Partitioning Between Solvents

Considering that, roughly speaking, the electrostatic component of the solvation free energy varies as the cube of the molecular dipole moment, it becomes obvious that the corrective term (13.1) should be taken into account in the determination of differential solvation properties of very polar solutes. In the computation of transfer free energies across an interface, it has been suggested that equation (13.1) be expressed as a function of the number density of one of the two media, so that the correction is zero in solvent 1 and zl,l lsl lll in solvent 2 [115]. 

Models of lipid bilayers have been employed widely to investigate diffusion properties across membranes through assisted and non-assisted mechanisms. Simple monovalent ions, e.g., Na+, K+, and Cl, have been shown to play a crucial role in intercellular communication. In order to enter the cell, the ion must preliminarily permeate the membrane that acts as an impervious wall towards the cytoplasm. Passive transport of Na+ and Cl ions across membranes has been investigated using a model lipid bilayer that undergoes severe deformations upon translocation of the ions across the aqueous interface [126]. This process is accompanied by thinning defects in the membrane and the formation of water fingers that ensure appropriate hydration of the ion as it permeates the hydrophobic environment. 

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Under these conditions, aggregates display emergent properties (e.g. the state of being soluble, see above) not seen in the neat state. The soluble state also exhibits emergent properties such as diffusibility, conductivity, partitioning between solvents and interfacial activity (Testa and Kier, 1991). What is lost here are many physical properties which have no meaning in the soluble state, namely properties of the crystal, gas or bulk liquid. 

Remark the year, 1976, of publication of this paper. It is one of the first proposals to use an effective QM Hamiltonian to treat solvation effects. The partitioning between solvent and solute is treated according to... 

Numerical values for the structural parameters of QSAR are obtained from an evaluation of the effect of the substituent on the properties (e.g., the rate or equilibrium constants) of a model reaction. The classification of these parameters is therefore model dependent. The model reactions are chosen to represent the most pervasive types of physicochemical phenomena (e.g., dissociation reactions, hydrolysis, substitution reactions, partition between solvents). 

In addition to the enhanced speed of synthesis, a microchannel system also provides a potential separation column and a non-turbulent environment for partition between solvents. Integration of a microreactor device, via purification, to one of the many highly sensitive microchannel-based biological assay systems would enable the compounds to be screened. Apart from the greatly reduced reaction times demonstrated for the microreactors, handling times to assay and chemical reagent costs would be virtually eliminated as shown diagrammatically in Fig. 14.5. 

Gel filtration/permeation chromatography (also known as molecular exclusion chromatography) is a form of partition chromatography in which the solute molecules are partitioned between solvent and a stationary phase of defined porosity without an attractive interaction between the two phases. Gel filtration generally refers to aqueous systems while gel permeation is used in nonaqueous systems. The technique is normally used for the separation of biomacromolecules on the basis of size. Solutes are eluted in the order of decreasing molecular size. Gel filtration chromatography is not used as the first step in... 

Nesbitt (1982) pointed out that using hydration numbers which are independent of solution concentration is unreasonable. For example, at about 4 molal MgCl2, and using the Stokes and Robinson hydration number (A) of 13.7, virtually all the water in solution would reside in hydration shells, leaving none as solvent. Nesbitt (1982) suggested a minor variation in the hydration scheme, in which water is partitioned between solvent and hydration shells, such that... 

Caffeine is a very weak base and its salts are decomposed by water hence it can be extracted from both acid and alkaline solution (more easily from the latter) by chloroform and this is generally employed as the method of estimation, the extracted anhydrous caffeine being weighed. Caffeine is only slightly soluble in ether and this solvent is unsuitable for its extraction. As caffeine is moderately soluble in water, the small partition between solvents demands a large number of extractions before the material is quantitatively removed. Caffeine is very susceptible to decomposition by strong alkali and should be extracted immediately from alkaline solution. 

Furthermore, most physicochemical properties are related to interactions between a molecule and its environment. For instance, the partitioning between two phases is a temperature-dependent constant of a substance with respect to the solvent system. Equation (1) therefore has to be rewritten as a function of the molecular structure, C, the solvent, S, the temperature, X etc. (Eq. (2)). 

In a simple liquid-liquid extraction the solute is partitioned between two immiscible phases. In most cases one of the phases is aqueous, and the other phase is an organic solvent such as diethyl ether or chloroform. Because the phases are immiscible, they form two layers, with the denser phase on the bottom. The solute is initially present in one phase, but after extraction it is present in both phases. The efficiency of a liquid-liquid extraction is determined by the equilibrium constant for the solute s partitioning between the two phases. Extraction efficiency is also influenced by any secondary reactions involving the solute. Examples of secondary reactions include acid-base and complexation equilibria. 

Prymnesin (toxic protein from phytoflagellate Pyrymnesium parvum) [11025-94-8]. Purified by column chromatography, differential soln and pptn in solvent mixtures and differential partition between diphasic mixtures. The product has at least 6 components as observed by TLC. [Ulitzur and Shilo Biochim Biophys Acta 301 350 1970.]... 

Consider a nucleus that can partition between two magnetically nonequivalent sites. Examples would be protons or carbon atoms involved in cis-trans isomerization, rotation about the carbon—nitrogen atom in amides, proton exchange between solute and solvent or between two conjugate acid-base pairs, or molecular complex formation. In the NMR context the nucleus is said to undergo chemical exchange between the sites. Chemical exchange is a relaxation mechanism, because it is a means by which the nucleus in one site (state) is enabled to leave that state. 

Filtration of the catalyst over a Hyflo pad and removal of the solvent left a yellow crystalline residue. The crude mixture of ketone and potassium acetate was partitioned between methylene chloride (300 cc) and water (1 liter), The layers were separated and the water layer washed with methylene chloride (3 x 50 cc). The organic layers were combined, washed with 3N sodium hydroxide solution (2 x 50 cc), water (3 x 100 cc), dried over anhydrous sodium sulfate and filtered. The solvent was removed and the product recrystallized from ethanol to give 2-amino-2 -fluorobenzophenone as yellow prisms melting at 126° to 128°C,... 

To a solution of 39.5 g (0.0845 mol) of 2-(N-phthalimidoacetyl-N-cyclopropylmethyl)amino-5-chlorobenzophenone in a mixture of 423 ml of chloroform and 423 ml of ethanol Is added 9.52 g (0.1903 mol) of hydrazine hydrate and 9.52 ml of water. This solution is allowed to stand at room temperature. In 3 hours a precipitate begins to form in the solution. After standing 16 to 24 hours a voluminous pulpy white precipitate forms. The solvents are removed under vacuum while keeping the temperature under 40 0 and the residue is partitioned between dilute ammonia water and ether. 

The reaction systems used for modification of triglycerides usually consist of a lipase catalyst and a small amount of water dispersed in a bulk organic phase containing the reactants and, if required, a water immiscible solvent. The small amount of water in the reaction system partitions between the catalyst and the bulk organic phase. 

In conventional solvent extraction, a solute is partitioned between two immiscible solvents. Here, used as an... 

Predictions of bioaccumulation assume a standard model of dissolution in fat and are based on partition between water and organic solvent. The better studied tributyltin has been shown to partition based on binding to protein rather than dissolution in fat this might account for discrepancies between observed and predicted BCFs. 

The main peculiarity of solutions of reversed micelles is their ability to solubilize a wide class of ionic, polar, apolar, and amphiphilic substances. This is because in these systems a multiplicity of domains coexist apolar bulk solvent, the oriented alkyl chains of the surfactant, and the hydrophilic head group region of the reversed micelles. Ionic and polar substances are hosted in the micellar core, apolar substances are solubilized in the bulk apolar solvent, whereas amphiphilic substances are partitioned between the bulk apolar solvent and the domain comprising the alkyl chains and the surfactant polar heads, i.e., the so-called palisade layer [24],... 

Raevsky, 0. A., Grigor ev, V. Ju., Raevskaja, 0. E., Schaper, K.-J. Physicochemical properties/descriptors governing the solubility and partitioning in water-solvent-gas systems. Part 1. Partitioning between octanol and air. 

Solute Flux Solute partitioning between the upstream polarization layer and the solvent-filled membrane pores can be modeled by considering a spherical solute and a cylindrical pore. The equilibrium partition coefficient 0 (pore/bulk concentration ratio) for steric exclusion (no long-range ionic or other interactions) can be written as... 

Various criteria can influence the choice of organic solvent that can be used in a biphasic bioreactor degree of solubility of substrates and/or products, inactivation effect, toxicity, flammability, and essentially reactant partition between the phases. Much research has been carried out on this topic [7,8,14,15,33,67]. 

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