Application of adjuvants in combination with active agrochemical molecules as well as mixed agrochemical compounds is becoming a dominant trait in modern agriculture. Mixture of agrochemicals is usually targeted at improving bio-activity, saving time and cost, also to manage resistance. It should be noted, however, mixing agrochemicals might influence their photochemical fate, the efficacy of agrochemicals would be attenuated if their photostability is harmed upon mixture. Several experimental studies on the influence of photostability of mixed agrochemicals have been performed, but there is no theoretical validation of the altered photostability upon mixture of agrochemicals and the understanding of the underlying mechanism is quite limited.<br/><br/>Herein, we performed computational studies on the photochemical fate of Cycloxydim (CD) and Chlorothalonil (CT) mixture. It is suggested by experiments that photodegradation of CD is accelerated in the presence of CT via triplet intermolecular hydrogen transfer, however, the detailed mechanism could not be identified with the experimental data. We identified the possible reaction pathways by locating the local minimum structures of CD/CT dimers at both the ground state and the first triplet state. Potential energy profiles along possible pathways were explored and compared to determine the preferential reaction pathway. To understand the underlying reason for the differences in the energy profiles for the possible pathways, natural population and surface charge analysis were performed, with possible reaction mechanism suggested. Computational studies investigating the effect of mixing herbicides and fungicides upon their photochemical processes have not previously been performed, therefore, this study provides the first computational study of the CD/CT system and evaluates the methodology to determine if it would be suitable to apply to future studies of interacting agrochemical compounds with altered photochemical properties.

Density functional theory study on triplet intermolecular hydrogen transfer between cycloxydim and chlorothalonil

253rd National Meeting (2017)

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