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Georges CohenLionel Asselineau Claude RaimbaultHenri Renon 《Chemical engineering science》1971,26(12):2051-2061
The NRTL equation (non random two liquids) associated with an equation of state of the vapour phase reprensents the vapor—liquid and liquid—liquid equilibria. 相似文献
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The effect of pressure on the retention behavior of insulin variants in RPLC on a YMC-ODS C18 column was investigated under linear conditions. The retention factors of these variants increase nearly 2-fold when the average column pressure is increased from 55 to 250 bar while their separation factors remain nearly unchanged. This effect is explained by a change of the partial molar volume of the insulin variants associated with their adsorption that decreases from -99 to -80 mL/mol for mobile-phase concentrations of acetonitrile increasing from 29 to 33% (v/v). This volume change is much larger than the one observed with low molecular weight compounds. For the same pressure variation, the average number Z of acetonitrile molecules displaced from the protein and the stationary phase upon adsorption increases from 22 to 23.3. The pressure-induced relative increase of the term b[S]/[D0]z (which corresponds to the initial slope of the adsorption isotherm) is approximately twice as large for Lispro than for porcine insulin. Because the binding constant of insulin decreases with increasing pressure, this suggests that the number of binding sites on the stationary phase increases even faster. Finally, it was observed that the column efficiency at flow rates higher than 0.6 mL/min increases slightly with increasing pressure. It is suggested that these observations are also valid for other proteins analyzed in RPLC. 相似文献
46.
Single component adsorption isotherms of phenol and caffeine were measured on six different commercial brands of end-capped C(18)-bonded silica columns (five monomeric bonded phases: Kromasil, Waters Symmetry, Phenomenex, Hypersil, and Chromolith from Merck; one polymeric bonded phase, Vydac) with the same methanol/water solution (30/70, v/v) as the mobile phase. Adsorption data were acquired by frontal analysis (FA) for all these columns in the same way. Depending on their solubility in the mobile phase, the concentrations used ranged between 1 and 100 g/L and between 0.35 and 35 g/L for phenol and caffeine, respectively. Twenty-two adsorption data points were recorded over these ranges. In each case, the best isotherm model accounting for all sets of adsorption data is the bi-Langmuir model, all columns behaving as heterogeneous adsorbents despite the endcapping. Depending on the column, the high-energy sites accounts for between 30 and 40% and between 4 and 7% of the total saturation capacity for phenol and caffeine, respectively. Except for the polymeric phase (Vydac), the ratio of the adsorption constants on the high- and low-energy sites is constant at around 10 for both phenol and caffeine, corresponding to an average adsorption energy difference of 5 kJ/mol between these two sites. The exact nature of the high-energy sites is illustrated by the following properties: (i) they have a very low selectivity for caffeine, with alpha(caffeine/phenol) close to 0.4 for the five monomeric columns, which suggests the complete derivatization of residual silanols; (ii) the high-energy sites account for a large fraction of the surface area of these packing materials (35% for phenol, 6% for caffeine); (iii) there is a small adsorption energy difference between high and low adsorption energy sites (5 kJ/mol); and (iv) the adsorption constants increase with increasing surface coverage of the monomeric columns. Thus, the high energy sites cannot be residual free silanols of the bare silica. More likely, they are related to the local heterogeneity of the C(18)-bonded-layer structure. Caffeine is more strongly retained on the low-energy sites than phenol (the product q(s,) (1)b(1) is larger for caffeine) but the contribution of the high-energy sites (q(s,) (2)b(2)) is markedly lower for caffeine than for phenol, despite the larger value of the adsorption constant, b(2). Because of a larger molecular size, caffeine cannot penetrate as deeply as phenol inside the bonded layer. This explains the paradox of a stronger retention for phenol than for caffeine on end-capped C(18)-bonded stationary phases. 相似文献
47.
Druon F Sanner N Lucas-Leclin G Georges P Hansen KP Petersson A 《Applied optics》2003,42(33):6768-6770
We present the use of a photonic crystal fiber to straightforwardly compress ultrashort pulses from a diode-pumped ytterbium laser emitting around 1 microm. 75-fs pulse generation and a large 1-1.3-microm tunability for sub-100-fs pulses is reported. 相似文献
48.
Christophe Serra Guy Schlatter Nicolas Sary Friedhelm Schönfeld Georges Hadziioannou 《Microfluidics and nanofluidics》2007,3(4):451-461
This paper investigates the modeling of styrene free radical polymerization in two different types of microreactor. A multiphysics
model which simultaneously takes into account the hydrodynamics, thermal and mass transfer (convection, diffusion and chemical
reaction) is proposed. The set of partial differential equations resulting from the model is solved with the help of the finite
elements method either in a 2D or a 3D approach. The different modeled microreactors are on one hand an interdigital multilamination
microreactor with a large focusing section, and on the other hand a simple T-junction followed by a straight tube with three
different radii. The results are expressed in terms of reactor temperature, polydispersity index, number-average degree of
polymerization and monomer conversion for different values of the chemical species diffusion coefficient. It was found that
the 2D approach gives the same results as the 3D approach but allows to dramatically reduce the computing time. Despite the
heat released by the polymerization reaction, it was found that the thermal transfer in such microfluidic devices is high
enough to ensure isothermal conditions. Concerning the polydispersity index, the range of diffusion coefficients over which
the polydispersity index can be maintained close to the theoretical value for ideal conditions increases as the tube reactor
radius decreases. The interdigital multilamination microreactor was found to act as a tubular reactor of 0.78 mm ID but with
a shorter length. This underlines that the use of microfluidic devices can lead to a better control of polymerization reactions. 相似文献
49.
Timpano G Tabarani G Anderluh M Invernizzi D Vasile F Potenza D Nieto PM Rojo J Fieschi F Bernardi A 《Chembiochem : a European journal of chemical biology》2008,9(12):1921-1930
The dendritic cell-specific intercellular adhesion molecule (ICAM) 3-grabbing nonintegrin (DC-SIGN) is a C-type lectin that appears to perform several different functions. Besides mediating adhesion between dendritic cells and T lymphocytes, DC-SIGN recognizes several pathogens some of which, including HIV, appear to exploit it to invade host organisms. The intriguing diversity of the roles attributed to DC-SIGN and their therapeutic implications have stimulated the search for new ligands that could be used as biological probes and possibly as lead compounds for drug development. The natural ligands of DC-SIGN consist of mannose oligosaccharides or fucose-containing Lewis-type determinants. Using the known 3D structure of the Lewis-x trisaccharide, we have identified some monovalent alpha-fucosylamides that bind to DC-SIGN with inhibitory constants 0.4-0.5 mM, as determined by SPR, and have characterized their interaction with the protein by STD NMR spectroscopy. This work establishes for the first time alpha-fucosylamides as functional mimics of chemically and enzymatically unstable alpha-fucosides and describes interesting candidates for the preparation of multivalent systems able to block the receptor DC-SIGN with high affinity and with potential biomedical applications. 相似文献
50.
Mundle SO Johnson T Lacrampe-Couloume G Pérez-de-Mora A Duhamel M Edwards EA McMaster ML Cox E Révész K Sherwood Lollar B 《Environmental science & technology》2012,46(3):1731-1738
Chlorinated ethenes are commonly found in contaminated groundwater. Remediation strategies focus on transformation processes that will ultimately lead to nontoxic products. A major concern with these strategies is the possibility of incomplete dechlorination and accumulation of toxic daughter products (cis-1,2-dichloroethene (cDCE), vinyl chloride (VC)). Ethene mass balance can be used as a direct indicator to assess the effectiveness of dechlorination. However, the microbial processes that affect ethene are not well characterized and poor mass balance may reflect biotransformation of ethene rather than incomplete dechlorination. Microbial degradation of ethene is commonly observed in aerobic systems but fewer cases have been reported in anaerobic systems. Limited information is available on the isotope enrichment factors associated with these processes. Using compound-specific isotope analysis (CSIA) we determined the enrichment factors associated with microbial degradation of ethene in anaerobic microcosms (ε = -6.7‰ ± 0.4‰, and -4.0‰ ± 0.8‰) from cultures collected from the Twin Lakes wetland area at the Savannah River site in Georgia (United States), and in aerobic microcosms (ε = -3.0‰ ± 0.3‰) from Mycobacterium sp. strain JS60. Under anaerobic and aerobic conditions, CSIA can be used to determine whether biotransformation of ethene is occurring in addition to biodegradation of the chlorinated ethenes. Using δ(13)C values determined for ethene and for chlorinated ethenes at a contaminated field site undergoing bioremediation, this study demonstrates how CSIA of ethene can be used to reduce uncertainty and risk at a site by distinguishing between actual mass balance deficits during reductive dechlorination and apparent lack of mass balance that is related to biotransformation of ethene. 相似文献