Cocatalyst or substrate? Competitive Fenton transformation of cysteine and salicylic acid

Abstract

Sulfhydryl compounds and quinone/hydroquinone analogues have been found to effectively accelerate the Fenton reaction by accelerating the Fe³⁺/Fe²⁺ redox cycle. However, the direct comparison of sulfhydryl compounds with quinone/hydroquinone analogues has been less reported. In this work, salicylic acid (SA) and cysteine (Cys) were put together in a “coexistence system”, and we found that Cys showed better catalytic performance than salicylic acid SA, with different pH values and atmospheres. Electrospray ionization mass spectrometry (ESI-MS) showed that in the coexistence system, Cys was not easily destroyed by hydroxyl radicals, and the transformation of SA was greatly accelerated. This further indicated the superior cocatalytic performance of Cys compared with quinone/hydroquinone analogues. Furthermore, the competitive transformation mechanism of Cys and SA in the coexistence system is proposed.