X-ray diagrams

The crystallographic world was stunned when at a meeting in Erice, Sicily, in 1982, Hartmut Michel of the Max-Planck Institute in Martinsried, Germany, displayed the x-ray diagram shown in Figure 12.12. Not only was this the first x-ray picture to high resolution of a membrane protein, but the crystal was... 

Because of its regularity it would be expected that the polymer would be capable of crystallisation. In practice, however, the X-ray pattern characteristics of crystalline polymer is absent in conventionally fabricated samples. On the other hand films which have been prepared by slow evaporation from solvent or by heating for several days at 180°C do exhibit both haziness and the characteristic X-ray diagram. The amount of crystallisation and the size of the crystallite structures decrease with an increase in the molecular weight of... 

Kreutz, W. and Welle, W. A General Theory for the Evaluation of X-Ray Diagrams of Biomembranes and Other Lamellar Systems. Vol. 30, pp. 161—225. 

The fact that the structure that I formulated for this alloy from chemical arguments with no knowledge about the X-ray diffraction diagram was found later to agree quantitatively with that diagram has convinced me that the structure is correct. I emphasize that I formulated only one structure, and that the X-ray diagram was not involved in any way in its formulation. The probability of chance agreement of the lattice constant to 0,1 A and of adherence to the selection rules for intensities is surely less than 1 in 1,000. 

Huxley, H.E. Brown, W. (1967). The low-angle X-ray diagram of vertebrate striated muscle and its behavior during contraction and rigor. J. Mol. Biol. 30,383-434. 

Figure 6. X-ray diagrams for TEG with Sn02 and for dispersed graphite with Sn02.

Further confirmation of the identity of bacterial and plant celluloses has been obtained by x-ray studies. From dried membranes prepared by the action of A. xylinum on sucrose, Eggert and Luft18 obtained x-ray diagrams similar to those of cotton cellulose. Hibbert and Barsha16 showed that a chloroform solution of the triacetate of cellulose... 

The analysis of x-ray diffraction data is divided into three parts. The first of these is the geometrical analysis, where one measures the exact spatial distribution of x-ray reflections and uses these to compute the size and shape of a unit cell. The second phase entails a study of the intensities of the various reflections, using this information to determine the atomic distribution within the unit cell. Finally, one looks at the x-ray diagram to deduce qualitative information about the quality of the crystal or the degree of order within the solid. This latter analysis may permit the adoption of certain assumptions that may aid in the solving of the crystalline structure. 

Fig. 28. X-ray diagrams showing differences in composition of various zones during heating of zinc-hy droxide-carbonate...

I am indebted to The Leverhulme Trost for the award of a Research Fellowship that made the writing of this review possible. I thank Dr. D. J. Williams (Imperial College London) and Mr. R. Zarzycki for their kind assistance in producing the computer drawn X-ray diagrams. 

About structures of lithium compounds LisMeFs we have but rare knowledge. Klemm, Brandt and Hoppe (193) report in accordance with Meyers and Cotton (225) that the x-ray-diagrams of the cobalt compound LisCoFe were of a poor quality. The polymorphism that Carton and Wanklyn (108) report of the aluminium compound LisAlFe points to a more complicated situation in this ternary fluoride. The sizes given of the unit cells do not show any simple relation to the cryolite cell. The same may be true of compounds LisMeFa of the transition metals. 

The dimensions of the unit cells do not seem to be related to each other, so that the compounds listed apparently are not iso-structural. In contrast to this Hoppe, Liebe and Ddhne (166) assume the manganese compounds AMnFs (A = K, Rb, Cs) to be of the same type. The x-ray diagrams are similar to each other, but stiU could not be indexed. It remains to be checked, whether the unit cell given later by Clark and Sadana (66) for KMnFs may be applicable to the Rb- and Cs-compounds. 

X-ray investigations by Hess Katz (Ref 4) suggest that the addition product is probably compatible with the formula C HjqOj.HNO The X-ray diagram of the compound is a characteristic one differing from that of cellulose. 

The studies of Miles and Craik [13] merit special attention since they obtained the following X-ray diagrams of ramie (Chinese nettle) cellulose, which is notable for a distinctly crystalline structure (Fig. 83). 

Fig. 83. X-Ray diagrams (according to Miles and Craik [13]) (a) ramie cellulose, (b) ramie cellulose dinitrate, (c) ramie cellulose trinitrate.

Mathieu [18] has shown that X-ray diagrams taken at frequent intervals during nitration of cellulose with N205 vapour indicate that the structure progresses through all the stages from cellulose to cellulose trinitrate. 

The X-ray experiments of Hess and Trogus [19] have shown that nitrocellulose immediately after formation gives a very diffuse X-ray diagram with barely legible interference bands, typical for swollen cellulose and nitrocellulose. 

Fig. 87. X-Ray diagrams (a) of nitrocellulose immediately after the separation from the nitrating acid, (b) of nitrocellulose after washing out the acid, (c) of stabilized nitrocellulose (Hess and...

Herzog and Londberg [20] have examined the X-ray diagrams of cellulose produced by denitration of a carefully nitrated product. The picture of the regenerated cellulose was in principle identical with that of cellulose before nitration. This observation suggests that a cautious nitration of cellulose that proceeds without oxidation or hydrolysis does not change the microcrystalline structure of the cellulose, i.e. this is a topochemical reaction, in which the product preserves the same... 

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