Oxidation of cod phospholipids in liposomes: Effects of salts,pH and zeta potential

This work examines how different salts and pH influence both the zeta potential and the lipid oxidation rate of liposomes made from cod phospholipids. The rate of Fe²⁺‐induced lipid oxidation was measured by consumption of dissolved oxygen by liposomes in a closed vessel. Cations (Na⁺, K⁺, Ca⁺, Mg⁺) did not influence the rate of oxidation in the tested range [ionic strength (I) 0–0.14 M). Among the tested anions, sulphates and nitrates did not significantly change the oxygen uptake rate, but chlorides (KCl, NaCl, CaCl₂) reduced the oxidation rate down to approximately 45%, and dihydrogen phosphate down to 14%, when I = 0.14 M. The effect of Cl^? and H₂PO4₄^? was additive. Addition of salts increased the zeta potential of the liposomes, divalent cation salts even resulted in a positive zeta potential. When the liposomes contained different concentrations of chlorides, a linear relationship between oxygen uptake rate and zeta potential was observed. When phosphate was added, the oxygen uptake rate was not related to the changes in zeta potential. The decrease in pH was followed by an increase in zeta potential. The oxygen uptake rate did not change significantly at different positive zeta potentials (pH <3). When the zeta potential was negative, the oxygen uptake rate was influenced by the zeta potential and may also be influenced by iron solubility. Absolute values of the zeta potential alone cannot be used to predict oxidation rates.     

Kinetics of vanillin oxidation

Vanillin can be produced by oxidation of kraft lignin, with air, in alkaline medium. The optimal conditions for vanillin production strongly depend on pH and temperature. This paper addresses the effect of temperature and pH on vanillin degradation by oxidation. Experiments were carried out in a wide range of vanillin concentration, oxygen partial pressure, temperature and pH. Simple models are proposed to explain the observed rate of vanillin consumption under conditions of high alkalinity (pH>12) and lower alkalinity (pH<12). At pH>12,the reaction rate of vanillin oxidation is first order in dissolved oxygen concentration [O₂] and in vanillin concentration [C], i.e., (?r_C) ∝[O₂][C]; at pH<12, the rate is zero order in oxygen concentration and second order in vanillin concentration, i.e., (?r_C)∝f(pH)[C]².     

Ozone treatment of textile effluents and dyes: effect of applied ozone dose,pH and dye concentration

The ozonation of wastewater supplied from a treatment plant (Samples A and B) and dye‐bath effluent (Sample C) from a dyeing and finishing mill and acid dye solutions in a semi‐batch reactor has been examined to explore the impact of ozone dose, pH, and initial dye concentration. Results revealed that the apparent rate constants were raised with increases in applied ozone dose and pH, and decreases in initial dye concentration. While the color removal efficiencies of both wastewater Samples A and C for 15 min ozonation at high ozone dosage were 95 and 97%, respectively, these were 81 and 87%, respectively at low ozone dosage. The chemical oxygen demand (COD) and dissolved organic carbon (DOC) removal efficiencies at several ozone dose applications for a 15 min ozonation time were in the ranges of 15–46% and 10–20%, respectively for Sample A and 15–33% and 9–19% respectively for Sample C. Ozone consumption per unit color, COD and DOC removal at any time was found to be almost the same while the applied ozone dose was different. Ozonation could improve the BOD₅ (biological oxygen demand) COD ratio of Sample A by 1.6 times with 300 mg dm^?3 ozone consumption. Ozonation of acid dyes was a pseudo‐first order reaction with respect to dye. Increases in dye concentration increased specific ozone consumption. Specific ozone consumption for Acid Red 183 (AR‐183) dye solution with a concentration of 50 mg dm^?3 rose from 0.32 to 0.72 mg‐O₃ per mg dye decomposed as the dye concentration was increased to 500 mg dm^?3. © 2002 Society of Chemical Industry     

Effects of membrane charges and hydroperoxides on Fe(II)-supported lipid peroxidation in liposomes

The processes in producing a lag phase in Fe²⁺-supported lipid peroxidation in liposomes were investigated. Incorporation of phosphatidylserine (PS) or dicetyl phosphate (DCP) into phosphatidylcholine [PC(A)] liposomes, which have arachidonic acid, produced a marked lag phase in Fe²⁺-supported peroxidation, where PS was more effective than DCP. Phosphatidylcholine dipalmitoyl [PC(DP)] with a net-neutral charge was still effective in producing a lag phase, though weak. Increasing concentrations of PS, DCP, and PC(DP) prolonged the lag period. Initially after adding Fe²⁺, slight oxygen consumption occurred in PC(A)/PS liposomes including hydroperoxides, followed by a lag phase. An increase in the hydroperoxide resulted in a shortening of the lag period. The initial events of Fe²⁺ oxidation accompanied by oxygen consumption were dependent on the hydroperoxide content, but significant changes in diene conjugation and hydroperoxide levels at this stage were not found. The molar ratios of both dis-appeared Fe²⁺ and consumed O₂ to preformed hydroperoxide in liposomes with or withouttert-butylhydroxytoluene were constant, regardless of the different amounts of lipid hydroper-oxides. The antioxidant completely inhibited the propagation of lipid peroxidation in the lipid phase, following a lag phase. In a model system containing 2,2′-azobis (2-amidinopropane) dihydrochloride, Fe²⁺ were consumed. We suggest that Fe²⁺ retained at a high level on membrane surfaces play a role in producing a lag phase following the terminating behavior of a sequence of free radical reactions initiated by hydroperoxide decompositin, probably by intercepting peroxyl radicals.     

射流曝气-压力式接触氧化法耗氧供氧特性研究

研究了射沆曝气-压力式接触氧化法的耗氧特性,分析了压力、气水比、溶解氧、耗氧速率、容积负荷等的相互关系。研究表明,射流曝气可有效提高游离微生物活性,压力可显著提高水中平衡溶解氧浓度,但对耗氧速率无直接影响,在一定的溶解氧范围内,同等负荷下耗氧速率仅取决于水中的平衡溶解氧浓度。     

Oxalate Ion Decomposition under UV Light from Low Pressure Mercury Vapor Lamps

Kinetics of oxalate ion decomposition under UV light from low pressure mercury vapor lamps (LPMVL) was studied in a batch reactor. The effects of UV light intensity (1.38×10^?6 to 5.27×10^?6 EL^?1s^?1, where E: Einstein or 1 mole of photons), temperature (15?35°C), initial oxalate concentration ((2.05?21.1)?×?10^?5 M), initial pH (5.45?8.94) and alkalinity (0–50 mg L^?1 as CaCO₃) on the photodecomposition kinetics of oxalate in de-ionized water were investigated. Oxalate decay followed split-rate pseudo-first-order kinetics. The decay rate constants decreased with increasing initial oxalate concentration, initial pH, alkalinity and temperature, but increased with UV light intensity. Solution pH increased during oxalate decomposition and reached a plateau as oxalate reached the analytical detection limit in de-ionized water. Addition of carbonate alkalinity virtually eliminated the pH profile. Time-dependent profiles for non-purgeable organic carbon (NPOC) and total carbon (TC) showed that the carbon not accounted for in NPOC is likely to have been converted to CO₂. The pH profile of oxalate decay was estimated using closed system carbonate equilibrium analysis. The dissolved oxygen (DO) utilization during oxalate decay ranged between 0.3–0.8 mol O₂ / mol oxalate. The effect of DO and the decay of natural dissolved organic carbon (DOC) were also explored. Natural DOC retarded oxalate photodecomposition. The decay rate constants were slightly lower in the absence of DO.     

Effects of reaction conditions on laccase‐catalyzed α‐naphthol polymerization

Enzymatic oxidative polymerization of α‐naphthol was carried out batch‐wise with the laccase enzyme, produced by Trametes versicolor (ATCC 200801). The polymerization reaction was conducted in a closed, temperature controlled system containing acetone (solvent) and sodium acetate buffer for pH control. The effects of the organic solvent (acetone) composition, monomer (α‐naphthol) and enzyme concentrations, buffer pH and temperature on the polymerization rate were investigated with respect to initial reaction conditions and depletion rate of dissolved oxygen. The optimum acetone composition, pH, monomer, dissolved oxygen and enzyme concentrations were determined as 50% (v/v), 5, 3409 gm⁻³, 20.3 gm⁻³ and 0.173 U cm⁻³, respectively; these values provided the most desirable conditions for initial reaction rate. Temperature rise supported the rate increase up to 37 °C, after which the rate tended to be stable due to a drop in dissolved oxygen concentration. The product polymer, poly(α‐naphthol), with an average molecular weight of 4920 Da was soluble in common organic solvents. © 2000 Society of Chemical Industry     

Behavior of cellulose graft copolymer towards persulphate oxidation. III. Poly(acrylonitrile) graft copolymers

Cotton cellulose was graft copolymerized with poly(acrylonitrile) to different levels. The copolymers so obtained together with the nongrafted cellulose were oxidized at different pH's (4–10) and temperatures (50–70°C) with potassium persulphate. The oxidation reaction was studied with respect to oxygen consumption, mass loss, and changes in copper number and carboxyl content of the cellulosic materials. It was found that the rates of oxidation at pH 4 for the copolymers are substantially higher than that of the nongrafted cellulose and the rate of oxidation is higher the higher the level of grafting. The reverse is the case at pH 10. The mass loss increases as the oxygen consumption increases irrespective of the substrate used and the pH employed. The magnitude of the mass loss is substantially lower in the case of grafted cellulose than in the case of nongrafted cellulose. The cellulosic copolymers with higher graft levels show lower mass loss than those having lower graft levels. However, the copper number and carboxyl content of the oxidized grafted cellulose are higher than those of the nongrafted cellulose at the same oxygen consumption. It is believed that the presence of poly(acrylonitrile) graft in the molecular structure of cellulose impedes cellulosic chain scission without necessarily preventing oxidation of cellulose hydroxyls.     

Electrosynthesis of ferrate in a batch reactor at neutral conditions for drinking water applications

We report on the electrochemical generation of ferrate species in a batch reactor at neutral conditions (pH ～7) using boron‐doped diamond (BDD) electrodes and Fe (III) salts for applications in drinking water treatment. The impact of several relevant variables, including current density (5–55 mA cm^?2), pH (5–8), and type and concentration of the dissolved iron salts on the production of ferrates were examined. In addition, linear sweep voltammetry (LSV) studies were conducted using buffered electrolytes with and without the presence of iron (III) to decouple the parasitic oxygen evolution reaction. The LSV measurements in the presence of iron (III) and with a neutral electrolyte exhibit oxidation peaks centered ～2.0 V (versus SHE), indicating the production of ferrates at this pH. The rate of ferrate generation is not strongly affected by the pH condition (≤ 20 %); however, current density and the source of iron were found to have a higher impact on the production rate of ferrates. The efficacy of the process was higher using FeCl₃ instead of other sources of iron such as Fe₂O₃ and FeO(OH). The batch reactor results were successfully interpreted by a simple model that considered the kinetics of the ferrate generation and degradation reactions.

     

Application of experimental design to the formulation of glucose oxidase encapsulation by liposomes

Fractional factorial screening design and response surface methodology were applied to optimize the entrapment of glucose oxidase in liposomes by the dehydration–rehydration vesicle (DRV) method. Phosphatidylcholine from different sources, cholesterol:phosphatidylcholine (Ch:PC) and enzyme:lipid (E:L) ratios, buffer pH, sonication frequency and trehalose concentration were the parameters selected for this study. The type of phosphatidylcholine was found to be the most important factor followed by the trehalose concentration, Ch:PC ratio, sonication frequency and E:L ratio. The pH did not play an important role in the response. By treating liposomes with trehalose, as cryoprotectant, the activity of entrapped enzyme decreased by 16%. Two of the factors (cholesterol:phosphatidylcholine and enzyme:lipid ratios) were further studied in a 3² central composite design. The optimized liposomal formulation with an entrapment efficiency of 24% was obtained for egg yolk PC with Ch:PC and E:L ratios of 0.95 and 14.69, respectively, at pH 6 and applying a sonication frequency of 150 W. Copyright © 2004 Society of Chemical Industry     

Electrochemical determination of dissolved oxygen based on three dimensional electrosynthesis of silver nanodendrites electrode

In this paper, a highly sensitive electrochemical sensor for dissolved oxygen was prepared. A glassy carbon electrode was modified with silver nanodendrites that were synthesized by electrochemical deposition on the electrode without the use of a surfactant or template. The electrode displayed efficient electrocatalytic reduction of dissolved oxygen to form hydroxy ions via a four-electron reduction pathway, and a significant decrease in the respective overvoltage. The sensor responded linearly to dissolved oxygen in the 1.0–66.7 μM concentration range, and had a remarkably good sensitivity (0.169 μA μM^?1) at an applied potential of ?300 mV (vs. Ag/AgCl). The lower detection limit was 0.043 μM (at the signal-to-noise ratio of 3), and the response time was 5 s. The good performance was attributed to the enlarged electro-active surface of the dendritic silver nanostructures and to the efficiency of electron transfer between dissolved oxygen and the electrode. The sensor also showed good reproducibility, long-term stability, and relative good selectivity.     

Surfactant Concentration,Antioxidants, and Chelators Influencing Oxidative Stability of Water‐in‐Walnut Oil Emulsions

Effects of surfactant concentration, antioxidants with different polarities, and chelator type on the oxidative stability of water‐in‐stripped walnut oil (W/O) emulsions stabilized by polyglycerol polyricinoleate (PGPR) were evaluated. The formation of primary oxidation products (lipid hydroperoxides) and secondary oxidation products (hexanal) decreased with increasing PGPR concentrations (0.3–1.0 wt% of emulsions). Excess surfactant might solubilize lipid hydroperoxides out of the oil–water interface, resulting in the decreased lipid oxidation rates in W/O emulsions. At concentrations of 10–1000 μM, the polar Trolox demonstrated concentration‐dependent antioxidant activity according to both hydroperoxide and hexanal formation. The antioxidant efficiency of the non‐polar α‐tocopherol was slightly reduced at the higher range of 500–1000 μM based on hydroperoxide formation. Both ethylenediaminetetraacetic acid (EDTA) and deferoxamine (DFO) at concentrations of 5–100 μM reduced the rates of lipid oxidation at varying degrees, indicating that endogenous transition metals may promote lipid oxidation in W/O emulsions. EDTA was a stronger inhibitor of lipid oxidation than DFO. These results suggest that the oxidative stability of W/O emulsions could be improved by the appropriate choice of surfactant concentration, antioxidants, and chelators.     

Inhibition of lipid oxidation by carnosine

The antioxidant activity of carnosine, a β-alanine-histidine dipeptide found in skeletal muscle, was investigated. Carnosine (25 mM) inhibited the catalysis of lipid oxidation by iron, hemoglobin, lipoxidase and singlet oxygen from 35–96% suggesting that the antioxidant mechanism of carnosine is not solely due to metal chelation. Heating the carnosine at 100°C for 15 min had no effect on its ability to inhibit these lipid oxidation catalysts, and the activity of carnosine was not affected over the pH range of 5.1–7.1. Studies using tocopherol-containing liposomes suggest that carnosine and tocopherol do not act synergistically to inhibit lipid oxidation. These data indicate that carnosine has excellent potential for use as a natural antioxidant in processed foods. This paper (90-5-5) is published with the approval of the Director of the University of Kentucky Agricultural Experiment Station.     

OPTIMIZATION OF PHOTOCATALYTIC PROCESS PARAMETERS FOR THE DEGRADATION OF 2,4,6-TRICHLOROPHENOL IN AQUEOUS SOLUTIONS

In the present study, the photocatalytic degradation of 2,4,6-trichlorophenol (2,4,6-TCP) was carried out in a batch reactor under UV light in aqueous solution for 5 h using titania P-25 (surface area 50 m²/g) as a photocatalyst and sodium hypochlorite as an oxidant. Variables studied include catalyst dose (0.25–1.25 g/L), pH (2–6), and concentration of the oxidant (3.06 × 10^?6M–15.3 × 10^?6M). The rate of degradation was studied in terms of changes in concentration of the pollutant and reduction in chemical oxygen demand. The optimal values of operational parameters leading to 2,4,6-TCP abatement were obtained by using response surface methodology. The percent degradation and COD reduction of 2,4,6-TCP was found to increase with increases in the catalyst dose up to the dose of 1.1 g/L, pH in the range of 4–4.5, and oxidant concentration of 9.95 × 10^?6M.     

Corrosion of tin in aqueous solutions of mono-, Di- and trichloroacetic acids

The corrosion behaviour of tin in stagnant mono-, di- and trichloroacetic acids solutions in the pH range 1–6 and at concentrations 4.0 to 5 × 10^?4 M was investigated. The results indicate behaviour that is generally the same but there is some dependence on the acid concentration and the pH value. In 4.0 to 10^?2 M solutions, the corrosion rate (W) increased with increasing acid concentration and decreasing pH value from 1 to 4 as follows: log W=a+b log C, where b=0.70, 0.42 and 0.35 for tri-, di- and mono-chloroacetic acids respectively. At high concentrations 4.0 to 10^?2 M and in the pH range 1–6, the steady state corrosion potential shifted in the negative direction with increase of acid concentration accompanied by an increase in the corrosion rate, indicating that the corrosion process becomes anodically controlled by the complexing of Sn²⁺ ions with organic acid anions and that the order of aggressiveness is mono-<di-<trichloroacetic acids. In dilute solutions (10^?2 to 5.10^?4 M) in the pH range 1–6 the steady state potential shifted in the noble direction with increase of acid concentration (accompanied by a remarkable decrease in the corrosion rate). Corrosion inhibition in dilute solutions was attributed to film formation on the surface of tin which may result from the hydrolysis of tin species.     

A system for accurate on-line measurement of total gas consumption or production rates in microbioreactors

A system has been developed, based on pressure controlled gas pumping, for accurate measurement of total gas consumption or production rates in the nmol/min range, applicable for on-line monitoring of bioconversions in microbioreactors. The system was validated by carrying out a bioconversion with known stoichiometric relation between gas consumption and substrate conversion, that is, the enzymatic oxidation of glucose to gluconic acid. The reaction was carried out in a stirred microreactor with a working volume of 100 μL, whereby the oxygen consumption was monitored on-line. Subsequently the system was applied to determine the oxygen transfer capacity of the microbioreactor. The dissolved oxygen concentration was measured with an optical dissolved oxygen sensor, which was integrated near the bottom of the reactor. Different stirrer sizes and geometries were investigated for their effect on the mass transfer of oxygen. A maximal k_La of 156±10 h⁻¹, allowing a maximal O₂-transfer rate up to 50 mmol O₂/L/h, was reached which is sufficient to grow cells aerobically in (fed-)batch mode at relatively high biomass concentrations.     

Catalytic wet oxidation of phenol with homogeneous iron salts

The catalytic wet oxidation of phenol has been investigated in a 1 L semi‐batch reactor in the presence of both ferrous and ferric salts. Oxidation reactions follow first‐order kinetics with respect to phenol and half‐order kinetics with respect to dissolved oxygen. The activation energy for the reaction was 44.5 and 48.3 kJ mol^?1 for runs employing Fe³⁺ and Fe²⁺, respectively. Rate constants and induction periods were also similar for both catalysts. This result could be explained by analysing the evolution of iron during the oxidation process. For pH > 2, Fe²⁺ was rapidly oxidized under reaction conditions to Fe³⁺, resulting in a unique catalytic redox system Fe²⁺/Fe³⁺. It was also shown that if pH < 2 the dissolved oxygen was unable to oxidize ferrous ion, resulting in a much slower oxidation rate of phenol. The absence of a redox pair resulted in a complete lack of catalytic activity of the dissolved iron salt. Copyright © 2005 Society of Chemical Industry     

Oxygen consumption upon electrochemically polarised zinc

A Pt microelectrode was used to measure the oxygen consumption by redox reduction (ORR) on electrochemically polarised zinc in the redox competition mode. Zinc was polarised in the active and passive state, using a pH 7 and pH 13 solution, respectively. At pH 7, the oxygen concentration measured at a distance of 50 μm from the zinc surface, using the Pt microelectrode, is 15–60 % of the bulk oxygen concentration. Therefore, correspondingly, the oxygen consumption by zinc (due to ORR) is 40–85 % of the bulk oxygen concentration. At pH 13, where zinc undergoes passivation, the oxygen consumption by zinc is 70–80 % of the bulk oxygen concentration. The ORR rate on the surface of zinc passive films (ZnO/Zn(OH)₂) is thus significant when compared to that on bare/actively corroding zinc. The influence of the electrode kinetics of zinc corrosion, on oxygen diffusion towards the metal surface has been investigated in this study.     

The effect of solids on the electrochemical treatment of olive mill effluents

The electrochemical oxidation of an olive mill effluent over Ti–Pt anodes was studied. The effluent had an average total chemical oxygen demand (COD) value of 234 g L^?1, soluble COD of 61 g L^?1, soluble phenolic content 3.4 g L^?1, total solids of 80 g L^?1 and pH = 5.1. Experiments were conducted in a 10 L vessel with the effluent recirculating at 1 L s^?1. The applied current was varied between 5 and 20 A, the salinity between 1 and 4% NaCl, and experiments were performed with the effluent diluted with water to achieve the desired initial concentration. Emphasis was given to the effect of the presence of solids as well as of varying operating conditions on process performance as assessed in terms of COD, color and phenols removal. In general, degradation of phenols occurred relatively fast with conversion increasing with increasing applied current and decreasing initial organic loading and this was accompanied by low COD removal levels and moderate decolorization. The presence of solids had practically no effect on phenols removal, which, in most cases, was complete in less than about 180 min of reaction. However, oxidation in the presence of solids resulted in a substantial solid fraction being dissolved and this consequently increased sample color and the soluble COD content. The solid content typically found in olive mill effluents may partially impede its treatment by electrochemical oxidation, thus requiring more severe operating conditions and greater energy consumption. Copyright © 2007 Society of Chemical Industry     

Nitrification of fertilizer wastewaters in a biofilm reactor

The nitrification characteristics of fertilizer wastes were investigated in a biofilm system using a submerged aerated filter. The attachment of biomass on packing media was studied. Supplement of organic carbon in the form of glucose and yeast extract enhanced biofilm formation although the nitrifiers did not require organic carbon for growth. After an attachment period, continuous operation of the reactor at different loading rates and dissolved oxygen levels was investigated. The maximum achievable nitrification rate was strongly dependent on the dissolved oxygen. In the dissolved oxygen range of 3·2–3·5 mg dm⁻³, the maximum ammonia removal rate was about 0·17 kg NH₄ N m⁻³ day⁻¹. When the dissolved oxygen was increased to 4·9 mg dm⁻³, removal rates as high as 0·41 kg NH₄ N m⁻³ day⁻¹ could be obtained. Nitrite accumulation depended on the bulk nitrogen and dissolved oxygen concentrations.