Fig. 1. (A) Biological cysteine oxoforms. (B) Sulfenic acid acts as a nucleophile and an electrophile. (C) Nucleophilic probes (Nu–) result in the formation of a thioether-type linkage and electrophilic probes (E+) result in the formation of a sulfoxide. (D) General structures of nucleophilic and electrophilic sulfenic acid probes. (E) Examples of currently known stable and transient small-molecule sulfenic acids.
