Solvent countercurrent distribution

The partition of different lipids between two immiscible solvents (countercurrent distribution) is useful for crude fractionation of lipid classes with greatly differing polarities. Repeated extractions in a carefully chosen solvent pair increase the effectiveness of the separation but in practice mixtures of lipids are still found in each fraction. A petroleum ether-ethanol-water system can be used to remove polar contaminants (into the alcoholic phase) when interest lies in the subsequent analysis of neutral glycerides, which may be recovered from the ether phase. Carbon... 

Oxytocin [50-56-6] M 1007.2, m dec on heating, [a] -26.2"(c 0.53, N AcOH). A cyclic nonapeptide which was purified by countercurrent distribution between solvent and buffer. It is soluble in H2O, rt-BuOH and isoBuOH. [Bodanszky and du Vigneaud J Am Chem Soc 81 2504 1959 Cash et al. J Med Pharm Chem 5 413 1962 Sakakibara et al. Bull Chem Soc Jpn 38 120 1965 solid phase synthesis Bayer and... 

Chromatography on thin layers of Avicel C (microcrystalline cellulose from American Viscose Division, F.M.C. Corp., Newark, Del.), in 1-butanol-water-acetic acid (4 5 1) with bromocresol green as indicator. Countercurrent distribution in same solvent by single withdrawal procedure with 299 transfers and 100 elements... 

Just one extraction performed on a solution of a complicated sample will likely not result in total or at least sufficient separation of the analyte from other interfering solutes. Not only will these other species also be extracted to a certain degree with the analyte, but some of the analyte species will likely be left behind in the original solvent as well. Thus, the analyst will need to perform additional extractions on both the extracting solvent, to remove the other solutes that were extracted with the analyte, and the original solution, to remove additional analyte that was not extracted the first time. One can see that dozens of such extractions may be required to achieve the desired separation. Eventually, however, there would be a separation. The process is called countercurrent distribution. 

Define recrystallization, distillation, fractional distillation, extraction, liquid-liquid extraction, solvent extraction, countercurrent distribution, liquid-solid extraction, and chromatography. 

Countercurrent distribution is a liquid-liquid extraction process in which actually dozens of extractions are performed when extracting solvent and sample solvent are contacted in the manner depicted in Figure 11.4. It is a process involving a series of separatory funnels in a way that approximates partition chromatography. 

Ac-Tyr- Met-Gly-Trp- Met- Asp-Phe-NH, (5 0.55 g, 0.56 mmol) was dissolved in a mixture of anhyd DMF (10 mL) and anhyd pyridine (5mL) and was then treated with pyridine/S03 (2g, 13 mmol) at rt for 24 h. The solvents were removed and the residue was dissolved in ice-cold H20 (20 mL) while keeping the pH at 7.0 with 10% aq Na2C03. The aqueous soln was then concentrated and after addition of DMF the inorganic salts were removed by filtration. The filtrate was taken to dryness and the resulting crude product purified by countercurrent distribution in the solvent system BuOH/EtOH/H2Q (5 1 8). Frac-... 

Martin and Porter (19) described a partition chromatographic procedure and first demonstrated the presence of at least one minor active component in the crystalline enzyme preparation. King and Craig (20) found a solvent system permitting effective countercurrent distribution of ribonuclease, ethanol water ammonium sulfate in the ratios 25.9 -57.6 16.5. The principal component of the Kunitz preparation behaved as an almost ideal solute with a partition ratio of 0.8. Albertsson has provided a liquid polymer countercurrent system based on dextrari and methyl cellulose (21). 

Sometimes requires large quantities of organic solvents poor resolution of mixtures of organic materials except by countercurrent distribution which is slow. 

Theoretically, any number of solutes can be separated in this manner and the method has been applied, for example, to the separation of fatty acids, amino acids, polypeptides and other biological materials with distribution ratios in some cases differing by less than 0.1. However, the procedure can be lengthy and consumes large volumes of solvents. It is frequently more convenient to use one of the chromatographic techniques described later in this chapter. These can be considered as a development of the principle of countercurrent distribution. 

Fresh plants were extracted with CH3OH separation from lipophilic compounds by organic solvents, ion exchange chromatography, and countercurrent distribution yielded 3 X 10 Vo... 

Fresh plants D. nobile) were extracted with CF130F1 separation from lipophilic compounds by organic solvents ion-exchange chromatography and countercurrent distribution yielded 1.7 X... 

The fundamental principle of separation for modem DuCCC is identical to classic countercurrent distribution. It is based on the differential partitions of a multicomponent mixture between two countercrossing and immiscible solvents. The separation of a particular component within a complex mixture is based on the selection of a two-phase solvent system, which provides an optimized partition coefficient difference between the desired component and the impurities. In other words, DuCCC and HSCCC cannot be expected to resolve all the components with one particular two-phase solvent system. Nevertheless, it is always possible to select a two-phase solvent system, which will separate the desired component. In general, the crude sample is applied to the middle of the coiled column through the sample inlet, and the extreme polar and nonpolar components are readily eluted by two immiscible solvents to opposite outlets of the column. 

The capability and efficiency of DuCCC in performing classic countercurrent distribution has been demonstrated in the isolation of bioactive lignans and triter-penoic acids from crude natural products and in the purification of synthetic polypeptides. DuCCC provides excellent resolution and sample loading capacity. It offers a unique feature of elution of the nonpolar components in the upper-phase solvent (assuming the upper phase is less polar than the lower phase) and concomitant elution of the polar components in the lower phase. This capability results in an efficient and convenient preparative method for purification of the crude complex mixture. The capability of DuCCC has not yet been fully explored. For instance, a particular solvent system can be selected to give the desired bioactive component a partition coefficient of 1. This... 

Adsorption or chromatography is one of the best known methods of approach to the problem of isolating an active principle. Once a suitable adsorbent has been found, the problem is not difficult. The approach used for countercurrent distribution can aid in understanding the process (solid phase which takes the place of the heavier phase in the series of separatory funnels. If an adsorbent and solvent is chosen so that about half the solute is adsorbed from the solution, the conditions are met for easy application... 

In order to choose the most effective fractionating technique we must know something of the nature of the compound in biochemistry particularly, something of the stability of the solutes involved. Unquestionably many compounds of importance have such poor stability except in solution in a certain environment that they can never be crystallized or obtained free of solvent. Yet such a substance could cause a very specific biochemical response and it would therefore be of the greatest interest to know if such a response were caused by a single chemical individual or whether a collection of individuals were responsible for the effect. In such a problem countercurrent distribution offers possibilities. 

Thadani et al.22 studied the purity of commercial penicillin V by countercurrent distribution in different solvent systems. They found 95.0% penicillin V and 2.9% penicillin J. 

---