Degradation of Tryptophan by UV Irradiation: Influencing Parameters and Mechanisms

The chlorination of dissolved amino acids can generate disinfection by-products (DBPs). To prevent the formation of DBPs, we examined the UV-induced degradation of tryptophan (Trp). In order to further understand the impact of UV disinfection on Trp, the effects of initial concentrations of Trp, pH, temperature, concentrations of NO3-, HCO3- and Cl- on Trp removal were investigated, and a degradation mechanism was also proposed. The results demonstrated that degradation fitted a pseudo first-order reaction kinetic model. The degradation of Trp was mainly caused by direct UV degradation. The apparent rate constant k(obs) decreased with the increase in initial Trp concentration and increased with increases in pH and temperature. The thermal degradation activation energy was 19.65 kJ/mol. Anions in water also had a significant influence on the degradation of Trp. HCO3- and NO3- contributed to the k(obs) of Trp, but Cl- inhibited the degradation rate. By electron paramagnetic resonance (EPR) spectroscopy, center dot OH was proven to be formed during the degradation of Trp by UV. Based on the intermediate products of C11H15NO3, C10H15N and C9H13N detected by LC-MS-MS, the degradation pathway of Trp was speculated.

Automated summary

The research found that the degradation of tryptophan (Trp) induced by UV follows a pseudo first-order reaction kinetic model, mainly caused by direct UV degradation. The apparent rate constant k(obs) decreases with increasing initial Trp concentration, while increases with rises in pH and temperature. Anions in water have a significant influence on the degradation of Trp, with HCO3- and NO3- contributing to the k(obs) of Trp, but Cl- inhibiting the degradation rate.