Cross-coupling of sulfonamide antimicrobial agents with model humic constituents

The oxidative cross-coupling of sulfonamide antimicrobials to constituents of natural organic matter was investigated. Sulfonamide antimicrobials were incubated with surrogate humic constituents in the absence and presence of phenoloxidases (viz., peroxidase, laccase, and tyrosinase) or acid birnessite. Substituted phenols were chosen as simple model constituents to determine the structures in humic substances important for cross-coupling reactions. The extent of sulfonamide transformation was evaluated by the disappearance of the parent compound from solution. Incubation with phenoloxidases in the absence of substituted phenols resulted in little or no sulfonamide transformation. In contrast to this, direct oxidation of sulfonamides by acid birnessite was significant. Inclusion of o-diphenols and 2,6-dimethoxyphenols in reaction mixtures resulted in significant phenoloxidase-mediated transformation of sulfonamides and enhanced antimicrobial transformation in the presence of acid birnessite. Phenolic compounds with other substitution patterns were less effective in promoting sulfonamide transformation. Nuclear magnetic resonance spectroscopy experiments provided direct evidence of peroxidase-mediated covalent cross-coupling of sulfamethazine with syringic and protocatechuic acids. Our results indicate that sulfonamide antimicrobials may be chemically incorporated into humic substances. This may result in their diminished mobility, bioavailability, and biological activity.     

Reduced toxicity of olive mill waste waters by oxidative coupling with biomimetic catalysis

Large quantities of environmentally toxic olive mill waste waters (OMWW) result from olive oil production worldwide. A synthetic water-soluble meso-tetra(2,6-dichloro-3-sulfonatophenyl)porphyrinate of iron(III) chloride (FePha) was used as biomimetic catalystto oxidatively couple toxic phenols in OMWW fractions obtained by micro-, ultra-, and nanofiltration, and reverse osmosis. The occurrence of oxidative coupling in different OMWW size-fractions was assessed by high performance size exclusion chromatography (HPSEC), before and after conformational disruption with acetic acid, and measurements of proton spin-lattice relaxation time in the rotating frame (T1(rho)H) through 13C-CPMAS-NMR spectroscopy. The concurrent reduction in toxicity of OMWW size-fractions brought about by the FePha treatment was monitored by an algal bioassay. HPSEC chromatograms of OMWW samples subjected to catalyzed coupling showed apparent weight-average molecular weight (Mwa) values varying from 18 to 185% larger than for control. Moreover, when such FePha-treated fractions were added to acetic acid prior to HPSEC, the Mwa values still ranged from 14 to 162% larger than for control fractions similarly treated with acetic acid. This evidence of polymerization among toxic phenols was confirmed by T1(rho)(H) values which were significantly enhanced by the FePha treatment, thereby indicating an increased conformational rigidity of OMWW materials. These molecular changes were reflected in a significantly reduced toxicity exerted on microalgae by the OMWW size-fractions subjected to catalyzed oxidative couplings. Our results suggest that OMWW can be effectively treated with a biomimetic catalyst to induce oxidative phenol polymerization and reduce their toxicity before amendments to soils or other disposal means.     

Oligomerization of humic phenolic monomers by oxidative coupling under biomimetic catalysis

Three humic phenolic monomers, catechol (CAT), caffeic acid (CAFF), and p-coumaric acid (COUM), were subjected to oxidative coupling catalyzed by biomimetic water-soluble iron-porphyrin (Fe(TDCPPS)CI) in either separate or mixed solution, and the reaction products were characterized by gas chromatography-mass spectrometry (GC-MS) and electrospray-mass spectrometry (ESI-MS). The GC-MS analysis proved the formation of C-C and C-O dimers, whereas the ESI-MS/MS analysis also suggested trimerization for all the monomers and tetramerization for CAT. On the basis of mass spectra, molecular structures were assigned to the observed oligomers. In the phenolic separate solutions, dimers represented about 65%, 44%, and 30% of reaction products for CAT, CAFF, and COUM, respectively, whereas trimers were from 4 to 5%. A relevant part of the products were unidentified oligomers and several degradation compounds, mostly aromatic aldehydes and alcohols and aromatic or aliphatic carboxylic acids. When all three humic phenolic monomers underwent the catalyzed coupling reaction in one mixed solution, 14% of the reaction products were identified as C-C dimers of CAT. Although no other C-O dimers of CAT, nor any dimers of COUM and CAFF, could be identified, some other structurally unknown oligomers were present among the reaction products of the mixed solution. However, no oligomers larger than tetramers were formed in either separate or mixed solutions. This work indicates the essential role of biomimetic metal-porphyrins in catalyzing the oxidative coupling of humic phenolic monomers in aqueous media, thereby promoting the polymerization of natural organic matter.     

OXYGEN-SCAVENGING ENZYMES IN BARLEY AND MALT AND THEIR EFFECTS DURING MASHING

Off the enzymes that may be involved in the scavenging off oxygen radicals in barley and malt, superoxide dismutase, catalase and peroxidase all increase their specific activities during malting, whereas polyphenol oxidase decreases to zero. Of these, however, only the isoenzymes of peroxidase survive (in part) in the mash, and are responsible for the oxidation of polyphenolic materials. The concentration of hydrogen peroxide normally found in wort limits their action. Addition of hydrogen peroxide to the mash or its generation via a glucose oxidase system greatly increases haze formation, decreases the polyphenol content and causes the development of a red coloration. When the same amount of the different malt peroxidase isoenzymes was added to mashes, the intensity of the red colour varied according to the isoenzyme used. The worts produced by enhanced peroxidation afford more colloidally stable beers. The effects however are limited by the dissolved oxygen concentration in the wort.     

Catalysis of Lipid Oxidation by Iron from an Insoluble Fraction of Beef Diaphragm Muscle

An insoluble fraction of beef diaphragm muscle was found to catalyze lipid oxidation in the presence of reducing compounds. Ascorbate (100 μM) catalyzed the formation of thiobarbituric acid reactive substances 3.3, 8.3 and 7.3-fold more effectively than cysteine, superoxide and NADPH, respectively. Ascorbate/insoluble fraction-catalyzed lipid oxidation was inhibited bv EDTA, ceruloolasmin, catalase and superoxide dismutase indicating the iivolvemknt of iron, hydrogen peroxide and superoxide anion. Both lipid oxidation and the release of iron from the insoluble fraction increased with increasing pH (5.0–7.0) in the presence of ascorbate. Iron bound to the insoluble components of beef muscle could be involved in catalysis of lipid oxidation.     

路边青多酚复配物对猕猴桃饮料的抗氧化稳定性影响

在猕猴桃饮料中添加路边青- 过路黄多酚复配物,考察紫外光、温度和氧化剂对饮料过氧化值的影响以及复配物配比与羟自由基清除率的关系。结果表明：90℃温度下加热6h,猕猴桃饮料中添加路边青- 过路黄多酚复配物(1:1,V/V)其过氧化值比加BHT 和不加抗氧剂分别减少8.55% 和24.57%;分别用0.5% H2O2 氧化处理和紫外光照射,添加复配物的猕猴桃饮料,其过氧化值比加BHT 分别减少9.08% 和1.83%,比不加抗氧剂分别减少17.55% 和3.57%。路边青- 过路黄多酚复配物配比以3:1(V/V)的抗氧化活性最好,饮料中添加该复配物,其过氧化值比不加抗氧剂减少56.27%;羟自由基清除率是BHT 的1.37 倍。     

Photoirradiation of dissolved humic acid induces arsenic(III) oxidation

The fate of arsenic in aquatic systems is influenced by dissolved natural organic matter (DOM). Using UV-A and visible light from a medium-pressure mercury lamp, the photosensitized oxidation of As(III) to As(V) in the presence of Suwannee River humic acid was investigated. Pseudo-first-order kinetics was observed. For 5 mg L(-1) of dissolved organic carbon (DOC) and 1.85 mEinstein m(-2) s(-1) UV-A fluence rate, the rate coefficient k degrees exp was 21.2 +/- 3.2 10(-5) s(-1), corresponding to a half-life <1 h. Rates increased linearly with DOC and they increased by a factor of 10 from pH 4 to 8. Based on experiments with radical scavengers, heavy water, and surrogates for DOM, excited triplet states and/or phenoxyl radicals seem to be important photooxidants in this system (rather than singlet oxygen, hydrogen peroxide, hydroxyl radicals, and superoxide). Photoirradiation of natural samples from freshwater lakes, rivers, and rice field water (Bangladesh) showed similar photoinduced oxidation rates based on DOC. Fe(III) (as polynuclear Fe(III)-(hydr)oxo complexes or Fe(III)-DOC complexes) accelerates the rate of photoinduced As(III) oxidation in the presence of DOC by a factor of 1.5-2.     

Gelatination Temperatures of Starch,as Influenced by Polyhydric and Monohydric Alcohols,Phenols, Carboxylic Acids and some other Additives

The effect of polyhydric and monohydric alcohols, of phenols, of carboxylic acids and their anions, of halide anions, of alkalimetalions and of some other compounds on the gelatination temperature of potato starch granules in aqueous solutions were studied. Polyhydric alcohols and methanol raise the gelatination temperature, whereas ethanol, propanol, butanol, p-dioxane, carboxylic acids, phenols, urea and hydrogen peroxide cause a decrease in the gelatination temperature. The effect of polyhydric alcohols may be attributed to the lessened tendency of the medium to rupture hydrogen bonds. Carboxylic acids, phenols, urea and hydrogen peroxide may act in a opposite way. The lowering effect of the monohydric alcohols, dioxane, and other non-polar substances may be due to structural and kinetic alterations of the aqueous medium, induced by the non-polar groups. At higher concentrations of ethanol, propanol, p-dioxane, acetic, propionic and butyric acid the gelatination temperature tends to increase. This is to be attributed to the association of solute molecules.     

Bactericidal effect of zero-valent iron nanoparticles on Escherichia coli

Zero-valent iron nanoparticles (nano-Fe0) in aqueous solution rapidly inactivated Escherichia coli. A strong bactericidal effect of nano-Fe0 was found under deaerated conditions, with a linear correlation between log inactivation and nano-Fe0 dose (0.82 log inactivation/mg/L nano-Fe0 x h). The inactivation of E. coli under air saturation required much higher nano-Fe0 doses due to the corrosion and surface oxidation of nano-Fe0 by dissolved oxygen. Significant physical disruption of the cell membranes was observed in E. coli exposed to nano-Fe0, which may have caused the inactivation or enhanced the biocidal effects of dissolved iron. The reaction of Fe(II) with intracellular oxygen or hydrogen peroxide also may have induced oxidative stress by producing reactive oxygen species. The bactericidal effect of nano-Fe0 was a unique property of nano-Fe0, which was not observed in other types of iron-based compounds.     

Effects of humic substances on the pattern of oxidation products of pentachlorophenol induced by a biomimetic catalytic system using tetra(p-sulfophenyl)porphineiron(III) and KHSO5

In the presence of humic substances (HSs), the oxidative conversion of pentachlorophenol (PCP) was found to be efficiently catalyzed by tetra(p-sulfophenyl)porphineiron(III) (Fe(III)-TPPS) using KHSO5 as an oxygen donor. Ortho-tetrachloroquinone (o-TeCQ), 2-hydroxyl-nonachlorodiphenyl ether (2H-NCDE), 4-hydroxyl-nonachlorodiphenyl ether (4H-NCDE), and octachlorodibenzo-p-dioxin (OCDD) were identified as the major byproducts of the reaction. Decreased amounts of these byproducts were produced in the presence of HS. In particular, the addition of HSs with a lower degree of humification resulted in a large decrease in the formation of dimers, such as 2H-NCDE, 4H-NCDE, and OCDD. More than 60% of the chlorine, which was released from PCP, was found in the HS fractions after the reaction. This suggests that chlorinated intermediates from PCP were incorporated into the HS. Pyrolysis-GC/MS and 13C NMR studies confirmed that the binding of the chlorinated intermediates was covalent in nature and that the intermediates were copolymerized with HS via oxidative coupling reactions. A Microtox test demonstrated that the toxicity of the HS fraction containing PCP-derived intermediates was much lower than that of the mixture of PCP and HS in the absence of a catalytic reaction.     

Reactions of hydroxyl radical with humic substances: bleaching, mineralization, and production of bioavailable carbon substrates

In this study, we examine the role of the hydroxyl (OH*) radical as a mechanism for the photodecomposition of chromophoric dissolved organic matter (CDOM) in sunlit surface waters. Using gamma-radiolysis of water, OH* was generated in solutions of standard humic substances in quantities comparable to those produced on time scales of days in sunlit surface waters. The second-order rate coefficients of OH* reaction with Suwannee River fulvic (SRFA; 2.7 x 10(4) s(-1) (mg of C/L)(-1)) and humic acids (SRHA; 1.9 x 10(4) s(-1) (mg of C/L)(-1)) are comparable to those observed for DOM in natural water samples and DOM isolates from other sources but decrease slightly with increasing OH* doses. OH* reactions with humic substances produced dissolved inorganic carbon (DIC) with a high efficiency of approximately 0.3 mol of CO2/mol of OH*. This efficiency stayed approximately constant from early phases of oxidation until complete mineralization of the DOM. Production rates of low molecular weight (LMW) acids including acetic, formic, malonic, and oxalic acids by reaction of SRFA and SRHA with OH* were measured using HPLC. Ratios of production rates of these acids to rates of DIC production for SRHA and for SRFA were similar to those observed upon photolysis of natural water samples. Bioassays indicated that OH* reactions with humic substances do not result in measurable formation of bioavailable carbon substrates other than the LMW acids. Bleaching of humic chromophores by OH* was relatively slow. Our results indicate that OH* reactions with humic substances are not likely to contribute significantly to observed rates of DOM photomineralization and LMW acid production in sunlit waters. They are also not likely to be a significant mechanism of photobleaching except in waters with very high OH* photoformation rates.     

Oxidation of Starch by Hydrogen Peroxide in the Presence of UV Light-Part II

Various reaction variables in the hydrogen peroxide oxidation of starch in the presence of UV light have been investigated. Higher carboxyl and carbonyl contents of oxystarches were obtained under acidic than under alkaline conditions. Extent of oxidation was found to increase with time. Increasing the concentration of hydrogen peroxide results in an increase in the carboxyl and carbonyl contents. Apparently, air has no effect on the degree of oxidation whereas, oxygen seems to accelerate it.     

Iron-catalyzed oxidation of arsenic(III) by oxygen and by hydrogen peroxide: pH-dependent formation of oxidants in the Fenton reaction

The oxidation kinetics of As(III) with natural and technical oxidants is still notwell understood, despite its importance in understanding the behavior of arsenic in the environment and in arsenic removal procedures. We have studied the oxidation of 6.6 microM As(II) by dissolved oxygen and hydrogen peroxide in the presence of Fe(II,III) at pH 3.5-7.5, on a time scale of hours. As(III) was not measurably oxidized by O2, 20-100 microM H2O2, dissolved Fe(III), or iron(III) (hydr)-oxides as single oxidants, respectively. In contrast, As(III) was partially or completely oxidized in parallel to the oxidation of 20-90 microM Fe(II) by oxygen and by 20 microM H2O2 in aerated solutions. Addition of 2-propanol as an *OH-radical scavenger quenched the As(III) oxidation at low pH but had little effect at neutral pH. High bicarbonate concentrations (100 mM) lead to increased oxidation of As-(III). On the basis of these results, a reaction scheme is proposed in which H2O2 and Fe(II) form *OH radicals at low pH but a different oxidant, possibly an Fe(IV) species, at higher pH. With bicarbonate present, carbonate radicals might also be produced. The oxidant formed at neutral pH oxidizes As(III) and Fe(II) but does not react competitively with 2-propanol. Kinetic modeling of all data simultaneously explains the results quantitatively and provides estimates for reaction rate constants. The observation that As(III) is oxidized in parallel to the oxidation of Fe(II) by O2 and by H2O2 and that the As(III) oxidation is not inhibited by *OH-radical scavengers at neutral pH is significant for the understanding of arsenic redox reactions in the environment and in arsenic removal processes as well as for the understanding of Fenton reactions in general.     

Decomposition of hydrogen peroxide and organic compounds in the presence of dissolved iron and ferrihydrite

This work examines the contribution of solution phase reactions, especially those involving a chain reaction mechanism, to the decomposition of hydrogen peroxide (H2O2) and organic compounds in the presence of dissolved iron and ferrihydrite. In solutions at pH 4, where Fe was introduced as dissolved Fe(III), both H2O2 and 14C-labeled formic acid decomposed at measurable rates that agreed reasonably well with those predicted by a kinetic model of the chain reaction mechanism, using published rate constants extrapolated to pH 4. The ratio of the formic acid and H2O2 decomposition rates, as well as the dramatic effect of tert-butyl alcohol on these rates, confirmed that a solution chain reaction mechanism involving *OH controlled the decomposition kinetics of both compounds. In the presence of ferrihydrite as the iron source, the ratio of the rate of formic acid decomposition to that of H2O2 decomposition was significantly lower than that observed in the presence of only dissolved Fe. Moreover, neither rate diminished drastically upon addition of tert-butyl alcohol, indicating that the solution phase chain reaction is not a dominant decomposition pathway of H2O2 and formic acid. Relative decomposition rates of formic acid and a second *OH probe, benzoic acid, were consistent with oxidation of these compounds by *OH. These observations can be reproduced by a kinetic model including (a) decomposition of H2O2 at the iron oxide surface, producing *OH with lower yield than the reaction sequence with dissolved Fe, and (b) low concentrations of dissolved Fe in the presence of ferrihydrite, preventing propagation of the solution phase chain reaction.     

Natural humics impact uranium bioreduction and oxidation

Although humic substances occur ubiquitously in soil and groundwater, their effect on the biological reduction of uranium(VI) and subsequent reoxidation of U(IV) is poorly understood. This study investigated the role of humics in enhancing the bioreduction of U(VI) in laboratory kinetic studies, in field push-pull tests, and in the presence or absence of metal ions such as Ca2+ and Ni2+, which are known to inhibit the biological reduction of U(VI). Results from laboratory experiments indicate that, under strict anaerobic conditions, the presence of humic materials enhanced the U(VI) reduction rates (up to 10-fold) and alleviated the toxicity effect of Ni2+ on microorganisms. Humic acid was found to be more effective than fulvic acid in enhancing the reduction of U(VI). Such an enhancement effect is attributed to the ability of these humics in facilitating electron-transfer reactions and/or in complexing Ca2+ and Ni2+ ions. Similarly, field push-pull tests demonstrated a substantially increased rate of U(VI) reduction when humic acid was introduced into the site groundwater. However, humics were also found to form complexes with reduced U(IV) and increased the oxidation of U(IV) (when exposed to oxygen) with an oxidation halflife on the order of a few minutes. Both of these processes render uranium soluble and potentially mobile in groundwater, depending on site-specific and dynamic geochemical conditions. Future studies must address the stability and retention of reduced U(IV) under realistic field conditions (e.g., in the presence of dissolved oxygen and low concentrations of complexing organics).     

Association of methylmercury with dissolved humic acids

Sorption of methylmercury (MeHg) to three different humic acids was investigated as a function of pH and humic concentration. The extent of sorption did not show a strong pH dependence within the pH range of 5-9. Below pH 5, a decrease in adsorption for all humic samples was observed. The experimental data for equilibrium sorption of MeHg were modeled using a discrete log K spectrum approach with three weakly acidic functional groups. The modeling parameters, which were the equilibrium binding constants and the total binding capacities, represented the data well at all MeHg and humic concentrations and pH values for a given humic sample. The estimated binding constants for complexes of MeHg with humic acids were similar in magnitude to those of MeHg with thiol-containing compounds, suggesting that binding of MeHg involves the thiol groups of humic acids. The results show that only a small fraction of the reduced sulfur species in humic substances may take part in binding MeHg, but in most natural systems, this subfraction is considerably higher in concentration than ambient MeHg. The model developed here can be incorporated into speciation models to assess the bioavailability of MeHg in the presence of dissolved organic matter and competing ligands such as chloride and sulfide.     

Temperature-dependence of rate of oxidation of rapeseed oil encapsulated in a glassy food matrix

Oxidation of stripped rapeseed oil, encapsulated in a carbohydrate/protein glassy matrix, initiated by a lipophilic free radical initiator (or not initiated) and monitored as peroxide value and conjugated dienes for 45 days, developed differently depending on storage temperature. At low temperature (5 °C), the encapsulated oil and bulk oil, as reference, showed little oxidation which, moreover, could be accounted for by the oxygen dissolved in the oil. At intermediate temperatures (25 and 45 °C), oxidation exceeded the level corresponding to dissolved oxygen and became dependent on oxygen transport through the matrix. At high temperature (60 °C), a rapid, linear increase in peroxide concentration was followed by an autocatalytic phase with a rapid increase in peroxides, subsequently reaching a steady-state concentration. The oxidation of the encapsulated oil was found to have a lower energy of activation (around 60 kJ/mol) than the bulk oil (around 80 kJ/mol), resulting in a protection of the encapsulated oil at higher temperatures. However, the temperature-dependence of the zeroth order rate constants for initial peroxide formation in the encapsulated oil showed a shift from a rate determining reaction at low temperature with a high energy of activation to a reaction at higher temperature with a smaller energy of activation, especially for the encapsulated oil without initiator added. At low temperature, lipid oxidation seems rate-determining while, at higher temperature, oxygen permeation through the matrix with a lower energy of activation becomes rate-determining. The glassy matrix yields only partly protection against lipid oxidation as it allows permeation of oxygen and other small molecules, as further confirmed by the effect of a hydrophilic radical initiator, incorporated in the matrix, on peroxide value of the encapsulated oil.     

Fulvic acid oxidation state detection using fluorescence spectroscopy

Humic substances are a heterogeneous class of moderate molecular weight, yellow-colored biomolecules present in all soils, sediments, and natural waters. Although humic substances are generally resistant to microbial degradation under anaerobic conditions, some microorganisms in soils and sediments can use quinone moieties in humic substances as electron acceptors. Laboratory experiments have shown that humic substances can act as electron shuttles in the microbial reduction of ferric iron. Field studies of electron shuttling processes have been constrained by the lack of methods to characterize the oxidation state of quinone moieties in humic substances at natural concentrations. All humic substances have fluorescent properties, and fluorescence spectroscopy can indicate differences in precursor organic source of humic substances. Here we show that the quinone moieties responsible for electron transfer reactions contribute significantly to the fluorescence of humic substances. Further we use fluorescence spectroscopy to elucidate the oxidation state of quinone moieties in humic substances at natural concentrations found in sediment interstitial waters.     

KOJIC ACID CONVERSION TO A YELLOW PRODUCT(S) VIA THE HORSERADISH PEROXIDASE/H2O2 SYSTEM1

Horseradish peroxidase in the presence of hydrogen peroxide oxidizes kojic acid (5-hydroxy-2-hydroxymethyl)-4H-pyran-4-one) to a yellow product(s). The yellow product(s) formed has a major absorbance peak at 375 nm and is fluorescent. The relationships between, and effects of, various concentrations of horseradish peroxidase, kojic acid and hydrogen peroxide on the rate of oxidation of kojic acid to the yellow product(s) are described. The observation that the oxidation of kojic acid to the yellow product(s) occurs best in the presence of very low concentrations of hydrogen peroxide, relative to that of kojic acid, suggests that kojic acid is a poor hydrogen donor (AH₂) for horseradish peroxidase.     

Transformation of substituted cinnamic acids using l-cysteine metal complexes in aqueous media

4-Hydroxycinnamic, 4-methoxycinnamic, ferulic and cinnamic acids were both non-oxidatively and oxidatively decarboxylated in alkaline aqueous media in the presence of l-cysteine–Fe(II) and l-cysteine–Co(II) heterogeneous catalysts using hydrogen peroxide or molecular oxygen. GC/MS analysis of diethylether extracts of reaction mixtures confirmed that the addition of hydrogen peroxide resulted predominantly in oxidative decarboxylation of substituted cinnamic acids, producing the corresponding carbonyl compounds (4-hydroxybenzaldehyde, 4-methoxybenzaldehyde, vanillin, benzaldehyde). On the other hand, saturation of this heterogeneous reaction system with molecular oxygen led to the formation of a variety of products, probably via peroxoacid anions or peroxoradical intermediates, e.g., ferulic acid was transformed to vinylguaiacol and vanillin with yields of 22% and 0.7%, respectively.