Low-angle diffraction

Figure 4. PXRD patterns (all intensities are normalized to the dioo reflection intensity of calcined MCM-41. Low angle diffractions (2-15° 20) (a) pure MCM-41 ao 4.44nm d oo-3.84nm) (b) 2x magnification of pure Cu6(TePh)6(PPh2Et)s, (c) Cu6(TePh)6(PPh2Et)5/MCM-41 treated at 70°C under dynamic vacuum (a<, 39.4nm dioo 3.41nm), (d)...

A typical low-angle diffraction pattern from relaxed bony fish muscle is shown in Fig. 4B. Much of the intensity that is seen comes from the organization of the myosin heads on the myosin filaments in the resting state (probably mainly MADP.Pi). We know that the myosin heads lie approximately on three co-axial helices of subunit translation 143 A and repeat 429 A. This is most easily represented by the radial net shown in Fig. 16B-D. The radial net in D is like an opened-out surface view of the filament in B. Here the helical tracks become straight lines, and the black blobs represent the origins on the myosin filament surface of the pairs of myosin heads in each myosin molecule. From early studies it is known that the three crowns within the 429 A repeat are not exactly the same and that there is a perturbation. 

Myosin filament structure has been described by Squire et al. (2005). In vertebrate striated muscles the myosin filaments can be described approximately as three-stranded 9/1 helices. The helix pitch is 1287 A, but, because there are three strands and nine subunits in each strand, the structure repeats after C = 1287/3 = 429 A. Figure 12 shows the expected form of the low-angle diffraction pattern from such filaments. The modeling of this structure by X-ray diffraction was described by Squire et al. in terms of the three crowns of heads within each 429 A repeat. The crown repeat of 143 A gives rise to an m = +1 meridional reflection, which has been labeled as the M3 reflection in many muscle studies (as in Fig. 12). The myosin head array also gives rise to layer lines at orders of the repeat of 429 A. The first myosin layer line (ML1) is at 1/429 A-1, the second (ML2) at 2/429 = 1/ 214.5 A-1, and so on. The M3 reflection occurs on the third layer line at 3/429 = 1/143 A-1. 

Fig. 12. (A) The left half of a low-angle diffraction pattern from bony fish muscle...

Several groups have studied the effects on the muscle low-angle diffraction pattern of applying various mechanical perturbations to steady-state structures, either isometric contractions or rigor muscle at various strain levels. Huxley et al. (1981, 1983) used whole frog muscles and followed the effects of step changes of length of various amplitudes applied at the plateau of an otherwise isometric tetanus. They studied the effects on the M3 intensity as a whole. More recendy, with the two components of the active M3 resolved, Huxley et al. (2003) and Reconditi et al. (2003) have studied the separate behavior of these components. Huxley et al. (2003) found that the intensity ratio of the M30 to M3 varied from an initial value... 

FIGURE 1.8 Low-angle diffraction pattern of n-butylammonium vermiculite at T = 6°C and an external salt concentration of c = 0.1 M. 

The effect of PEG on thermal stability of the mesostructured Ce02 powders has been observed by comparing the difference of properties between the samples CPN-2 and CN. Figure 10 shows the small angle XRD patterns of the samples CPN-2 and CN. After calcination at 673K, the low-angle diffraction peak in the XRD pattern of CN disappeared, but still existed in that of CPN-2. This may be attributed to the thermal stability improvement deriving from non-ionic surfactant PEG. 

Polyacetylene containing a phenylcyclohexyl meso-gcnic side chain on every repeat unit has been synthesized by Yoshino et al. [158], employing the Araya method for a substituted 1-pentyne. The polymer shows the smectic A phase, and retains the layer structure upon cooling to the solid state. Only a low-angle diffraction corresponding to a spacing of 20-22 A is reported. 

The X-ray diffraction patterns for Ge02 (H) and Ge02 (T) have been accurately determined and can be used to identify films as thin as 500 A (using low angle diffraction). Here again, the monoxide phase cannot be identified by this means since no diffraction pattern has been observed for that phase. Some other non-destructive techniques have been used such as low energy electron diffraction (LEED), electron loss spectroscopy (ELS), Raman scattering, etc. but usually they are so sensitive to contamination that the results cannot easily be used for simple phase identification. Such techniques are therefore more useful for physical property studies. 

Table 4.3 Ratio of complex formation obatined by mixing and grinding the component crystals of aromatic compounds with heteroatoms and the cationic surfactants. The ratios were calculated using the peak heights of the low-angle diffractions of their X-ray powder patterns...

---