Characterization of Oxidation Products from HOCl Uptake by Microhydrated Methionine Anions Using Cryogenic Ion Vibrational Spectroscopy

The oxidation of the amino acid methionine (Met) by hypochlorous acid (HOCl) to yield methionine sulfoxide (MetO) has been implicated in both the interfacial chemistry of tropospheric sea spray aerosols and the destruction of pathogens in the immune system. Here, we investigate the reaction of deprotonated methionine water clusters, Met(-)center dot(H2O)(n), with HOCl and characterize the resulting products using cryogenic ion vibrational spectroscopy and electronic structure calculations. Capture of the MetO(-) oxidation product in the gas phase requires the presence of water molecules attached to the reactant anion. Analysis of its vibrational band pattern confirms that the sulfide group of Met(-) has indeed been oxidized. Additionally, the vibrational spectrum of the anion corresponding to the uptake of HOCl by Met(-)center dot(H2O)(n) indicates that it exists as an exit-channel complex in which the Cl- product ion is bound to the COOH group following the formation of the S=O motif.

Automated summary

In this study, the reaction between deprotonated methionine water clusters and hypochlorous acid was investigated using cryogenic ion vibrational spectroscopy and electronic structure calculations. The results showed that the presence of water molecules attached to the reactant anion is necessary for the capture of the methionine sulfoxide oxidation product in the gas phase. The vibrational spectrum confirmed the oxidation of the sulfide group of methionine. Additionally, the vibrational spectrum revealed the formation of an exit-channel complex in which the Cl- product ion is bound to the COOH group following the reaction of hypochlorous acid with methionine water clusters.