Crystallization methods

Crystallization Method. Such methods as mechanical separation, preferential crystallisation, and substitution crystallisation procedures are included in this category. The preferential crystallisation method is the most popular. The general procedure is to inoculate a saturated solution of the racemic mixture with a seed of the desired enantiomer. Resolutions by this method have been reported for histidine (43), glutamic acid (44), DOPA (45), threonine (46), A/-acetyl phenylalanine (47), and others. In the case of glutamic acid, the method had been used for industrial manufacture (48). 

Crystallization methods are widely used for the separation, or resolution, of enantiomer pairs. Enantiomer mixtures may essentially crystallize in two different ways. In around 8 per cent of cases, each enantiomer crystallizes separately, giving rise to a mechanical mixture of crystals of the two forms, known as a conglomerate. Conglomerates may usually be separated by physical methods... 

The same paper also described an analogous complex of 1,4-dibromotetra-fluorobenzene, 17-8, whose molecular structure, as obtained by single crystal methods, is shown as Fig. 17. 

Spinning a crystal during measurement of WAXS patterns is an old method that turns any scattering pattern into a fiber pattern. The rotational axis becomes the principal axis. Thereafter isotropization of the scattering data is simplified because the mathematical treatment can resort to fiber symmetry of the measured data. In the literature the method is addressed as the rotating-crystal method or oscillating-crystal method. 

It should be clear that the Darwin equation with its special LoRENTZ-polariza-tion factor as reported by Warren ([97], Eq. (4.7)) is only valid for unpolarized laboratory sources and the rotation-crystal method. An application to different setup geometries, for example to synchrotron GIWAXS data of polymer thin films is not appropriate. 

Since Steiner s aim was to improve immaterial qualities of foods, anthroposophic scientists have developed analytical methods, which aim to visualize this kind of inner quality. This is done by preparing watery solutions of the plant, meat or milk (= juices) which are then brought into reaction with metallic salts like copper chloride (copper chloride crystallization method)... 

Except through the study of linear and nonlinear optical properties of molecular crystals, methods to determine the nature of / require evaluation of appropriate characteristics of... 

The structures of 16 copper(II) complexes of bidentate amidino-O-alkylureas ([CuL jyXj) have been determined by single crystal methods [59-61,63-66]. The range of ligands and of copper(II) salts studied is summarised in Table 2. Although the N-alkylamidino-O-alkylurea derivatives form part of the systematic study by Suksangpanya et al. [59-61] [Cu(LHm)2]Cl2 [66], [Cu(LHm)2]Br2 [63], [Cu(LHe)2] Cl2 [64] and [Cu(LHe)2]Br2 [65] were prepared in independent studies. 

A batch cooling crystallization is one of the most commonly used crystallization method. In this process super saturation of a liquid is achieved by means of a cooling process. The solubility of the solute (in the solvent) decreases with a decrease in temperature this leads to precipitation of the solute. 

The kinetic resolution using a chiral zirconocene-imido complex 286 took place with high enantioselectivity to result in chiral allenes 287 (up to 98% ee) (Scheme 4.74) [116]. However, a potential drawback of these methods is irreversible consumption of half of the allene even if complete recovery of the desired enantiomer is possible. Dynamic kinetic resolutions avoid this disadvantage in the enantiomer-differentiating reactions. Node et al. transformed a di-(-)-L-menthyl ester of racemic allene-l,3-dicarboxylate [(S)- and (RJ-288] to the corresponding chiral allene dicarbox-ylate (R)-288 by an epimerization-crystallization method with the assistance of a catalytic amount of Et3N (Scheme 4.75) [117]. 

Fig. 11.2 Changes in the concentration of Me-est from ethanol solutions using the rapid cooling crystallization method...

Derewenda ZS. 2004. The use of recombinant methods and molecular engineering in protein crystallization. Methods 34 354-363. 

Wiener MC. 2004. A pedestrian guide to membrane protein crystallization. Methods 34 364-372. 

The simplest conditioner is a perfect crystal of the same type as the specimen, using the same reflecting planes, with the deviation of the diffracted beam in the opposite sense to that at the specimen. This is the classic +, - symmetrical double crystal method , as shown inFigrrre 1.5, which gives excellent and easily interpreted resrrlts. Many variations are, however, possible, for example to maximise the sensitivity to strain, or to emphasise the contribution of near-srrrface layers to the diffraction, and we shall treat these in detail in this book. 

There are many methods of X-ray topography, though the most popitlar are the Lang method with slit-collimated radiation and the double-crystal methods, which may be thought of as high resolution diffractometry with an imaging... 

Another way of looking at the traditional double-crystal method is that it measures the difference in reflectivity between the specimen and a reference perfect crystal. This is the original high resolution method and is still the best choice when good reference crystals are available and the specimens to be... 

Crystallization method employing microwave radiation. US Patent 4,778,666. 

Microbatch can be performed either manually or automatically (Chayen et ah, 1992). It is the simplest crystallization method and therefore can be easily performed in high-throughput trials. Current robots can dispense microbatch trials down to 1 nl volumes. Depending on the type of oils used to cover the trials, this technique can be harnessed for both screening and optimization experiments. 

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