Figure 4. Chemical tools to study redox biology.

(a) The conversion of boronates to phenols by H₂O₂ has been used to create a suite of novel fluorescent probes with various properties, such as red-shifted emission (Peroxy Orange 1, PO1), mitochondrial localization (Mitochondria Peroxy Yellow 1, MitoPY1) and enhanced sensitivity through cytosolic trapping groups (Peroxyfluor-6 acetoxymethyl ester, PF6-AM). (b) A mitochondrial-targeted MS probe, which similarly uses the conversion of a boronic acid to a phenol, allows ratiometric detection and quantification of H₂O₂ in vivo by analysis of the ion count ratios between the protected and deprotected form of the probe, which can be distinguished by differences in mass to charge (m/z) ratios. (c) Dimedone-based reactivity probes can trap oxidized cysteine residues from a sulfenic acid and when coupled to purification or labeling groups, allow the identification of the redox-modified target.