Molecular characterization of the hypochlorite peroxyl radical (OClOO•), a reactive agent in acidic chlorite solutions and a potentially new disinfectant.

Abstract

The COVID-19 pandemic led to a global increase in the use of disinfectants such as sodium hypochlorite (NaOCl) and sodium chlorite (NaClO2). NaClO2 is generally recognized as safe (GRAS) and exhibits strong bactericidal activity when converted to acidified sodium chlorite (ASC) immediately before use. Although ASC is effective against various pathogens, including coronaviruses, the chemical species responsible for its bactericidal activity and the underlying disinfection mechanisms remain unclear. In this study, the reactions of NaOCl and NaClO2 under acidic conditions were investigated using UV-visible spectrophotometry (UV-vis), ion chromatography (IC), electron spin resonance (ESR), and mass spectrometry (MS). ESR analysis detected an unknown chlorine-containing peroxyl radical species (X-OO•), whose spectroscopic characteristics were consistent with a radical containing chlorine and oxygen atoms based on its hyperfine coupling constants and g values. MS analysis further provided evidence consistent with the presence of an OClO-containing dimetric species. Because NaClO2 is generally produced through reactions involving chlorine dioxide and sodium hydroxide (NaOH), such a dimetric species may be present as a relatively stable species in solution. Based on the combined experimental findings, we propose that the detected X-OO• species is a novel hypochlorite peroxyl radical (OClOO•) generated through reactions between NaClO2 and NaOCl under acidic conditions. Furthermore, bacterial inactivation was enhanced under conditions that promoted radical formation. Collectively, these findings suggest that OClOO• may contribute substantially to the bactericidal activity of ASC and provide new insights into the chemical basis of chlorine-based disinfectants.

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