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A QSPR (quantitative structure-property relationship) study of the anaerobic biodegradation of chlorophenols could lead to an improvement in the disposal of these potentially carcinogenic industrial waste products. Youzhi Dai, Dasen Yang, Fei Zhu, Lanyan Wu, Xiangzheng Yang, and Jianhua Li of the Department of Environmental Engineering, at Xiangtan University, People's Republic of China have based their analysis on quantum chemical and physicochemical descriptors, using partial least squares analysis to obtain a good prediction of the QSPR for the disappearance rate constant (logK) of chlorophenols (CPs) in an anaerobic microbial culture. Chlorophenols have been used widely in the chemical industry for the manufacture of pesticides, herbicides, dyes and wood preservers, explain Dai and colleagues. However, in the late 1970s evidence began to emerge of their carcinogenicity, and as such safety and environmental impact moved higher on the agenda. Anaerobic biodegradation and biotransformation are important in the degradation of soil pollutants but whether or not chlorophenols are effectively degraded through this route and how is not entirely clear. Improved understanding of such mechanisms could b exploited in creating bio-reactors for the dechlorination of these compounds. Dai and colleagues have looked at the disappearance rate constant (logK) of chlorophenols because this value is considered to be a "key descriptor", which can describe the degree to which particular chlorophenols are susceptible to reductive dechlorination. Each chlorophenol undergoes degradation through subtly different mechanisms, so the team enlisted QSPR to help them untangle the various reaction threads and to reveal any inherent patterns that might offer clues as to how to carry our remediation of waste waters and contaminated soils more effectively. The result of their analysis of 13 chlorophenols as a training set, with logK values as a dependent variable and 29 chemical descriptors as independent variables, allowed them to produce a PLS model of chlorophenol reductive dechlorination. They found that the larger the chlorophenol molecule, the higher the absolute value of its hardness, and the smaller the bond energy, the quicker the molecule will degrade. "Obviously, the breakage of the weakest carbon-chlorine bond plays an important role in the reductive chlorine processes", Dai and colleagues explain. Related links:
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