Oxidation Of Bromide Ions Research Articles

Improvement of bromide ions on the degradation of sulfamerazine by horseradish peroxidase-H2O2 system and its interaction mechanisms

Degradation of sulfonamide antibiotics (SAs) by horseradish peroxidase (HRP) is an eco-friendly and sustainable approach but with relatively low efficiency. In this study, we present bromide (Br−) enhances sulfamerazine (SMR) degradation in the process of HRP/H2O2. The removal rate of SMR is positively related to Br− concentration and increases over three times within 4 h as Br− concentration increases from 0 to 1 mM. The mechanism of promoting SMR degradation is mainly through oxidation and substitution by reactive bromine, which comes from the oxidation of bromide ions by HRP/H2O2. Moreover, structure and kinetics analysis of HRP confirm that Br− altered the hydrophobic structure of HRP and made it accessible to bind with SMR. Furthermore, eight degradation products are determined by ESI-Q-TOF-MS mass spectrometry. SMR transformation mainly involves two pathways: one way is hydrolysis and then breaking up of sulfonamide bond to generate small fragments, and another is demethylation and Smile rearrangement firstly, then through hydroxylation, SO2 extrusion, and bromine substitution to form other products. Bacteria growth experiments present the fact that neither the degradation products nor bromate formed in the process inhibited bacteria growth, indicating they have no obvious environmental risk. This study first reports Br− could accelerate the degradation of SMR by HRP and proposes the scheme of bromine species changes and SMR transformation pathways. This study not only develops a novel method to enhance the degradation of sulfonamides, but also provides a reference for the environmental risk assessment of sulfonamides.

From Reactive Oxygen Species to Reactive Brominating Species: Fenton Chemistry for Oxidative Bromination

Fenton chemistry (Feᴵᴵ + H₂O₂ → HO•/HOO• + H₂O) generates reactive oxygen species (ROS) that are used for treatment of wastewater and oxidation of organic molecules and play a key role in biological oxidation systems. This study shows that Fenton chemistry can be used for generation of reactive brominating species (RBS) under neutral conditions at room temperature. The in situ RBS are successfully used for three types of oxidative bromination reactions. This green and nonacidic new method addresses the safety and environmental challenges of existing oxidative bromination methods. Additionally, this neutral Fenton–bromide system addresses the long-lasting problem of many functional haloperoxidase mimics that required strong acids for oxidation of bromide ion with hydrogen peroxide. This new green and mild method for generating RBS will significantly benefit the wide applications of brominated organic compounds in organic synthesis and the fine chemical and pharmaceutical industries.

Formal Ring Contraction of Cyclic N‐Sulfonamides via C−N Bond Cleavage and α‐Amination by Oxidation of Halides

AbstractAn oxidative C−N bond cleavage reaction of substituted cyclic sulfonamides that proceeds via oxidation of bromide ion in hydrogen bromide solution was developed to furnish N‐sulfonamide‐protected acyclic amino ketones in high yields. The subsequent α‐amination of the amino ketones via the oxidation of iodide in tetrabutylammonium iodide provided 2‐acyl cyclic sulfonamides in good yields. The combination of these transformations involving the oxidation of halides resulted in a formal ring contraction of substituted cyclic amides.magnified image

Assessment of individual and mixed toxicity of bromoform, tribromoacetic-acid and 2,4,6 tribromophenol, on the embryo-larval development of Paracentrotus lividus sea urchin.

Water chlorination is the most widely used technique to avoid microbial contamination and biofouling. Adding chlorine to bromide-rich waters leads to the rapid oxidation of bromide ions and leads to the formation of brominated disinfection by-products (bromo-DBPs) that exert adverse effects on various biological models. Bromo-DBPs are regularly encountered within industrialized embayments, potentially impacting marine organisms. Of these, bromoform, tribromoacetic acid and tribromophenol are among the most prevalent. In the present study, we tested the potential toxicity and genotoxicity of these disinfection by-products, using sea urchin, Paracentrotus lividus, embryos. We highlighted that tribromophenol showed higher toxicity compared to bromoform and tribromoacetic acid. Furthermore, a synergistic effect was detected when tested in combination. Pluteus cells exposed for 1h to mixtures of DBPs at several concentrations demonstrated significant DNA damage. Finally, when compared to a non-exposed population, sea urchins living in a bromo-DPB-polluted area produced more resistant progenies, as if they were locally adapted. This hypothesis remains to be tested in order to better understand the obvious impact of complex bromo-DBPs environments on marine wildlife.

Non-catalytic and catalytic ozonation of simple halohydrins in water

This study compares degradation of two hazardous halohydrins, namely 2,3-dibromopropan-1-ol (2,3-DBP) and 1,3-dichloro-2-propanol (1,3-DCP) by non-catalytic ozonation in acidic, neutral and basic water and catalytic ozonation with Co loaded on Fe prepared by (i) co-precipitation (Co-ppt) and (ii) a simple physical mixing (Mixed) method. The brominated halohydrin showed a higher reactivity with ozone than the chlorinated halohydrin. With uncatalysed ozonation, dehalogenation rate of both pollutants improved with increase in hydroxide ion concentration, however, complete removal of total organic carbon (TOC) and efficient organic by-product (Org-BP) minimization could not be achieved. Bromide ion oxidation to bromate ion was slower in acidic water, but increased as the hydroxide ion content increased. Ozonation in the presence of Fe:Co (Co-ppt) and Fe:Co (Mixed) catalyst enhanced substrate degradation, TOC removal and considerably minimized Org-BP formation. BET and SEM data revealed that Fe:Co (Co-ppt) catalyst has better textural properties compared to Fe:Co (Mixed) catalyst, and it displayed superior catalytic activity for degradation of toxic pollutants and Org-BP minimization. The Fe:Co (Mixed) catalyst was able to significantly suppress the formation of toxic bromate through lowering of solution pH from 6.8 to 5.7. Unlike bromide, the chloride ion was found be refractory during ozonation. NH3-TPD analysis and pZc values indicate that Fe alone has negligible acidic sites, while 9:1 Fe:Co (Co-ppt) has more acidic sites (6 cm3 g−1 STP) than 9:1 Fe:Co (Mixed) (2 cm3 g−1 STP) catalyst, hence promoting the decomposition of ozone to hydroxyl radicals on the Fe:Co (Co-ppt) surface.

Two dinuclear oxidovanadium(V) complexes of N2O2 donor amine-bis(phenolate) ligands with bromo-peroxidase activities: Kinetic, catalytic and computational studies

Two dinuclear oxidovanadium(V) complexes [LiVVO(µ2-O)VVO(Li)] (i = 1, H2L1, complex 1 and i = 2 for H2L2, complex 2) of two ONNO donor amine-bis(phenolate) ligands have been synthesized and characterized by X-ray diffraction studies which exhibited distorted octahedral geometry around each V center. In MeCN the complexes exist as dimers as indicated by HRMS studies, however, in the presence of 2 or more equivalents of H+ the dimers turned into monomers, ([LiVV = O]+ which exists in equilibrium with ([LiVV = OH]2+ and evidenced from the shift in λmax from 685 nm to 765 nm for complex 1 and 600 to 765 nm for complex 2. The complexes 1 and 2 efficiently catalyze the oxidative bromination of salicylaldehyde in the presence of H2O2 to produce 5-bromo-salicylaldehyde as the major product with TONs 405 and 450, respectively in the mixed solvent system (H2O:MeOH:THF = 4:3:2, v/v). The kinetic analysis of the bromide ion oxidation reaction indicates a mechanism which is first order in peroxidovanadium complex and bromide ion and limiting first-order on [H+]. The evaluated kBr and kH values are (8.82 ± 0.35) and (65.0 ± 2.23) M−1 s−1 for complex 1 and (6.74 ± 0.19) and (61.87 ± 2.27) M−1 s−1 for complex 2, respectively. The Ka of protonated species ([LiVV = OH]2+ are: Ka = (4.3 ± 0.40) × 10−3 (pKa = 2.37) and (4.7 ± 0.50) × 10−3 (pKa = 2.33) for complex 1 and 2 respectively. On the basis of the chemistry displayed by these model compounds, a mechanism of bromide oxidation and a tentative catalytic cycle have been framed which might be relevant to vanadium haloperoxidase enzymes and supported by DFT calculations.

Visible-Light Photocatalytic Double C–H Functionalization of Indoles: A Synergistic Experimental and Computational Study

Herein is disclosed a novel visible-light photocatalytic double C–H functionalization of indoles. The reaction affords 2,3-difunctionalized indoles in up to 84% yield, but the reaction rate depends strongly on electronic substituent effects. Mechanistic DFT studies and control experiments suggest that the secondary functionalization occurs through an independent photocatalytic oxidation of bromide ions formed during the reaction to generate molecular bromine capable of electrophilic C-3 bromination.

Interaction of ozone and carbon dioxide with polycrystalline potassium bromide and its atmospheric implication

It has been discovered for the first time that gaseous ozone in the presence of carbon dioxide and water vapor interacts with crystalline potassium bromide giving gaseous Br2 and solid salts KHCO3 and KBrO3. Molecular bromine and hydrocarbonate ion are the products of one and the same reaction described by the stoichiometric equation 2KBr(cr.) + O3(gas) + 2CO2(gas) + H2O(gas) → 2KHCO3(cr.) + Br2(gas) + O2(gas). The dependencies of Br2, KHCO3 and KBrO3 formation rates on the concentrations of O3 and CO2, humidity of initial gas mixture, and temperature have been investigated. A kinetic scheme has been proposed that explains the experimental regularities found in this work on the quantitative level. According to the scheme, the formation of molecular bromine and hydrocarbonate is due to the reaction between hypobromite BrO−, the primary product of bromide oxidation by ozone, with carbon dioxide and water; bromate results from consecutive oxidation of bromide ion by ozone Br−→+O3,−O2BrO−→+O3,−O2BrO2−→+O3,−O2BrO3−.

Current and potential oscillations during the electro-oxidation of bromide ions

Electrochemical oxidation of bromide ions was investigated in aqueous solution, in which sustained oscillations in both current and potential were observed. Under galvanostatic conditions the electrode potential only oscillates within two narrow regions around 0.9V and 1.6V, respectively. Sustained current oscillations at the high potentials applied were accompanied with bubble formation and are often irregular, implicating that their development may be attributed with convection-driven processes. At the low potentials, the current oscillations exhibit several features associated with a capacitance mediated electrochemical oscillator, such as (1) taking place around a current plateau in a cyclic voltammogram, (2) occurring without the need of an external resistor, (3) showing a decreasing amplitude with the increase of external resistance, and (4) emerging on a positive differential resistance branch. Admittance spectra at a potential close to the bifurcation point also exhibit resonance behavior. The reversible formation and dissolution of tribromide complexes (Br3−) from the reaction between bromide (Br−) and its electro-oxidation product bromine (Br2) play a key role in this system.

Ab initio study of the reaction of ozone with bromide ion.

Surface level ozone destruction in polar environments may be initiated by oxidation of bromide ions by ozone, ultimately leading to Br2 production. Ab initio calculations are used to support the development of atmospheric chemistry models, but errors can occur in study of the bromide-ozone reaction due to inappropriate treatment of the many-electron species and the ionic nature of the reaction. In this work, a high level ab initio study is used to take into account the electronic correlation and the polarization effects. Our results show three possible pathways for the reaction. In particular, we find that this process, though endothermic on the singlet spin state surface, can be energetically feasible on the triplet surface. The triplet surface can be reached through photoexcitation of ozone or by the spin crossing of the potential energy surface. Because this process is known to occur in the dark, it may be that it occurs after intersystem crossing to a triplet surface. This paper also provides a starting point calibration for any future ab initio calculation studies of the bromide-ozone reaction, from the gas to the condensed phase.

Oxidation of Bromide Ions by Hydroxyl Radicals: Spectral Characterization of the Intermediate BrOH•–

The reaction of (•)OH with Br(-) has been reinvestigated by picosecond pulse radiolysis combined with streak camera absorption detection and the obtained spectro-kinetics data have been globally analyzed using Bayesian data analysis. For the first time, the absorption spectrum of the intermediate species BrOH(•-) has been determined. This species absorbs in the same spectral domain as Br(2)(•-): the band maximum is roughly at the same wavelength (λ(max) = 352 nm instead of 354 nm) but the extinction coefficient is smaller (ε(max) = 7800 ± 400 dm(3) mol(-1) cm(-1) compared with 9600 ± 300 dm(3) mol(-1) cm(-1)) and the band is broader (88 nm versus 76 nm). Quantum chemical calculations have also been performed and corroborate the experimental results. In contrast to Br(2)(•-), the existence of several water-BrOH(•-) configurations leading to different transition energies may account for the broadening of the absorption spectrum in addition to the higher number of degrees of freedom.

A comparative study of anodic oxidation of bromide and chloride ions on platinum electrodes in 1-butyl-3-methylimidazolium hexafluorophosphate

The anodic processes of bromide and chloride ions on platinum electrodes were investigated in an ionic liquid, 1-butyl-3-methylimidazolium hexafluorophosphate, under the same conditions. The halide anions were added to the ionic liquid as their 1-butyl-3-metylimidazolium salts or tetrabutylammonium salts to high concentrations (up to 1.1molL−1). Analysis and comparison of the electrode reactions were made through cyclic voltammetry, chronoamperometry, and double potential step chronocoulometry with a platinum micro-disk electrode, and bulk potentiostatic electrolysis and UV–Vis spectroscopy. Both halide anions exhibited anodic oxidation. The main difference as revealed by cyclic voltammetry was that the chloride ion exhibited only one anodic current peak, whilst the bromide ion underwent clearly distinguished two oxidation steps. This difference is attributed to different electrode kinetics and stabilities of the two tri-halide ions. Bulk electrolysis and UV–Vis spectroscopy confirmed that the tri-bromide ion was the main product from the overall oxidation of the bromide ion, although bromine formation was indicated by cyclic voltammetry at potentials of the second anodic peak.

New insight into photo-bromination processes in saline surface waters: The case of salicylic acid

It was shown, through a combination of field and laboratory observations, that salicylic acid can undergo photo-bromination reactions in sunlit saline surface waters. Laboratory-scale experiments revealed that the photochemical yields of 5-bromosalicylic acid and 3,5-dibromosalicylic acid from salicylic acid were always low (in the 4% range at most). However, this might be of concern since these compounds are potential inhibitors of the 20α-hydroxysteroid dehydrogenase enzyme, with potential implications in endocrine disruption processes. At least two mechanisms were involved simultaneously to account for the photo-generation of brominated substances. The first one might involve the formation of reactive brominated radical species (Br, Br2−) through hydroxyl radical mediated oxidation of bromide ions. These ions reacted more selectively than hydroxyl radicals with electron-rich organic pollutants such as salicylic acid. The second one might involve the formation of hypobromous acid, through a two electron oxidation of bromine ions by peroxynitrite. This reaction was catalyzed by nitrite, since these ions play a crucial role in the formation of nitric oxide upon photolysis. This nitric oxide further reacts with superoxide radical anions to yield peroxynitrite and by ammonium through the formation of N-bromoamines, probably due to the ability of N-bromoamines to promote the aromatic bromination of phenolic compounds. Field measurements revealed the presence of salicylic acid together with 5-bromosalicylic and 3,5-dibromosalicylic acid in a brackish coastal lagoon, thus confirming the environmental significance of the proposed photochemically induced bromination pathways.

Vanadium pentoxide nanoparticles mimic vanadium haloperoxidases and thwart biofilm formation

Marine biofouling--the colonization of small marine microorganisms on surfaces that are directly exposed to seawater, such as ships' hulls--is an expensive problem that is currently without an environmentally compatible solution. Biofouling leads to increased hydrodynamic drag, which, in turn, causes increased fuel consumption and greenhouse gas emissions. Tributyltin-free antifouling coatings and paints based on metal complexes or biocides have been shown to efficiently prevent marine biofouling. However, these materials can damage the environment through metal leaching (for example, of copper and zinc) and bacteria resistance. Here, we show that vanadium pentoxide nanowires act like naturally occurring vanadium haloperoxidases to prevent marine biofouling. In the presence of bromide ions and hydrogen peroxide, the nanowires catalyse the oxidation of bromide ions to hypobromous acid (HOBr). Singlet molecular oxygen ((1)O(2)) is formed and this exerts strong antibacterial activity, which prevents marine biofouling without being toxic to marine biota. Vanadium pentoxide nanowires have the potential to be an alternative approach to conventional anti-biofouling agents.

“Long-life” atom-free radical: Generation and reactions of bromine atom-free radical

In order to study the damaging or beneficial properties of bromine atom-free radical, reaction of the free radical (Br•) with some biologically important compounds were investigated. Br• was generated through electrochemical oxidation of bromide ion (Br–). First the reactivity of Br• atom-free radical vis a vis its dimerization to form Br2, was studied using cyclic voltammetry and spectroelectrochemistry. Through these techniques it was ascertained that the substrates understudy and the under experimental conditions used, underwent reactions with Br• and not with dibromine (Br2). The monitoring of the reactions of Br• with glycine and cytosine led us to conclude that whereas cytosine reacted with Br• as simple chemical reaction (EC mechanism), glycine underwent a catalytic reaction (EC′ mechanism).

Bromide Oxidation and Formation of Dihaloacetic Acids in Chloraminated Water

A comprehensive reaction model was developed that incorporates the effect of bromide on monochloramine loss and formation of bromine and chlorine containing dihaloacetic acids (DHAAs) in the presence of natural organic matter (NOM). Reaction pathways accounted for the oxidation of bromide to active bromine (Br(l)) species, catalyzed monochloramine autodecomposition, NOM oxidation, and halogen incorporation into DHAAs. The reaction scheme incorporates a simplified reaction pathway describing the formation and termination of Br(l). In the absence of NOM, the model adequately predicted bromide catalyzed monochloramine autodecomposition. The Br(l) reaction rate coefficients are 4 orders of magnitude greater than HOCl for the same NOM sources under chloramination conditions. Surprisingly, the rate of NOM oxidation by Br(l) was faster than bromide catalyzed monochloramine autodecomposition by Br(l) so that the latter reactions could largely be ignored in the presence of NOM. Incorporation of bromine and chlorine into DHAAs was proportional to the amount of NOM oxidized by each halogen and modeled using simple bromine (alpha(Br)) and chlorine (alpha(Cl)) incorporation coefficients. Both coefficients were found to be independent of each other and alpha(Br) was one-half the value of alpha(Cl). This indicates that chlorine incorporates itself into DHAA precursors more effectivelythan bromine. Model predictions compared well with DHAA measurements in the presence of increasing bromide concentrations and is attributable to the increased rate of NOM oxidation, which is rate limited by the oxidation of bromide ion in chloraminated systems.

Toxicity of ozonated seawater to marine organisms

Ballast water transport of nonindigenous species (NIS) is recognized as a significant contributor to biological invasions and a threat to coastal ecosystems. Recently, the use of ozone as an oxidant to eliminate NIS from ballast while ships are in transit has been considered. We determined the toxicity of ozone in artificial seawater (ASW) for five species of marine organisms in short-term (< or = 5 h) batch exposures. Larval topsmelt (Atherinops affinis) and juvenile sheepshead minnows (Cyprinodon variegatus) were the most sensitive to oxidant exposure, and the mysid shrimp (Americamysis bahia) was the most sensitive invertebrate. Conversely, benthic amphipods (Leptocheirus plumulosus and Rhepoxinius abronius) were the least sensitive of all species tested. Mortality from ozone exposure occurred quickly, with median lethal times ranging from 1 to 3 h for the most sensitive species, although additional mortality was observed 1 to 2 d following ozone exposure. Because ozone does not persist in seawater, toxicity likely resulted from bromide ion oxidation to bromine species (HOBr and OBr-), which persist as residual toxicants after at least 2 d of storage. Total residual oxidant (TRO; as Br2) formation resulting from ozone treatment was measured in ASW and four site-specific natural seawaters. The rate of TRO formation correlated with salinity, but dissolved organic carbon and total dissolved nitrogen did not affect TRO concentrations. Acute toxicity tests with each water over 48 h using mysid shrimp, topsmelt, and sheepshead minnows yielded results similar to those of batch exposure. Addition of sodium thiosulfate (Na2S2O3) to ozonated waters resulted in TRO elimination and survival of all organisms. Our results provide necessary information for the optimization of an efficacious ozone ballast water treatment system.

Kinetics and Mechanism of Acid-Catalyzed Oxidation of Bromide Ions by the Aqueous Chromyl(IV) Ion

The reaction between the aqueous chromyl ion, CraqO2+, and Br- is acid-catalyzed and generates Br2. Kinetic studies that utilized a superoxochromium ion, CraqOO2+, as a kinetic probe yielded a mixed third-order rate law, -d[CraqO2+]/dt=k[CraqO2+][Br-][H+], where k=608+/-11 M-2 s-1. Experimental data strongly favor a one-electron mechanism, but the reaction is much faster than predicted on the basis of the reduction potential for the Br*/Br- couple. The reduction of CraqO2+ by transition-metal complexes, on the other hand, exhibits "normal" behavior, that is, k=(1.37x10(3)+1.94x10(3) [H+]) M-1 s-1 for Os(1,10-tris-phenanthroline)(3)2+ and <10 M-1 s-1 for Ru(2,2'-bipyridine)3(2+) at 0.1 M H+. The reduction of CraqOO2+ by Br2*- takes place with a rate constant k=(1.23+/-0.20)x10(9) M-1 s-1, as determined by laser-flash photolysis.

Evaluation of Kojic Acid for Determining Heme and Nonheme Haloperoxidase Activities Spectrofluorometrically

Heme‐containing haloperoxidases (heme haloperoxidases) catalyze peroxide‐dependent oxidation of halide ions to hypohalite ions. Nonheme haloperoxidases catalyze peroxidation of alkyl acids to peroxyacids that subsequently oxidize halide ions to hypohalite ions. Hypohalite ions react with kojic acid spontaneously with concomitant production of fluorescence. This reaction was examined for suitability in assaying heme and nonheme haloperoxidase activities spectrofluorometrically. Heme haloperoxidases were assayed directly from hypohalite generation whereas nonheme enzymes were assayed by coupling peroxyacid formation to bromide ion oxidation. Peroxidation of kojic acid by chloroperoxidase and myeloperoxidase did not require halide ions and was not increased upon their addition, demonstrating that haloperoxidase activity was not distinguished from the classical peroxidase‐like activity of these enzymes. Addition of bromide ions to specimens of nonheme haloperoxidase, however, resulted in increased rates of fluorescence generation, indicative of the presence of distinct peroxidase and haloperoxidase enzymes. The heme poison sodium azide inhibited chloroperoxidase, myeloperoxidase, and horseradish peroxidase activities totally but inhibited only a portion of nonheme haloperoxidase activity, verifying that the last specimen was contaminated with heme‐containing peroxidase. Results show the utility of kojic acid for fluorometrically measuring haloperoxidase activity, particularly that of the nonheme enzyme.

Vanadium Bromoperoxidase-Catalyzed Biosynthesis of Halogenated Marine Natural Products

Marine red algae (Rhodophyta) are a rich source of bioactive halogenated natural products. The biogenesis of the cyclic halogenated terpene marine natural products, in particular, has attracted sustained interest in part because terpenes are the biogenic precursors of many bioactive metabolites. The first enzymatic asymmetric bromination and cyclization of a terpene, producing marine natural products isolated from red algae, is reported. Vanadium bromoperoxidase (V-BrPO) isolated from marine red algae (species of Laurencia, Plocamium, Corallina) catalyzes the bromination of the sesquiterpene (E)-(+)-nerolidol producing alpha-, beta-, and gamma-snyderol and (+)-3beta-bromo-8-epicaparrapi oxide. alpha-Snyderol, beta-snyderol, and (+)-3beta-bromo-8-epicaparrapi oxide have been isolated from Laurencia obtusa, and each have also been isolated from other species of marine red algae. gamma-Snyderol is a proposed intermediate in other bicyclo natural products. Single diastereomers of beta-snyderol, gamma-snyderol, and mixed diastereomers of (+)-3beta-bromo-8-epicaparrapi oxide (de = 20-25%) are produced in the enzyme reaction, whereas two diastereomers of these compounds are formed in the synthesis with 2,4,4,6-tetrabromocyclohexa-2,5-dienone (TBCO). V-BrPO likely functions by catalyzing the two-electron oxidation of bromide ion by hydrogen peroxide producing a bromonium ion or equivalent in the active site that brominates one face of the terminal olefin of nerolidol. These results establish V-BrPO's role in the biosynthesis of brominated cyclic sesquiterpene structures from marine red algae for the first time.