Search results for "kinetics"
showing 10 items of 2224 documents
Brain choline has a typical precursor profile.
1998
Choline is product and precursor to both acetylcholine and membrane phospholipids, and, in the brain, is ultimately provided by the circulation. The brain is protected from excess choline and choline deprivation by a refined system of homeostatic mechanisms that maintain a level of extracellular choline that, for its role as precursor, meets saturation criteria under normal conditions. The kinetic and activity profiles of choline are typical for a biosynthetic precursor.
Uptake and release kinetics of134Cs by Goldfish (Carassius auratus) and137Cs by Zebra Fish (Brachydanio rerio) in controlled aquatic environment
1994
The uptake and release kinetics of134Cs by Goldfish (Carassius auratus) and137Cs by Zebra Fish (Brachydanio rerio) from aquatic media of different ionic compositions and temperature was studied in controlled laboratory conditions. The accumulation of radiocesium in the case ofBrachydanio rerio is observed to be strongly dependent on the potassium ion concentration of the aquatic medium, but in the case ofCarassius auratus this dependence is quite weak. The biological half-lives of the cesium isotopes incorporated into the fish investigated in the present work vary from 19 to 80 days and are influenced by the temperature and the ionic composition of the aquatic medium.
Deuterium isotope effect on the induction period of the cerium catalyzed Belousov-Zhabotinsky reaction
2009
Abstract In this work we present results about the deuterium isotopic effect on the global kinetics of a cerium catalyzed Belousov–Zhabotinsky reaction. A nonlinear dependence of the induction period upon the percentage of deuterated reactants was found in batch conditions. In order to understand this result, we investigated two reaction pathways responsible for the length of the induction period, namely: (a) the reaction between the enolic form of the malonic acid with molecular bromine and (b) the oxidation of malonic acid by the Ce(IV) ion. In both cases we obtained a linear dependence of the kinetic constants on the percentage of deuterated reactants. Nevertheless, by inserting the expe…
Cr(VI) sorption by intact and dehydrated Candida utilis cells: differences in mechanisms
2001
The Cr(VI) sorption kinetics by intact and dehydrated Candida utilis cells were studied. Yeast dehydration led to enhanced Cr(VI) sorption activity by cells during the first 15–20 min of rehydration. In experiments with K2Cr2O7 as a chromium source, [Cr2O7]2− was converted into [CrO4]2− during incubation with dehydrated biomass. An effect of the considerably enhanced Cr(VI) sorption activity by dehydrated cells in the buffered media at pH≈8.0 can serve as another confirmation of the different sorption mechanisms of intact and dehydrated C.utilis cells. This effect was not revealed in water solution at pH 8.0. This phenomenon will be studied in further investigations.
Kinetics and equilibrium in insulin radioimmunoassay.
2002
The kinetics of insulin reaction has been studied with its specific antibody immobilized on the inner wall of the reaction tube; the radioimmunoanalytical determination of such a substance is based on the reaction. Independent variables were labelled and unlabelled insulin concentrations, temperature, viscosity, and the medium's ionic strength. Biexponential kinetics was found to be dependent on the concentrations fitted to the models discussed in the paper. The effect of temperature shows activation parameters similar to the viscous flow energy of water, which suggests that the reaction is diffusion-controlled. The results of the viscosity analysis points at the clearly negative influence …
Rate-limiting reaction of C 3 S hydration - A reply to the discussion “A new view on the kinetics of tricalcium silicate hydration” by E. Gartner
2018
Abstract In the case of coupled solids-solution reactions, any mean accelerating or decelerating one of the reaction, will also change the other reaction(s) in the same way, through the coupling mediated by the solution. The observation of any kinetic change by one of these means should not lead to too rapid conclusion on the limitation of kinetics and it must be done with great caution. Contrary to what Gartner mentioned, the acceleration of C3S hydration by the addition of calcium silicate hydrate seeds, is not a trivial evidence suggesting that hydration kinetics “has to be” limited by the C-S-H precipitation and that the C3S dissolution can be neglected. In our paper, efforts have been …
Photoinduced ultrafast dynamics of Ru(dcbpy)2(NCS)2-sensitized nanocrystalline TiO2 films:The influence of sample preparation and experimental condit…
2004
In most of the previous ultrafast electron injection studies of Ru(dcbpy)2(NCS)2-sensitized nanocrystalline TiO2 films, experimental conditions and sample preparation have been different from study to study and no studies of how the differences affect the observed dynamics have been reported. In the present paper, we have investigated the influence of such modifications. Pump photon density, environment of the sensitized film (solvent and air), and parameters of the film preparation (crystallinity and quality of the film) were varied in a systematic way and the obtained dynamics were compared to that of a well-defined reference sample: Ru(dcbpy)2(NCS)2−TiO2 in acetonitrile. In some cases, …
Interactions between chemical evolution (hydration) and physical evolution (setting) in the case of tricalcium silicate
1994
This paper describes recent experimental results concerning investigation of the parameters which determine, on the one hand, the kinetics of hydration of tricalcium silicate and the thermodynamic, morphological and structural characteristics of C-S-H and, on the other hand, the evolution of the particle interactions at the origin of setting. It is shown that, in both cases, lime concentration in solution is the most important parameter. As a consequence, the chemical evolution of the system, which controls the lime concentration in solution, determines the nature of particle interactions and the physical evolution of the suspension or paste. In return, the contacts, between particles, resu…
Application of solid-state electrochemistry techniques to polyfunctional organic–inorganic hybrid materials: The Maya Blue problem
2013
Abstract The time evolution of indigo plus palygorskite powdered mixtures during isothermal heating at different temperatures between 120 and 180 °C to form Maya Blue-type materials has been monitored by means of infrared spectrometry, diffuse reflectance spectrometry in the visible region and solid state electrochemical techniques. The kinetics of the formation process of such materials can be described in terms of two consecutive reactions, the first one consisting of the loss of zeolitic water of the palygorskite coupled with clay-indigo attachment and partial indigo to denydroindigo oxidation. The palygorskite dehydration acts as a rate-determining step fitting to a 3D Avrami-Erofe’ev k…
Chemical Reactivity in AOT Microemulsions: Kinetics of Water Replacement in a Square-Planar Palladium(II) Aquo Complex by Monoalkylthioureas
1998
The kinetics of water replacement in the cationic palladium(II) aquo complex [Pd(Et4dien)(H2O)]2+, where Et4dien = Et2N(CH2)2NH(CH2)2NEt2, by thiourea, methylthiourea, and ethylthiourea have been studied at 25.0 °C in heptane−AOT−water microemulsion over a wide range of the molar ratio R (=[H2O]/[AOT]) at the constant surfactant concentration of 0.13 mol dm-3. The reaction rates are significantly higher in microemulsions than in bulk water and decrease rapidly as the parameter R increases. The kinetic data, interpreted quantitatively by applying the pseudophase model to the microemulsion, indicate that there is a weak partitioning of the nucleophiles between the water core and the AOT inter…