Structure sheet

In order to control the tightness of welded joints on various products and structures, a range of units and complexes for control of pipes, pipelines, tanks, protective casings were developed, in particular, a set of put-on vacuum chambers for sheet structures. 

Black phosphorus is formed when white phosphorus is heated under very high pressure (12 000 atmospheres). Black phosphorus has a well-established corrugated sheet structure with each phos phorus atom bonded to three neighbours. The bonding lorces between layers are weak and give rise to flaky crystals which conduct electricity, properties similar to those ol graphite, it is less reactive than either white or red phosphorus. 

Alpha/beta twisted open-sheet structures contain a helices on both sides of the p sheet... 

Third, in open-sheet structures the a helices are packed against both sides of the p sheet. Each p strand thus contributes hydrophobic side chains to pack against a helices in two similar hydrophobic core regions, one on each side of the p sheet. 

Open p-sheet structures have a variety of topologies... 

We have described a general relationship between structure and function for the a/p-barrel structures. They all have the active site at the same position with respect to their common structure in spite of having different functions as well as different amino acid sequences. We can now ask if similar relationships also occur for the open a/p-sheet structures in spite of their much greater variation in structure. Can the position of the active sites be predicted from the structures of many open-sheet a/p proteins ... 

In almost every one of the more than 100 different known a/p structures 1 of this class the active site is at the carboxy edge of the p sheet. Functional residues are provided by the loop regions that connect the carboxy end of the strands with the amino end of the a helices. In this one respect a fun-I damental similarity therefore exists between the a/p-barrel structures and the I open a/p-sheet structures. 

Edison, A.S. Propagation of an error p-sheet structures. Trends Biochem. Sci. 15 216-217, 1990. 

These results indicate that is it possible to change the fold of a protein by changing a restricted set of residues. They also confirm the validity of the rules for stability of helical folds that have been obtained by analysis of experimentally determined protein structures. One obvious impliction of this work is that it might be possible, by just changing a few residues in Janus, to design a mutant that flip-flops between a helical and p sheet structures. Such a polypeptide would be a very interesting model system for prions and other amyloid proteins. 

Fnr stripping service, as in a glycol or amine contactor (see Chapt 7 a bubble cap trays are the most common. In recent years, there has b growing movement toward crimped sheet structured packing. Improved vapor and liquid distributor design in conjunction with struc-... 

FIGURE 6.32 Examples of andparallel /3-sheet structures iu proteins. (Jane Richardson)... 

FIGURE 6.34 Sheet structures formed from andparallel arrangements of /3-strands, (a) Streptomyces suh i x Xu inhibitor, (b) glutathione reductase domain 3, and (c) the second domain of glyceraldehyde-3-phosphate dehydrogenase represent minimal andparallel /S-sheet domain structures. In each of these cases, an andparallel /S-sheet is largely exposed to solvent on one face and covered by helices and random coils on the other face. (Jane Richardson)... 

Figure 22.5 Alternative representations of (a) the sheet structure of NbF4 and (b) the chain structure of MX4 (M = Nb, Ta X = Cl, Br, I) showing the displacement of the metal atoms which leads to diamagnetism.

It has a VF4 type puckered sheet structure with 6-coordinated ruthenium four fluorines bridge, two non-bridging ones are trans with the terminal distances shorter as expected (Table 1.1). It is paramagnetic (/xeff = 3.04/xB at room temperature). 

This is an extracellular deposition of an insoluble protein, which has adopted a (3-sheet structure due to an unknown event that induced misfolding of unstable proteins. The name amyloid has been given according to the amyloid staining properties, which are similar to carbohydrate deposits, e.g., amyloid can be identified with Congo red and seen under polarized light (birefringence test). 

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]. 

In 1990, Baumeister et al. [127] described the crystal and molecular structure of 4-ethoxy-3 -(4-ethoxyphenyliminomethyl)-4 -(4-methoxy-benzoy-loxy)azobenzene. The molecules have a bifurcated shape. The phenyliminom-ethyl branch is bent markedly from the nearly linear three ring fragment, but is almost coplanar with the azobenzene moiety. They found that the molecular conformation is affected by an intramolecular interaction of the carboxylic and azomethine groups. The crystal packing was described in terms of a sheet structure with interdigitating rows of molecules. 

Extended Peptide Strands, Turns and Formation of Sheet Structures... 

---