Density fluctuations, during crystallization

Imai, M., Kaji, K. and Kanaya, T., Structural formation of polyethylene terephthalate) during the induction period of crystallization. 3. Evolution of density fluctuations to lamellar crystal, Macromolecules, 27, 7103-7108 (1994). 

Figure 7.2 shows WAXS, SAXS and SALS results during isothermal crystallization of EH064. The crystallization kinetics is accurately resolved by X rays at temperatures below the peak melting temperature = 95° C (Fig. 7.3). As the crystallization temperature increases close to the peak melting temperature, both the changes in the SAXS invariant and crystallinity determined from WAXS are very small and close to the detection limits. This is because, at these high crystallization temperatures, large thermal fluctuations and the low density contrast between crystal and amorphous phase make it difficult to detect the changes in crystallinity and structure [27,29,39 1].To resolve early stage crystallization behavior without the influence of crystal...

Figure 1.20 Variation of density fluctuation (2 ) and orientation fluctuation (Qs) with time during isothermal crystallization of iPP [116].

Present knowledge of the details of the conformation of proteins is based almost exclusively on results of studies of protein crystals by x-ray diffraction. Protein crystals contain anywhere from 20 to 80% solvent (1 ) (dilute buffer, often containing a high molarity of salt or organic precipitant). While some solvent molecules can be discerned as discrete maxima of the electron density distribution calculated from the x-ray results, the majority of the solvent molecules cannot be located in this manner most of the solvent appears to be very mobile and to have a fluctuating structure perhaps similar to that of liquid water. Many additional distinct locations near which a solvent molecule is present during much of the time have been identified in the course of crystallographic refinement of several small proteins (2,3,4,5, 6), but in all cases the description of solvent structure in the crystal is incomplete probably because only a statistical description is inherently appropriate. 

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