The design of fluorescein-ferrocene derivatives as HOCl-triggered turn-on fluorescent probes and anticancer prodrugs.

Overexpressed HOCl in tumors can behave as an activator for imaging-guided precision therapy. Herein, a new kind of HOCl-activated molecular platform has been developed aiming at the integration of detection, imaging, and anticancer functions. The design strategy uses a five-membered heterocyclic ring to bridge the fluorescent fluorescein part (FL) and the anticancer ferrocene part (Fc). Three derivatives, namely FL-Fc, FL-NP-Fc and FL-TEG-Fc, were designed with different grafted chains on the fluorescein mother to modulate the hydrophilic and biocompatible capacity. In these molecular platforms, the ferrocene unit serves as the fluorescence emission quencher and masked prodrug. These three could respond to HOCl with good selectivity and sensitivity, showing a turn-on fluorescence signal and anticancer efficacy. FL-TEG-Fc with the highest sensitivity (6.5 × 10-6 M) was successfully used for imaging endogenous HOCl in AGS cells, in which it presented strong toxicity IC50 = 9.5 ± 0.3 µM. The mechanistic study revealed that the five-membered heterocyclic ring of FL-TEG-Fc was broken specifically and effectively by HOCl to release strongly fluorescent fluorescein and a bioactive ferrocene derivative; the obtained ferrocene derivative further generated cytotoxic ˙OH through a Fenton-like reaction. This study provides a potential theranostic strategy against HOCl-overexpressing cancers.

The mechanism of Fe (III)-catalyzed ozonation of phenol.

Fe (III)-catalyzed ozonation yielded better degradation rate and extent of COD (Chemical Oxygen Demand) or oxalic acid as compared with oxidation by ozone alone. Two parameters with strong effects on the efficiency of ozonation are pH of the solution and the catalyst (Fe(3+)) dosage. The existence of a critical pH value determining the catalysis of Fe (III) in acid conditions was observed in phenol and oxalic acid systems. The best efficiency of catalysis was obtained at a moderate concentration of the catalyst. A reasonable mechanism of Fe (III)-catalyzed ozonation of phenol was obtained based on the results and literature.