Crystal structure Sheet

Fig. 1. Crystal structures of (a) cubic diamond and (b) lonsdaleite. A, B, and C indicate the stacking sequence of sheets of atoms.

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. 

Fig. 4.1.13 A ribbon representation of the crystal structure of recombinant acquorin molecule showing the secondary structure elements in the protein. Alpha-helices are denoted in cyan, beta-sheet in yellow, loops in magenta coelenterazine (yellow) and the side chain of tyrosine 184 are shown as stick representations. From Head et al., 2000, with permission from Macmillan Publishers.

Kashiwagi et al.10) determined the second moment anisotropy for the one-way drawn polyethylene terephthalate sheets discussed above. The three lattice sums S00, S2q and S4o were calculated from the crystal structure determination of Daubeny et al., the proton positions being calculated on the basis of known bond angles and lengths. The isotropic lattice sum S00 was adjusted to a value consistent with the measured isotropic second moment of 10.3G2. The values for P200, P220 etc. were then used to predict the optical anisotropy. The predicted refractive indices for the sheets of draw ratio 2 1 and 2.5 1 are shown in Fig. 10, together with the experimental... 

Dithiocarbamate complexes of copper have been sythesized at a high rate. Reports of new complexes include the morpholine-4- (44), thio-morpholine, AT-methylpiperazine-4-, and piperidine- (291) dithiocarba-mates. Novel, polymeric complexes of the type Cu(pipdtc)2 (CuBr) in = 4, or 6) and Cu(pipdtc)2 (CuCl)4 have been prepared by reactions of[Cu(pipdtc)2] with the respective copper halide in CHCla-EtOH (418). The crystal structures of the polymers are known to consist of sheets of individual [Cu(pipdtc)2] molecules linked to polymeric CuBr chains via Cu-S bonds. A series of copper(I) dtc complexes have been the subject of a Cu and Cu NQR-spectral study (440). 

In 1978, Bryan [11] reported on crystal structure precursors of liquid crystalline phases and their implications for the molecular arrangement in the mesophase. In this work he presented classical nematogenic precursors, where the molecules in the crystalline state form imbricated packing, and non-classical ones with cross-sheet structures. The crystalline-nematic phase transition was called displacive. The displacive type of transition involves comparatively limited displacements of the molecules from the positions which they occupy with respect to their nearest neighbours in the crystal. In most cases, smectic precursors form layered structures. The crystalline-smectic phase transition was called reconstitutive because the molecular arrangement in the crystalline state must alter in a more pronounced fashion in order to achieve the mesophase arrangement [12]. 

Hartung et al. [120] determined the crystal structure of the mesogenic 6-hexylamino-l,2,4,5-tetrazin-3-yl 4-pentyloxybenzoate. The plane of the bridging carboxylic group is inclined to those of the phenyl and the tetrazine rings by 12.1 and 76.3°, respectively. The molecules are arranged in sheets parallel to (021). 

Fig. 2.28 X-ray crystal structures of parallel sheet-forming and all-un//fce-/F -peptides 116 and 117 [10, 191]. Views along the parallel amide planes and crystal packing diagram show the parallel pleated sheet arrangement (view perpendicular to the amide planes).

N-H--0) are 149.7° (inner H-bond) and 144.7° (outer H-bond). (B) Hybride -peptide 120 with a D-Pro-Gly type IT -turn segment (gray color) X-ray crystal structure [192]. The intramolecular H-bond N---0 distances are shown. The angles (N-H---0) are 147° (inner H-bond) and 155° (outer H-bond). The inter-molecular NH-0=C H-bonds (with N-H -O angles of 160 and 133 °) connect the hairpin into an infinitely extended -sheet... 

Fig. 2.38 sheet forming y-peptides. (A) Crystal structure of the two stranded antiparallel sheet formed by a,j -unsaturated y-dipeptide 152 with a-methyl substituted residues [208], Both intermolecular H-bonds are characterized by a N---0 distance of 2.84 A and an angle (N-H- -O) ofl54.2°. (B) Crystal structure of the infinite parallel sheet arrangement formed by vinylogous dipeptide 153 [208], Intermolecular H-bonds are characterized by a N -O distance of 2.88 A and 3.24 A and an... 

The crystal structure of one LRR protein, the RNAse inhibitor, has revealed that leucine-rich repeats correspond to p-a structural units. This units are arranged for a parallel p-sheet with one surface exposed to solvent so that the protein acquires an unusual non-globular shape, which may be responsible for proteinbinding functions [57]. 

Zaleski-Ejgierd, P., Hakala, M. and Pyykkd, P. (2007) Comparison of chain versus sheet crystal structures for the... 

The unit layers stack together face-to-face and are held in place by weak attractive forces. The distance between corresponding planes in adjacent unit layers is called the c-spacing. A clay crystal structure with a unit layer consisting of three sheets typically has a c-spacing of about 9.5 X 10 mm. 

The crystal structures of both the cis and the trans isomers of 2,8-dihydroxy-2,4,4,6,6,8,10,10,12,12-decamethylcyclohexasiloxane have been determined. In this case (unlike the cyclotetrasiloxane in Fig. 26), the cis isomer does contain an intramolecular hydrogen bond, and intermolecular hydrogen bonds link the molecules into cyclic pairs 57. The trans isomer cannot form intramolecular hydrogen bonds, but forms cyclic tetramers which are further hydrogen-bonded to form infinite sheets 58 (280). 

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