Oxidative polymerization of phenolic compounds

Six different phenols, including mono (p-hydroxybenzoic acid; 2,6-dimethoxyphenol; p-cresol; p-nitrophenol) and di-phenols (catechol; l-DOPA), at concentration 2 mM, were evaluated for oxidative polymerization. The phenolic compounds (2 mM) were placed in 250 mL conical flasks containing 50 mL of the reaction mixture in 50 mM sodium phosphate buffer (pH 7.0). TyrB at 10.0 U mL⁻¹ was added, followed by incubation in the dark for 48 h. One mL of aliquot was transferred into 2.5 mL microfuge tubes and centrifuged for 10 min at 2500 rpm in a microfuge (Bio-Rad, Hercules, USA). The oxidative polymerization of phenols was measured by following previously described methods [23, 24]. Further, 10 µL of the liquid sample was applied to the diamond Attenuated Totally Reflection (ATR) crystal and analyzed in JASCO 7000 Fourier Transform Infrared (FT-IR). The samples were subjected to IR radiation to obtain the corresponding spectra, and the average was computed from several data acquisitions. The FT-IR spectra were generated in the wavenumber range of 700–4000 cm⁻¹ with a resolution of 4 cm⁻¹. After each measurement, the crystalline surface was washed with acetone and dried using a soft paper [23].