Methods fractions

Although fractional crystallization has always been the most common method for the separation of diastereomers. When it can be used, binary-phase diagrams for the diastereomeric salts have been used to calculate the efficiency of optical resolution. However, its tediousness and the fact that it is limited to solids prompted a search for other methods. Fractional distillation has given only limited separation, but gas chromatography and preparative liquid chromatography have proved more useful and, in many cases, have supplanted fraetional crystallization, especially where the quantities to be resolved are small. 

TBT of mark tch , is used which was distiled in vacuum, three times selecting fraction with boiling temperature 7j,=430-432 K at pressure 1,33 Gpa [6]. Obtaited by such method fraction was preserved under molecular sieve 4 A. 

For resolution of the racemate 12 two different procedures can be applied 124 the en-antioselective enzymatic deacylation of chloroacetyl-DL-a-aminosuberic acid at pH 7.2 with Taka-acylase or the enantioselective salt precipitation of Z-dl-Asu-OH with D-tyrosine hydrazide according to the method of Vogler et alJ25 Complete enzymatic digestion is achieved in about ten days at 37 °C, and the optically pure L-enantiomer is obtained in 80% yield but the overall efficiency is lower than that of the chemical method. Fractional crystallization affords in good yields the Z-l-Asu-OH derivative 13 which is then used directly as a suitably protected intermediate in subsequent derivatization steps (see Scheme 6). Moreover, the recovery of the D-enantiomer from the mother liquors is also easy in this case. 

Figure 6. Fractionation of a mutagenic drinking water concentrate with Sephadex LH20. On a Sephadex LH20 column, 1.6 mL of a drinking water concentrate (IX 106-fold concentrated, neutral fraction) was separated by using stepwise isopropyl alcohol (ISOP) and dioxane/water (D/W) elution as described in Material and Methods. Fractions were pooled as indicated. After reconcentration the fractions were assayed for mutagenic activity in the Salmonella mutagenicity test and CHO cells (Table I).

Termed Fractional Destraction, the method fractionates residuum according to the solubility of its constituent components in a supercritical fluid. The novel aspect of the approach is the incorporation of a system to promote reflux of less-soluble components onto a packed bed. 

A number of multidimensional analyses have been developed that provide powerful methods for characterizing these polymers. Linking a liquid chromatogram to a pyrolysis gas chromatograph [l 9] can determine the breadth of the composition distribution, as the method fractionates the SAN copolymer before pyrolysis. This information is useful for determining the source of variation in SAN copolymer properties. Composition drift towards high acrylonitrile-containing fractions can lead to undesirable yellow color, and excessively broad composition drift can cause opacity and brittleness in the material due to phase separation... 

Figure 2. Analytical DEAE chromatography of K-ras from Baculovirus infected insect cells. Purified K-ras was separated by DEAE chromatography as described in Methods. Fractions were collected and subjected to ESI-MS analysis. 

The classical chemical methods to separate lanthanoids were based upon the redox behavior of Ce, Sm, Eu, and Yb , Other classical methods (fractional crystallization) are essentially physical processes. Cerium is oxidized to the 4-I- state and separated from the 3+ rare earths by solvent extraction, iodate precipitation, or selective hydrolysis or precipitation of basic Ce(IV) compounds in weakly acidic solution. Europium is reduced and maintained in H2O as Eu " by Zn amalgam and precipitated as EUSO4. Sm and Yb are extracted from H2O by reduction into dilute Na or Li amalgam. 

In the industrial method, fractionation is achieved by the method of rectification. Using this method, the fractions with boiling point up to 350°C are separated at atmospheric pressure. These are called the light fractions. Usually, during atmospheric rectification, the following individual fractions are obtained ... 

FRACTIONATION METHODS Fractional precipitation in toluene/ methanol (solvent/nonsolvent) mixtures at40/20°C. ... 

Ethanolic sesame seed extracts were purified to obtain a taurine transport inhibitory substance (TTIS) using a two-step method. Fractions were collected... 

Precipitation Fractionation. In this method, fractions of decreasing molecular weights are obtained in each successive fractionation step. Because of the decreasing molecular weight of the fractions, this technique is also called downward precipitation fractionation, to distinguish it from another variant named upward precipitation fractionation that will be described later in this section. In either case, it is instructive to notice that precipitation fractionation is a misnomer, since the polymer does not in fact precipitate, but rather forms a separate polymer-rich liquid phase. 

A variation of this technique involves the use of quartz tubes coated on the inner surface with silica gel or silica gel -f CuO instead of adsorbent-coated glass rods. In the tubular TLC (TTLC) method, fractionation on the chromatotubes is carried out as in conventional TLC, followed by drying of solvent by... 

Fig. 28. Protein electrophoretic pattern of unfractionated chloroplast membranes from C. rein-hardi y-1 and of fractions produced by Triton X-lOO treatment. Electrophoresis was carried out by the phenol-acetic acid method." Fraction 2 consists of PSII particles and is highly enriched in a main peak (3 cm from the origin) identical with the L protein. Fraction 3 consists of PSI particles and is relatively poor in this protein. (For experimental details see ref. 81.)...

FIGURE 3. Elution of a and 3 from a CM-Sephadex column in 8 M urea. The column was run and the samples were eluted isocratically as described in Materials and Methods. Fractions (2 mL) were monitored by their absorbance at 280 nm and were analyzed by SDS gel electrophoresis on 15% polyacrylamide gels. Fractions 10-13 contained the 3 subunit and were pooled. Fractions 19-25 contained the a subunit. 

---