Colorimetric quantification of vancomycin by highly active nitroxyl radical compounds

Nitroxyl radicals, represented by 2,2,6,6-tetramethylpiperidine N-oxyl (TEMPO), are highly stable organic free radicals with unique properties and are used as functional molecules in various fields. However, TEMPO had low reactivity and sometimes did not provide enough response. Therefore, highly active nitroxyl radical compounds have been developed in which bicyclo and tricyclo structures stabilize the radicals. In this study, we found that nortropine N-oxyl (NNO), a type of highly active nitroxyl radical, can oxidize the 2,2′-dihydroxybiphenyl structure under physiological conditions, and succeeded in the colorimetric quantification of vancomycin containing 2,2′-dihydroxybiphenyl moieties in the molecular structure. The reaction took only a few minutes to complete and could be confirmed with the naked eye, with a quantitative range of 10–100 μM. High-performance analytical probes are expected to be developed that use highly active nitroxyl radical derivatives to replace TEMPO derivatives.