Fast coupling and detoxification of aqueous halobenzoquinones by extracellular nucleophiles: The relationship among structures, pathways and toxicity.

[Display omitted] • The influences of 31 nucleophiles on the removal of dichlorobenzoquinones (DCBQs) was studied. • Degradation kinetics, pathways and toxicity evolution of DCBQs were characterized. • Fast removal and detoxification of DCBQs was achieved with the presence of thiol compounds. • Role of amino acids in promoting DCBQs hydrolyzation was revealed. • Relationships among nucleophilic structures, transformation pathways and products were found. Halobenzoquinones (HBQs), a metabolism of pentachlorophenol, arouse increasing concern for their high toxicity. This paper systematically studied the influences of 31 extracellular nucleophiles on the removal of dichlorobenzoquinones (DCBQs). The results showed that at pH 6.0–8.0, the transformation of DCBQs followed a pattern of pseudo first-order reaction. With the presence of different thiol compound (ratio 1:1), the apparent rate constant of 25DCBQ and 26DCBQ was between 0.028 and 0.204 min−1 and 0.061–0.156 min−1, respectively, which was 6.6–48.3 times faster than direct hydrolysis and 1.9–23.4 times of that with histidine, a typical amino acid. This was attributed to the different transformation pathways of DCBQs with thiol or amino groups. According to the MS spectrum and transition state theory, thiol compounds was stably incorporated into DCBQs via Michael addition or substitution, which also decreased the oxidative stress of DCBQs by 35.5–86.4% and cytotoxicity of hydrolyzed DCBQ by 44.9–100%, respectively. Conversely, amino acids promoted the hydrolysis of DCBQs by forming unstable AA-DCBQ intermediates that can be further hydrolyzed to OH-DCBQs, leading to an increased selectivity of OH-DCBQs, and increased the oxidative stress of 25DCBQs by 0.2–31.2% and cytotoxicity of hydrolyzed 25DCBQ by 42.0–52.7%. Such difference was inherently related to the nucleophilicity of different atoms. Moreover, it was revealed that the maximum condensed local nucleophilicity index of nucleophiles (N k, max) can joint describe the relationship among nucleophilic structures, transformation pathways and toxicity of DCBQs. This paper provided a comprehensive perspective on the fast removal and detoxification of HBQs in extracellular environment. [ABSTRACT FROM AUTHOR]