X-ray fiber diffraction patterns

The F-actin helix has 13 molecules of G-actin in six turns of the helix, repeating every 360 A. Oriented gels of actin fibers yield x-ray fiber diffraction patterns to about 6 A resolution. Knowing the atomic structure of G-actin it was possible for the group of Ken Holmes to determine its orientation in the F-actin fiber, and thus arrive at an atomic model of the actin filament that best accounted for the fiber diffraction pattern. 

Different kinds of disorder may affect differently the X-ray diffraction pattern of the crystals. Depending on the features present in the X-ray fiber diffraction pattern, it is useful to distinguish three main classes of disordered structures170 ... 

Mesomorphic forms characterized by conformationally ordered polymer chains packed in lattices with different kinds of lateral disorder have been described for various isotactic and syndiotactic polymers. For instance, for iPP,706 sPP,201 sPS,202 syndiotactic poly(p-methylstyrene) (sPPMS),203 and syndiotactic poly(m -methylstyrene),204 mesomorphic forms have been found. In all of these cases the X-ray fiber diffraction patterns show diffraction confined in well-defined layer lines, indicating order in the conformation of the chains, but broad reflections and diffuse haloes on the equator and on the other layer lines, indicating the presence of disorder in the arrangement of the chain axes as well as the absence of long-range lateral correlations between the chains. 

The notion of a common core structure has been further supported by synchrotron X-ray fiber diffraction patterns of several amyloid fibrils the patterns show common reflections in addition to those at 4.7 and 10 A (Sunde et al., 1997). Although these data give some insight into the arrangement of the amyloid fibril core, the exact molecular structure and organization of the proteins making up this common core have yet to be uniquely defined. The inherently noncrystalline, insoluble nature of the fibrils makes their structures difficult to study via traditional techniques of X-ray crystallography and solution NMR. An impressive breadth of biochemical and biophysical techniques has therefore been employed to illuminate additional features of amyloid fibril structure. 

Figure 2. X-ray fiber diffraction pattern from K " chondroitin 4-sulfate. (Reproduced with permission from ref. 18. Copyright 1983 Academic Press Inc.)...

Figure 2.32 X-ray fiber diffraction pattern of poly(dichlorophosphazene). The layerline separation distance corresponds to a polymer fiber axis repeating distance of 4.92 A. Reproduced by permission of Academic Press.

Figure 1. (a) (top) X-ray fiber diffraction pattern of i-PMMA. Fiber axis vertical. 

Figure 2. X-ray fiber diffraction patterns of i-PS gels, (a) (top) i-PS in trans-decalin showing rather weak, odd-order layer lines at 3.06-nm spacing, (b) (bottom,) i-PS in cis-decalin showing very strong first order layer line again with...

Figure 1 Example of an x-ray fiber diffraction pattern suitable for analysis using AXIS. The spots are discrete, there is no layer line streaking, and the background scatter may be seen clearly. The sample (potassium hyaluronate) was slightly tilted out of the plane perpendicular to the x-ray beam.

Figure 6. X-ray fiber diffraction pattern obtained (in conjunction with Dr. H. Chanzy) from an oriented film oj the sodium salt oj Klebsiella K63...

Figure 15. X-ray fiber diffraction pattern obtained from an oriented film of the sodium salt of Klebsiella K8. It is evident that there is a slight perturbation from perfect four-fold symmetry giving rise to some weaker forbidden meridional...

Figure 2. X-ray fiber diffraction patterns for ("top, left to right) V -amylose VrnlSo-amylose KOH-amylose (bottom, left to right) B-amylose, amylose triacetate I, triethylamylose I-nitromethane complex...

Figure 5.4 X-ray powder diffractogram recorded for (a) A-type amylodextrins and (b) B-type amylodextrins grown as spherulites. X-ray fiber diffraction patterns (fiber axis vertical) for (c) A-amylose (fiber spacing 1.04 nm) and (d) B-amylose (fiber spacing 1.05 nm). (Reproduced with permission from references 30 and 31). Microcrystal of (e) A-starch and (f) B-starch observed by low dose electron microscopy. Inset the electron diffraction diagrams recorded under frozen wet conditions (e). (Reproduced with permission from references 32 and 34)...

The hydrogen bonding in cellobiose and methyl cellobioside as models for that in the celluloses. In the absence of crystal structure analyses of higher oligomers of 1 - 4-linked /5-glucopyranose, cellobiose is frequently used as a model for interpreting the X-ray fiber diffraction patterns of the celluloses, especially since the cellobiose unit is considered to be the repeating unit of the polysaccharide chain. 

FIGURE 2.30 Schematic diagram of x-ray fiber diffraction pattern. 

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