X-ray diffractometric studies

Hizukuri, S. (1961). X-ray diffractometric studies on starches. Agric. Biol. Chem. 25, 45 9. 

Sankar, G. and Thomas, J. M. In situ combined X-ray absorption spectroscopic and X-ray diffractometric studies of solid catalysts, Top. Catal., 1999, 8, 1-21. 

In the high temperature x-ray diffractometric studies, Perri et al. (7J) indicate that WOg undergoes a phase transition from monoclinic to orthorhombic at approximately 593 K and from orthorhombic to tetragonal at 993 K. 

Quite early in the x-ray diffractometric studies of cellulose it was recognized that its crystallinity is polymorphic. It was established that native cellulose, on the one hand, and both regenrated and mercerized celluloses, on the other, represent two distinct crystallographic allomorphs (14). Little has transpired... 

One of the discoveries growing out of the early diffractometric studies of cellulose was that it can occur in a number of allomorphic forms in the solid state, each producing distinctive X-ray diffractometric patterns. In addition to the cellulose II form, which has been discussed extensively, two other forms have been recognized these are cellulose III and cellulose IV. It is of interest to consider them briefly because they reflect the capacity of cellulose to aggregate in a wide variety of secondary and tertiary structures and because some of the higher plant celluloses produce diffraction patterns that are not unlike those of cellulose IV. Furthermore, they reflect the tendency for some of the celluloses to retain some memory of their earlier states of aggregation in a manner not yet understood. 

On the other hand the X-ray diffractometric scans (168) show clear features of semicrystalline products. The X-ray data in (45) confirm this, but some distinct differences were found between the copolymer and homopolymer spectra, suggesting a possibility of isomorphism in this system. A more elaborate X-ray study is probably needed to explain the divergence between the IR and X-ray estimates of copolymer blockiness. 

The primary sources of information concerning the molecular structure of cellulose have been x-ray and electron diffractometric studies, conformational analyses, and vibrational spectroscopy. The work up to 1971 was very ably reviewed by Jones (10), and by T0nnesen and Ellefsen (II, 12). They generally concluded that although much evidence can be interpreted in terms of cellulose chains possessing a two-fold axis of symmetry, in both Celluloses I and II, none of the structures proposed... 

Duddu, S.P. Khin-Khin, A. Grant, D.J.W. Suryanarayanan, R. A novel X-ray powder diffractometric method for studying the reaction between pseudoephedrine enantiomers. J. Pharm. Sci. 1997, 86 (3), 340-345. 

Saesmaa T, Makela T, Tannienen VP. Physical studies on the benzathine and emanate salts of some /3-lactam antibiotics. Part 1. X-ray powder diffractometric study. Acta Pharm Perm 1990 99 157-162. 

In most of the studies these reflections, which are usually weak relative to the other main reflections, are assumed to be negligible. The controversy continues because the relative intensities can be influenced by experimental conditions such as the periods of exposure of the diffractometric plates. Furthermore, the disallowed reflections tend to be more intense in electron diffractometric measurements than in x-ray diffraction measurements. Thus, more often than not, investigators using electron diffraction challenge the validity of the assumption of twofold screw axis symmetry. 

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