Computational insights into E/Z isomerism of fluoxastrobin, an antifungal agent: A DFT/TD-DFT study

Abstract

Herein, inspired by the success of strobilurins in fungicidal activity bioassays, DFT (Density Functional Theory)-based quantum chemical computations were performed on fluoxastrobin, a fluorinated strobilurin fungicide. Its formulation has E/Z isomerism around the C=N bond. It is highly advantageous to utilize quantum chemical methods to acquire more insights into E/Z isomerism and to gain supplemental confirmations in terms of experimental results. In this respect, the geometries of the E and Z isomers of fluoxastrobin were optimized both in the vacuum and in 1-octanol, acetonitrile, DMSO, and water phases using the DFT/B3LYP/6-311++G (d, p) methodology. Both experimental and theoretical FTIR and UV-vis evaluations were performed for the isomers. TD-DFT/B3LYP/6-311++G (d, p) theory level computations were determined that the observed peaks were mostly caused from the π→π∗ and n→π∗ transitions. Also, quantum chemical reactivity descriptors and physicochemical parameters were calculated for both vacuum and solvent phases. Accordingly, computations in all studied phases estimate the E isomer to be preferred with energy values in the range of 2.51-3.77 kcal/mol. Natural bond orbital (NBO) analysis was also carried out to determine the intermolecular interactions and their corresponding stabilization energies. Last, with the help of Gibbs solvation free energy values, 1-octanol/water partition coefficients were calculated and lipophilicity evaluations of both isomers were performed.