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Physicochemical Model (physicochemical + model)
Selected AbstractsMethyl- tert -hexyl ether and methyl- tert -octyl ether as gasoline oxygenates: Anticipating widespread risks to community water supply wells,ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 11 2007Jeff Snelling Abstract The widespread contamination of groundwater resources associated with methyl- tert -butyl ether (MtBE) use has prompted a search for replacement oxygenates in gasoline. Among the alternatives currently under development are higher methyl- tert -alkyl ethers, notably methyl- tert -hexyl ether (MtHxE) and methyl- tert -octyl ether (MtOcE). As was the case with MtBE, the introduction of these ethers into fuel supplies guarantees their migration into groundwater resources. In the present study, a screening-level risk assessment compared predicted well water concentrations of these ethers to concentrations that might cause adverse effects. A physicochemical model which has been successfully applied to the prediction of MtBE concentrations in community water supply wells (CSWs) was used to predict well water concentrations of MtHxE and MtOcE. The results indicate that these ethers are likely to contaminate water supply wells at slightly lower levels than MtBE as a result of migrating from leaking underground fuel tanks to CSWs. Because very little data is available on the physicochemical and environmental properties of MtHxE and MtOcE, estimation methods were employed in conjunction with the model to predict well water concentrations. Model calculations indicated that MtHxE and MtOcE will be present in many CSWs at concentrations approaching the concentrations that have caused widespread public health concern for MtBE. Based on these results and the possibility that MtHxE and MtOcE are potential carcinogens, testing of the toxicological properties of these ethers is recommended before they are used to replace MtBE in gasoline. [source] Copper and cadmium extraction from highly concentrated phosphoric acid solutions using calcium alginate gels enclosing bis(2,4,4-trimethylpentyl)thiophosphinic acidJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 8 2006Argune Ocio Abstract The availability of alginate gels enclosing Cyanex 302 [bis(2,4,4-trimethylpentyl)thiophosphinic acid] for the uptake of cadmium and copper from highly concentrated solutions of industrial phosphoric acid wet process phosphoric acid (WPA)] was studied. For this purpose, beads of alginate gels enclosing microdrops of kerosene solutions of the industrial extractant Cyanex 302 at different concentrations were prepared. The experimental procedure gives rise to a composite bead in which alginate is the continuous phase and the organic extractant forms the discrete homogeneously distributed phase within the bead. The equilibrium in this three-phase system (phosphoric acid,extractant solution,alginate gel) was modelled in terms of the corresponding distribution factors, the main chemical reactions and their equilibrium constants. Retention isotherms of both metal ions were obtained experimentally at four concentrations (1.0, 2.5, 5.0 and 7.5 mol L,1) of pure phosphoric acid. High metal removal efficiency, due to liquid,liquid extraction processes, was observed even in the most acidic conditions. High values of the extraction constants were estimated, with the distribution coefficients between aqueous and alginate phase being near unity. Finally, the results obtained with industrial WPA are in close agreement with those predicted by the physicochemical model developed in synthetic media. Copyright © 2006 Society of Chemical Industry [source] Time-averaged predictions of folded and misfolded peptides using a reduced physicochemical modelJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 7 2008Oliver J. Clarke Abstract Energy-based methods for calculating time-averaged peptide structures are important for rational peptide design, for defining local structure propensities in large protein chains, and for exploring the sequence determinants of amyloid formation. High-end methods are currently too slow to be practicable, and will remain so for the foreseeable future. The challenge is to create a method that runs quickly on limited computer resources and emulates reality sufficiently well. We have developed a simplified off-lattice protein model, incorporating semi-empirical physicochemical potentials, and combined it with an efficient Monte Carlo method for calculating time-averaged peptide structures. Reasonably accurate predictions are found for a set of small ,-helical and ,-hairpin peptides, and we demonstrate a potential application in measuring local structure propensities in protein chains. Time-averaged structures have also been calculated for a set of small peptides known to form ,-amyloid fibrils. The simulations were of three interacting peptides, and in each case the time-averaged structure describes a three-stranded ,-sheet. The performance of our method in measuring the propensities of small peptides to self-associate into possible prefibrillar species compares favorably with more detailed and CPU-intensive approaches. © 2007 Wiley Periodicals, Inc. J Comput Chem, 2008 [source] Theoretical Trends of Diffusion and Reaction into Tubular Nano- and Mesoporous Structures: General Physicochemical and Physicomathematical ModelingCHEMISTRY - A EUROPEAN JOURNAL, Issue 18 2008Christian Amatore Prof. Abstract A general and adaptable physicochemical model is presented to evaluate the mass transport within nanopores of mesoporous particles when the mass transport is coupled to heterogeneous kinetics occurring at active sites located onto the nanopore walls surface. The model framework encompasses almost all situations of practical interest in solutions and may be used for characterizing the kinetic rates and constants controlling the system under different sets of experimental conditions. Furthermore, it allows the delineation of simple effective parameters, which should be most useful for optimizing a given material in view of specific applications. For the sake of clarification the simplified model is presented and its results discussed by specializing it for cases where the reactions involve a simple adsorption of a target species on the nanopore immobilized sites as observed for inorganic sponges used in water decontamination. Yet it may easily be extended further to encompass a wider variety of situations where the sites immobilized onto the nanopore walls perform chemical or biochemical transformations as occur in supported catalysis in liquid solution. [source] | ||||||||||