Diffraction indices

Cellulose is the main component of the wood cell wall, typically 40—50% by weight of the dry wood. Pure cellulose is a polymer of glucose residues joined by 1,4-P-glucosidic bonds. The degree of polymerization (DP) is variable and may range from 700 to 10,000 DP or more. Wood cellulose is more resistant to dilute acid hydrolysis than hemiceUulose. X-ray diffraction indicates a partial crystalline stmcture for wood cellulose. The crystalline regions are more difficult to hydrolyze than the amorphous regions because removal of the easily hydrolyzed material has Htde effect on the diffraction pattern. 

Reflex type Relative intensity Diffraction indices (hkl) Interplanar spacing d/, / (A) Glancing angle for CuK -2Q/, ( )... 

Those containing less than 7.5% N show a fiber character and give no X-ray diffraction indicating nitration, but only the pattern of mercerized cellulose... 

FIG. 33 X-Ray Diffraction Patterns of Ammonium Dodecane 1-Sulfonate. 2-D (a) and 3-D plots (b) of oriented samples. Both pictures show the presence of a nonordered smectic phase, since the diffuse, weak, wide-angle diffraction indicates only an average distance between the molecules and the sharp, intense small angle reflections a very well defined layer distance. The reflections are perpendicular to each other, so the structure should correspond to an orthogonal smectic A type. The pictures were obtained using an x-1000 area detector from Siemens. 

The overall compositions of films 2 and 4 was such that homogeneous alloys were not expected, and the X-ray diffraction peaks showed evidence of phase-separation with two maxima corresponding to the compositions recorded in column 8, Table II. When palladium was deposited on top (and the film was rather light) then the apparent surface composition after annealing was 10% Rh and X-ray diffraction indicated a phase also containing 10% Rh (film 2). This convenient result was not observed when the order of deposition was reversed (film 4). These differences between apparent surface composition and the overall composition of the homogeneous alloy (or one of the phases in the miscibility gap) are discussed in Moss and Gibbens (34), with further examples. The main point to be made here is the rather variable nature of the surface composition compared with that expected, due to the operation of a number of factors. 

A second form of storage iron is haemosiderin (Weir et al., 1984). This is deposited in humans as a response to the condition of iron overload. Haemosiderin forms as insoluble granules with electron dense cores surrounded by a protein shell. It exists in two forms primary haemosiderin is the result of iron overload due to excessive adsorption of iron in the gut, whereas the secondary form is caused by the numerous blood transfusions which are used to treat thallassaemia (a form of anaemia). Electron diffraction indicated that the iron core in primary haemosiderin is a 3-line ferrihydrite with magnetic hyperfine splitting only below 4 K and, in the secondary form, consists of poorly ordered goethite. As goethite is less soluble in ammonium oxalate buffer solution (pH 3) it has a lower intrinsic toxicity (Mann et al., 1988). 

The last molecule we shall consider in this chapter is diborane, B2H6. Electron diffraction indicates the molecular structure of B2Hg as shown in Figure 7-12. Ha, H, H, and Hg lie in the yz plane, while B2H2 lies in the xz plane. 

In the first place, DNA molecules are quite large, sufficiently so to permit them to be seen individually in photographs taken with electron microscopes. The molecular weights vary considerably, but values of 1,000,000 to 4,000,000,000 are typical. X-ray diffraction indicates that DNA is made up of two long-chain molecules twisted around each other to form a double-stranded... 

Therefore, in spite of the identical microanalysis data for the initial product and the destilled one, the X-ray powder diffraction indicates the presence of the admixture phases in the latter [950,968]. Details of the physicochemical characteristics of different derivatives are provided in Chapter 12. They are also described in the review part of the book by Bradley et al. [223]. 

Tregear, R. T., Edwards, R. J., Irving, T. C., Poole, K. J., Reedy, M. C., Schmitz, H., Towns-Andrews, E., and Reedy, M. K. (1998). X-ray diffraction indicates that active crossbridges bind to actin target zones in insect flight muscle. Biophys.J. 74, 1439-1451. 

Another intercalation was observed in the inclusion crystals of CA with n-propylbenzene [32c], Heat treatment of a 1 1 molar ratio of CA with n-propyl-benzene gave intermediate inclusion crystals with the same guests at 2 1 stoichiometry. Comparison of both crystal structures by powder X-ray diffraction indicated that the bilayers slide past each other on the lipophilic sides by ca. 4.5 A in the horizontal direction. The 2 1 crystals can be returned to the original crystal (1 1) by soaking them in the liquid n-propy I benzene, and the bilayer can slide back to the initial position without changing to the amorphous state. 

The cause of this conversion point is not known and X-ray analyses gave no indication of changes j however, electron diffraction indicated the... 

Now it is known that Ln(III)(H20)9 can be formed by all lanthanide ions in crystals. Solution studies by X-ray diffraction indicate that the same tricapped trigonal prism exists in solution for Pr(III) and La(III) but there may well be variation in the relative... 

FIGURE 5 Characterization of iron ammonia synthesis catalyst. High-resolution laboratory diffraction indicated a reversible modification of the iron (111) line profile. Under catalytic reaction conditions, a sub-nitride with x = 15-18 is present in addition to the bulk iron matrix. The fitting and assignment of the data were substantiated by observations of the line profile during step changes in the composition of the gas atmosphere. Details and references are given in the text. 

The electron diffraction results support the occurrence of soft-segment crystallinity and a more disordered hard-segment phase in the solvent-cast samples. Moreover, electron diffraction indicates isolated crystalline soft-segment regions persist even in samples of up to 43% hard segment. Electron diffraction is very sensitive to small local fluctuations in the overall structure because the diffraction patterns can be obtained from regions less than 1 /un in diameter and less than. l-/un thick, whereas DSC and WAXS, of course, measure bulk polymer which yields averages over the whole sample. 

---