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Initial Rate (initial + rate)
Terms modified by Initial Rate Selected AbstractsDecorin synthesized by arterial smooth muscle cells is retained in fibrin gels and modulates fibrin contractionJOURNAL OF CELLULAR BIOCHEMISTRY, Issue 2 2007Pamela Y. Johnson Abstract Fibrin serves as a provisional extracellular matrix (ECM) for arterial smooth muscle cells (ASMC) after vascular injury, yet little is known about the effect of fibrin on ECM remodeling by these cells. To address this question, monkey ASMC were grown on fibrin gels and tissue culture (TC) plastic, and proteoglycan synthesis and accumulation were assessed by radiolabeling. Initial rates of 35S-sulfate incorporation into proteoglycans were identical for both groups, but increased proteoglycan accumulation was observed in cultures grown for 48 h on fibrin. This increased accumulation on fibrin was due to reduced proteoglycan turnover and retention within the fibrin gel. Decorin and biglycan constituted 40 and 14% of the total proteoglycan in the fibrin gels, whereas their combined contribution was only 12% in control matrices. To explore whether the retention of decorin in fibrin had any influence on the properties of the fibrin gel, ASMC-mediated fibrin contraction assays were performed. Both de novo synthesis of decorin as well as decorin added during polymerization inhibited the ability of the cells to contract fibrin. In contrast, decorin added exogenously to mature fibrin matrices had no effect on fibrin gel contraction. This study illustrates that decorin derived from ASMC selectively accumulates in fibrin and modifies fibrin architecture and mechanical properties. Such an accumulation may influence wound healing and the thrombotic properties of this provisional pro-atherosclerotic ECM. J. Cell. Biochem. 101: 281,294, 2007. © 2007 Wiley-Liss, Inc. [source] Nested allosteric interactions in the cytoplasmic chaperonin containing TCP-1PROTEIN SCIENCE, Issue 2 2001Galit Kafri Abstract Initial rates of ATP hydrolysis by the chaperonin containing TCP-1 (CCT) from bovine testis were measured as a function of ATP concentration. Two allosteric transitions are observed: one at relatively low concentrations of ATP (<100 ,M) and the second at higher concentrations of ATP. The data suggest that CCT has positive intra-ring cooperativity and negative inter-ring cooperativity in ATP hydrolysis, with respect to ATP, as previously observed in the case of GroEL. It is shown that the relatively weak positive intra-ring cooperativity found in the case of CCT may be due to heterogeneity in its subunit composition. Our results suggest that nested allosteric behavior may be common to chaperone double-ring systems. [source] An Experimental Investigation of Landscape Resistance of Forest versus Old-Field Habitats to Emigrating Juvenile AmphibiansCONSERVATION BIOLOGY, Issue 5 2002Betsie B. Rothermel Larval amphibians,spotted salamander (Ambystoma maculatum), small-mouthed salamander (A. texanum), and American toad ( Bufo americanus ),were added to artificial pools in four dispersal arrays on forest edges. Each array consisted of a pool surrounded by a circular drift fence with pitfall traps and two 2.5 × 50 m enclosures (runs) extending into forest and old-field habitat. Juveniles captured at the circular fences were individually marked and released into either field or forest runs. We determined initial distance, initial rate, total distance, and net distance moved by juveniles in the field versus forest from recaptures in the runs. We also conducted 24-hour dehydration trials to compare the rates of evaporative water loss by spotted and small-mouthed salamanders in field and forest. Initial orientation of spotted salamanders and toads was significantly biased toward forest. Orientation of small-mouthed salamanders did not differ significantly from random expectations. The avoidance of open-canopy habitat by juvenile American toads in particular indicates that predictions of dispersal behavior based on adult habitat use may be misleading. Spotted salamanders moved almost four times farther and toads more than three times farther into the forest than into the field, and recapture rates of both species were much lower in the field. We attribute the lower recapture rates and shorter distances moved in the field to higher mortality due to desiccation or an abundance of predators. Juvenile spotted and small-mouthed salamanders experienced greater evaporative water loss in the field. Our data on movement behavior and dehydration rates suggest that old-field habitats offer greater landscape resistance to dispersing juveniles of some species. Thus, forest fragmentation is likely to reduce dispersal rates between local populations of these three species, with potentially negative consequences for population persistence in altered landscapes. Resumen: Utilizamos un enfoque experimental para investigar los efectos de la composición del paisaje sobre el éxito inicial de dispersión de anfibios juveniles. Colcamos larvas de anfibios (salamandras manchadas [Ambystoma maculatum] y A. texanum y sapo americano [Bufo americanus] ) en estanques artificiales en cuatro secuencias de dispersión en bordes de bosque. Cada secuencia consistió de un estanque rodeado por un cerco circular con trampas de fosa y dos encierros (corridas) de 2.5 × 50 m que se extendían hacia el hábitat de bosque y de campo viejo. Los juveniles capturados en los cercos circulares fueron marcados individualmente y liberados en las corridas de bosque o de campo. A partir de recapturas en las corridas, determinamos la distancia inicial, la tasa inicial, las distancia total y la distancia neta recorrida por juveniles en el campo versus el bosque. También realizamos pruebas de deshidratación de 24 horas para comparar las tasas de pérdida de agua por evaporación en salamandras en el campo y el bosque. La orientación inicial de Ambystoma maculatum y Bufo americanus estuvo significativamente sesgada hacia el bosque. La orientación inicial de A. texanum no fue significativamente diferente de las expectativas aleatorias. La evasión del hábitat abierto en particular por juveniles de sapo americano indica que las predicciones del comportamiento de dispersión basadas en el uso del hábitat por adultos pueden llevar a conclusiones erróneas. Las salamandras manchadas se movieron cuatro veces mas lejos y los sapos más de tres veces más lejos dentro del bosque que dentro del campo, y las tasas de recaptura de ambas especies fueron mucho menores en el campo. Atribuimos las bajas tasas de recaptura y las distancias menores a la mayor mortalidad debido a la desecación o a la abundancia de depredadores. Los juveniles de las dos especies de salamandras experimentaron mayor pérdida de agua por evaporación en los campos. Nuestros datos del comportamiento de movimiento y las tasas de deshidratación sugieren que los hábitats de campo viejo ofrecen mayor resistencia de paisaje para los juveniles dispersantes de algunas especies. Por tanto, es probable que la fragmentación de bosques reduce las tasas de dispersión entre poblaciones locales de estas tres especies, con consecuencias potencialmente negativas para la persistencia de la población en paisajes alterados. [source] Oxidation of oleuropein studied by EPR and spectrophotometryEUROPEAN JOURNAL OF LIPID SCIENCE AND TECHNOLOGY, Issue 2 2008Evaggelia D. Tzika Abstract The autoxidation at alkaline pH and enzymatic oxidation by mushroom tyrosinase of oleuropein, the dominant biophenol present in the fruits and leaves of Olea europea, was followed by both electron paramagnetic resonance (EPR) and absorption spectroscopy. For comparison, the same oxidation processes were applied to 4-methylcatechol, a simple polyphenol present in olive mill wastewaters. EPR spectra of stable o -semiquinone radicals produced during autoxidation at pH,12 and short-lived o -semiquinone free radicals produced during autoxidation at pH,9.0 or tyrosinase action and stabilized by chelation with a diamagnetic metal ion (Mg2+) were recorded for both polyphenols, and the corresponding hyperfine splitting constants were determined. The UV-Vis spectral characteristics of the oxidation of polyphenols were highly dependent on the type of polyphenol, oxidant type and the pH of the reaction. The kinetic behavior of tyrosinase in the presence of oleuropein and 4-methylcatechol was followed by recording spectral changes at 400,nm (absorption maximum) over time. The tysosinase activity with oleuropein showed a pronounced pH optimum at pH,6.5 and a minor one around pH,8. From the data analysis of the initial rate at pH,6.5, the kinetic parameters Km = 0.34,±,0.03,mM and Vmax = 0.029,±,0.002 ,A400,min,1 were determined for oleuropein. [source] Fermentation characteristics and aerobic stability of grass silage inoculated with Lactobacillus buchneri, with or without homofermentative lactic acid bacteriaGRASS & FORAGE SCIENCE, Issue 4 2001F. Driehuis Aerobic spoilage by yeasts and moulds is a major cause of reduced nutritional value of silage and increases the risk of potential pathogenic microorganisms. Recent studies have shown that inoculation with Lactobacillus buchneri inhibits yeast growth and reduces the susceptibility to aerobic spoilage of various ensiled forages. The aim of this study was to determine whether these effects are retained when L. buchneri is added in combination with homofermentative lactic acid bacteria. In three experiments, silages were produced from perennial ryegrass [240,421 g kg,1 dry matter (DM)] inoculated with L. buchneri or L. buchneri plus a mixture of Pediococcus pentosaceus and Lactobacillus plantarum (inoculant PL). Uninoculated silage and silage inoculated with PL alone served as controls. Silages were examined for pH and DM loss in the course of ensilage and chemical and microbiological composition and aerobic stability after 3,4 months. L. buchneri plus PL and PL alone increased the initial rate of pH decline. L. buchneri alone and L. buchneri plus PL enhanced aerobic stability and, in general, reduced yeast and mould counts. In addition, these inoculants increased the final pH and DM loss and the concentrations of acetic acid and 1,2-propanediol (or propionic acid and 1-propanol instead of 1,2-propanediol), and decreased the concentration of lactic acid. The effects of L. buchneri on fermentation products increased with decreasing DM content. In silages of less than 270 g kg,1 DM, L. buchneri increased the ammonia-N concentration. It is suggested that this was associated with the relatively high final pH resulting from the high metabolic activity of L. buchneri in these silages. [source] Sensitivity of the 2-oxoglutarate carrier to alcohol intake contributes to mitochondrial glutathione depletionHEPATOLOGY, Issue 3 2003Olga Coll The mitochondrial pool of reduced glutathione (mGSH) is known to play a protective role against liver injury and cytokine-mediated cell death. However, the identification of the mitochondrial carriers involved in its transport in hepatocellular mitochondria remains unestablished. In this study, we show that the functional expression of the 2-oxoglutarate carrier from HepG2 cells in mitochondria from Xenopus laevis oocytes conferred a reduced glutathione (GSH) transport activity that was inhibited by phenylsuccinate, a specific inhibitor of the carrier. In addition, the mitochondrial transport of GSH and 2-oxoglutarate in isolated mitochondria from rat liver exhibited mutual competition and sensitivity to glutamate and phenylsuccinate. Interestingly, the kinetics of 2-oxoglutarate transport in rat liver mitochondria displayed a single Michaelis-Menten component with a Michaelis constant of 3.1 ± 0.3 mmol/L and maximum velocity of 1.9 ± 0.1 nmol/mg protein/25 seconds. Furthermore, the initial rate of 2-oxoglutarate was reduced in mitochondria from alcohol-fed rat livers, an effect that was not accompanied by an alcohol-induced decrease in the 2-oxoglutarate messenger RNA levels but rather by changes in mitochondrial membrane dynamics induced by alcohol. The fluidization of mitochondria by the fluidizing agent 2-(2-methoxyethoxy)ethyl 8-(cis-2-n-octylcyclopropyl) (A2C) restored the initial transport rate of both GSH and 2-oxoglutarate. Finally, these changes were reproduced in normal liver mitochondria enriched in cholesterol where the fluidization of cholesterol-enriched mitochondria with A2C restored the order membrane parameter and the mitochondrial 2-oxoglutarate uptake. In conclusion, these findings provide unequivocal evidence for 2-oxoglutarate as a GSH carrier and its sensitivity to membrane dynamics perturbation contributes in part to the alcohol-induced mGSH depletion. [source] Kinetic study of hydroperoxide epoxidation of 1-octene in the presence of molybdenum disilicide as a catalyst in a low concentration range of olefinINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 10 2009Yuriy B. Trach The kinetic regularities of the influence of low 1-octene concentrations on its epoxidation by tert -butyl hydroperoxide in the presence of molybdenum disilicide (MoSi2) as a catalyst were investigated. The minimum in the dependence of the initial rate of hydroperoxide consumption on 1-octene concentration was observed. The kinetic scheme of epoxidation, which includes the competition between hydroperoxide and olefin for the catalytic active centers, was proposed. The equation for the reaction rate was derived according to the kinetic scheme. The kinetic parameters of epoxidation were calculated. © 2009 Wiley Periodicals, Inc. Int J Chem Kinet 41: 623,628, 2009 [source] Kinetics and simulations of reaction between safranine- O and acidic bromate and role of bromide thereinINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 9 2002S. B. Jonnalagadda Safranine- O, a dye of the phenazinium class, was found to exhibit intricate kinetics during its reaction with bromate at low pH conditions. Under conditions of excess concentrations of acid and bromate, safranine- O (SA+) initially depleted very slowly (k = (3.9 ± 0.3) × 10,4 M,3 s,1) but after an induction time, the reaction occurred swiftly. Bromide exhibited a dual role in the reaction mechanism, both as an autocatalyst and as an inhibitor. The added bromide increased the initial rate of depletion of SA+, but delayed the transition to rapid reaction. The overall stiochiometric reaction was found to be 6SA+ + 4 BrO3, = 6SP + 3N2O + 3H2O + 6H+ + 4Br,, where SP is 3-amino-7-oxo-2,8-dimethyl-5-phenylphenazine. The fast kinetics of the reaction between aqueous bromine and safranine- O (k = (2.2 ± 0.1) × 103 M,1 s,1) are also reported in this paper A 17-step mechanism, consistent with the overall reaction dynamics and supported by simulations, is proposed and the role of various bromo and oxybromo species is also discussed. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 34: 542,549, 2002 [source] Isothermal kinetics of (E)-4-(4-metoxyphenyl)-4-oxo-2-butenoic acid release from a poly(acrylic acid- co -methacrylic acid) hydrogelJOURNAL OF APPLIED POLYMER SCIENCE, Issue 5 2008Borivoj Adnadjevic Abstract A kinetic study of the release of the drug (E)-4-(4-metoxyphenyl)-4-oxo-2-butenoic acid (MEPBA) from a poly(acrylic acid- co -methacrylic acid) (PAA- co -MA) hydrogel was performed. The isothermal kinetic curves of MEPBA release from the PAA- co -MA hydrogel in bidistilled water at different temperatures ranging from 20 to 40°C were determined. The reaction rate constants of the investigated process were determined with the initial rate, the saturation rate, and Peppas's semiempirical equation. Also, a model-fitting method for the determination of the kinetics model of drug release was applied. The influence of , at the values of the kinetic parameters and the presence of a compensation effect was established. A procedure for the determination of the distribution function of the activation energies was developed. This procedure was based on the experimentally determined relationship between the activation energy and ,. The mechanism of active compound release is discussed. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] Long-Term Outcome of Atrial Fibrillation Ablation: Impact and Predictors of Very Late RecurrenceJOURNAL OF CARDIOVASCULAR ELECTROPHYSIOLOGY, Issue 10 2010ANITA WOKHLU M.D. Long-Term Outcome of AF Ablation. Introduction: Ablation eliminates atrial fibrillation (AF) in studies with 1 year follow-up, but very late recurrences may compromise long-term efficacy. In a large cohort, we sought to describe the determinants of delayed recurrence after AF ablation. Methods and Results: Seven hundred and seventy-four patients with AF (428 paroxysmal [PAF, 55%] and 346 persistent or longstanding persistent [PersAF, 45%]) underwent wide area circumferential ablation (WACA, 62%) or pulmonary vein isolation (38%). Over 3.0 ± 1.9 years, there were 135 recurrences in PAF patients and 142 in PersAF patients. AF elimination was achieved in 61% of patients with PersAF at 2 years after last ablation and in 71% of patients with PAF (P = 0.04). This finding was related to a higher initial rate of very late recurrence in PersAF. From 1.0 to 2.5 years, the recurrence increased by 20% (from 37% to 57%) in PersAF patients versus only 12% (from 27% to 39%) in PAF patients. Independent predictors of overall recurrence included diabetes (HR 1.9 [1.3,2.9], P = 0.002) and PersAF (HR 1.6 [1.2,2.0], P < 0.001). Independent predictors of very late recurrence included PersAF (HR 1.7 [1.1,2.7], P = 0.018) and WACA (HR 1.8 [1.1,2.7], P = 0.018), while diabetes came close to significance. In PAF patients, left atrial size >45 mm was identified as an AF-type specific predictor (HR 2.4 [1.3,4.7], P = 0.009), whereas in PersAF patients, no unique predictors were identified. Conclusion: Late recurrences reduced the long-term efficacy of AF ablation, particularly in patients with PersAF and underlying cardiovascular diseases. (J Cardiovasc Electrophysiol, Vol. 21, pp. 1071-1078) [source] The effect of headspace pressure on the performance of a fluidised-bed bioreactorJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 10 2002J Fung Abstract This study compares the biological performance of three fluidised-bed biological reactors under conditions of different headspace pressures. The application of pressure can have a profound effect on the initial rate of bed growth. However, once the fluidised-bed reaches full expansion, the biological performance at higher pressures is greater than those at lower pressures. There appears to be an almost linear relationship between the application of pressure and the performance of the fluidised-bed biological reactors in removing soluble BOD5. This can be attributed to the increase in the oxygen concentration in the bulk liquid and a greater oxygen penetration depth within the biofilm. © 2002 Society of Chemical Industry [source] Effect of Slaughter Method on Postmortem Changes of Grass Carp (Ctenopharyngodon idella) Stored in IcestiJOURNAL OF FOOD SCIENCE, Issue 5 2005Rodrigo Scherer ABSTRACT: The effect of 2 slaughter methods (immersion in ice-water slurry and electrical stunning followed by ice slurry asphyxiation) on the quality of grass carp (Ctenopharyngodon idella) stored in ice for 20 d was evaluated using sensory and chemical analysis. Electricity immediately stunned the fish and did not induce blood spots in the flesh. Fish killed by electricity showed a faster initial rate of ATP degradation and entered into rigor mortis earlier, but did not show significant differences in the sensory score when compared with fish killed by immersion in ice-water slurry. Thus, no differences were observed in the shelf life of carps between the 2 slaughter methods evaluated. The limit for acceptability of grass carp stored in ice was around 13 to 16 d. Grass carp accumulated more inosine than hypoxanthine. K, Ki, P, Fr, and H values were highly correlated with storage time and with the TFRU sensory scores in both groups; these could be used to assess the freshness quality of grass carp. [source] Lipase-mediated Acidolysis of Fully Hydrogenated Soybean Oil with Conjugated Linoleic AcidJOURNAL OF FOOD SCIENCE, Issue 1 2004J. Ortega ABSTRACT: Interesterification (acidolysis) of fully hydrogenated soybean oil (melting point = 69.9 °C) with conjugated linoleic acid (CLA) was carried out in a batch reactor at 75 °C. Lipases from Candida antarctica, Rhizomucor miehei, Pseudomonas sp., and Thermomyces lanuginosus were used at 5% (wt/wt) of the total substrate load. The lipase from Rhizomucor miehei produced the fastest reaction rates, and the greatest extent of incorporation of CLA residues in acylglycerols was achieved in 12 h. Lipases from C. antarctica and T. lanuginosus produced slower initial rates, and maximum extents of incorporation of CLA residues were achieved in 24 h. The lipase from Pseudomonas sp. produced the slowest initial rate. The corresponding maximum extent of incorporation was reached in 48 h. Differential scanning calorimetry analysis of the triacylglycerol (TAG) fractions produced by C. antarctica, R. miehei, and T. lanuginosus lipases after purification by solid phase extraction showed little variation in melting point (60.4 °C, 62.8 °C, and 60.1 °C, respectively). By contrast, the corresponding TAG fraction produced by the Pseudomonas sp. lipase melted at 48.4 °C. The positional distribution of the TAGs produced by the lipase from Pseudomonas sp. differed appreciably from those produced by the other enzymes. [source] Mathematical modeling of 13C label incorporation of the TCA cycle: The concept of composite precursor functionJOURNAL OF NEUROSCIENCE RESEARCH, Issue 15 2007Kai Uffmann Abstract A novel approach for the mathematical modeling of 13C label incorporation into amino acids via the TCA cycle that eliminates the explicit calculation of the labeling of the TCA cycle intermediates is described, resulting in one differential equation per measurable time course of labeled amino acid. The equations demonstrate that both glutamate C4 and C3 labeling depend in a predictible manner on both transmitochondrial exchange rate, VX, and TCA cycle rate, VTCA. For example, glutamate C4 labeling alone does not provide any information on either VX or VTCA but rather a composite "flux". Interestingly, glutamate C3 simultaneously receives label not only from pyruvate C3 but also from glutamate C4, described by composite precursor functions that depend in a probabilistic way on the ratio of VX to VTCA: An initial rate of labeling of glutamate C3 (or C2) being close to zero is indicative of a high VX/VTCA. The derived analytical solution of these equations shows that, when the labeling of the precursor pool pyruvate reaches steady state quickly compared with the turnover rate of the measured amino acids, instantaneous labeling can be assumed for pyruvate. The derived analytical solution has acceptable errors compared with experimental uncertainty, thus obviating precise knowledge on the labeling kinetics of the precursor. In conclusion, a substantial reformulation of the modeling of label flow via the TCA cycle turnover into the amino acids is presented in the current study. This approach allows one to determine metabolic rates by fitting explicit mathematical functions to measured time courses. © 2007 Wiley-Liss, Inc. [source] The use of simple dynamic mucosal models and confocal microscopy for the evaluation of lyophilised nasal formulationsJOURNAL OF PHARMACY AND PHARMACOLOGY: AN INTERNATI ONAL JOURNAL OF PHARMACEUTICAL SCIENCE, Issue 6 2007Fiona McInnes A range of methods is reported in the literature for assessing hydration and adhesion parameters in the performance of nasal bioadhesive formulations; however, these tests do not always represent the dynamic conditions in the nasal cavity. Lyophilised formulations intended for nasal administration were evaluated using in-vitro tests designed in an attempt to mimic relevant processes in the nasal cavity, and intended to discriminate between different formulations. Initial investigative studies using scanning electron microscopy revealed that the lyophilisate had a highly porous internal structure, expected to provide an ideal porous pathway for re-hydration. Vapour sorption analysis demonstrated substantial weight gain of the lyophilisates on exposure to 95% relative humidity, ranging from 38% to 66%. Agar was used as a synthetic mucosal model designed to provide a standardised quantity of water available for rehydration of the formulations in in-vitro tests. A dynamic adhesion test and a texture analyser sliding test were designed to quantify different aspects of the spreading and adhesion of the hydrating formulations on the synthetic mucosal surface. Examination of the lyophilised formulations using confocal microscopy allowed visualisation and quantification of the initial rate of water ingress into the lyophilisates, which was found to consist of an initial rapid phase, followed by a slower steady-state phase. The results demonstrated that the use of a combination of methods representing the dynamic conditions of the nasal cavity is advisable in order to evaluate a formulation fully and to avoid misleading conclusions. [source] THE ANALYSIS OF STRESS RELAXATION DATA OF SOME VISCOELASTIC FOODS USING A TEXTURE ANALYZER,JOURNAL OF TEXTURE STUDIES, Issue 4 2006H. SINGH ABSTRACT Uniaxial compression test for dough and several commercial products like jello, mozzarella cheese, cheddar cheese, tofu and sausage (cooked and uncooked) was performed using a texture analyzer (TA). Percent stress relaxation (%SR ), k1 (initial rate of relaxation), k2 (extent of relaxation) and relaxation time (RT) were calculated and compared for different products. The TA software was used to convert the raw SR data into a linear form. Constants k1 and k2 were determined from the intercept and slope of the linear data. Higher values of %SR and k2 (90 and 9, respectively) indicated higher elasticity for jello, whereas wheat flour dough samples showed the lowest values (20,30) for %SR and 1 to 2 for k2. The RT and k1 values were not good indicators for differentiating different products based on their viscoelastic behavior. Measurement of RT was limited by the maximum time for which the data were collected, whereas k1, because of its mathematical form, needed careful interpretation. In this study, %SR was found to be a good measure to interpret viscoelasticity of different food samples. [source] Scanning electron microscopy investigations on bis(2-ethylhexyl)phthalate treated Mycobacterium cellsMICROSCOPY RESEARCH AND TECHNIQUE, Issue 8 2006B. Angelova Abstract Comparative investigation of steroid transforming activity and ultrastructural changes of bis(2-ethylhexyl)phthalate (BEHP, phthalate) treated Mycobacterium sp. NRRL B-3805 cells was carried out. Transformation of ,-sitosterol into androstenedione (AD) and androstadienedione (ADD) was performed in phthalate medium by resting cells preincubated in the organic solvent for a period from 3 to 24 h. It was observed that a preincubation greater than 12 h leads to the development of dense formations on the cells surface, reduction in the cell turgor, disruption in the cell walls, and formation of zones with reduced electron density. The preincubation for 24 h causes deeper changes in the cell ultrastructure but the treated cells retain their steroid transforming activity, allowing up to 80% of the substrate to be converted into AD and ADD. A preincubation of the resting Mycobacterium cells in BEHP for 6 h might be recommended as it leads to an achievement of stoichiometrical transformation of the substrate into AD and ADD and slightly higher initial rate of the reaction performed. Microsc. Res. Tech., 2006. © 2006 Wiley-Liss, Inc. [source] Spatial variability in the mineralisation of the phenylurea herbicide linuron within a Danish agricultural field: multivariate correlation to simple soil parameters,PEST MANAGEMENT SCIENCE (FORMERLY: PESTICIDE SCIENCE), Issue 9 2005Jim Rasmussen Abstract The spatial variability in the mineralisation rate of linuron [N -(3,4-dichlorophenyl)- N,-methoxy- N,-methylurea] was studied within a previously treated Danish agricultural field by sampling soils from eleven different plots randomly distributed across an area of 20 × 20 m. The soils were characterised with respect to different abiotic and biotic properties including moisture content, organic matter content, pH, nutrient content, bacterial biomass, potential for mineralisation of MCPA [(4-chloro-2-methylphenoxy)acetic acid] and linuron. Five soils had a potential for mineralisation of linuron, with 5,15% of the added [ring -U- 14C]linuron metabolised to 14CO2 within 60 days at 10 °C, while no extensive mineralisation of linuron was observed in the six remaining soils within this period. A TLC analysis of the methanol-extractable residues showed no development of 14C-labelled metabolites from linuron in any of the samples. Multivariate analysis was conducted to elucidate relationships between the intrinsic properties of single soil samples and initial rate of linuron mineralisation. The analysis indicated that important soil parameters in determining the spatial heterogeneity included the Ctotal/Ntotal ratio, pH and the water-extractable potassium contents, with the first of these highly negatively correlated and the last two highly positively correlated to the initial linuron mineralisation rate. This study shows that enhanced biodegradation of linuron may develop with successive field treatments, but that considerable in-field spatial heterogeneity in the degradation rate still exists. Combined with a parallel enrichment study focused on the underlying microbial processes, the present results suggest that intrinsic soil properties affect the linuron-metabolising bacterial population and thereby determine the spatial variability in the linuron mineralisation activity. Copyright © 2005 Society of Chemical Industry [source] Utilization of inorganic carbon in the edible cyanobacterium Ge-Xian-Mi (Nostoc) and its role in alleviating photo-inhibitionPLANT CELL & ENVIRONMENT, Issue 12 2004B. S. QIU ABSTRACT The present work investigated the inorganic carbon (Ci) uptake, fluorescence quenching and photo-inhibition of the edible cyanobacterium Ge-Xian-Mi (Nostoc) to obtain an insight into the role of CO2 concentrating mechanism (CCM) operation in alleviating photo-inhibition. Ge-Xian-Mi used HCO3, in addition to CO2 for its photosynthesis and oxygen evolution was greater than the theoretical rates of CO2 production derived from uncatalysed dehydration of HCO3,. Multiple transporters for CO2 and HCO3, operated in air-grown Ge-Xian-Mi. Na+ -dependent HCO3, transport was the primary mode of active Ci uptake and contributed 53,62% of net photosynthetic activity at 250 µmol L,1 KHCO3 and pH 8.0. However, the CO2 -uptake systems and Na+ -independent HCO3, transport played minor roles in Ge-Xian-Mi and supported, respectively, 39 and 8% of net photosynthetic activity. The steady-state fluorescence decreased and the photochemical quenching increased in response to the transport-mediated accumulation of intracellular Ci. Inorganic carbon transport was a major factor in facilitating quenching during the initial stage and the initial rate of fluorescence quenching in the presence of iodoacetamide, an inhibitor of CO2 fixation, was 88% of control. Both the initial rate and extent of fluorescence quenching increased with increasing external dissolved inorganic carbon (DIC) and saturated at higher than 200 µmol L,1 HCO3,. The operation of the CCM in Ge-Xian-Mi served as a means of diminishing photodynamic damage by dissipating excess light energy and higher external DIC in the range of 100,10000 µmol L,1 KHCO3 was associated with more severe photo-inhibition under strong irradiance. [source] Modification of polystyrene properties through grafting with N -vinylcarboxamido-2-methylpropane sulfonic acid monomerPOLYMER INTERNATIONAL, Issue 12 2004A Aggour Abstract Polystyrene (PS) possesses good mechanical properties, but its surface is relatively inert and hydrophobic. Grafting of N -vinylcarboxamido-2-methylpropane sulfonic acid (VCMP) is useful to hydrophilize the PS surface. Grafting was performed using benzoyl peroxide (BPO) as an initiator in toluene:methanol solvent mixture (3:1 volume ratio). The influence of the main factors on grafting, such as temperature, time, concentrations of initiator, PS and VCMP, has been studied. The results show that the initial rate of polymerization and percentage of grafting are enhanced by increased temperature. Furthermore, the specific rate constants of the first order reaction/are determined, and the activation energy of the grafting reaction is estimated. The grafting parameters are established and a suitable mechanism of the reaction is proposed. The grafted PS is to characterized through infrared spectra, intrinsic viscosity, thermogravimetric analysis (TGA) and differential gravimetric analysis (DTG). The kinetics of thermal degradation and the order of the thermal stabilities are given. Also the decomposition activation energies of the thermal degradation are determined, and confirm the thermal stabilities of the polymers used. © 2004 Society of Chemical Industry [source] Comparative study of the radiation-induced grafting of styrene onto poly(tetrafluoroethylene- co -perfluoropropylvinyl ether) and polypropylene substrates.POLYMER INTERNATIONAL, Issue 5 2003I: Kinetics, structural investigation Abstract A comparative study has been made of the radiation grafting of styrene onto poly(tetrafluoroethylene- co -perfluoropropyl vinyl ether) (PFA) and polypropylene (PP) substrates, using the simultaneous irradiation method. Effects of grafting conditions such as monomer concentrations, type of solvent, dose rate and irradiation dose on the grafting yield were investigated. Under the same grafting conditions it was found that a higher degree of grafting of styrene was obtained using a mixture of dichloromethane/methanol solvents for PFA and methanol for PP and the degree of grafting was higher in PP than in PFA at all doses. However, the micro-Raman spectroscopy analysis of the graft revealed that, for the same degree of grafting, the penetration depth of the grafted polystyrene into the substrate was higher in PFA than in PP substrates. In both polymers the crystallinity was hardly affected by the grafting process and the degree of crystallinity decreased slightly with grafting dose. The dependence of the initial rate of grafting on the dose rate and the monomer concentration was found to be 0.6 and 1.4 order for PFA and 0.15 and 2.2 for PP, respectively. The degree of grafting increased with increasing radiation dose in both polymers. However, the grafting yield decreased with an increase in the dose rate. The increase in the overall grafting yield for PFA and PP was accompanied by a proportional increase in the penetration depth of the graft into the substrates. Copyright © 2003 Society of Chemical Industry [source] Oxidative polymerization of N -vinylcarbazole in polymer matrixPOLYMER INTERNATIONAL, Issue 6 2001Belkis Ustamehmeto Abstract A new class of soluble conductive poly(N -vinylcarbazole) (PVCz) compounds has been developed by oxidative matrix polymerization of N -vinylcarbazole (NVCz) by Ce(IV) in the presence of poly(ethylene glycol) (PEG). PEG was found to be a more suitable matrix with which to obtain a stable homogenous ternary complex solution when compared with poly(acrylic acid) (PAA) and poly(vinylpyrrolidone) (PVP). The role of PEG, NVCz and Ce(IV) concentration, order of component addition, the structure of the polymer matrix, molecular weight of polymer and the effect of solvent have been investigated. Obtaining soluble PEG,Ce(III),PVCz ternary complexes was shown by cyclic voltammetric measurements, and the initial rate of formation NVCz cation radicals as calculated using UV,visible spectrophotometry. Advantageously with these soluble complexes, conductivities could be measured both in solution and in the solid state. © 2001 Society of Chemical Industry [source] Reaction kinetics of graft copolymerization and thermochemical studies of the degradation of poly(vinyl alcohol) graft copolymerPOLYMER INTERNATIONAL, Issue 3 2001Yassin A Aggour Abstract Poly(vinyl alcohol) (PVA) is a water-soluble and biomedical polymer. 2-Acrylamido-2-methyl-1-propanesulfonic acid was grafted onto PVA using ammonium persulfate as radical initiator. The influences of synthesis conditions such as temperature, concentrations of initiator, PVA and monomer were investigated. Both the initial rate of grafting and the final percentage of grafting were increased by an increase in reaction temperature. The reaction kinetics were studied to determine the rate constants of the first-order reactions. An activation energy of 16.3,kJ,mol,1 was found for the grafting reaction. The graft copolymers were characterized by IR and intrinsic viscosity measurements. A proposed mechanism of the grafting reaction is discussed. Kinetics of the thermal degradation were studied using a thermogravimetric method and the order of thermal stabilities are given. The apparent activation thermodynamic parameters, Ea, ,H*, ,S* and ,G* were determined and correlated to the thermal stabilities of the homo- and grafted polymers. © 2001 Society of Chemical Industry [source] Bacterial contamination of PCA and epidural infusion devicesANAESTHESIA, Issue 7 2009M. Rothwell Summary We prospectively audited the bacterial contamination of re-useable analgesia infusion pumps. In a one-month period, 112 samples from the handset and keypads of our analgesia infusion pumps were cultured for bacterial contamination. Forty-five percent of handset swabs and 46% of keypad swabs grew bacteria; the commonest organism being coagulase-negative staphylococcus. An additional cleaning step using 70% isopropyl alcohol wipes was introduced and the contamination rate was re-audited in 100 samples. The contamination rate was reduced to 6% of handset swabs and 4% of keypad swabs. A high initial rate of bacterial contamination of re-useable analgesia infusion pumps was significantly reduced by the implementation of a simple, additional cleaning procedure. [source] A mechanistic model of the enzymatic hydrolysis of celluloseBIOTECHNOLOGY & BIOENGINEERING, Issue 1 2010Seth E. Levine Abstract A detailed mechanistic model of enzymatic cellulose hydrolysis has been developed. The behavior of individual cellulase enzymes and parameters describing the cellulose surface properties are included. Results obtained for individual enzymes (T. reesei endoglucanase 2 and cellobiohydrolase I) and systems with both enzymes present are compared with experimental literature data. The model was sensitive to cellulase-accessible surface area; the EG2,CBHI synergy observed experimentally was only predicted at a sufficiently high cellulose surface area. Enzyme crowding, which is more apparent at low surface areas, resulted in differences between predicted and experimental rates of hydrolysis. Model predictions also indicated that the observed decrease in hydrolysis rates following the initial rate of rapid hydrolysis is not solely caused by product inhibition and/or thermal deactivation. Surface heterogeneities, which are not accounted for in this work, may play a role in decreasing the hydrolysis rate. The importance of separating the enzyme adsorption and complexation steps is illustrated by the model's sensitivity to the rate of formation of enzyme,substrate complexes on the cellulose surface. Biotechnol. Bioeng. 2010;107: 37,51. © 2010 Wiley Periodicals, Inc. [source] Altering lipase activity and enantioselectivity in organic media using organo-soluble bases: Implication for rate-limiting proton transfer in acylation stepBIOTECHNOLOGY & BIOENGINEERING, Issue 2 2006Chun-Chi Chen Abstract With the hydrolytic resolution of (R,S)-naproxen 2,2,2-trifluoroethyl esters via a partially purified papaya lipase (PCPL) in water-saturated isooctane as the model system, the enzyme activity, and enantioselectivty is altered by adding a variety of organo-soluble bases that act as either enzyme activators (i.e., TEA, MP, TOA, DPA, PY, and DMA) or enzyme inhibitors (i.e., PDP, DMAP, and PP). Triethylamine (TEA) is selected as the best enzyme activator as 2.24-fold increase of the initial rate for the (S)-ester is obtained when adding 120 mM of the base. By using an expanded Michaelis,Menten mechanism for the acylation step, the kinetic analysis indicates that the proton transfer for the breakdown of tetrahedral intermediates to acyl-enzyme intermediates is the rate-limiting step, or more sensitive than that for the formation of tetrahedral intermediates when the enzyme activators of different pKa are added. However, no correlation for the proton transfers in the acylation step is found when adding the bases acting as enzyme deactivators. © 2006 Wiley Periodicals, Inc. [source] Enhanced kinetic extraction of parvovirus B19 structural proteinsBIOTECHNOLOGY & BIOENGINEERING, Issue 3 2002Colleen Sico Abstract Recombinant structural proteins (VP1 and VP2) of the human parvovirus B19 have been expressed simultaneously using the baculovirus expression system to form virus-like particles (VLPs) that have potential use as vaccines. In this study, we report optimization of extraction conditions to recover these VLPs from cell paste. Under hypotonic conditions with neutral pH these VLPs were poorly extracted (up to 3% extraction). Addition of reducing agents, detergents, salts, and sonication did not improve the extractability. While screening for conditions to improve the extractability of the VLPs, we discovered that a combination of higher pH and elevated processing temperature significantly increased the extraction. Whereas increasing pH alone increased extractability from 3% to 6% (pH increased from 8.0 to 9.5), the effect of elevated temperature was much more substantial. At 50°C, we observed the extraction to be more than fivefold higher than that at room temperature (up to 25% extracted at pH 9.0). The kinetics of extraction at elevated temperatures showed a rapid initial rate of extraction (on the order of minutes) followed by a plateau. In addition, we compared the extraction of VP1 expressed alone. VP1 expressed alone is incapable of forming VLPs. We observed that non-VLP VP1 was easily extractable (up to 60% extracted) under conditions in which the VP1 + VP2 VLPs were not extractable. From these studies we conclude that parvovirus B19 structural proteins expressed to form VLPs have a hindered extractability as compared with non-VLP protein. This hindrance to extraction can be significantly reduced by processing at elevated temperatures and an increased pH, possibly due to the enhanced rates of solubilization and diffusion. © 2002 Wiley Periodicals, Inc. Biotechnol Bioeng80: 250,256, 2002. [source] Polyamide Synthesis from 6-Aminocapronitrile, Part 1: N -Alkyl Amide Formation by Amine Amidation of a Hydrolyzed NitrileCHEMISTRY - A EUROPEAN JOURNAL, Issue 27 2007Adrianus Abstract The synthesis of N -hexylpentanamide from a stoichiometric amount of pentanenitrile and hexylamine has been studied as a model reaction for the synthesis of nylon-6 from 6-aminocapronitrile. The reaction was carried out under mild hydrothermal conditions and in the presence of a homogeneous ruthenium catalyst. For the mild hydrothermal conditions the presence of hexylamine distinctively increases the nitrile hydrolysis compared to the nitrile hydrolysis in the absence of hexylamine. Amine-catalyzed nitrile hydrolysis mainly produces the N-substituted amide. A clear product development is observed, consisting of first the terminal amide formation and second the accumulation of N -hexylpentanamide. With a maximum conversion of only 80,% after 18,h, the nitrile hydrolysis rate at 230,°C is still much too low for nylon-6 synthesis. Ruthenium dihydride phosphine was therefore used as a homogeneous catalyst, which significantly increases the nitrile hydrolysis rate. At a temperature of 140,°C and with only 0.5,mol,% [RuH2(PPh3)4] a 60,% nitrile conversion is already reached within 2,h. Initially the terminal amide is the sole product, which is gradually converted into N -hexylpentanamide. The reaction has a high initial rate, however, for higher conversions a strong decrease in hydrolysis rate is observed. This is ascribed to product inhibition, which results from the equilibrium nature of the reaction. [source] Photofading of phenylazo-aniline, -pyridone and -quinolone disperse dyes on a nylon 6 substrateCOLORATION TECHNOLOGY, Issue 2 2009Yasuyo Okada The photofading of phenylazo-aniline, -pyridone and -quinolone disperse dyes on nylon fabric was analysed using the Kubelka,Munk (K/S) spectra of fabrics exposed to a carbon arc in air. The exposure of dyed fabric through ultraviolet and coloured filters, which do not shield the main absorption band, showed a large decrease in the initial rate (KPA) of fading. Compared with the KPA values without filters, the values using filters were half as large for dyes without the nitro groups and a quarter as large for dyes with the nitro groups. The KPA values may be qualitatively explained by the sum of azo scission (decrease of K/S value at ,max) and the conversion of nitro groups to nitroso groups. These phenomena occur, respectively, via thermal disproportionation reactions between hydrazinyl radicals (from the azo group) and the reaction between hydrazinyl and N-centred nitrosyl hydroxide radicals (from the nitro group). The azo scission is promoted by N-centred nitrosyl hydroxide radicals via the latter reactions. [source] Individual trajectories of substance use in lesbian, gay and bisexual youth and heterosexual youthADDICTION, Issue 6 2009Michael P. Marshal ABSTRACT Aims Several decades of research have shown that lesbian, gay and bisexual (LGB) adults are at high risk for substance use and substance use disorders, and a recent meta-analysis shows that these disparities most probably begin in adolescence; however, no studies to date have examined longitudinal growth in substance use in LGB youth and heterosexual youth to determine if they follow different trajectories into young adulthood. The primary aims of this paper were to estimate individual trajectories of substance use in youth and examine differences between self-identified LGB and heterosexual subsamples. Method A school-based, longitudinal study of health-related behaviors of adolescents and their outcomes in young adulthood was used to test our hypotheses (The National Longitudinal Study of Adolescent Health). Participants were included if they were interviewed at all three waves and were not missing information regarding self-identified sexual orientation (n = 10 670). Results Latent curve models (LCMs) showed that LGB identity was associated significantly with individual variability in substance use intercepts and slopes, above and beyond age, race and gender. Self-identified LGB youth reported higher initial rates of substance use and on average their substance use increased over time more rapidly than did substance use by heterosexual youth. Two other indicators of sexual orientation (same-sex romantic attraction and same-sex sexual behavior) were also associated with substance use trajectories, and differential results were found for youth who identified as ,mostly heterosexual' and bisexual compared with youth who identified as completely heterosexual or homosexual. Conclusions Sexual orientation is an important risk marker for growth in adolescent substance use, and the disparity between LGB and heterosexual adolescents increases as they transition into young adulthood. More research is needed in order to examine: causal mechanisms, protective factors, important age-related trends (using a cohort-sequential design), the influence of gay-related developmental milestones, curvilinear effects over time and long-term health outcomes. [source] | |||||||||||||||||||