Effect of carboxyl and amino groups in fluorescein molecules on their peroxidase-like activity

Recently, an important and intriguing property of fluorescein to function as an artificial peroxidase was found. Although, as a new class of small molecule enzyme mimics, the catalytic activities should be highly associated with the composition and structure, little is known about the mechanism underlying the functional groups mediated enzyme-like activities. Herein, we report for the first time that fluorescein derivatives, i.e. , carboxyfluorescein (CF) and aminofluorescein (AF) possess peroxidase-like activity, and investigate the impact of different functional groups on the catalytic performance. By systematically evaluating absorption intensity, electron spin resonance (ESR) signals, enzyme kinetic parameters and activation energies, we obtain evidence that the carboxyl group can enhance catalytic activity and may serve as substrate-binding sites, but the amino group can even inhibit the catalytic reaction. Correspondingly, the theoretical study further identified these experimental results in molecular-level. These observations pave the way for identifying highly effective functional groups that promote the overall performance of fluorescein-based artificial peroxidase. Meanwhile, this work should facilitate the design and construction of tailor-made small molecule peroxidase mimics.