Oxidative Deamination of Dipeptides By Synthetic Manganese Oxide Characterized By High Resolution Mass Spectrometry

Abstract

Manganese oxides (MnO2) are ubiquitous in soils and have been implicated in the degradation of organic molecules including peptides, antibiotics, herbicides, and pesticides. In a previous study, glycine-glycine (gly-gly) was reacted with MnO2 to yield Mn (II) and ammonia (NH4+), but the main degradation product was only qualitatively inferred. Using high resolution liquid chromatography-mass spectrometry (LC-MS), we identified and quantified the products formed following batch reactions with birnessite (δ-MnO2) and dipeptides: gly-gly and alanine-glycine (ala-gly). After 24 h, the dipeptide concentration decreased by up to 70% for gly-gly and 40% for ala-gly (additional methyl group at the N-terminus α-carbon). Furthermore, we found that when gly-gly was in the presence of bicarbonate (HCO3-), degradation was impeded to only 10% after 24 h. The degradation products were identified with mass-to-charge ratio (m/z) of 130.049 and 144.065 for gly-gly and ala-gly respectively and are a result of N-terminal oxidative deamination at the α-carbon. These findings may be useful in elucidating the oxidized products of organic toxins with manganese oxides, as well as potentially producing a site specific aldehyde for synthetic chemistry purposes.