Crystal structures macromolecular crystals

B. Wunderlich, Macromolecular Physics, Crystal Structure, Morphology and Defects, Vol. 1, Academic Press, New York, 1973. 

Wunderlich B (1973) Macromolecular physics, vol 1. Crystal structure, morphology, defects. Academic, New York, p 68... 

B. WunAetlvda., Macromolecular Physics Vol.l (Crystal Structure, Morphology, Defects), Academic Press (1973). 

The recommendations embodied in this document are concerned with the terminology relating to the structure of crystalline polymers and the process of macromolecular crystallization. The document is limited to systems exhibiting crystallinity in the classical sense of three-dimensionally periodic regularity. The recommendations deal primarily with crystal structures that are comprised of essentially rectilinear, parallel-packed polymer chains, and secondarily, with those composed of so-called globular macromolecules. Since the latter are biological in nature, they are not covered in detail here. In general, macromolecular systems with mesophases are also omitted, but crystalline polymers with conformational disorder are included. 

Figure 3.2 Dispensing of a microbatch trial under oil. The dashed circle represents the initial position of the crystallization drop at the time of dispensing. The grey circle represents the final position of the drop after it had made its way to the bottom of the well (due to its higher density compared to that of the oil). Modified from Chayen (1997). The role of oil in macromolecular crystallization. Structure 5, 1259-1274, Copyright Elsevier.

In the debate about existence of pre-ordered states in the polymer melt, as advocated recently, polyolefins with chiral side chains may well become a major investigation tool. Indeed, the macromolecular amplification induces a pre-organization, or at least a preferred helical conformation in the polymer melt or solution. As such, these polymers display very precisely the behavior that is assumed by some of the recent crystallization schemes or scenarios. Furthermore, for the P4MH1 systems considered so far at least, the confor-mationally racemic character of the stable crystal structure implies that half of the stems must change their helical hands at some stage in the crystallization process - which may greatly delay the formation of this stable crystal structure, as illustrated by P(S)4MH1. 

In modern crystallography virtually all structure solutions are obtained by direct methods. These procedures are based on the fact that each set of hkl planes in a crystal extends over all atomic sites. The phases of all diffraction maxima must therefore be related in a unique, but not obvious, way. Limited success towards establishing this pattern has been achieved by the use of mathematical inequalities and statistical methods to identify groups of reflections in fixed phase relationship. On incorporating these into multisolution numerical trial-and-error procedures tree structures of sufficient size to solve the complete phase problem can be constructed computationally. Software to solve even macromolecular crystal structures are now available. 

Wunderlich B, "Macromolecular Physics", Academic Press, New York, "Crystal Structure", Vol. I, 1973 "Crystal Nucleation and Growth", Vol. 2,1976 "Crystal Melting , Vol. 3,1980. 

In macromolecular crystallography, this process cannot be observed because hydrogen atoms are not located and dynamic processes cannot be seen . However, in the crystal structure of vitamin B12 studied by X-ray and neutron diffraction methods, an interpretation of the water movement could be derived [127, 880, 881]. 

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