title: Dibenzothiophene oxidation by horseradish peroxidase in organic media: effect of the DBT:H2O2 molar ratio and H2O2 addition mode.
abstract: Its is well known that in the biodesulfurization (BDS) process the low water solubility of sulfur compounds hinders its transference from the oil phase to the cells being the rate-limiting step in the metabolism of dibenzothiophenes (DBT). Thus sulfur compounds derivatives with high water solubility could be more easily transported increasing the BDS efficiency. The present work performed a stepwise evaluation of the enzymatic oxidation of DBT by horseradish peroxidase (HRP). Reactions were carried out in monophasic organic media containing 25% (v/v) acetonitrile. The following parameters were evaluated: DBT:H2O2 molar ratio (1:1-1:20); H2O2 addition mode (single or stepwise); pH (6.0-8.0) and temperature (37-50 degrees C). Best results were observed in a reaction medium at pH 8.0 presenting HRP 0.06IUml(-1), DBT 0.267mM, DBT:H2O2 molar ratio of 1:20 (stepwise hydrogen peroxide addition) and incubated at 45 degrees C for 60min. Under these conditions 60% of DBT was converted into dibenzothiophene sulfoxide (12%) and dibenzothiophene sulfone (46%). The DBT oxidation rate observed in this work, of 5mmolmin(-1)g(-1) of HRP, was 250-fold higher than the BDS rate, 20mumolmin(-1)g(-1) of catalyst. As such a combined enzyme-microbial desulfurization process could be envisaged. Products were determined by HPLC RP C-18.
authors.affiliation: Department of Biochemistry, Chemistry Institute, Federal University of Rio de Janeiro - UFRJ, Brazil.
authors.forename: Luciana
authors.initials: L
authors.lastname: da Silva Madeira
authors.forename: Viridiana Santana
authors.initials: VS
authors.lastname: Ferreira-Leitão
authors.forename: Elba Pinto
authors.initials: EP
authors.lastname: da Silva Bon
mesh_terms: D006735:Horseradish Peroxidase / Q000737:chemistry*; D006861:Hydrogen Peroxide / Q000737:chemistry*; D009930:Organic Chemicals / Q000737:chemistry*; D010084:Oxidation-Reduction; D013876:Thiophenes / Q000737:chemistry*
chemical_list: D009930:Organic Chemicals; D013876:Thiophenes; D006861:Hydrogen Peroxide; D006735:Horseradish Peroxidase; C016366:dibenzothiophene