Interactions of di- and trihydroxybenzenes with transition metals and their biological consequences

Iron can be found in all mammalian cells and is of critical significance to diverse cellular activities within human bodies. Widespread applications and the underlying chemical and biological funda...

Chemiluminescence of the Fenton reaction and a dihydroxybenzene-driven Fenton reaction

New insights in the dihydroxybenzenes-driven Fenton reaction: electrochemical study of interaction between dihydroxybenzenes and Fe(III)

Tribromophenol (TBP) is a halogenated phenol mainly used as an intermediate of flame retardants in the electronics manufacturing industry as well as a fungicide in the wood industry to prevent fungal wood stain and decay. As a result of this massive use, its bio-availability, toxicity, and environmental fate are of increasing concern worldwide. TBP degradation by a catechol (CAT)-driven Fenton reaction was studied. In order to achieve the best yield in TBP degradation, an experimental design was applied for multivariate optimization of the experimental degrading system variables. At optimized concentrations, the CAT- driven Fenton reaction yielded 75% TBP degradation in 2 h at room temperature. The multivariate optimization showed that the highest TBP degradation (1 mol base) was obtained at a ratio of CAT: FeCl3: H2O2 = 0.150 : 0.211: 5.100 at pH = 3.4. A time course degradation of TBP comparing the CAT-driven Fenton reaction with the classical Fenton reaction is also presented. During the first hours of reaction (up to 8h), increased degradation efficiencies were observed in the CAT-driven Fenton reaction in comparison with the conventional Fenton reaction. Possible causes for the observed behavior are also discussed.

Fe/H2O2 and Co/PMS reactions were compared for l-proline degradation under different initial pH values, various transition metal salt and oxidant agent concentrations, as well with and without irradiation. The Fenton reaction took 60 min to degrade 90% of the l-proline, whereas the Fenton-like reaction achieved the same degradation after only 15 min. The best conditions for the Fenton-like reaction resulted from using 0.8 mM of cobalt salt with low PMS concentration (20 mM) at a neutral initial pH and without irradiation. Further experiments were performed using the Co/PMS system to estimate the effects of the other reaction conditions. The results of these experiments showed that pH, reagent concentration, and UV (λ = 365 nm) radiation had no significant effect on the degradation. Additionally, the Fenton-like reaction was made in heterogeneous phase, showing that the reaction proceed equally at same pH than homogeneous phase reaction with no significant effect of phase type used. Significant amount of cobalt was found being leached from the solid media to the water at acidic pH values during the heterogeneous process so the best process conditions were found at neutral pH where the amount of cobalt being leached was found negligible. The heterogeneous Fenton-like process was found feasible to be used for different contaminants degradation with no risk of increased toxicity related with cobalt leachate. The results of this work provide a good evaluation of heterogeneous and homogeneous Fenton-like reaction and suggest that high reagent concentrations are unnecessary for efficient contaminant removal in aqueous phase.

Development of a PEG Derivative Containing Hydrolytically Degradable Hemiacetals

ABSTRACTThe authors report the spontaneous formation of water-soluble chitosan-tartaric acid (CS-TA) spherical particles. Particles are formed by heating chitosan in the presence of tartaric acid under hydrothermal conditions. Tartaric acid serves as an ionic cross-linker, a depolymerizing agent, and a particle stabilizer in aqueous phase. The CS-TA particles exhibit superior colloidal stability at a wide pH range due to their surface charge tunability, which is due to the colocalization of surface hydroxyl, amine, and carboxyl groups. At physiological pH condition, particles have zwitterionic structure as determined by the zeta potential measurements. Still, CS-TA maintains colloidal stability at neutral pH due to the abundance of surface hydroxyl groups. As a proof-of-concept study, the CS-TA particles were labeled with a model insoluble cargo (fluorescein isothiocyanate [FITC]) to demonstrate their capacity for solubilizing hydrophobic drugs. The CS-TA/FITC conjugates were found to remain well dispersed at neutral pH, while maintaining FITC fluorescence properties.

Yeast Atg8 and its mammalian homolog LC3 are ubiquitin-like proteins involved in autophagy, a primary pathway for degradation of cytosolic constituents in vacuoles/lysosomes. Whereas the lipid phosphatidylethanolamine (PE) was identified as the sole in vivo target of their conjugation reactions, in vitro studies showed that the same system can mediate the conjugation of these proteins with phosphatidylserine as efficiently as with PE. Here, we show that, in contrast to PE conjugation, the in vitro phosphatidylserine conjugation of Atg8 is markedly suppressed at physiological pH. Furthermore, the addition of acidic phospholipids to liposomes also results in the preferential formation of the Atg8-PE conjugate. We have successfully captured authentic thioester intermediates, allowing us to elucidate which step in the conjugation reaction is affected by these changes in pH and membrane lipid composition. We propose that these factors contribute to the selective formation of Atg8-PE in the cell.

Thiamine deficiency is an important issue for many diseases and thus a facile method of detection is clinically important to improve the health of humans. For that purpose, we have developed a new thiamine sensor using starch stabilized copper nanoparticles (CSNP) at neutral pH and also improved the sensitivity of the sensor using cucurbit[7]uril (CB[7]) through host-guest chemistry. Often thiamine is not detected directly, but through the oxidation of thiamine to thiochrome (TC); TC is a fluorescent emitting molecule, through which thiamine has been measured indirectly. Here, we have demonstrated a new approach for a thiamine sensor, based on the formation of TC by the addition of hydrogen peroxide and CSNP. Unlike the other reported thiamine sensors, our method works advantageously at physiological pH conditions (pH 7, 27 °C). Furthermore, addition of CB[7] to TC, increased the sensitivity of the sensor approximately one order magnitude, through encapsulation; which can be reversed upon addition of a stronger competitive guest such as adamantylamine to confirm the encapsulation of TC. Thus, this new thiamine sensor not only performed well under physiological pH conditions, but also improved the fluorescence of TC, when encapsulated by CB[7].

Inhibitory Effects of Procainamide and Probenecid on Renal Excretion of Sultopride Enantiomers in Rats

Chemical coprecipitation technique is proven to be a beneficial method to prepare uniformly mixed catalyst metal and Kraft lignin precursors. Coprecipitation is a simple, yet very complex process which is highly sensitive to the reaction conditions, particularly temperature. In an exothermic coprecipitation process, the reaction rate can become uncontrollable over certain temperatures which could lead to a thermal runaway reaction. In this work, metal-lignin nanocomposites were synthesized by coprecipitation of metal (M) salts and Kraft lignin. Kraft lignin and metal salts were dissolved in organic solvents and DI water, respectively, to make lignin solution/suspension and metal salt aqueous solution. The aqueous solutions of metal salts were then added to the lignin solutions/suspensions and mixed well, resulting in chelation of transition metal ions to the functional groups of lignin chains and co-precipitation of metal-lignin composites from the solvents. To develop a safe process for producing M-lignin composites in a large volume, potential reactions, exothermic or endothermic processes, hazards gases, and volatiles were evaluated during the coprecipitation process. The effects of transition metal type, solvent selection, concentration of metal salts, and initial solution temperature on the interactions between metal ions and Kraft lignin, metal uniformity in the lignin matrix, and morphology of the metal-lignin composites were investigated during the coprecipitation process. Cu, Mo, Ni, and Fe were investigated as the transition metals for the metal-lignin composites. Fenton or Fenton-like reactions were discovered to occur during the Fe- and Cu-lignin coprecipitation process and tremendous heat evolved, which lead to the overshoot of the reaction system temperature in a very short time (i.e. a few seconds). Significant amounts of CO2 and toxic NO2 gasses were released during the coprecipitation process when Fenton or Fenton-like reactions occurred. No interaction or a very weak interaction occurred between lignin and Mo(VI) ions when mixing both solutions. Ni ions were coordinated strongly to oxygen-containing functional groups in lignin, but no Fenton or Fenton-like reaction was detected during Ni-lignin coprecipitation. Fenton reaction or Fenton-like reaction occurred when tetrahydrofuran (THF) and acetone were used to dissolve Kraft lignin, and the reaction became highly fierce and unmanageable with increasing of iron content in the composite. The reaction initialization time was shortened with increase of initial solution temperature and thermal runaway reaction might occur if the initial mixing temperature reached 60 °C or above.

Modified fenton reaction for trichlorophenol dechlorination by enzymatically generated H 2O 2 and gluconic acid chelate

Oxygen contribution to phenolic evolution during aging of red wines

Synthetic boron-doped diamond thin film is a new promising anode material. Because of its properties (high anodic stability under drastic conditions and wide potential window), it is widely investigated for numerous possible electrochemical applications such as electrosynthesis, preparation of powerful oxidants and electroincineration. In the first part of this work, simple charge transfer was investigated at boron-doped diamond electrode through the study of an outer sphere system in the potential region of water stability. In a second part of this work, the electrochemical oxygen transfer reaction (EOTR) was studied in more details. Hydroxyl radicals are one of the most important intermediates produced during EOTR. Their formation depends on the electrode material as well as the potential and implies different mechanisms and reactivities. At low potential, hydroxyl radicals are produced by the dissociative adsorption of water followed by the hydrogen discharge. This reaction is assumed to take place at electrocatalytic material like platinum. When the potential is higher than 1.23 V vs SHE (thermodynamic potential of water decomposition in acidic medium), the water discharge occurs, leading to the formation of hydroxyl radicals. From this, two classes of materials can be distinguished: active and non active electrodes. It is well established that at active electrodes, a strong interaction with hydroxyl radicals exists and the EOTR occurs via the formation of an higher oxide. In contrast, at non active electrodes, the substrate does not participate in the process and the oxidation is assisted by hydroxyl radicals that are weakly adsorbed at the electrode surface. Assuming that hydroxyl radicals are the main intermediates of the reaction, a model was developed to predict the organic compounds oxidation (COD-ICE model). Another part of this work deals with the validation of the theoretical models. In addition to the COD-ICE model, another model describing the oxidation reaction in terms of flux of both hydroxyl radicals and organics (γ-ν model) was developed. Both models permitted on the one hand to predict and describe the evolution of the oxidation reaction, and on the other hand to confirm the role of hydroxyl radicals. Moreover, it was possible to perform, depending on the conditions of applied current, either a partial oxidation (into intermediates) or a total incineration (into CO2) of the organic compound. The models, developed for a one-compartment electrochemical flow cell, were also validated in both a two-compartments cell and a new electrochemical cell, called turbine cell. In addition, the development of this cell allowed us to work with well established hydrodynamic conditions. The wide potential window that exists at boron-doped diamond electrode (BDD) theoretically allows the formation of free hydroxyl radicals, whose redox potential is estimated at about 2.6 V (vs SHE). The principal aim of this work was to highlight the presence of hydroxyl radicals at BDD electrode and to study their reactivity. First, we have investigated the production of hydrogen peroxide and the competitive reaction of carboxylic acids, both of which indicated the presence of hydroxyl radicals. Then, spin trapping was performed to detect hydroxyl radicals. This method consists in trapping the radical with an appropriate scavenger to produce a stable adduct, which can be analyzed by different techniques such as electron spin resonance (ESR), UV-visible and liquid chromatography (HPLC) measurements. The spin trapping at BDD electrode was performed through three experiments, viz., the electrolysis of a solution of 5,5-dimethyl- 1-pyrroline-N-oxide (DMPO) or 4-nitroso-N,N-dimethylaniline (p-nitrosoaniline or RNO) and the hydroxylation of salicylic acid using ESR, UV and HPLC analysis, respectively. These results have confirmed the presence and the key role of hydroxyl radicals during oxidative processes at BDD electrode. The hydroxylation of salicylic acid, whose oxidation mechanism is well established and yields to two dihydroxylated isomers (2,3- and 2,5-DHBA), was investigated in more details to study the reactivity of hydroxyl radicals. The results were compared to the reactivity of hydroxyl radicals chemically produced by Fenton reaction and UV-photolysis. The comparison was based on the investigation of the isomer distribution. On the basis of our results and by analogy with chemical and biological results, a mechanism for salicylic acid hydroxylation was proposed.

Fenton‐and Fenton‐like AOPs systems have been utilized for the oxidative degradation of some chlorinated pollutants such as chloral hydrate or 1,1,1‐trichloroethane, and for the treatment of real industrial wastewaters. Both ferrous sulfate (FeSO4 · 7 H2O) and Mohr's salt (NH4)2Fe(SO4)2. 6 H2O have been used as Fe2+ ion sources. With Mohr's salt (MS) the Fenton‐and Fenton‐like reaction has been successfully carried out under acidic (pH 3) and neutral (pH 7) reaction conditions. The new Fenton‐like system utilizes zero‐valent iron (Feo) instead of ferrous sulfate has been applied for the 1,1,1‐trichloroethane and chloral hydrate degradation. Similarly, the application of catechol‐ and hydroquinone‐driven Fenton reaction for the degradation of chloral hydrate under acidic and neutral pH is a new Fenton‐like AOPs approach. The photo‐Fenton‐like reactions such as Fe3+/hν, Fe2+/H2O2/hν, and ferrioxalate system have been also studied for the degradation of chloral hydrate. As an irradiation source a daily light or sun light have been used. In comparison with photoreactor experiments the best system was observed to be Fe3+/hν. In some experiments the influence of standing time prolongation after Fenton reaction on the final degradation efficiency due to hydrolysis of intermediates such as phosgene (CCl2˭O) has also been studied. The Fenton reaction was successfully utilized for the treatment of real industrial wastewaters, in two cases even in plant‐scale applications.