Initial Rate Of Disappearance Research Articles

English

This study aimed at investigating the effect of consortia of three types of indigenous bacteria (Corynebacterium sp., Sphingobacterium gobiense and Kocuria flava) and earthworm (at 5 and 10 earthworms/kg soil) and their combination on the percentage removal of chlorpyrifos from chlorpyrifos contaminated soil in Sudan. Silt soil (Gerf soil) samples were mixed with known concentration of chlorpyrifos (450 mgkg-1) and incubated for various exposure periods (3, 7, 15 and 45 days) with the bacterial consortia alone, low and high densities of earth worm and their combinations under laboratory conditions. Remaining chlorpyrifos residues were measured by gas chromatograph equipped with flame ionization detector. Degradation rates and half-lives were found to follow biphasic model with an initial fast rate of disappearance followed by a second phase of slow disappearance. All treatments caused significant (PE‚0.05) effect on the degradation rates of chlorpyrifos compared to the control. The bacterial consortia alone induced the highest effect (73.83%) on the percentage removal of chlorpyrifos, followed by the bacterial consortia plus high density of earth worm (71.22%). Earth worm alone induced the least effect on the rate degradation of chlorpyrifos (64.27 and 66.49% for the high and low concentrations respectively). Based on this finding indigenous bacterial consortia represent a promising bioremediation agent for treatment of chlorpyrifos contaminated soil and therefore may deserve further investigation under different experimental conditions as well as validation of results under real contaminated soil conditions. Key words: Sudan, earthworm, indigenous bacteria, chlorpyrifos.

Kinetics of the ruthenium‐catalyzed hydrogenation of levulinic acid to γ‐valerolactone in aqueous solutions

Levulinic acid (LA) is an especially promising feedstock for the production of chemicals and biofuels, because it can be prepared from lignocellulosic biomass. Its conversion to γ‐valerolactone (GVL), a fuel additive and precursor to transportation fuels, appears preferential. In this study, a heterogeneous Ru/C catalyst was employed for investigating the hydrogenation reaction of LA to GVL in the aqueous phase in a three‐phase mechanically agitated contactor. To explore kinetics, runs were performed in a chemical‐control regime between the temperatures 323–353 K, H2 partial pressures 0.69–2.07 MPa, initial LA concentrations 4.31–12.93 mmol/L, and catalyst loadings 0.3–0.7 kg/m3. Langmuir‐Hinshelwood‐Hougen‐Watson (LHHW) models were applied to describe the initial rates of LA disappearance. The model, which presumed that surface reaction between non‐dissociatively chemisorbed H2 and LA is limiting, was most suited to describe reaction kinetics. From an Arrhenius plot, it was found that the value of Eact is 68.1 kJ/mol.

Reaction pathways and kinetics of cholesterol in high-temperature water

We investigated the reaction of cholesterol, a model compound for sterols in microalgae, in high-temperature water at 300, 325, and 350°C. Products nearly entirely consisted of cholestadienes, with cholesta-2,4-diene, cholesta-3,5-diene, and cholesta-4,6-diene being the most abundant isomers. Cholesta-3,5-diene was the only primary product, formed via dehydration of cholesterol. Cholesta-2,4-diene and cholesta-4,6-diene likely formed from cholesta-3,5-diene by double-bond migration. We report conversion and product molar yields for each reaction condition. The initial rate of disappearance of cholesterol was first-order with an activation energy of Ea=127±12kJmol−1 and A=108.35±2.41s−1. We used a delplot analysis and mechanistic considerations to develop a reaction network for conditions relevant to hydrothermal liquefaction of microalgae.

The Effects of 16 Weeks of Intensive Cycling Training on Seminal Oxidants and Antioxidants in Male Road Cyclists

To examine the effects of 16 weeks of intensive cycling training on seminal reactive oxygen species (ROS), malondialdehyde (MDA), superoxide dismutase (SOD), catalase, and total antioxidant capacity (TAC) in male road cyclists. Repeated measures design. The Exercise Physiology Laboratory of the Urmia University. Twenty-four healthy nonprofessional male road cyclists (aged 17-26 years) participated in this study. All subjects participated in 16 weeks of intensive cycling training. The semen samples were collected, respectively, at baseline (T1), immediately (T2), 12 (T3), and 24 (T4) hours after the last training session in week 8; immediately (T5), 12 (T6), and 24 (T7) hours after the last training session in week 16; and 7 (T8) and 30 (T9) days after the last training session in week 16. Total antioxidant capacity and SOD were measured by colorimetric assay. The levels of ROS were measured by a chemiluminescence assay. Malondialdehyde levels were measured by thiobarbituric acid reactive substance assay. Catalase was measured by monitoring the initial rate of disappearance of hydrogen peroxide (initial concentration 10 mM) at 240 nm. The levels of seminal ROS and MDA increased (P < 0.008) and remained high after 30 days of recovery. The levels of seminal SOD, catalase, and TAC decreased (P < 0.008) and remained low after 30 days of recovery (P < 0.008). Sixteen weeks of intensive cycling training may have deleterious consequences for spermatozoa and hence may affect sperm healthy parameters in male cyclists.

Kinetics of Aqueous-Phase Hydrogenation of Levoglucosan over Ru/C Catalyst

Bio-oil from biomass fast pyrolysis can be transformed into hydrogen (H2) or alkanes (C1–C6) by aqueous phase processing (APP). Low temperature hydrogenation of the water-soluble portion of bio-oil is a useful intermediate step of APP. In the present work, the anhydrosugar levoglucosan (LG) was selected as a model compound of the bio-oil aqueous fraction. LG hydrogenation was studied in a slurry reactor using heterogeneous Ru/C catalyst. Kinetic data were obtained experimentally in the range of temperatures, 398 to 433 K, H2 partial pressures, 0.69 to 2.07 MPa, initial LG concentrations, 0.6 to 3.1 mM and catalyst loading, 0.5 to 1.5 kg/m3. Langmuir–Hinshelwood–Hougen–Watson (LHHW) kinetics was used for modeling initial rates of LG disappearance. Two kinetic models assuming that surface reaction is rate-controlling reasonably represented the kinetic data. Model 1 assumed competitive adsorption of dissociatively chemisorbed H2 and LG, whereas model 2 was based on competitive adsorption of molecular H2 and LG. However, model II seemed to be not feasible, because of the low activation energy value and the assumption of reaction with molecular H2.

Kinetics of the photocatalytic degradation of methylamine: Influence of pH and UV-A/UV-B radiant fluxes

Adsorption, photolysis and photocatalytic degradation of methylamine (MA) were investigated using titanium dioxide (TiO2) as photocatalyst. The influence of various parameters such as concentrations, irradiation time, pH, UV domain and UV-A/UV-B radiant flux has been studied. Optimum conditions for the complete degradation of MA in water have been identified. By investigating the pH-dependent kinetics, it was found that the neutral species CH3NH2 are more rapidly degraded than their protonated form CH3NH3+ because the OH radicals favourably reacted with the lone-pair electron on the nitrogen atom. The nitrogen atom in MA was photoconverted predominantly into NH4+. No nitrite neither nitrate were detected at pH 3.1 and 5.2 by a contrast of a high production at pH 12. The initial disappearance rates r0 were determined at different UV-A radiant fluxes which could be modelized by the Langmuir–Hinshelwood model. It was shown that the rate constant (k) increases with UV-A radiant flux. The efficiency of different UV-A and UV-B radiant fluxes were compared. Whatever the energy of photons (UV-A or UV-B), the same quantum yield equal to 0.033 was obtained considering the ability of TiO2 to absorb UV-A or UV-B radiation.

Correlation Between Seminal Oxidative Stress Biomarkers and Antioxidants with Sperm DNA Damage in Elite Athletes and Recreationally Active Men

To evaluate the seminal plasma 8-isoprostane, reactive oxygen species (ROS), malondialdehyde (MDA), superoxide dismutase (SOD), catalase, total antioxidant capacity (TAC), and levels of sperm DNA fragmentation in elite athletes and recreationally active men. Prospective design was used for this study. The study was performed in the Exercise Physiology Laboratory of the Urmia University. Fifty-six elite athletes and 52 recreationally active men (18-28 years) participated in this study. All subjects had a semen sampling at baseline. Total antioxidant capacity and SOD activity were measured by colorimetric assay. Levels of ROS were measured by a chemiluminescence assay. Malondialdehyde levels were measured by thiobarbituric acid reactive substance assay. Catalase activity was measured by monitoring the initial rate of disappearance of hydrogen peroxide. Concentration of free 8-isoprostane was measured by enzyme immunoassay method. Sperm DNA fragmentation was evaluated with the terminal deoxynucleotidyl transferase-mediated fluorescein dUTP nick end-labeling assay. Recreationally active men have significantly higher levels of body fat, seminal SOD, TAC, and catalase and lower levels of V[Combining Dot Above]O2max, seminal ROS, MDA, and 8-isoprostane and subsequently lower rate of sperm DNA fragmentation when compared with elite athletes (P < 0.001). Significantly negative correlation was observed between sperm DNA fragmentation with body fat, seminal SOD, catalase, and TAC levels (P < 0.001). Significantly positive correlation was observed between sperm DNA fragmentation with V[Combining Dot Above]O2max, seminal 8-isoprostane, ROS, and MDA levels (P < 0.001). Spermatozoa from recreationally active men may be less susceptible to oxidative stress-induced DNA damage and hence infertility.

Photocatalytic degradation of the Acid Blue 113 textile azo dye in aqueous suspensions of four commercialized TiO2 samples

The apparent first-order rate constant, kapp, of the Acid Blue 113 textile azo dye photocatalytic disappearance in aqueous suspensions of 4 commercialized TiO2 samples (50 m2 g−1-Degussa P25; 54 m2 g− 1-Millennium Chemicals PC50; 250–270 m2 g−1-Sachtleben Chemie Hombikat UV100; 320 m2 g−1-Ishihara ST01) was determined from the decrease in the calibrated 566 nm-absorbance of the supernatant. Under the conditions used (1 liter-batch reactor; water-filtered irradiation from a Philips HPK 125-W high-pressure mercury lamp; [TiO2] = 1 g/L; [dye] = 70 mg/L), the kapp ranking was: UV100 > PC50 > P25 > ST01. The corresponding maximal difference in kapp was roughly equivalent to that caused by adding an optimal dose of H2O2 to the P25 suspension. Taking into account the dye adsorbed amount, qads, in the dark, it is deduced that the recombination rate kr of photogenerated charges was higher for poorly crystallized TiO2 samples, as expected; additionally, a low content of impurities is suggested to be at the origin of the low kr of UV100 relative to ST01. It is also argued that differences in the values of qads divided by the surface area, S, was less due to pores inaccessible to the dye than to thicker layers of surface tightly bound water for the samples with high S. A FTIR study showed that the dye weakly interacted with TiO2 and, however, remained the dominant adsorbed species during the degradation. This latter conclusion was in accord with the fact that the dye initial disappearance rates—directly measured or calculated from kapp—were almost equal, indicating that the intermediate products of degradation did not significantly compete with the remaining dye for active species.

Kinetic analysis of supported Ni-catalyzed CO2/CH4 reactions using photoacoustic spectroscopy

CO2 photoacoustic spectroscopy was employed to analyze kinetically the CO2/CH4 reaction catalyzed by 14 wt% Ni/Al2O3 and 14 wt% Ni/TiO2. The catalytic reaction was carried out in the temperature range of 673-923 K at various partial pressures of CO2 and CH4 (40 Torr total pressure) in a closed-circulating reactor system. The CO2 photoacoustic signal, measured by using a differential photoacoustic cell, was recorded as a function of reaction time. Under these conditions, Al203 and TiO2 used as supports do not promote the reaction as noted by the lack of changes in the CO2 photoacoustic signal. Reactions run in the presence of H2-reduced supported Ni catalysts are associated with significant time dependent changes in the CO2 photoacoustic signal, while processes carried out in the presence of unreduced catalysts do not. Changes in the CO2 photoacoustic signal at early reaction times provide precise data for the rate of CO2 disappearance. The rate of CO2 disappearance is observed to increase with increasing temperature in the range of 673-923 K. Apparent activation energies for CO2 consumption were calculated to be 15.4 kcal mol(-1) for the Ni/Al2O3- and 14.3 kcal mol(-1) for the Ni/TiO2-catalyzed reactions. Reaction orders, determined from initial rates of CO2 disappearance at 873 K, were found to be 0.48 in CH4 and 0.45 in CO2 for the Ni/Al2O3-promoted process, and 0.38 in CH4 and 0.32 in CO2 for the Ni/TiO2-catalyzed reaction. The results of this effort were compared with those reported previously and were used to construct a mechanism for the low pressure CO2/CH4 reaction.

Efficient Sonochemical Degradation of 4-Chlorophenol Catalyzed by Titanium Dioxide Hydrate

Abstract A nanocrystalline anatase hydrate (Titanhydrat-0, TH) is a highly efficient catalyst for low intensity sonochemical degradation of 4-chlorophenol (4-CP). The initial disappearance rate of 4-CP increases by a factor of 95 under the TH dosage of 0.5 g dm−3. After 120 min of ultrasonic irradiation 63% of 4-CP is completely mineralized under the TH dosage of 0.5 g dm−3. However, in homogeneous sonochemical degradation, no mineralization at all occurs. Moreover, we deduce that the process of sonochemical mineralization mainly occurs at the interface region of TH. The process of sonocatalytic degradation is simple and inexpensive, and appears to be a potentially powerful method of remediation of contaminants in water.

Kinetic study of the crosslinking reaction of 1,2‐polybutadiene with dicumyl peroxide in the absence and presence of vinyl acetate

AbstractThe crosslinking reaction of 1,2‐polybutadiene (1,2‐PB) with dicumyl peroxide (DCPO) in dioxane was kinetically studied by means of Fourier transform near‐infrared spectroscopy (FTNIR). The crosslinking reaction was followed in situ by the monitoring of the disappearance of the pendant vinyl group of 1,2‐PB with FTNIR. The initial disappearance rate (R0) of the vinyl group was expressed by R0 = k[DCPO]0.8[vinyl group]−0.2 (120 °C). The overall activation energy of the reaction was estimated to be 38.3 kcal/mol. The unusual rate equation was explained in terms of the polymerization of the pendant vinyl group as an allyl monomer involving degradative chain transfer to the monomer. The reaction mixture involved electron spin resonance (ESR)‐observable polymer radicals, of which the concentration rapidly increased with time owing to a progress of crosslinking after an induction period of 200 min. The crosslinking reaction of 1,2‐PB with DCPO was also examined in the presence of vinyl acetate (VAc), which was regarded as a copolymerization of the vinyl group with VAc. The vinyl group of 1,2‐PB was found to show a reactivity much higher than 1‐octene and 3‐methyl‐1‐hexene as model compounds in the copolymerization with VAc. This unexpectedly high reactivity of the vinyl group suggested that an intramolecular polymerization process proceeds between the pendant vinyl groups located on the same polymer chain, possibly leading to the formation of block‐like polymer. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4437–4447, 2004

Epimer interconversion, isomerization, and hydrolysis of tetrahydrouridine: Implications for cytidine deaminase inhibition

Tetrahydrouridine (THU) is an inhibitor of cytidine deaminase (CDA), the enzyme responsible for the deactivation of ara‐C and other cytidine analogues in vivo, and therefore is capable of improving the therapeutic efficacy of these antitumor agents. In aqueous solution formulations, THU exists as a mixture of epimers differing in stereochemistry of the 4‐OH substituent. The aims of this study were to investigate the interconversion kinetics of the epimers of THU, the CDA inhibitory effects of these epimers, and the stability and degradation mechanisms of THU epimer mixtures in aqueous solution with the ultimate goal of developing optimal conditions for a parenteral formulation of THU. A stability indicating HPLC assay utilizing a derivatized β‐cyclodextrin column was developed to separate the two epimers of THU and to monitor their reversible isomerization to their β‐ribopyranosyl counterparts and their hydrolysis to form N‐glycosidic bond cleavage products. MS and one‐ and two‐dimensional 1H‐ and 13C‐NMR measurements were conducted to identify THU epimers and degradation products and to quantitatively model the degradation kinetics. The interconversion reaction between the two THU epimers is acid catalyzed with a first‐order rate constant for conversion of epimer 11 to epimer 12 of (7.4 ± 0.3) × 10−3 h−1 and an equilibrium constant ([12]/[11] of 1.7 ± 0.1 at pH 7.4 and 25°C. Epimer interconversion was therefore sufficiently slow at pH 7.4 to allow the isolation of each and evaluation of their CDA inhibitory activities utilizing 1% (w/v) mouse kidney homogenates as a source for cytidine deaminase and cytidine as a substrate. Inhibition constants for the two THU epimers (11 and 12) were determined to be 8 ± 1 × 10−7 M and 6.2 ± 0.2 × 10−8 M, respectively. Studies at elevated temperature suggested that THU degradation from epimer mixtures is biphasic with the initial rate of disappearance being acid catalyzed and first order in initial THU concentration, thus ruling out dimerization as a potential reaction mechanism. NMR/MS analyses revealed that the major degradation products included the β‐ribopyranosyl THU isomers (two epimers), the reduced pyrimidinone base (tetrahydrouracil), and various anomers of D‐ribose formed through N‐glycosidic bond cleavage, and the products of subsequent reactions of the base. Kinetic modeling of the data obtained from both HPLC and NMR measurements indicated that in an acidic solution THU β‐ribofuranosyl → β‐ribopyranosyl isomerization is a rapid equilibrium reaction, which proceeds through an intermediate observable in 1H‐NMR, and is followed by slower N‐glycosidic bond hydrolysis. All the reactions between THU, its ribopyranosyl isomers, the intermediate, and the base are acid catalyzed and appear to proceed through the same sugar ring‐opened intermediate (carbinolamine), consistent with previous literature. © 2003 Wiley‐Liss, Inc. and the American Pharmacists Association J Pharm Sci 92:2027–2039, 2003

Degradation of surfactants by hydroxyl radicals photogenerated from hydroxoiron(III) complexes.

The Fe(III)-photoinduced oxidation of anionic lauryl sulfate (LS-) and cationic cetyltrimethylammonium (CTA+) surfactants has been investigated in aqueous solution. Competition experiments using 2-propanol showed that the initial rate of disappearance is proportional to the concentration of the photogenerated HO* radicals scavenged by the surfactants (the degradation of lauryl sulfate involves attack by HO* only) and no direct photoinduced charge-transfer reaction occurs between the Fe(III) species and the surfactant ions. Ageing of the Fe(III) solution did not significantly influence the efficiency of photodegradation in air-saturated systems. Conversion of Fe(III) to Fe(II) in aerated solution reached a steady-state level of ca. 50% after 2 h irradiation. In nitrogen-saturated systems, the rate of surfactant oxidation decreased due to the total reduction of Fe(III). Addition of H2O2 doubled the quantum yield of the disappearance of both detergents as a result of the photo-Fenton reaction. The photoinduced oxidation of both surfactants was most efficient in acidic solutions of pH 2-3, without H2O2, and for the photo-Fenton system; the quantum yields are phi(NaLS) = 0.011, phi(CTAB) = 0.012 without H2O2, and phi(NaLS) = 0.024, phi(CTAB) = 0.027 in the photo-Fenton system with irradiation at 366 nm. For the disappearance of 4 x 10(-4) M detergent, due to the first oxidation step, 4 h of irradiation (at pH 2.6) is sufficient, whereas 100% mineralization of the total organic carbon content requires prolonged photolysis for at least 10 h. The formation of carbon dioxide dramatically accelerated after a 2 h induction period (1 h in the photo-Fenton system), indicating the cleavage of the long hydrocarbon chains to shorter intermediates in the first stage of the mechanism. The following step is total mineralization of these smaller compounds, which were identified as mostly hydroxy acids via GC-MS.

Fourier transform near-infrared and electron spin resonance studies on the crosslinking reaction of liquid carboxylated poly(acrylonitrile-co-butadiene) rubber with dicumyl peroxide in dioxane

The crosslinking reaction of liquid carboxylated poly(acrylonitrile-co-butadiene) [or nitrile rubber (NBR); acrylonitrile = 10 wt %] with dicumyl peroxide (DCPO) was studied in dioxane by means of Fourier transform near-infrared spectroscopy (FT-NIR) and electron spin resonance spectroscopy (ESR). Among the three butadiene units (1,2, cis-1,4, and trans-1,4 units) of NBR, only the pendant vinyl group of the 1,2 unit showed an absorption at 6110 cm−1 from the FT-NIR examination of dioxane solutions of NBR, 1-octene, 3,3-dimethyl-1-butene, trans-2-octene, cis-5-octen-1-ol, poly-cis-1,4-butadiene, and poly-1,2-butadiene. The crosslinking reaction was followed in situ in dioxane by the monitoring of the disappearance of the pendant vinyl double bond with FT-NIR. The initial disappearance rate (R0) of the vinyl group was expressed by R0 = k[DCPO]0.9[NBR]−0.2 (120°C). The overall activation energy of the reaction was calculated to be 20.7 kcal/mol. This unusual rate equation suggests unimolecular termination due to degradative chain transfer and depressed reactivity of the vinyl group caused by crosslinking. ESR study of the reaction mixture revealed that an allyl-type polymer radical was formed in the reaction, and its concentration increased with time and was then saturated. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2095–2101, 2003

Effect of high hydrostatic pressure on the steady-state kinetics of tryptic hydrolysis of β-lactoglobulin

The rate of hydrolysis of β-lactoglobulin (genetic variant B) by trypsin in aqueous solution at pH of 7.6 and ionic strength 0.08 M (NaC1) at 25.0 °C increased with increasing hydrostatic pressure. At constant pressure (ambient, 100, 150 and 250 MPa studied), the initial rate of disappearance of β-lactoglobulin B could be analyzed using Michaelis–Menten kinetics (five initial substrate concentrations ranging from 0.11 to 0.88 mM used at each pressure). The over-all catalytic efficiency (ratio between catalytic constant kc and Michaelis constant Km) increased by a factor of 103 at 250 MPa compared with ambient pressure. While kc increased only for pressures up to 100 MPa, corresponding to an initial pressure-melted state (factor of 102 up to 100 MPa) with no further increase at higher pressure, Km continuously decreased up to 250 MPa, corresponding to a binding volume of −37 ml mol−1 of β-lactoglobulin to trypsin. Thus, the enhanced digestibility of β-lactoglobulin at elevated pressure is the result of a volume decrease during the association process and a volume decrease during the catalytic step. Pressure treatment of whey concentrates should be considered as an alternative processing technology for reduction of allergenicity of whey products.

The kinetics of the reduction of NO to N 2 by reaction with particles of Fe

The reaction 3NO+2Fe→Fe2O3+3/2N2(I)is important for converting the pollutant NO into harmless N2 in combustion systems, particularly fluidized beds. Its initial rate has been measured thermogravimetrically at 1 bar and 500–900 °C for particles of Fe sufficiently small for the reaction to be kinetically controlled. A detailed analysis of the measured rates for a variety of [NO] and two different particle sizes indicates that the measured initial rate of disappearance of NO fits well to r=α8[NO(1+(α8NOβ8)1/2)2per unit surface area. The most likely mechanism involves dissociative adsorption of NO, followed by the desorption of N2 and also O2− ions diffusing into the particle. There is another rate-law, which is almost as good, with the measured r=α9[NO]0.68. This rate expression could originate from NO adsorbing according to the Freundlich isotherm, followed by surface reaction to give N2 and O2−. Kinetic parameters together with activation energies and so on are all measured. Reaction I has a second stage, whose rate is determined by the amount of oxide product around each particle.

New industrial titania photocatalysts for the solar detoxification of water containing various pollutants

A new series of titania industrial photocatalysts have been elaborated by Millennium Inorganic Chemicals and were denoted Millennium-PC/10, PC/25 and PC/50 with respective specific surface areas equal to 11, 23 and 43m2g−1. Their photocatalytic activities have been determined and compared in the solar pilot CPC-photoreactor at the Plataforma Solar de Almeria (PSA) (Spain) in the photocatalytic degradation of four different representative pollutants (4-chlorophenol, nitrobenzene, 2-chlorobenzoic acid and hydrobutanedioic (malic) acid), whose degradation pathways had previously been elucidated in laboratory experiments with artificial light, using titania Degussa P-25 as a reference photocatalyst. The study concerned the influence of (i) the nature of organic pollutants, (ii) the surface area and (iii) the concentration of suspended TiO2. The affinity of the pollutants for TiO2 and the presence of heteroatoms in the reactant molecules intervened on the activities of Millennium-PCs when compared to Degussa P-25. The higher the affinity of the organic pollutants for titania, the higher the efficiency of Millennium-PC/10 photocatalyst calibrated on the initial rate of pollutant disappearance. The degradation pathways were found similar for both photocatalysts and the primary steps of the degradation for the different types of molecules were discussed.4-Chlorophenol (4-CP), a model pollutant for waste waters, was then chosen for the study of the influence of the surface areas and of the concentration of Millennium-PC photocatalysts. The initial apparent rate constants of 4-CP degradation in presence of all Millennium-PC catalysts were all higher than that obtained with Degussa P-25. When choosing the total organic carbon (TOC) disappearance rate as an overall kinetic parameter, Millennium-PC/10 and PC/25 appeared as less active than Degussa P-25, with longer solar exposures (by about 10%) necessary to obtain a total mineralisation. However, Millennium-PC/50 resulted as the best catalyst in all cases. The optimal slurry concentration (gl−1) has been determined for each Millennium TiO2 sample.While the optimum of Degussa P-25 had previously been found equal to 0.2gl−1, higher amounts of Millennium-PC samples were required. A twice higher concentration (0.4gl−1) increased the activities by factors equal to 1.2 and 1.5 for Millennium-PC/50 and PC/10, respectively. The rate constants of disappearance of intermediates and of TOC were quantitatively affected by factors in agreement with a multiple consecutive reactions model. In any case, titania Millennium-PC/50 appeared as the best catalyst among all those tested, including Degussa P-25.

Effects of pH, Temperature and Various Anions on Thiourea Disappearance in Aqueous Media with Titanium Dioxide Under UV-Irradiation. Photomineralization Kinetics

Disappearance of thiourea in aqueous suspensions of TiO2 or ZnO occurs under near-UV irradiation. The effects of some parameters such as initial concentration of thiourea, temperature, pH and common inorganic anions were examined. The results indicate that the process follows the Langmuir-Hinshelwood type kinetics. In the presence of anions such as nitrates, chlorides and sulfates, the initial disappearance rate of thiourea at pH 6 drops. It is found that the initial rate of thiourea disappearance increases when temperatue of reaction mixture increases. Finally, kinetics of thiourea photomineralization to nitrite, nitrate, sulfite and sulfate are established.

Effects of Amount and Source of Fat on the Rates of Lipolysis and Biohydrogenation of Fatty Acids in Ruminal Contents

Because the percentage loss of unsaturated fatty acids across the rumen has varied considerably in previous in vivo studies, we conducted five experiments to identify potential factors that might affect the in vitro rates of lipid lipolysis and biohydrogenation in ruminal contents. The factors examined included the amount of fat added to the substrate, the source of added fat, the diet fed to the donor fistulated cow, and the time of collection of inoculum from the donor cow. Lipolysis and biohydrogenation were expressed as the rates of disappearance of neutral lipid and unsaturated fatty acids, respectively, from the culture contents over time using a first-order model. The rate of lipolysis of soybean oil declined from 44%/h to less than 30%/h as the percentage of soybean oil in the culture substrate increased from 2 to 10%. The overall rate of biohydrogenation of C18:2 was 14.3%/h, but declined 1.2%/h for each percentage unit increase in C18:2 added to the substrate. Compared with C18:2, the rates of biohydrogenation of C18:1 were generally lower (averaged 3.6%/h) for all fat sources. The rate of biohydrogenation of C18:2 in soybean oil was not affected by the amount of grain or fat fed to the donor cow, or the time after feeding that ruminal inoculum was collected. Based on these findings, high linoleic acid concentrations in the diet would possibly reduce biohydrogenation and increase the postruminal flow of this unsaturated fatty acid. Also, lipolysis may vary considerably due to amount and source of lipid added to the diet, but this has little influence on the initial disappearance rates of linoleic or oleic acids from ruminal contents.

Matrix Metalloproteinases Cleave Tissue Factor Pathway Inhibitor: EFFECTS ON COAGULATION

Matrix Metalloproteinases Cleave Tissue Factor Pathway Inhibitor: EFFECTS ON COAGULATION