroxyl-amino exchange in protonated arginine ( 86 ), an isomerization process similar to that proposed here. These ion-neutral complexes are especially stable due to the high degree of electron delocalization ( 87 ) which covers almost the entire heterocycle.…”