Early crystallographic studies

The application of monoclinic monazites to the chemical sequestration of radioactive wastes has been noted in a prior section of the present chapter, and it is reviewed in detail by Ewing and Wang (this volume). From the crystal-chemical point of view, it has been previously suggested (Beall et al. 1981) that the observed ability of monazites to incorporate the diverse set of cations found in most radioactive wastes may be due to a relaxation of chemical constraints associated with the irregular 9-fold coordination. 

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Early crystallographic studies of TMADH provided data from two derivatives at 6 resolution that revealed the domain structure and certain elements of secondary structure (Lim et al., 1982 Lim et al., 1984). Higher resolution data at 2.4 resolution have been collected and the structure solved by the multiple isomorphous replacement method with anomolous scattering (Lim et al., 1986). Analysis of the diffraction pattern lead to the identification of ADP as the third cofactor in TMADH. At the time the 2.4 data set was analysed, there was no sequence information available for TMADH (Lim et al., 1986), except for a 12 residue peptide which contained the covalently bound flavin (Kenney et al., 1978). Gas-phase sequencing of isolated peptides initially provided 80% of the primary sequence of... 

Since electron microscopy requires minute samples, the crystallography of materials that are available only as small particles (e.g., catalysts) can be studied in direct and reciprocal space. The early crystallographic studies on Cuy and C70 crystals were for instance, performed by electron diffraction (194. Even fine powders or finegrained ceramics contain single crystal particles large enough to produce a single crystal electron... 

Early crystallographic studies revealed the hexameric nature (R = Et, E r) (328,329) of silver(I) dithiocarbamate complexes in the solid state, although in solution they are believed to be in equilibrium with monomeric species (329). More recently, the diethyldithiocarbamate complex has been the subject of two further crystallographic studies (Fig. 241) (330,331). Delgado and Diez (329)... 

There has been considerable work in the literature on the structure of very small particles and clusters. Interest in this field has been primarily due to Ino s (1966) early experimental studies of normally fee metals prepared by vapour condensation which showed that a sizable portion of the particles exhibited non-crystallographic structures. These non-crystallographic atomic clusters or polycrystalline nuclei have been observed to consist of pentagonal bi-pyramid or icosahedra form of twinned structures and are known as multiply twinned particles (MTPs). EM studies of supported transition metal catalyst systems have indicated that MTPs sinter faster in catalytic reactions leading to the loss of surface area and are not beneficial to catalysis (Gai 1992). We describe the structure and the role of MTPs in catalysis in the following sections. 

The structure of atisinium chloride as 5 was confirmed recently by a single-crystal X-ray analysis (SO). The absolute configuration of atisinium chloride was determined as 45, 5S, 8/ , 10/ , 12/ , and 155 by Hamilton s method and confirmed by examination of sensitive Friedel pairs. A recent X-ray crystallographic study of isoatisine confirmed the assigned structure 75. The absolute configuration was established as 45, 55, 8/ , 10/ , 12/ , 155, and 195 for isoatisine. It is worth noting that isoatisine does not exist as a mixture of C-19 epimers. Early work on the chemistry of atisine and isoatisine... 

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