Crystallographic analyses

The anomalous low density of poly(4-methyl pent-l-ene) for a crystalline hydrocarbon polymer has been resolved in a new crystallographic analysis. The isotactic polymer crystallizes as a 2 helix with symmetry PAb and unit cell with dimensions a= 18.70 and c= 13.68 A. There are four chains with seven 

Wunderlich, Macromolecular Physics , Volume 2, Academic Press, New York, 1976. 

Kusangi, M. Takase, Y. Chatangi and H. Tadokoro, J. Polymer Sci., Polymer Phys., 1978,16, 131. 

A similar isotactic polymer, poly(pent-l-ene) exists in two crystallographic forms which can be separated by temperature. On quenching below 29 K, form I is produced with a monoclinic unit cell with dimensions u=22.4 0.2, fr=6.49 0.01, c=21.0 0.2 A and =91 1°. The higher temperature form II converts into I on ageing it also is a monoclinic unit cell with a=24.3, b=6.50, and c=19.3 A and =96 2 . Both forms form a 3j helix. 

Syndiotactic polypropylene also exists as two crystalline modifications, the more stable one possessing a helical conformation and the other a planar zig-zag, A detailed analysis of the Raman spectrum confirms these structures and there is an excellent correlation between observed and predicted vibrational modes of the helical structure. Painter et al. have made a Fourier transform infrared spectroscopic study of isotactic polypropylene in the crystalline and amorphous state. The spectrum of the amorphous regions is broadly similar to that of the melt, but there is evidence for short sequences of helical segments in the amorphous phase, while the crystalline phase has longer sequences. This puts a different interpretation on the distinction between amorphous and crystalline regions than previously considered. 

Paulin-Dandurand, S. Perey, J.-F. Revel, and F. Brosse, Polymer, 1979, 20,419. 

Nylon-12 fibres have been analysed and their thermal behaviour examined. The A -ray-determined unit cells characteristic of various poly(aryl ether ketones) have been listed and used as models for the structure of poly(phenylene oxide) and poly(phenylene sulphide). 

The crystal structure of poly[l,2-bis(4-methoxy benzene sulphonyl methyl)-l-butene-3-ynylene] has been determined since it is central to the topochemical polymerization of disubstituted diacetylenes, e.g. 

Fibres of poly(A-vinyl carbazole)with a high modulus have been prepared by melt extrusion. They have a highly ordered one dimensional rod-like morphology with a hexagonal unit cell, a = b = c— 1.23 nm. 

Studies of the unique piezo- and pyro-electric properties of poled poly(vinylidene fluoride) have made a fundamental understanding of origin of the properties the subject of intense activity.Central to this study is the structure determination of the four phases, I, II, III, and IV, and their interconversion to test the correlation between orientation, crystal structure, and activity. The greatest piezoelectric activity is found with phase I, produced by subjecting phase II, the normal form produced on melt crystallizing, to intense electric fields up to 5 x 10 V cm, i.e. poling. The activity has been attributed to bulk polarization of the poly(vinylidene 

The electron density in a crystal is a three-dimensional periodic function. As the most general case consider the crystallization of a molecular compound. If, in the process, two identical molecules interact more efficiently for a specific mutual orientation, it is most likely that all molecules will adopt this 

An alternative grid, shown in red, defines an alternative set of planes that also contains all equivalent atoms, and under different conditions, also satisfies Bragg s equation. Such planes, which may be constructed in an endless number of ways, all have one property in common - they make rational intercepts on the axes of the unit cell. The fractional intercepts are defined as a/h, h/k, c/l in terms of the unit cell constants and the integer Miller indices, hkl. 

This construction is valid for each atom in the unit cell, and all atoms 

Thus j)a = 2nh(x/a) = 2irhu, etc., for fractional coordinates u,v,w. The total phase difference is  

The one-dimensional Fourier transform of the density function becomes (u = 

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Verschueren K H G, Seljee F, Rozeboom J, Kalk K H and Dijkstra B W 1993 Crystallographic analysis of the catalytic mechanism of haloalkane dehalogenase Nature 363 693-8... 

Another technique often used to examine the stmcture of double-heUcal oligonucleotides is two-dimensional nmr spectroscopy (see AfAGNETiC SPIN resonance). This method rehes on measurement of the nuclear Overhauser effects (NOEs) through space to determine the distances between protons (6). The stmcture of an oligonucleotide may be determined theoretically from a set of iaterproton distances. As a result of the complexities of the experiment and data analysis, the quality of the stmctural information obtained is debated. However, nmr spectroscopy does provide information pertaining to the stmcture of DNA ia solution and can serve as a complement to the stmctural information provided by crystallographic analysis. 

Cromakalim (137) is a potassium channel activator commonly used as an antihypertensive agent (107). The rationale for the design of cromakalim is based on P-blockers such as propranolol (115) and atenolol (123). Conformational restriction of the propanolamine side chain as observed in the cromakalim chroman nucleus provides compounds with desired antihypertensive activity free of the side effects commonly associated with P-blockers. Enantiomerically pure cromakalim is produced by resolution of the diastereomeric (T)-a-meth5lben2ylcarbamate derivatives. X-ray crystallographic analysis of this diastereomer provides the absolute stereochemistry of cromakalim. Biological activity resides primarily in the (—)-(33, 4R)-enantiomer [94535-50-9] (137) (108). In spontaneously hypertensive rats, the (—)-(33, 4R)-enantiomer, at dosages of 0.3 mg/kg, lowers the systoHc pressure 47%, whereas the (+)-(3R,43)-enantiomer only decreases the systoHc pressure by 14% at a dose of 3.0 mg/kg. 

Tolypomycins. The addition of small amounts of iron salts to the fermentation medium increases the production of tolypomycin Y (48) (7,203,204), the stmcture of which was arrived at by chemical degradation (205,206) and confirmed by x-ray crystallographic analysis (207) (Fig. 5). Mild acid hydrolysis of tolypomycin Y yields tolypomycinone [22356-23-6] (49, R = H), C27H42NO23, and tolyposamine [34174-76-0] C23H23NO2, (50). Further hydrolysis of tolypomycinone using acid yields tolyponone [24317-12-2] (51), which is also formed upon mild acid hydrolysis of rifamycia S. 

Additional compounds having similar biological activities and stmctural components were isolated resulting in the recognition of PGs as a family of closely related compounds. Stmctural and stereochemical assignments of PGE and PGF, were confirmed by x-ray crystallographic analysis of their... 

X-ray crystallographic analysis of the sodium thiosulfate pentahydrate [10102-17-7] crystal indicates a tetrahedral stmcture for the thiosulfate ion. The S—S bond distance is 197 pm the S—O bond distance is 148 pm (5). Neutron diffraction of a barium thiosulfate monohydrate [7787-40-8] crystal confirms the tetrahedral stmcture and bond distances for the thiosulfate ion (6). 

The 1-alkoxytitatranes can be synthesized by the reaction of equimolar amounts of tetraalkyl titanates and triethanolamine (105). X-ray crystallographic analysis of the soHd isolated from the reaction of one mole of triethanolamine and one mole of TYZOR TPT confirms the stmcture as a centrosymmetric dimer having a Ti isopropoxy nitrilotriethoxy ratio of 1 1 1. The titanium atoms have achieved a coordination number of six via a rather unsymmetrical titanium—oxygen bridge (106). 

J Soman, S Iismaa, CD Stout. Crystallographic analysis of two site-directed mutants of Azotobacter vmelandii feiredoxin. J Biol Chem 266 21558-21562, 1991. 

Knight, S., Andersson, I., Branden, C.-I. Crystallographic analysis of ribulose-l,5-bisphosphate carboxylase from spinach at 2.4 A resolution. Subunit interactions and active site. /. Mol. Biol. 215 113-160,... 

Luisi, B.F., et al. Crystallographic analysis of the interaction of the glucocorticoid receptor with DNA. 

Jardetzky, T.5., Wiley, D.C. Crystallographic analysis of endogenous peptides associated with HLA-DRl suggests a common, polyproline Il-like conformation for hound peptides. Proc. Natl. Acad. Sci. USA 93 734-728, 1996. 

R. Castaing. Application of Electron Probes to Local Chemical and Crystallographic Analysis. Ph.D. thesis. University of Paris, 1951. 

FIGURE 5.2 The peptide bond is shown in its usnal trans conformation of carbonyl O and amide H. The atoms are the oi-carbons of two adjacent amino acids joined in peptide linkage. The dimensions and angles are the average valnes observed by crystallographic analysis of amino acids and small peptides. The peptide bond is the light gray bond between C and N. (Adapted from Ramachandran, G. A., ct ai, 1974. Biochimica Biophysica Acta 359 298-302.)... 

What molecular architecture couples the absorption of light energy to rapid electron-transfer events, in turn coupling these e transfers to proton translocations so that ATP synthesis is possible Part of the answer to this question lies in the membrane-associated nature of the photosystems. Membrane proteins have been difficult to study due to their insolubility in the usual aqueous solvents employed in protein biochemistry. A major breakthrough occurred in 1984 when Johann Deisenhofer, Hartmut Michel, and Robert Huber reported the first X-ray crystallographic analysis of a membrane protein. To the great benefit of photosynthesis research, this protein was the reaction center from the photosynthetic purple bacterium Rhodopseudomonas viridis. This research earned these three scientists the 1984 Nobel Prize in chemistry. 

Thermal decomposition of [N(PPh3)2]" -[S4N5] in MeCN yields sequentially the corresponding salts of S3N3 and S4N (50% yield). An X-ray crystallographic analysis of the dark-blue air-stable product [N(PPh3)2] [S4N] revealed the presence of the unique acyclic anion [SSNSS] whose structure is in Fig. 15.42c. The anion is planar with cis-trans configuration. 

The structure of ( )-169 is determined to have a ( )-3a,3a -bispyrrolo[2,3-(j] indole skeleton by carrying out X-ray single crystallographic analysis of its derivative 252 (99H1237). Compound 252 is obtained from ( )-169 by the following sequence of reactions (1) alkaline hydrolysis of ( )-169 to 249 (88%), (2) conversion of 249 to 251 (71%) by treatment with NaH and chloroacetyl chloride, (3) substitution of chlorine on the chloroacetyl group for acetate 252 (93%) by the reaction with NaOAc. 

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