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Infinite Dilution (infinite + dilution)
Selected AbstractsGroup contribution prediction of surface charge density profiles for COSMO-RS(Ol)AICHE JOURNAL, Issue 12 2007Tiancheng Mu Abstract A new method for predicting the surface charge density distribution (, profile) and cavity volume of molecules based on group contributions was developed. The original , profiles used for the regression were obtained using Gaussian 03 B3LYP/6-311G(d,p). In total 1363 , profiles were used for the regression of group parameters. Group definitions are identical to those used previously for boiling point estimation. Original and estimated , profiles were used to predict activity coefficients at infinite dilution and VLE data of binary systems using the COSMO-RS(Ol) model. The results were compared with the experimental data stored in the Dortmund Data Bank. In many cases the results were of comparable accuracy. However, for a few compounds, poor results were obtained, in particular for conjugated components like nitrobenzenes. The method offers a fast and reliable generation of , profiles to be used with COSMO-RS(Ol) within its range of applicability. © 2007 American Institute of Chemical Engineers AIChE J, 2007 [source] Prediction of phase equilibria and excess properties for systems with sulfonesAICHE JOURNAL, Issue 2 2003Roland Wittig The group contribution method modified UNIFAC (Dortmund) has become very popular because of its broad applications, and reliable predictions for vapor-liquid equilibria, solid-liquid equilibria, liquid-liquid equilibria, activity coefficients at infinite dilution, azeotropic data and excess enthalpies in a wide temperature range. Therefore, the existing parameter matrix for the modified UNIFAC method is continuously extended with the help of the Dortmund Data Bank and by carrying out systematic measurements. The new main group for sulfones, such as that required to describe systems with the selective solvent sulfolane, is introduced, as well as ten new pairs of group interaction parameters for modified UNIFAC. [source] Surface characterization of salmeterol xinafoate powders by inverse gas chromatography at finite coverageJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 3 2005Henry H.Y. Tong Abstract In our previous studies, surface analysis by inverse gas chromatography (IGC) at infinite dilution (zero coverage) was performed on four salmeterol xinafoate (SX) powdered samples, viz, two supercritical CO2 -processed Form I (SX-I) and Form II (SX-II) polymorphs, a commercial granulated SX (GSX) raw material and its micronized product (MSX). Both GSX and MSX are also of the same Form I polymorph. To further probe the differences in surface properties between the samples, the present study has extended the IGC analysis to the finite concentration range of selected energy probes. The adsorption isotherms of the SX samples were constructed using (nonpolar) octane, (polar acidic) chloroform, and (polar basic) tetrahydrofuran as liquid probes. Type II adsorption isotherms with weak knees were observed with each probe for all SX Form I samples. The extents of probe adsorption by the samples at various relative pressures follow the rank order: SX-II,>,GSX,,,MSX,>,SX-I, indicating that the SX-I has fewer high-energy adsorption sites than GSX and MSX. Type III isotherms were observed for SX-II with the two polar probes, indicative of weak adsorbate,adsorbent interactions. The additional information generated shows that IGC analysis at finite coverage is a valuable complementary tool to that at infinite dilution. © 2005 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 94:695,700, 2005 [source] Chaperonin-assisted folding of glutamine synthetase under nonpermissive conditions: Off-pathway aggregation propensity does not determine the co-chaperonin requirementPROTEIN SCIENCE, Issue 12 2000Paul A. Voziyan Abstract One of the proposed roles of the GroEL-GroES cavity is to provide an "infinite dilution" folding chamber where protein substrate can fold avoiding deleterious off-pathway aggregation. Support for this hypothesis has been strengthened by a number of studies that demonstrated a mandatory GroES requirement under nonpermissive solution conditions, i.e., the conditions where proteins cannot spontaneously fold. We have found that the refolding of glutamine synthetase (GS) does not follow this pattern. In the presence of natural osmolytes trimethylamine N-oxide (TMAO) or potassium glutamate, refolding GS monomers readily aggregate into very large inactive complexes and fail to reactivate even at low protein concentration. Surprisingly, under these "nonpermissive" folding conditions, GS can reactivate with GroEL and ATP alone and does not require the encapsulation by GroES. In contrast, the chaperonin dependent reactivation of GS under another nonpermissive condition of low Mg2+ (<2 mM MgCl2) shows an absolute requirement of GroES. High-performance liquid chromatography gel filtration analysis and irreversible misfolding kinetics show that a major species of the GS folding intermediates, generated under these "low Mg2+" conditions exist as long-lived metastable monomers that can be reactivated after a significantly delayed addition of the GroEL. Our results indicate that the GroES requirement for refolding of GS is not simply dictated by the aggregation propensity of this protein substrate. Our data also suggest that the GroEL-GroES encapsulated environment is not required under all nonpermissive folding conditions. [source] Sequestration of organometallic compounds by natural organic matter. binding of trimethyltin(IV) by fulvic and alginic acidsAPPLIED ORGANOMETALLIC CHEMISTRY, Issue 10 2006Alba Giacalone Abstract The binding capacity of fulvic and alginic acids towards trimethyl tin(IV) cation was quantitatively determined in order to evaluate the sequestering ability of toxic organometallic compounds by natural organic matter. Investigations were performed in the pH range of natural waters (5,8.5) where the carboxylate groups, largely present in both sequestering agents, are the main binding sites. A chemical interaction model, according to which both the protonation of polyelectrolyte ligands and the hydrolysis of the organotin cation in NaCl aqueous solution were considered, was used to define the speciation of the systems under investigation. Measurements performed at different ionic strength values (0.1, 0.25, 0.5 and 0.7 mol L,1, NaCl) allowed us to consider the dependence of stability constants on the ionic strength, and to calculate the formation constants at infinite dilution. Results obtained show the formation of the complex species TMT(L), TMT(L)2 and TMT(L)(OH) for L = fulvic acid and TMT(L) for L = alginic acid, respectively. In order to compare the strength of interaction of these natural poly electrolytes with other analogous synthetic polyelectrolytes, measurements were also carried out on the trimethyltin(IV),polyacrylate (5.1 kDa) system, and in this case the formation of TMT(L), TMT(L)2 and TMT(L)(OH) species was found. Results show the following trend of stability for the species TMT(L) in the systems investigated: TMT,fulvate , TMT,polyacrylate > TMT,alginate. On the basis of the stability data obtained, the lowest concentration of fulvic and alginic acids, able to act as sequestering agents towards triorganotin(IV) cation in the conditions of natural waters, was also calculated. Copyright © 2006 John Wiley & Sons, Ltd. [source] Effects of physical properties estimation on process design: a case study using AspenPlusASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 5 2009Loic Cadoret Abstract This study focuses on the physical property model parameters estimation in order to accurately simulate separation processes for a given set of components. The non-random two-liquid (NRTL) model was chosen and parameters were calculated using different methods: experimental data regression and UNIFAC and COSMO-SAC (conductor-like screening model, segment activity coefficient) predictive models. The vapor-liquid equilibrium (VLE) obtained from these different models was compared and results showed that COSMO-SAC can be a reliable tool when data or functional groups are missing. Results also showed that the use of UNIFAC to estimate activity coefficients at infinite dilution can, in some cases, leads to inaccurate results and strongly impact process simulation results. Copyright © 2009 Curtin University of Technology and John Wiley & Sons, Ltd. [source] | ||||||||||