Dibenzothiophene Sulfoxide Research Articles

Hydrophobic Modification of Halloysite Nanotubes Loaded with a Small Amount of Tungsten Oxide for Efficient Oxidative Desulfurization.

Transition metal oxides can be used as efficient multiphase catalysts in the field of catalysis. In this study, a hydrophobic halloysite nanotube (HNT) catalyst was designed and prepared with a low loading. Tungsten oxide was immobilized on the inner surface of the HNT, through electrostatic adsorption and calcination. Furthermore, a dual-functional W/HMT/M catalyst was prepared by hydrophobic modification of the outer surface of HNT through a harmless and nontoxic method. The catalyst was applied in the oxidative desulfurization (ODS) of dibenzothiophene (DBT), and characterized by inductively coupled plasma (ICP), contact angle tests, and other methods. Systematic characterization further confirmed that W/HNT/M has a low loading (0.48 wt %) and a relatively high contact angle of 92.6°. Oxidative desulfurization experiments demonstrated that the high contact angle corresponds to good hydrophobicity. The low loading and high activity of the catalyst enabled it to achieve a removal efficiency of 100% for DBT under conditions of 60 °C and an O/S = 4. The hydrophobic surface of HNT allowed better dispersion in the oil phase, while its hydrophilic inner cavity could adsorb H2O2 and the converted dibenzothiophene sulfoxide, thereby reducing the subsequent extraction steps after oxidative desulfurization and enhancing the reaction environment for reactants and active oxygen. W/HNT/M maintained high activity for at least 5 cycles. Additionally, the potential mechanism of the catalyst in the aqueous ODS reaction was proposed. This study demonstrates that HNT-supported metal oxides have desulfurization potential and provides ideas for improving ODS catalytic activity of the ODS through low loading, high activity, and unique hydrophobicity design.

Controlling product selectivity in oxidative desulfurization using an electrodeposited iron oxide film.

Sulfur-containing compounds must be removed from raw fuel oils before use and recently, there has been an effort to identify and optimize a more energy efficient method of oil processing. One promising route is electrochemical oxidative desulfurization (ODS), and in this work, we investigate an electrodeposited iron oxide film (FeOx(OH)y) as a working electrode to catalyze the oxidation of dibenzothiophene (DBT). The FeOx(OH)y film displays unexpected selectivity for the DBT sulfoxide (DBTO)-departing from the catalytic behavior of gold, which favors the dimerization of DBT. In addition, we observe a morphological change within our FeOx(OH)y film from γ-FeOOH to γ-Fe2O3. This change provides insight to the activity of each structure for ODS as the rate of oxidation increases after the incorporation of γ-Fe2O3. Our experimental observations are corroborated with DFT calculations, which suggest that the adsorption energy of DBT on Au is significantly greater than on the FeOx(OH)y, favoring the formation of dimeric and oligomeric products. Calculations also demonstrate that DBT binds preferably in a monodentate configuration but that oxidation occurs via DBT bound via a bidentate configuration. Monodentate binding on γ-FeOOH is significantly stronger than binding on γ-Fe2O, resulting in easier conversation to bidentate binding on γ-Fe2O3.

Comparison of Material Activity and Selectivity in the Electrocatalytic Oxidation of Dibenzothiophene

There is an increasing demand for efficient methods to remove sulfur from oil products, such as oxidative desulfurization. In this work, a set of five materials (gold, glassy carbon, nickel, palladium and platinum) were evaluated as electrochemical catalysts for the oxidation of dibenzothiophene (DBT). Bulk electrolysis performed without water present produced DBT dimer, while the addition of 2 M water produced dibenzothiophene sulfoxide (DBTO), both more polar than DBT. LC-MS and NMR were used to characterize the oxidation products. Faradaic efficiencies ranged from 18.4%–56.5% for DBT consumption without water present, and there was a correlation between higher rate constants, lower activation energies, and more efficient DBT oxidation. With water present, selectivity for DBTO formation was highest using gold with a Faradaic efficiency of 87.9%. Group ten metals demonstrated low Faradaic efficiencies due to competitive water oxidation. Though there were differences in the observed selectivity for DBT oxidation, all catalysts reduced the concentration of DBT in solution by similar amounts. Our findings indicate that the overall percent conversion does not give a complete picture of catalytic activity. Of the materials tested, gold was the most selective for oxidation to DBTO, with the presence of water improving the overall reaction activity.

Two-step Two-intermediate Photorelease Bolm-McCulla Reaction: Dual Release of Nitrene and Atomic Oxygen Reactive Intermediates.

This article is a highlight of the paper by Isor etal. in this issue of Photochemistry and Photobiology. It describes the photolysis of a dibenzothiophene sulfoximine (bearing N-phenyl imino and S-oxide groups) to produce two reactive intermediates in tandem. The sulfoximine undergoes a S-N and S-O photocleavage to release phenyl nitrene and atomic oxygen [O(3 P)]. The phenyl nitrene dimerizes to azobenzene or is trapped by diethylamine to reach an azepine. From there, atomic oxygen arises in a secondary photolysis of dibenzothiophene sulfoxide. A computational analysis also reveals that the S-N bond is labile for initial nitrene release, with the secondary release of atomic oxygen by S-O cleavage. Whether future sulfoximine scaffolds can produce the reverse order release of O(3 P) then nitrene, or release both simultaneously, is yet to be established. Nonetheless, molecules with dual-intermediate release, such as coupled photoaffinity labeling and cellular oxidation, are worth pursuing.

Electrocatalytic Oxidation of Dibenzothiophene and 4,6-Dimethyldibenzothiophene at Gold-Polyaniline (Au-PANI) Composite Electrodes

In this study, glassy carbon electrodes modified with gold-polyaniline (Au-PANI) were evaluated for the ability to electrochemically oxidize dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (4,6-DMDBT). Au-PANI was characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), transmission electron micrograph (TEM), and scanning electron micrograph (SEM). The role of nitrogen groups of PANI on the formation of Au-PANI was shown by FT-IR. XPS confirmed the various electronic states and environment of oxygen, nitrogen, gold, and carbon in Au-PANI film. TEM results indicated that Au particle size is in the range of 3.50–6.97 nm, while SEM results confirmed the heterogeneous nature of PANI and Au-PANI surfaces. In this study, density functional theory (DFT) with the B3LYP functional and 6-311++G** basis set was used to examine the electronic properties of DBT/4,6-DMDBT onto the surface of PANI nanocomposite. Electrochemical tests indicate that the Au-PANI exhibits high catalytic activity for DBT and 4,6-DMDBT electrooxidation. Oxidation products such as DBTO = dibenzothiophene sulfoxide; 4,6-DMDBTO = 4,6-dimethydibenzothiophene sulfoxide; DBTO2 = dibenzothiophene sulfone; and 4,6-DMDBTO2 = 4,6-dimethydibenzothiophene sulfone were confirmed by means of gas chromatograph coupled to mass spectrometer (GC-MS), 1H, and 13C NMR.

Homology Modeling and In Silico Docking Studies of DszC Enzyme of Streptomyces sp. VUR PPR 101

Sulfur dioxide released during the combustion of fossil fuels causes hazardous effects to living beings. The traditional hydrodesulfurization (HDS) which is employed to remove sulfur components from fossil fuels is not effective in the reduction in aromatic organosulfur compounds like benzothiophene (BT), dibenzothiophene (DBT) and its derivatives. Biodesulfurization process by microorganisms is considered as an effective one over HDS in the removal of sulfur from fuels. DBT, which is a typical recalcitrant organosulfur compound, is considered as a model compound for biodesulfurization studies. Microbes which employ 4S pathway for the removal of sulfur from DBT are commercially so significant. The 4S pathway encompasses four reactions involving three enzymes. The present work deals with the DszC enzyme which catalyzes the first two reaction steps of 4S pathway. The 3D structure of DszC enzyme protein of Streptomyces sp. VUR PPR 101 was modeled and validated. Four mutant DszC enzyme proteins viz., Q119I, H221L, F161A and N129A, were constructed. Wild and mutant DszC proteins were docked against the substrates, DBT and dibenzothiophene sulfoxide (DBTO). Based on the Libdock scores of the docked complexes, the mutant proteins F161A and H221L were found with the highest affinity toward DBT and DBTO, respectively.

Synthesis of N-benzylated cobalt phthalocyaninetetrasulfonamide and its application in oxidative desulfurization catalysis

The FeCl2/K2CO3 catalyst system was used successfully for the synthesis of oil soluble N-benzylated cobalt phthalocyaninetetrasulfonamide by the reaction of benzyl alcohol on water-soluble cobalt phthalocyaninetetrasulfonamide via heating at 135 °C for 20 h under N2. The new oil-soluble peripherally N-benzylated phthalocyanine was characterized by elemental analysis, FT-IR, UV–vis, TG and mass spectrometry. The catalytic activity of this new cobalt complex for oxidation of dibenzothiophene (DBT) was evaluated in n-dodecane (a middle distillate model compound) using H2O2 as an oxidant. The acetonitrile was taken as an extracting solvent for further extracting DBT sulfoxide and sulfone. The novel peripherally substituted cobalt(II) complex showed better oxidative desulfurization catalytic activity than cobalt phthalocyanine and cobalt phthalocyaninetetrasulfonamide. DBT oxidation kinetics were evaluated by lumped nth- and first-order kinetic models. The maximum removal of the DBT was found to be 85% at the optimized dose and experimental conditions.

Synthesis and crystal structures of a copper(ii) dinuclear complex and zinc(ii) coordination polymers as materials for efficient oxidative desulfurization of dibenzothiophene

Dinuclear copper(ii) complex [Cu2(BAc)4(QX)2], and 2D zinc(ii) coordination polymer, [Zn(TDPA)2(TMPy)2]n, presented high oxidation and adsorption thermodynamics for dibenzothiophene sulfoxide (DBTO).

Synthesis of silica@C-dots/phosphotungstates core-shell microsphere for effective oxidative-adsorptive desulfurization of dibenzothiophene with less oxidant

A core-shell microsphere catalyst with a solid silica core and a mesoporous shell made up of quaternary ammonium phosphotungstate and carbon dots (C-dots) was successfully synthesized for the oxidative-adsorptive desulfurization (OADS) of dibenzothiophene (DBT) in fuel oil. The phosphotungstic acid used for the synthesis of the catalyst was calcined to enhance its activity. XRD, FT-IR and catalytic test showed that the defective Keggin anion [PW12O38]3− formed under proper calcination conditions could explain the activity enhancement. EPR measurement indicated that hydroxyl radicals were generated from H2O2 by the interaction with C-dots, which proved C-dots to be an efficient cocatalyst in the system. The synergetic effect of [PW12O38]3− and C-dots in the synthesized catalyst remarkably improve the utilization efficiency of H2O2. When the loading amount of phosphotungstate and C-dots were optimized to 25% and 0.45%, the OADS system showed best desulfurization capacity under 50 °C. A high OADS efficiency of 98.08% could still be achieved even when the ratio of n(H2O2)/n(DBT) was reduced to 1.75. The existence of dibenzothiophene sulfoxide (DBTO) in the acetonitrile eluent of spent catalyst was confirmed by LC–MS spectra. The characterization results indicated that part of the DBT was oxidized to its corresponding sulfoxide which need less oxidant than sulfone. Both of the oxidation products could be eliminated from oil phase by adsorption on the catalyst.

Investigating the Kinetics, Mechanism, and Reaction Pathway of a Biodesulfurizing Enzyme from Rhodococcus erythropolis, Dibenzothiophene Monooxygenase

Fossil fuel combustion is a major source of sulfur dioxide, dangerous to respiratory health and the environment. Sulfur removal from fossil fuels eases these effects, however, the current method, hydrodesulfurization, requires costly high temperatures and pressures. The bacterial species Rhodococcus erythropolis uses a four‐step enzymatic process, known as biodesulfurization, to remove sulfur in fuel compounds. The first enzyme in the pathway, dibenzothiophene monooxygenase (DszC), uses reduced flavin and molecular oxygen to generate a flavin intermediate that oxygenates its substrate, dibenzothiophene, to dibenzothiophene sulfoxide, then dibenzothiophene sulfone. Our objectives are to understand DszC's enzymatic mechanism and steps of the catalytic pathway to engineer DszC to accept various organosulfur compounds and increase catalytic efficiency. Towards our goals, we have purified active DszC; determined steady‐state kinetic parameters of DszC as a function of dibenzothiophene, dibenzothiophene sulfoxide, and flavin substrates; performed steady‐state experiments to describe DszC's enzymatic mechanism; and used transient‐state kinetics to ascertain the effects of dibenzothiophene and age times on flavin binding. Using affinity chromatography, we purified DszC at 0.5 gram/liter of culture in its native tetrameric state. Reverse‐phase HPLC experiments showed DszC had faster product turnover using dibenzothiophene sulfoxide as substrate versus dibenzothiophene (11.8 × 10−3 s−1 vs. 4.84 × 10−3 s−1). HPLC assays also demonstrated that having equimolar flavin and DszC resulted in a faster turnover rate than using excess flavin (4.84 × 10−3 s−1 vs. 1.49 × 10−3 s−1). Varying flavin and dibenzothiophene concentrations under steady‐state conditions indicated DszC likely forms a ternary complex with the flavin intermediate and dibenzothiophene to facilitate oxygenation. Using stopped‐flow spectrophotometry, we observed fast flavin binding (<1 second) and that having equimolar dibenzothiophene and DszC increased intermediate formation rates. Dibenzothiophene pre‐incubation with DszC, however, decreased intermediate formation rates, suggesting reduced flavin is the initial substrate to bind to DszC. These results provided us kinetic and mechanistic insights towards understanding the full catalytic pathway of DszC to support our goals of engineering a robust and efficient DszC enzyme for industrial applications.Support or Funding InformationNational Institute of Health (SCORE 5SC2AI109500)Research Corporation CCSA 22672MARC/RISE Program (NIH Grant Number 2R25GM063787‐10)CSUPERB New Investigator GrantThis abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Hemin-utilizing G-quadruplex DNAzymes are strongly active in organic co-solvents

The widespread use of organic solvents in industrial processes has focused in recent years on the utility of “green” solvents – those with less harmful environmental, health, and safety properties – such as methanol and formamide. However, protein enzymes, regarded as green catalysts, are often incompatible with organic solvents. Herein, we have explored the oxidative properties of a Fe(III)-heme, or hemin, utilizing catalytic DNA (heme·DNAzyme) in different green solvent-water mixtures. We find that the peroxidase and peroxygenase activities of the heme·DNAzyme are strongly enhanced in 20–30% v/v methanol or formamide, relative to water alone. Protic solvent content of >30% v/v gradually diminishes heme·DNAzyme catalytic activity; however, the heme·DNAzyme is still active in as high as 80% v/v methanol. In contrast to protic solvents, aqueous dimethylformamide solutions largely inhibit heme·DNAzyme activity. In view of the strong catalytic activity of heme·DNAzyme in aqueous methanol, we were able to determine that a 60% v/v methanol-water mixture gives the most optimal yield of the dibenzothiophene sulfoxide (DBTO) oxidation product of petroleum-derived dibenzothiophene (DBT). The high product yield reflects both DNAzyme catalysis and a high substrate availability. Overall, these results emphasize the excellent promise of G-quadruplex forming DNA catalysts in application to “greener” industrial chemistry. This article is part of a Special Issue entitled “G-quadruplex” Guest Editor: Dr. Concetta Giancola and Dr. Daniela Montesarchio.

Oxidative desulfurization of fuels promoted by choline chloride-based deep eutectic solvents

In this study, a new type of “green solvents” named deep eutectic solvents (DESs) has been synthesized by combining hydrogen bond acceptors (HBAs) and hydrogen bond donors (HBDs). Choline chloride (ChCl) was chosen as typical HBA, and polyethylene glycol (PEG), 1,3-butyleneglycol (BG), ethylene glycol (EG), glycerol (Gl), propionate (Pr), malonic acid (MA) and urea (U) were chosen as HBDs. The extraction and catalytic oxidative desulfurization (ECODS) system was evaluated with phosphotungstic acid (HPW) as catalyst and 30wt% H2O2 as oxidant. Among all the neutral, acid and basic DESs, choline chloride/2polyethylene glycol (ChCl/2PEG) showed the best performance and 99.1% of dibenzothiophene (DBT) could be eliminated from model oil at 50°C within 3h. Interestingly, the volume ratio of DES to model oil was just 1:10, which was much less than the amount of extractant in the literature. The gas chromatography–mass spectrometer (GC–MS) analysis demonstrated that DBT sulfoxide (DBTO) and sulfone (DBTO2) were the products of oxidation of DBT. The desulfurization efficiency of the five sulfides in ECODS system occured in the following order: DBT>4-MDBT>4,6-DMDBT>3-MBT>BT.

Electrochemical Oxidation of Dibenzothiophene in Acetonitrile and Acetonitrile-Water Mixtures

Crude oil is basically formed of a mixture of many hydrocarbons containing a wide variety of heteroatoms like sulfur and nitrogen. The content of sulfur in crude oil can vary from 0.05% to 10% [1]. This percentage is low; however, this amount is particularly important due to environmental implications [2, 3]. The major sulfur compounds present in crude oil are thiophenes, benzothiophenes, dibenzothiophenes, which are carcinogens. For that reason, the hydrodesulfurization [4], which is the method used in refineries, does not remove all the sulfur compounds, mainly dibenzothiophene and derivatives. To reach this objective, several methods have been proposed to remove the sulfur compounds by converting them into hydrogen sulfide or more polar compounds [5]. For that reason, it has been of interest to explore the electro-oxidative behavior of these compounds to convert them to more polar compounds that are easier to extract with water as solvent [6]. It is known that refractory organosulphur compounds such as dibenzothiophene (DBT) can be oxidized to dibenzothiophenesulfoxide (DBTO) and dibenzothiophenesulfone (DBTO2), that can be removed by physical methods such as extraction and adsorption using polar solvents. Therefore, in this work the electrochemical oxidation of a model sulfur aromatic compound such as dibenzotiophene (DBT) was studied in acetonitrile in the presence of low ( < 0.1 M ) and high ( > 1 M) content of water on carbon electrodes. This study is focused to obtain mechanistic information about the products formed. Cyclic voltammetry of DBT in acetonitrile in the presence of < 0.1 M water on glassy carbon electrode showed three chemically irreversible anodic peaks. The first and second peaks involve a global transfer of one electron which allows respectively the formation of sulfoxide and sulfone derivatives as well as the release of one equivalent of protons, according to the global proposed reaction. DBT – e- + H2O = DBTO + H+ + 1/2H2 When water was added to the acetonitrile solution ( >1 M ), the voltammetric pattern was maintained, however the global mechanism giving rise to the sulfoxide and sulfone derivatives was modified to two electrons with the release of two equivalents of protons. DBT – 2e- + H2O = DBTO + 2H+ The proton formation was confirmed by cyclic voltammetry using acetate ions as proton probe while the products dibenzothiophene sulfoxide and dibenzothiophene sulfone were prepared by constant potential electrolysis and characterized by HPLC-MS-TOF and 1H and 13C NMR experiments. The analysis of the variation of the peak potential and half-peak width with the scan rate was used to establish the relevant role of water on the reaction mechanism, which changes from an ECCCC to an ECCEC pathway when water is present in excess According to the above mentioned results, different oxidation products can be formed depending on the electrolysis conditions and for this reason, this work deals with the anodic oxidation process of DBT in acetonitrile to determine how the intermediates and the composition of the electrolyte solution govern the formation of the oxygenated products. Cyclic voltammetry, sampled current chronoamperometry, coulometry, preparative electrolysis, chromatography coupled with mass spectrometry and nuclear magnetic resonance (NMR) spectroscopy were used as analytical techniques Acknowledgements The authors acknowledge CONACYT for financial support through the project 221548. E.M.A also acknowledges B.R. Díaz and G. Cuellar for their assistance in some electrochemical, NMR and MS analysis respectively.

Role of water in the formation of sulfoxide and sulfone derivatives during the electrochemical oxidation of dibenzothiophene in acetonitrile

The electrochemical oxidation of the model sulfur-containing compound dibenzothiophene (DBT) was analyzed in acetonitrile with carbon electrodes in order to obtain mechanistic information about the products formed. Cyclic voltammetry of DBT on a glassy carbon electrode showed three chemically irreversible anodic peaks. The first and second peaks involve a global transfer of one electron which allows the formation of sulfoxide and sulfone derivatives, respectively, as well as the release of one equivalent of protons. When water was added to the acetonitrile solution, the voltammetric pattern was maintained; however, the global mechanism giving rise to the sulfoxide and sulfone derivatives was modified to two electrons with the release of two equivalents of protons. The proton formation was confirmed by cyclic voltammetry with acetate ions as a proton probe, and the products dibenzothiophene sulfoxide and dibenzothiophene sulfone were prepared by constant-potential electrolysis and characterized by HPLC–MS-TOF and 1H and 13C NMR experiments. The analysis of the variation of the peak potential and half-peak width with the scan rate was used to establish the relevance of water on the reaction mechanism, which changes from an ECCCC to an ECCEC pathway when water is present in excess.

Electrochemical Desulfurization of Dibenzothiophene Sulfone in Acetonitrile/Sodium Nitrate (aq)

Electrochemical techniques have attracted much attention in the last decade for oxidative and reductive desulfurization because they require less drastic conditions of temperature and pressure in comparison to other processes that are used for desulfurization. It is known that dibenzothiophene (DBT) can be oxidized progressively to dibenzothiophene sulfoxide (DBTO) and dibenzothiophene sulfone (DBTO2). However, it is interesting to know whether a more complete oxidation of DBTO2 is possible by electrochemical treatment in a liquid-liquid two-phase system.

Crystal structures of apo-DszC and FMN-bound DszC from Rhodococcus erythropolis D-1.

The release of SO2 from petroleum products derived from crude oil, which contains sulfur compounds such as dibenzothiophene (DBT), leads to air pollution. The '4S' metabolic pathway catalyzes the sequential conversion of DBT to 2-hydroxybiphenyl via three enzymes encoded by the dsz operon in several bacterial species. DszC (DBT monooxygenase), from Rhodococcus erythropolis D-1 is involved in the first two steps of the '4S' pathway. Here, we determined the first crystal structure of FMN-bound DszC, and found that two distinct conformations occur in the loop region (residues 131-142) adjacent to the active site. On the basis of the DszC-FMN structure and the previously reported apo structures of DszC homologs, the binding site for DBT and DBT sulfoxide is proposed. The atomic coordinates and structure factors for apo-DszC (PDB code: 3X0X) and DszC-FMN (PDB code: 3X0Y) have been deposited in the Protein Data Bank (http://www.rcsb.org).

Crystal structure of DszC from Rhodococcus sp. XP at 1.79 Å

The dibenzothiophene (DBT) monooxygenase DszC, which is the key initiating enzyme in "4S" metabolic pathway, catalyzes sequential sulphoxidation reaction of DBT to DBT sulfoxide (DBTO), then DBT sulfone (DBTO2). Here, we report the crystal structure of DszC from Rhodococcus sp. XP at 1.79 Å. Intriguingly, two distinct conformations occur in the flexible lid loops adjacent to the active site (residue 280-295, between α9 and α10). They are named "open"' and "closed" state respectively, and might show the status of the free and ligand-bound DszC. The molecular docking results suggest that the reduced FMN reacts with an oxygen molecule at C4a position of the isoalloxazine ring, producing the C4a-(hydro)peroxyflavin intermediate which is stabilized by H391 and S163. H391 may contribute to the formation of the C4a-(hydro)peroxyflavin by acting as a proton donor to the proximal peroxy oxygen, and it might also be involved in the protonation process of the C4a-(hydro)xyflavin. Site-directed mutagenesis study shows that mutations in the residues involved either in catalysis or in flavin or substrate-binding result in a complete loss of enzyme activity, suggesting that the accurate positions of flavin and substrate are crucial for the enzyme activity.

Ultraviolet treatment and biodegradation of dibenzothiophene: Identification and toxicity of products.

Biodegradation of pollutants often results in incomplete mineralization and formation of degradation products with unknown chemical and toxicological characteristics. Ultraviolet (UV) irradiation, a common technology used in water and wastewater treatment, may help reduce aqueous concentrations of degradation products produced during biological treatment and their associated hazards. Combined biological and UV transformations may be important in natural systems as well. We investigated the effects of UV irradiation (254 nm) on dibenzothiophene (DBT), a sulfur-containing polyaromatic hydrocarbon, in artificial seawater, and its effects on biodegradation products produced from mixed-community microbial transformations of DBT, including DBT sulfone, DBT sulfoxide, hydroxylated and carboxylated benzothiophenes, thiosalicylic acid, and others. Toxicity of solutions after UV exposure was monitored using bioluminescent bacteria (Vibrio fischeri) and by evaluating cardiac deformities in Fundulus heteroclitus embryos. The highest UV fluence reduced DBT concentration by 28% when DBT was present as the sole organic solute. In postbiodegradation solution, the same fluence reduced the initial concentration of DBT by 81%, and 11 DBT biodegradation products to trace levels. Regardless of UV fluence, DBT by itself produced minimal effects in Fundulus embryos but was moderately toxic to V. fischeri. Postbiodegradation solutions were highly toxic to both test organisms. The highest UV fluence slightly reduced toxicity of postbiodegradation solution to V. fischeri but exacerbated cardiac deformities in Fundulus embryos. Toxicity could not be attributed to specific products and was likely a result of mixture effects. These results emphasize that toxicity can increase during remediation and that multiple assays may be necessary for evaluation. The novel approach of combined biodegradation/UV treatment is promising, although further research is needed to reduce toxicity in the case of DBT.

Desulfurization of Dibenzothiophene and Oxidized Dibenzothiophene Ring Systems

Lithium, used in conjunction with sodium metal, produces a high yield of biphenyl when reacted with dibenzothiophene, dibenzothiophene sulfoxide or dibenzothiophene sulfone.

Conversion of dibenzothiophene by the mushrooms Agrocybe aegerita and Coprinellus radians and their extracellular peroxygenases

The conversion of the heterocycle dibenzothiophene (DBT) by the agaric basidiomycetes Agrocybe aegerita and Coprinellus radians was studied in vivo and in vitro with whole cells and with purified extracellular peroxygenases, respectively. A. aegerita oxidized DBT (110 microM) by 100% within 16 days into eight different metabolites. Among the latter were mainly S-oxidation products (DBT sulfoxide, DBT sulfone) and in lower amounts, ring-hydroxylation compounds (e.g., 2-hydroxy-DBT). C. radians converted about 60% of DBT into DBT sulfoxide and DBT sulfone as the sole metabolites. In vitro tests with purified peroxygenases were performed to compare the product pattern with the metabolites formed in vivo. Using ascorbic acid as radical scavenger, a total of 19 and seven oxygenation products were detected after DBT conversion by the peroxygenases of A. aegerita (AaP) and C. radians (CrP), respectively. Whereas ring hydroxylation was favored over S-oxidation by AaP (again 2-hydroxy-DBT was identified), CrP formed DBT sulfoxide as major product. This finding suggests that fungal peroxygenases can considerably differ in their catalytic properties. Using H(2)(18)O(2), the origin of oxygen was proved to be the peroxide. Based on these results, we propose that extracellular peroxygenases may be involved in the oxidation of heterocycles by fungi also under natural conditions.