Crystal Structure of the p Form

Stacking faults was detected. The molecular mechanism and the difficulty in eliminating the stacking faults by annealing were discussed on the basis of the structural model of the fault. 

Tosaka et al. [63] found that, according to the analysis of electron diffraction pattern of the P modification, the probability values were greater than 0.5, indicating that the succession of the motifs of the same type comprising the monoclinic layer of the faulted structures is the dominant structure. 

Napolitano et al. [65] investigated the adjacent re-entry folds of chains of SPS crystallized in the P form by molecular mechanics. Various models of chain fold along bilayers have been found. The results are in agreement with the literature experimental data indicating that the fold surface is 

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The atomic-level crystal structures of the p form of saturated monoacid TAGs were first clarified almost four decades ago (34—36). Based on these structural data, Lutton postulated the p form structures of saturated monoacid and diacid TAGS (37). 

Quite recently, van Langevelde et al. examined the crystal structures of the p form of tripalmitin (PPP) in comparison with the results of tricaprin (CCC) (38, 39), trilaurin (LLL) (36), and predicted the p form structure of trimyristin (MMM) (38). As shown in Table 1, the unit cell parameters, double-chain length structure, and T// subcell structure of the three TAGs are almost the same, except... 

Atomic-Level Crystal Structures of p Form We discuss crystal structures of the p forms of two saturated diacid TAGs, C10C12C10 (41) and C16C16C14 (42). Both are the first p polymorphs of TAG that have been analyzed at the atomic level by using single crystals. Two different types of the p structures were found as revealed in the unit cell parameters shown in Table 3. 

In this connection, one may refer to polymorphism of a homologous series of n n+2 n in which n was even-numbered carbon atoms ranging from 10 to 16 (24,25). In these TAG, the most stable form is P, and no P form was observed. The crystal structure of the P form y> simply and symbolically, be illus-... 

The crystal structure of the P-form of ReCl4 obtained by the reaction of Re3Cl9 or SbCl3 with ReClj has been investigated. This polymorph is composed of RejClg units, each of which comprises two face-sharing ReClg octa-hedra, linked by shared terminal chlorine atoms. The Re—Re separation in... 

Conti et al. (1996) solved the crystal structure of the P. pyralis luciferase at 2.0 A resolution. The protein is folded into two compact domains, a large N-terminal portion and a small C-terminal portion. The former portion consists of a /1-barrel and two /1-sheets. The sheets are flanked by a-helices to form an aflafia five-layered structure. The C-terminal portion of the molecule forms a distinct domain, which is separated from the N-terminal domain by a wide cleft. It is suggested that the two domains will close up in the course of the luminescence reaction. 

Just as an example, the X-ray diffraction patterns of compression moulded samples of PVDF, poly(vinylfluoride), and of some VDF-VF copolymers of different compositions are shown in Fig. 17 [90]. The degrees of crystallinity of the copolymer samples (40-50%) are high and analogous to those of the homopolymer samples. This indicates a nearly perfect isomorphism between the VF and VDF monomeric units [90, 96], The diffraction patterns and the crystal structures of the copolymers are similar to those of PVF, which are in turn similar to the X-ray pattern and crystalline structure of the P form of PVDF. On the contrary, the X-ray pattern of a PVDF sample crystallized under the same conditions (Fig. 17 a) is completely different, that is typical of the non-piezoelectric a form [90]. 

Sequential steps are proposed (75- 77) with two monomeric units combining to form first a single hydroxo-bridged dimer, which in turn closes to give the double hydroxo-bridged dimer. This latter species [(H20)4Cr(0H)2Cr(0H2)4]4+ is one of the major products from the 02 oxidation of [Cr(OH2)6]2+ (11) (Section I,A), and the crystal structure of the p-toluenesulfonate salt has been determined (78). 

Ciba, Ltd. (1965) Dutch Patent Application 6,405,130. Chem. Abstr.,63,15103. [262] Ciechanowicz, M., Skapski, A. C. and Troughton, P. G. H. (1976). The crystal structure of the orthorhombic form of hydridodicarbonylbis(triphenylphosphine)-iridium(I) successful location of the hydride hydrogen atom from x-ray data. Acto Crystallogr. B, 32, 1673-80. [44]... 

Serpins consist of a conserved core of three P-sheets and eight or nine a-helices that act collectively in the inhibitory mechanism. As with the Kazal- and Kunitz-type inhibitors, the mechanism involves a surface exposed loop that is termed the reactive center loop (RCL). The RCL presents a short stretch of polypeptide sequence bearing the Pl-Pl scissile bond. Like other serine protease inhibitor families, the PI residue dominates the thermodynamics that govern the interaction between protease and inhibitor. Exposure of the PI residue to solvent is typically brokered by 15 amino acids N-terminal to the PI residue and 5 residues on the C-terminal prime side of the scissile bond. Evidence for dramatic conformational change in the inhibitory mechanism was first provided by the crystal structure of the cleaved form of ai-antitrypsin (37). In this structure and unlike the native form, the reactive center loop was not solvent exposed but occurred as an additional P-strand within the core of the structure. 

The activating effect of the various deletion mutants prior to the C-helix is also interpretable by a review of the crystal structures of the inactive form of the kinase. In this C-helix-out form, the helix itself is unwound a turn compared to the active form, and the amino acid chain connecting the P-loop to the helix is extended.70 Removing a portion of this sequence would result in... 

De Rosa C, Guerra G, Petraccone V, Corradini P (1991) Crystal Structure of the a-Form of Syndiotactic Polystyrene. Polymer Journal 23 1435-1442... 

Petraccone V, La Camera D, Caporaso L, De Rosa C (2000) Crystal Structure of the Clathrate Form of Syndiotactic Poly(p-methylstyrene) Containing o-Dichlorobenzene. Macromolecules 33 2610-2615... 

The crystal structiue of the p form of iPP was only recently described despite the fact that this phase has been known to exist for 40 years. The structure consists of sections of three isochiral helices packed in a trigonal cell. One of the three helices is embedded in a crystallographic environment which is different from the other two, i.e. the structure is frustrated [5]. AFM studies of the (110) plane confirmed this frustrated character. In addition, it seems that in epitaxy the chains in the contact plane of polymer crystals (grown on dicyclohexylterephthalamide) expose rows of 2, 2 and 1 methyl groups. 

CHANDRA, V, JASTI, J., KAUR, R, BETZEL, C., SRINIVASAN, A. SINGH, T. P. 2002. First structural evidence of a specific inhibition of phospholipase A2 by alpha-tocopherol (vitamin E) and its implications in inflammation Crystal structure of the complex formed between phospholipase A2 and alpha-tocopherol at 1.8 A resolution. J Mol Biol, 320, 215-22. 

A polymorph of the quinoid red crystal form of fluorescein was one of the first examples of a complex molecule whose structure was determined by a real-space approach based on the Monte-Carlo method [37]. The same method has been used to solve the structure of the p-form of the latent pigment boc-DPP (Figure 8.6). The kinetics of the thermal fragmentation to DPP differs for both forms. The more reactive a-form crystallizes (less ordered) with three conforma-tionally different half-molecules in the asymmetric unit. This structure was initially solved from single-crystal data. However, it could be improved substantially by Rietveld refinement, thus demonstrating the potential of this technique [38]. 

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