Fractionation methods solvent extraction, preferential

The so-called solvent extraction method by toluene, o-xylene or carbon disulfide is the most common and frequently used extraction method, in which metallofullerenes and hollow fullerenes are preferentially dissolved in solvents. The so-called Soxhlet extraction (a continuous and hot solvent extraction) or ultrasonic extraction is normally employed to increase the solvent extraction efficiency (Khemani et al., 1992). Insolubles in soot are easily separated from this solution by filtration. However, in many cases, the toluene or CS2 extraction is not sufficient, since nearly half of the metallofullerene still remains in the residual soot even after the extensive CS2 extraction. It has been found that metallofullerenes are further extracted from the residual soot by such solvents as pyridine (Inakuma et al., 1995) and 1,2,4-trichlorobenzene (Yamamoto et al., 1994a,b). The metallofullerenes were found to be concentrated in this pyridine or trichlorobenzene extracted fraction. When necessary, the metallofullerene extracts can be stored in carbon disulfide solution for an extended period of time, up to a year. 

Rosenkrantz (1957) has written one of the earlier articles on the utilization of fractionation procedures with infrared analysis and has listed several types of fractionation techniques chromatography, countercurrent distribution, preferential solvent extraction, sublimation, fractional crystallization, molecular distillation, dialysis, centrifugation, electrophoresis, diffusion, and freeze-drying. He has also given references to work in which these methods have been used to fractionate a large variety of biological compounds. Elvidge and Sammes (1966) have discussed many of the techniques mentioned above. 

If both anomers of the glycoside are obtained in a reaction, it is necessary to separate them. One separation method that has been used is the preferential extraction101 of the anomers with a volatile solvent. After extraction of the individual glycoside, the solvent is removed by evaporation, and the glycoside may be obtained in crystalline form. A second method of separation utilizes fractional recrystallization, and it may be possible by proper selection of the solvent to obtain both anomers in crystalline form. A third method utilizes chromatography for separating the anomers, and the pure anomers may be obtained from appropriate fractions from the column. The anomeric configuration of the anomers which have been obtained in pure form will need to be determined. Such determinations can be made by measurement of physical constants, from the n.m.r. spectra, and from the susceptibility of the anomer to enzymes of known specificity. 

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