SIMULATION OF THE ELECTRONIC ABSORPTION SPECTRA OF PHENOLS AND PRODUCTS OF THEIR ENZYMATIVE OXIDATION

Abstract

The possibility of obtaining absorption spectra of phenols and products of their laccase oxidation by quantum-chemical modeling methods is considered. The primary optimization of the structures was carried out by the semi-empirical PM3 method, and the spectra were simulated within the framework of the density functional theory by the DFT/B3LYP/6-311G++dp method in an aqueous medium using the Gamess US program. For most of the studied phenols and their corresponding quinones, spectra containing one absorption band were obtained by calculation methods, for some - a larger number of bands, while in the experimental absorption spectra of these substances in the operating range of the spectrophotometer, as a rule, two bands are visible with different reliability. For most substances, the wavelengths of the absorption maxima of the calculated spectra differ from the experimental ones by no more than 10 nm. The calculated extinction coefficients, as a rule, exceed the experimental ones by 1,5–2 times. For phenols that cannot be directly oxidized to quinones, oligomeric products are considered as products. Their calculated spectra also correlate quite well with the experimental spectrum of the reaction mixture. The spectral characteristics obtained by modeling under these conditions can be used for a rough estimate of the composition of the reaction mixture, but additional studies are needed for their use in accurate quantitative analysis and kinetic studies.