Hydroxylation Of Aromatic Ring Research Articles

Removal of antibiotic cloxacillin by means of electrochemical oxidation, TiO2 photocatalysis, and photo-Fenton processes: analysis of degradation pathways and effect of the water matrix on the elimination of antimicrobial activity.

This study evaluates the treatment of the antibiotic cloxacillin (CLX) in water by means of electrochemical oxidation, TiO2 photocatalysis, and the photo-Fenton system. The three treatments completely removed cloxacillin and eliminated the residual antimicrobial activity from synthetic pharmaceutical wastewater containing the antibiotic, commercial excipients, and inorganic ions. However, significant differences in the degradation routes were found. In the photo-Fenton process, the hydroxyl radical was involved in the antibiotic removal, while in the TiO2 photocatalysis process, the action of both the holes and the adsorbed hydroxyl radicals degraded the pollutant. In the electrochemical treatment (using a Ti/IrO2 anode in sodium chloride as supporting electrolyte), oxidation via HClO played the main role in the removal of CLX. The analysis of initial by-products showed five different mechanistic pathways: oxidation of the thioether group, opening of the central β-lactam ring, breakdown of the secondary amide, hydroxylation of the aromatic ring, and decarboxylation. All the oxidation processes exhibited the three first pathways. Moreover, the aromatic ring hydroxylation was found in both photochemical treatments, while the decarboxylation of the pollutant was only observed in the TiO2 photocatalysis process. As a consequence of the degradation routes and mechanistic pathways, the elimination of organic carbon was different. After 480 and 240min, the TiO2 photocatalysis and photo-Fenton processes achieved ∼45 and ∼15% of mineralization, respectively. During the electrochemical treatment, 100% of the organic carbon remained even after the antibiotic was treated four times the time needed to degrade it. In contrast, in all processes, a natural matrix (mineral water) did not considerably inhibit pollutant elimination. However, the presence of glucose in the water significantly affected the degradation of CLX by means of TiO2 photocatalysis.

Properties of the humic-like material arising from the photo-transformation of l-tyrosine

The UVB photolysis of l-tyrosine yields species with fluorescence and absorption spectra that are very similar to those of humic substances. By potentiometric measurements, chemical modeling and the application of NMR, mass spectrometry and laser flash photolysis, it was possible to get insights into the structural and chemical properties of the compounds derived by the l-tyrosine phototransformation. The photolytic process follows aromatic-ring hydroxylation and dimerization. The latter is presumably linked with the photoinduced generation of tyrosyl (phenoxy-type) radicals, which have a marked tendency to dimerize and possibly oligomerize. Interestingly, photoinduced transformation gives compounds with protogenic and complexation capabilities similar to those of the humic substances that occur naturally in surface waters. This finding substantiates a new and potentially important abiotic (photolytic) pathway for the formation of humic compounds in surface-water environments.

Revealing the mechanism, pathways and kinetics of UV254nm/H2O2-based degradation of model active sunscreen ingredient PBSA

Transformation byproducts and pathways for the degradation of 2-phenylbenzimidazole-5-sulfonic acid (PBSA), a widely used organic active sunscreen agent, by UV254nm/H2O2 advanced oxidation process (AOP) were elucidated by mass spectrometry. Fourteen byproducts were identified, including environmentally hazardous benzamide (BD) and benzamidine (BZD). Beside of aromatic ring opening, desulfonation (−80Da) and hydroxylation (+16Da) were also two main reaction pathways. Degradation kinetics were compared with two PBSA structurally related compounds 2-phenylimidazole (2-PIZ) and benzimidazole (BZ) to estimate the application feasibility of the studied AOP. No apparent photolysis was noticed while the degradation of 1μM pollutants in the presence of 1mM H2O2 followed pseudo-first-order kinetics, with their observed rate constant (kobs) in the order of 2-PIZ>PBSA>BZ>BD>BZD, which is consistent with their respective second-order rate constant with hydroxyl radical. However, at high pollutant and oxidant concentrations, i.e., 50μM and 5mM, respectively, light attenuation contributed significantly to the change in kobs in the following manner, 2-PIZ∼BZ>PBSA∼BD>BZD. SO42− and NH4+ were the major inorganic mineral ions monitored in this study. Release of SO42− from PBSA degradation system reached 70% at 190min. At the same time interval, NH4+ were ⩽50% for all pollutants studied. Ultimate mineralization of PBSA, 2-PIZ, BZ, BD and BZD in terms of %TOC at 190min was found to be 23%, 38%, 45%, 57% and 62%, respectively. UV/H2O2 was shown to be efficient for the removal of organic sunscreen agents from water, however, special care toward the formation of environmentally hazardous byproducts should be considered.

Electrokinetic analysis of PES/PVP membranes aged by sodium hypochlorite solutions at different pH

This study focused on the impact of ageing solution pH (200ppm TFC sodium hypochlorite) on the electrokinetic properties of a commercial PES/PVP UF membrane. PVP oxidation, leading to an increase in the negative charge density of aged membranes, was pointed out whatever the ageing solution pH although different mechanisms might be involved depending on the ageing pH. PES degradation was also demonstrated. Electrokinetic measurements highlighted the formation of functional groups with very weak acid properties on the surface of membranes aged in sodium hypochlorite at pH 8.0 and to a lesser extent at pH 6.0 and 11.5. These results were found to be consistent with the formation of phenol groups due to the radical hydroxylation of PES aromatic rings. Moreover, the disappearance of the isoelectric point of membranes aged in sodium hypochlorite at pH 6.0 and 8.0 gave evidence for the formation of strong acid groups such as sulfonic acids. These results suggested some PES-chain scissions, which was confirmed by XPS measurements. The disappearance of the isoelectric point was not observed for membranes aged in sodium hypochlorite at pH 11.5, thus indicating that ClO− was not involved in PES-chain scissions for the ageing conditions considered in this work. Finally, electrokinetic measurements performed with the addition of tertiobutanol (free radical scavenger) and thermo-oxidation experiments revealed for the first time that, although both HClO and free radicals species contributed to PES-chain scissions, HClO had the greater impact on PES degradation.

Drugs with susceptible sites for free radical induced oxidative transformations: the case of a penicillin

Penicillins, as bactericidal antibiotics, have been widely used to treat infections for several decades. Their structure contains both aromatic and thioether moieties susceptible to free radical oxidation. The •OH induced oxidation mechanism of amoxicillin was investigated by pulse radiolysis techniques and by final product analysis performed after steady-state γ-irradiation. The predominant sites of the •OH attack are suggested to be the thioether group, initially yielding an •OH adduct to the sulfur, and the aromatic ring. This adduct to the sulfur converts to sulfur radical cation, which has three competitive reaction paths: (1) by deprotonation at the adjacent carbon α-(alkylthio)alkyl radicals form, which undergo disproportionation leading presumably to sulfoxide as main product; (2) via the pseudo-Kolbe mechanism it may transform to α-aminoalkyl radicals; (3) the radical cation can be stabilized through intramolecular S.˙.O bond formation. The reaction mechanism suggests the presence of a short-living and a stabilized (via hydrogen bonding) long-living •OH adduct to the sulfur. The three-electron bonded dimers of amoxicillin were not formed owing to steric hindrance. Thiyl radicals were also present in equilibrium with α-aminoalkyl radicals. In the presence of dissolved oxygen, aromatic ring hydroxylation occurred along with complex reactions resulting in e.g. oxidation of the methyl groups. The formation of the sulfoxide is especially effective in the presence of dissolved oxygen, under anaerobic condition, however, it is also generated owing to H2O2 and α-(alkylthio)alkyl radicals. The thioether moiety appears to be more sensitive to oxidation compared to the aromatic ring in case of amoxicillin.

Pathways of α-methylstyrene Oxidation by P. aeruginosa DS-26

Today in world practice the biotechnological methods of cleaning of environment from oil and oil products are widely used. They based on the use of microorganisms-destructors that are able to utilize<br />hydrocarbons. The microbial object of the research was bacterial strain <em>P. aeruginosa</em> DS-26. This bacterial culture was isolated from sewage water of rubber industry. This strain was able to grow in a medium, which contained <em>α</em>-methylstyrene. This compound, which is widely used as an active component in many industries, has a<br />strong toxic effect on living organisms including humans. Different types of microbial metabolism play an important role in the hydrocarbon degradation process in the environment Metabolism of <em>α</em>-methylstyrene by <em>P. aeruginosa</em> DS-26 characterized by variety and in depth of carried out transformations. The analysis of the obtained data allowed offering two ways of oxidation of α-methylstyrene. The first way, primary, was accompanied by formation of products of the direct hydroxylation of aromatic ring - cis-2.3-dihydroxy-1-isopropenyl-6-cyclohexene and 3-isopropyl-catehol which are later metabolized by meta-pathway with formation of keto-acids. The next, secondary pathway came true through oxidation of α-phenylpropionic acid and 4-methylbenzene alcohol with formation of acetophenone as a final product.<br />There are many researches that are devoted to study biochemical conversion of oil hydrocarbons. In order to utilize specific compounds as the only one source of carbon, microorganisms have to actively maintain a specific system of enzymes. Investigation of <em>α</em>-methylstyrene degradation by <em>P. aeruginosa</em> DS-<br />26 enzymes has revealed specific enzymes that oxidize aromatic hydrocarbons. Investigation results of the studying strain enzymes can be confirmation of the proposed above scheme of primary α-methylstyrene metabolic pathway oxidized by <em>P. aeruginosa</em> DS-26.

The Baeyer‐Villiger oxidation versus aromatic ring hydroxylation: competing organic peracid oxidation mechanisms explored by multivariate modelling of designed multi‐response experiments

Peroxy acids can be used as the terminal oxidant for the Baeyer–Villiger oxidation of acetophenones and for direct ring hydroxylation of methoxy‐substituted benzenes. An oxidative system involving 3‐chloroperbenzoic acid (mCPBA) and 2,6‐dimethoxyacetophenone as model substrate was investigated by means of statistical experimental design, multivariate modelling and response surface methodology. The outcome of the organic peracid oxidation experiments was portrayed by a multi‐response matrix consisting of the yields of three different compounds; 2,6‐dimethoxyphenyl acetate, 1‐(4‐hydroxy‐2,6‐dimethoxy‐phenyl)ethanone and 3‐hydroxy‐2,6‐dimethoxy‐phenyl acetate. The optimized reaction protocol was utilized to investigate a series of various substituted acetophenones. The overall investigation revealed that both the molecular structure of the acetophenone substrate and the experimental conditions exhibited a substantial impact on whether the oxidation reaction follows the oxygen insertion or direct ring hydroxylation mechanism. An improved protocol for the direct ring hydroxylation was also obtained from the experimental and modelling described herein. Copyright © 2015 John Wiley & Sons, Ltd.

Aromatic hydroxylation using an oxo-bridged diiron(III) complex: a bio-inspired functional model of toluene monooxygenases.

In biology, aromatic hydroxylation is carried out using a family of heme and nonheme oxygenases, such as cytochrome P450, toluene monooxygenases (TMOs), and methane monooxygenase (MMO). In contrast, a vast majority of synthetic iron based catalysts employed so far in aromatic hydroxylation are monomeric in nature. Herein, we have employed a diferric complex of an aminopyridine ligand ([(bpmen)2Fe2O(μ-O)(μ-OH)](ClO4)3 (2), bpmen = N,N'-dimethyl-N,N'-bis(2-pyridylmethyl)-1,2-diaminoethane) towards aromatic hydroxylation with H2O2 and acetic acid. The diiron(iii) complex shows promising reactivity in the hydroxylation of benzene and alkylbenzenes with a higher selectivity towards aromatic ring hydroxylation over alkyl chain oxidation. The μ-oxo diiron(iii) core has been shown to be regenerated at the end of catalytic turnover. However, mechanistic studies indicate that the diiron(iii) complex undergoes dissociation into its monomeric congener and the resulting iron(iii) complex mitigates aromatic hydroxylation.

ChemInform Abstract: Direct Introduction of OH Group to Sp2‐Carbon on Platinum‐Loaded Titanium Oxide Photocatalyst

AbstractReview: 52 refs.

Chemical modification of amino acids by atmospheric-pressure cold plasma in aqueous solution

Plasma medicine is an attractive new research area, but the principles of plasma modification of biomolecules in aqueous solution remain elusive. In this study, we investigated the chemical effects of atmospheric-pressure cold plasma on 20 naturally occurring amino acids in aqueous solution. High-resolution mass spectrometry revealed that chemical modifications of 14 amino acids were observed after plasma treatment: (i) hydroxylation and nitration of aromatic rings in tyrosine, phenylalanine and tryptophan; (ii) sulfonation and disulfide linkage formation of thiol groups in cysteine; (iii) sulfoxidation of methionine and (iv) amidation and ring-opening of five-membered rings in histidine and proline. A competitive reaction experiment using 20 amino acids demonstrated that sulfur-containing and aromatic amino acids were preferentially decreased by the plasma treatment. These data provide fundamental information for elucidating the mechanism of protein inactivation for biomedical plasma applications.

Chemical degradation of fluorosulfonamide fuel cell membrane polymer model compounds

The durability of a polymer electrolyte fuel cell membrane, along with high proton conductivity and mechanical performance is critical to the success of these energy conversion devices. Extending our work in perfluorinated membrane stability, aromatic trifluoromethyl sulfonamide model compounds were prepared, and their oxidative degradation was examined. The chemical structures for the models were based on mono-, di- and tri-perfluorinated sulfonamide modified phenyl rings. Durability of the model compounds was evaluated by exposure to hydroxyl radicals generated using Fenton reagent and UV irradiation of hydrogen peroxide. LC–MS results for the mono-substituted model compound indicate greater stability to radical oxidation than the di-substituted species; loss of perfluorinated fonamide side chains appears to be an important pathway, along with dimerization and aromatic ring hydroxylation. The tri-substituted model compound also shows loss of side chains, with the mono-substituted compound being a major oxidation product, along with a limited amount of hydroxylation and dimerization of the starting material.

Direct Introduction of OH Group to sp2-Carbon on Platinum-Loaded Titanium Oxide Photocatalyst

Photocatalytic oxidation of various organic compounds by using molecular oxygen has been broadly investigated as a valuable synthetic route, but the application has been still limited because the active oxygen species from the molecular oxygen are usually difficult to be controlled. In this short review, we describe two kinds of photocatalytic oxygenation with H2O molecule as a source of OH group; i.e., photocatalytic hydroxylation of aromatic ring and photocatalytic hydration of alkene, on Pt/TiO2 photocatalyst. In both reactions, a photoformed active oxygen species attacks to the sp2-carbon to form a reaction intermediate. In the aromatic ring hydroxylation, the elimination of the H atom from the intermediate proceeds while the conjugate double bond of the aromatic ring maintains. In the alkene hydration, the addition of the H radical to the intermediate results in forming an alcohols molecule with the saturation of the double bond. In the former case, the electrophilic property of the active oxygen species predominantly determines the orientation of the OH group in the produced phenols. On the other hand, in the latter case, the thermodynamic stability of the intermediate radical species leads the active oxygen species preferentially to the terminal sp2-carbon, which makes it possible to provide the unique regioselectivity of alcohol according to the anti-Markovnikov rule.

Electrochemical treatment of wastewaters containing 4-nitrocathecol using boron-doped diamond anodes

The electrochemical oxidation of aqueous wastes polluted with 4-nitrocathecol has been studied on boron-doped diamond electrodes in an acidic medium. The voltammetric results showed that 4-nitrocathecol is oxidized in the potential region where the supporting electrolyte is stable. Galvanostatic electrolysis study showed that the oxidation of these wastes in a single-compartment electrochemical flow cell with boron-doped diamond anodes results in the complete mineralization of the organics. Cathecol, benzoquinone, 4-aminocathecol, maleic and oxalic acids have been detected as soluble organics, polymeric product as solid product at the cathode surface and NO3− as mineral product during the electrolysis of 4-nitrocathecol. The electrochemical oxidation of 4-nitrocathecol consists of a sequence of steps: release of NO2 and (or) hydroxylation of the aromatic ring; formation of quinonic compounds; oxidative opening of aromatic ring to form carboxylic acids; and oxidation of carboxylic acids to carbon dioxide. Both direct and mediated oxidation processes are involved in these stages.

Degradation of atenolol by UV/peroxymonosulfate: Kinetics, effect of operational parameters and mechanism

Photoactivation of peroxymonosulfate (PMS) with UV (254nm) irradiation was used to generate the SO4--based advanced oxidation process, which was adopted to degrade atenolol (ATL) in water. The second-order reaction rate constants of ATL with HO and SO4- were determined, and the effects of operational parameters (dose of PMS, solution pH, HCO3-, humic acids (HA), and N2 bubbling) were evaluated as well. Finally the main transformation intermediates were identified and possible degradation pathways were proposed. The results showed that there was a linear positive correlation between the degradation rate of ATL and specific dose of PMS (1–16M PMS/M ATL). Increasing solution pH from 3 to 9 promoted elimination of ATL due to the pH-dependent effect of PMS photodecomposition, while further pH increase from 9 to 11 caused slowing down of degradation because of apparent conversion of HO to SO4-. 1–8mM HCO3- exerted no more than 5.3% inhibition effect on ATL destruction, suggesting HCO3- was a weak inhibitor. Absorption (or complexation) and photosensitized oxidation induced by HA improved ATL degradation during the first minute of degradation process, whereas photon competition and radical scavenging effects became the leading role afterward. Bubbling with nitrogen enhanced the degradation rate due to the stripping of dissolved oxygen. Hydroxylation of aromatic ring, cleavage of ether bond, oxidation of primary and secondary amine moieties, and dimerization were involved in the degradation mechanism of ATL by UV/PMS.

Direct Functionalization of Aromatic Rings on Platinum-loaded Titanium Oxide Photocatalyst

Abstract Organic syntheses by using TiO2 photocatalysts have been extensively studied in view of green and sustainable chemistry. This highlight review shows our recent studies on photocatalytic direct functionalization of aromatic rings, i.e., aromatic ring hydroxylation with H2O and aromatic ring amination with aqueous NH3 on Pt-loaded TiO2 photocatalysts. Both reactions involve two key steps: one is an activation of a rather stable molecule (H2O or NH3) by a photoexcited hole on the TiO2 surface to produce its radical species, and the other is an aromatic substitution by the radical species through an addition–elimination mechanism. Interestingly, the radical species produced from H2O (surface oxygen radical or hydroxyl radical) is electrophilic while that produced from NH3 (amide radical) is electroneutral. These properties determine the regioselectivity in the functionalization of substituted benzene.

Carcinogenic liver fluke Opisthorchis viverrini oxysterols detected by LC–MS/MS survey of soluble fraction parasite extract

Liquid chromatography in tandem mass spectrometry (LC–MS/MS) has emerged as an informative tool to investigate oxysterols (oxidized derivatives of cholesterol) in helminth parasite associated cancers. Here, we used LC–MS/MS to investigate in soluble extracts of the adult developmental stage of Opisthorchis viverrini from experimentally infected hamsters. Using comparisons with known bile acids and the metabolites of estrogens, the LC–MS data indicated the existence of novel oxysterol derivatives in O. viverrini. Most of these derivatives were ramified at C-17, in similar fashion to bile acids and their conjugated salts. Several were compatible with the presence of an estrogen core, and/or hydroxylation of the steroid aromatic ring A, hydroxylation of both C-2 and C-3 of the steroid ring and further oxidation into an estradiol-2,3-quinone.

Lorazepam photofate under photolysis and TiO2-assisted photocatalysis: Identification and evolution profiles of by-products formed during phototreatment of a WWTP effluent

This manuscript reports on the study of Lorazepam (LZP) phototransformation pathways under artificial UV and natural solar irradiation, through photolytic and TiO2-assisted photocatalytic processes. Three experimental set-ups were employed: two lab-scale photoreactors, each provided with an UV lamp (one medium pressure mercury lamp and one blacklight blue lamp), and a pilot-scale Solar Plant with Compound Parabolic Collectors (CPCs). Samples collected along the different phototreatment experiments were analyzed by ultra-high performance liquid chromatography–quadrupole-time-of-flight–mass spectrometry (UHPLC/QqToF-MS). The key assumption of the analytical approach was that related compounds (LZP and its by-products (LBPs)) provide identical “diagnostic fragment ions”. Identification was also based on the chlorine atoms specific isotopic pattern, as well as accurate masses. Six major LBPs were identified and elucidated, with nominal [M + H]+ masses of 337, 303, 319, 275, 291 and 293 Da. The proposed LZP photodegradation mechanism included the initial opening of the diazepinone seven-membered ring, followed by a rearrangement into a highly stabilized six-membered aromatic ring and subsequent cleavage and/or hydroxylation reactions. The evolution profiles of LBPs were described for each of the three experimental prototypes and the CPCs Solar Pilot Plant proved to be the most efficient one. Finally, LZP photocatalytic degradation was further assessed on a municipal effluent, where the photoproducts generated showed to be more persistent than LZP itself.

Photocatalytic transformation of sixteen substituted phenylurea herbicides in aqueous semiconductor suspensions: Intermediates and degradation pathways

The photocatalytic degradation of sixteen substituted phenylurea herbicides (PUHs) in pure water has been studied using zinc oxide (ZnO) and titanium dioxide (TiO2) as photocatalyst under artificial light irradiation. Photocatalytic experiments showed that the addition of these chalcogenide oxides in tandem with the oxidant (Na2S2O8) strongly enhances the degradation rate of these compounds in comparison with those carried out with ZnO and TiO2 alone and photolytic tests. Comparison of catalysts showed that ZnO is the most efficient for the removal of such herbicides in optimal conditions and at constant volumetric rate of photon absorption in the photoreactor. Thus, the complete disappearance of all the studied compounds was achieved after 20min of illumination in the ZnO/Na2S2O8 system. The main photocatalytic intermediates detected during the degradation of PUHs were identified. The probable photodegradation pathways were proposed and discussed.The main steps involved: N-demethylation of the N,N-dimethylurea-substituted compounds followed of N-demethylation and N-demethoxylation of the N-methoxy-N-methyl-substituted ureas and hydroxylation of aromatic rings and their aliphatic side-chains of both, parent compounds and intermediates.

Microbial transformations of antimicrobial quinolones and related drugs

The quinolones are an important group of synthetic antimicrobial drugs used for treating bacterial diseases of humans and animals. Microorganisms transform antimicrobial quinolones (including fluoroquinolones) and the pharmacologically related naphthyridones, pyranoacridones, and cinnolones to a variety of metabolites. The biotransformation processes involve hydroxylation of methyl groups; hydroxylation of aliphatic and aromatic rings; oxidation of alcohols and amines; reduction of carboxyl groups; removal of methyl, carboxyl, fluoro, and cyano groups; addition of formyl, acetyl, nitrosyl, and cyclopentenone groups; and cleavage of aliphatic and aromatic rings. Most of these reactions greatly reduce or eliminate the antimicrobial activity of the quinolones.

Reaction Mechanism of Aromatic Ring Hydroxylation by Water over Platinum-Loaded Titanium Oxide Photocatalyst

Direct aromatic ring hydroxylation of benzene derivatives by using water as an oxidant over platinum-loaded titanium oxide photocatalyst proceeded with high selectivity under the light of selected wavelength. Two kinds of electrophilic active species, which depended on the reaction condition, were proposed: a surface oxygen radical in neutral or acidic conditions and a hydroxyl radical in basic condition, both of which were produced by a photoformed hole on the surface of titanium oxide. In both cases, these active species can attack the aromatic ring to form an intermediate, followed by the formation of a hydroxylated product. Thus, the reaction proceeds through the addition–elimination mechanism. On the other hand, a photoformed electron reduces a proton to form a hydrogen radical, which reacts with the intermediate to produce a hydroxylated product and a molecular hydrogen or with another hydrogen radical to form a molecular hydrogen.