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Photodegradation of Sulfathiazole Under Simulated Sunlight: Kinetics, Photo-Induced Structural Rearrangement, and Antimicrobial Activities of Photoproducts

Photodegradation of Sulfathiazole Under Simulated Sunlight: Kinetics, Photo-Induced Structural Rearrangement, and Antimicrobial Activities of Photoproducts

Xi-Zhi Niu, Julie Glady-Croué, Jean-Philippe Croué

Water Res. 2017 Nov 1;124:576-583.

PMID: 28810229

Abstract:

Photolysis is a core natural process impacting the fate of some sulfonamide antibiotics in sunlit waters. In this study, sunlight-induced phototransformation of sulfathiazole was investigated. A photolytic quantum yield of 0.079 was obtained in buffered water (pH = 8.0). Different natural organic matter isolates inhibited the photolysis of sulfathiazole by light screening effect. A kinetic model was developed to predict the photodegradation rate of sulfathiazole using the light screening correction factor of the water matrix in the wavelength range of 300-350 nm. An isomeric photoproduct of sulfathiazole with a longer retention time was observed on liquid chromatography. Based on its MS/MS spectra and absorption characteristics, the isomer was postulated as 2-imino-3-(p-aminobenzenesulfinyl-oxy)-thiazole. A reaction mechanism for the photo-cleavage and photo-induced structural rearrangement was proposed. The formation mechanism of the isomer was supported by photochemical experiments spiking synthetic 2-aminothiazole; while the formation kinetics were treated with a partly-diffusion-controlled model. The three identified products showed significantly enhanced photo-stability. Antimicrobial assay of irradiated sulfathiazole solutions with Escherichia coli indicated little antimicrobial potency ascribed to photoproducts. This study demonstrates the efficacy of sunlight in rapidly degrading sulfathiazole at a predictable rate, leading to photoproducts of low antimicrobial potency. The mass spectrometry and mechanistic work described here are new insights into the photochemistry of sulfonamides.

Chemicals Related in the Paper:

Catalog Number	Product Name	Structure	CAS Number	Price
AP72140-A	Sulfathiazole		72-14-0	Price

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