X-Ray Crystal Structure Data

Identification of proteins that bind to Z-DNA added one further step to the establishment of the presence of Z-DNA in vivo and its possible biological role. Herbert and Rich [22] demonstrated an in vitro assay system where one type of double-stranded RNA adenosine deaminase, called DRAD-binding Z-DNA. There are evidences that topoisomerase II from Drosophila, hiunan and calf thymus recognizes a number of DNA shapes, including Z-DNA [34,35]. Bloomfield and coworkers [36] have found that the condensation of plasmids is enhanced by Z-DNA conformation in d(CG)n repeats. The information related to B-Z transition [31], the effect of ligands on it [28,29] and X-ray crystal structure data [37,38] appear to suggest that the possible biological role of this polymorphic form of DNA will be soon established. 

In collaboration with Prof. Herman Ammon (University of Maryland), MOLPAK/WMIN computational methods [6-12] have been employed successfully to predict the crystal densities of (i) several isomerically pure monomethylated PCU alkene dimers [13] and (ii) several polycyclic epoxides [14]. The crystal densities calculated from X-ray crystal structure data are compared with the corresponding calculated values. Attempts have been made to address discrep>-ancies that may exist between computed densities and those derived from A-ray data by using advanced theoretical methods. 

A very helpful attempt to classify organohydrazido and related complexes of Group 7 elements by analysis of their X-ray crystal structure data has been undertaken in a review which also covers the structural chemistry of this type of complexes up to the year 1996. The convention applied in this article will also be used here to classify hydrazido and related complexes. 

X-ray crystal structure data unless otherwise specified. b Differences between long and short Ni—N bonds. c EXAFS data. 

Fluorination and methylation have been used to synthesize975 related fluorinated nitronium ions [Eq. (4.231)]. The trifluoromethyl(methyl)nitronium ion ON(Me) CF3 + exits in the keto form in solution, but X-ray crystal structure data indicate that the enol form HON(CH2)CF3+ exists in the solid state stabilized by a hydrogen bond between the enolic OH group and one of the fluorines of the counterion. 

Many examples of the interaction between lithium and diverse it systems are documented in the literature. In the first review in this field Stucky (/) described the structure and bonding in it complexes of N-chelated lithium units. More recently, the synthesis and structure of organolithium compounds, including those containing unsaturated organic systems, have been reviewed by Wardell (2). A collection of X-ray crystal structure data of... 

The bonding in the cation LXX can be qualitatively explained in the same way as the bonding in the corresponding germanium species. The cationic pentamethylcyclopentadienyltin unit acts as a Lewis acid in its reactions with pyridine, pyrazine, and 2,2 -bipyridine, in which the adducts LXXXIa-d are formed [Eq. (41)] (205). X-Ray crystal structure data of adducts LXXIa and c... 

X-Ray crystal structure data on [Co(ete)(N02)Cl]Cl (ete = l,9-diamino-3,7-dithianonane) indicates the complex to have the uns-cis structure with the nitro-group trans to the nitrogen and the chlorine trans to the sulphur, showing that in its formation from u-cis[Co(ete)(N02)2]+ the greater trans effect of sulphur allows the trrws-nitro-group to be replaced.403... 

Dibromodimethylplatinum(IV) is a yellow crystalline solid that decomposes at 180-190°. It is insoluble in water and sparingly soluble in organic solvents. Although no X-ray crystal structure data are available, the complex is expected to be polymeric if the usual six-coordination of platinum(IV) is maintained. In methanol solution it is monomeric. Its reactivity with a variety of ligands has been described.7 Sharp infrared absorption bands at 1220 (s), 1222 (w, sh), 1245 (w), and 1252 (m) cm-1 in the CH3 deformation region are characteristic of the compound. 

A semiquantitative correlation of the structure of the protein in solution with the crystal was attempted. Since the relative relaxation of resonances induced by Gd3+ is proportional to the relative values of 1 /r6 for the different nuclei, where r is the distance between the lanthanide and the nucleus of interest, a plot of the calculated distances and experimental values from the X-ray structure was made [ 108]. Allowance has been made for the rotation of methyl groups and for flipping of tyrosine residues. The correlation of NMR data with X-ray crystal structure data shown in Fig. 10.31, is reasonably good, with the exception of resonances for val-109 and others at longer distances (r > 14 A). 

A number of other mechanistic sequences are thought to occur in alkyne trimerizations mediated by other metal systems. Catalysts derived from Co2(CO)s follow a characteristic sequence of steps that involves exclusively dinuclear complexes (Scheme 26). The nature of the final (alkyne)3C02(CO)4 intermediate, a so-called flyover complex, is supported by both X-ray crystal structure data as well as its involvement in forming other products besides benzenes. These dinuclear cobalt systems are note-... 

Dzakpasu, A. A., Phillips, S. E. V., Scheffer, J. R., and Trotter, J. Intramolecular photochemical hydrogen abstraction reactions in the solid state. Correlation with X-ray crystal structure data. J. Amer. Chem. Soc. 98, 6049-6051 (1976). Trotter, J. Structural aspects of the solid-state photochemistry of tetrahydron-aphthoquinones. Acta Cryst. B39, 373-381 (1983). 

---