Partitioned systems

Mueller [103-104] has adopted the polyethylene glycol)-dextran partition system pioneered by Albertson [105] to develop an efficient chromatographic method for the resolution of proteins and nucleic acids. He used supports such... 

The liquid junction potential from the organic side may be negligible, owing to the use of a nitrobenzene-water partition system containing tetraethylammonium picrate as the salt bridge. The mobilities of both ions in nitrobenzene are similar, and they have similar Gibbs energies of... 

AM columns are another means of measuring lipophilic characteristics of drug candidates and other chemicals [99-103]. 1AM columns may better mimic membrane interactions than the isotropic octanol-water or other solvent-solvent partitioning system. These chromatographic indices appear to be a significant predictor of passive absorption through the rat intestine [128]. 

Leahy, D. E., Morris, J. J., Taylor, P. J., Wait, A. R. Membranes and their models towards a rational choice of partitioning system. In QSAR Rational Approaches to the Design of Bioactive Compounds, Silipo, G., Vittoria, A. (eds.), Elsevier, Amsterdam, 1991, pp. 75-82. 

A comparahve analysis of coefficients and descriptors clarifies the relationship between lipophilicity and hydrophobicity (Y in Eq. 4 is the molar volume which assesses the solute s capacity to elicit nonpolar interactions (i.e. hydrophobic forces) which, as also clearly stated in the International Union of Pure and Applied Chemistry definitions [3] are not synonyms but, when only neutral species are concerned, may be considered as interchangeable. In the majority of partitioning systems, the lipophilicity is chiefly due to the hydrophobicity, as is clearly indicated by the finding that the product of numerical values of the descriptors V and of the coefficient v is larger in absolute value than the corresponding product of other couples of descriptors/coefficients [9]. This explains the very common linear rela-... 

To shed light on this topic, we propose a general equation (Eq. 5) that can be applied to all electrical species and all partitioning systems [3] ... 

The liquid-liquid partition systems discussed above are in fact very similar to various membrane-type interfaces and may serve as a model for them. A good example is, for instance, the distribution of a dissociated salt between aqueous solution and a permeable organic polymer [60]. 

Decaffeination of green coffee beans is most usually carried out with a water/solvent partition system. The green coffee beans are first steamed until they are hot, wet, and swollen, to make the caffeine available. Solvent is then used to extract the caffeine out of the aqueous phase of the beans. Finally, the beans are steamed to drive off residual solvent. The coffee beans lose their wax surface covering in the process, as well as some flavor components. For this reason, the Robusta and Brazilian Arabica coffees that are dry-processed and have the most powerful flavors are usually the types that are decaffeinated. They become milder in the process. Mechanical polishing is used to improve the appearance of decaffeinated green coffee beans if they are not to be roasted immediately. Extra care is required, however, to store these decaffeinated beans since the loss of wax covering as well as caffeine renders them much more susceptible to fungal attack. 

Ottiger, C. Wunderli-Allenspach, H., Immobilized artificial membrane (IAM)-HPLC for partition studies of neutral and ionized acids and bases in comparison with the liposomal partition system, Pharm. Res. 16, 643-650 (1999). 

Rogers, J. A. Choi, Y. W., The liposome partitioning system for correlating biological activities for imidazolidine derivatives, Pharm. Res. 10, 913-917 (1993). 

Figure 37 Correlations of log monolayer permeability coefficients for a series of related peptides and various physicochemical indices (see Table 14). In plot (C) the log PC values refer to the immiscible n-heptane/ethylene glycol partitioning system. [Redrawn from Kim et al. (1993) with permission from the publisher.]...

RN Smith, C Hansch, MM Ames. Selection of a reference partitioning system for drug design work. I Pharm Sci 64 599-606, 1975. 

A further partition system based on the use of liposomes, and marketed as Transil , has also been investigated [105, 106]. 

In a partition system the stationary phase is a liquid coated onto a solid support (p. 97). Silica gel, kieselguhr (diatomaceous earth) or cellulose powder are the most frequently used. Conditions closely resemble those of counter-current distribution so that in the absence of adsorption by the solid support, solutes move through the system at rates determined by their... 

In principle the wide range of stationary phases used in GLC can be used in liquid-liquid partition systems, but problems can arise from mutual solubility effects which may result in the stationary phase being stripped from the column. 

Basically, the Rf value of a solute is determined by its distribution ratio which in turn is dependent on relative solubilities for partition systems or relative polarities for adsorption systems. For example, if adsorption TLC is used to separate a mixture of squalene (a hydrocarbon), methyl oleate, cholesterol and a-tocopherol (vitamin E), then squalene, being the least polar, will move furthest and the cholesterol, being the most polar, will remain close to the origin. Methyl oleate is less polar than a-tocopherol and will therefore be found between it and the squalene. The role of polarity is discussed more fully on p. 82. 

Columns of gel beads are more often used than thin layers. The process can be considered analogous to a partition system wherein molecules which are completely excluded from the gel have a distribution ratio of 0 whilst those small enough to penetrate all parts of the structure have a value of 1. Adsorption or ion-exchange effects can cause the distribution ratios of polar molecules to exceed 1. Components of a mixture are characterized by their retention volume, VR, which is determined by the distribution ratio. 

From a preparative aspect, Peck et alX have employed the counter-current distribution technique with a partition system of water/ butanol/p-toluene sulphonic acid to separate and purify the neamine (neomycin A) present in commercial neomycin. 

Partition system specification into subject areas. Define early the key type model attributes or effects that one subject area depends on another subject area can specify the detailed constraints on those attributes or effects. Always have a mechanism (such as attributes or effects) that relates subject areas to one another. 

Chiou chose glyceryl trioleate (triolein) as model lipid because of its similarity to triglycerides which are abundant in organisms [109], Triolein is also a bulk lipid and the good correlation with the bioconcentration factor is restricted to neutral compounds of moderate hydrophobicity. No attempts were made to measure partitioning of ionogenic compounds with the glyceryl trioleate-water partition system. 

Fujiwara, H., Da, Y-Z., Ito, K., Takagi, T., and Nishioka, Y. The energy aspect of oilAvater partition and its application to the analysis of quantitative structure-activity relationships. Aliphatic alcohols in the liposomeAvater partition system. Bull. Chem. Soc. Jpn., 64(12) 3707-3712, 1991. 

Different balance between intermolecular forces can be accessible via partition coefficients measured in solvents systems other than the traditional 1-octanol/water. Therefore there was a growing interest in the partition processes in several solvent/ water systems [64, 65] and in particular the critical quartet of solvents which was designed to merge the main information about a solute concerning its partition and transport. Only a few studies have been performed to characterize the lipophilicity profile of new chemical entities in different solvent/water systems and consequently the number of methods attempting to model such partitioning systems is limited. 

Platis, D. and Lebrou, N.E. (2006). Development of an aqueous two-phase partitioning system for fractionating therapeutic proteins from tobacco extract. J. Chromatogr.A 1128(1-2) 114-124. 

Abraham, M.H., Zissimos, A.M., Huddleston, J.G., Willauer, H.D., Rogers, R.D., Acree, W.E., Some novel liquid partitioning systems Water-ionic liquids and aqueous biphasic systems, Ind. Eng. Chem. Res., 42, 413-418,2003. 

The sorption of two weak acids (warfarin and thiopentone) and two weak bases (chlorpromazine and diltiazem) into PVC infusion bags was described by a constant partition model. PVC-water partition coefficients were obtained using three different methods equilibrium values for sorption into PVC bags, the sorption versus pH relationship, and partition into PVC strips. The data were compared with similar values derived from a liquid-liquid partition system and different organic solvents (octanol, dichloromethane, carbon tetrachloride, and hexane). Octanol is the preferred solvent, and it is suggested that octanol-water partition data can be used to predict sorption behavior [182]. 

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