Natural crystal structure

The contribution of resonance Raman spectroscopy, as one of an array of techniques, in helping to unravel important issues in catalysis and especially in oxidation catalysis is exemplified in the recent reports by Nam and coworkers on the isolation of three oxygen activated iron intermediates implicated in various catalytic cycles namely [Fe(III)(TMC)(00)] (1), [Fe(III)(TMC)(OOH)] (2) and [Fe(IV)(TMQ(0)] (3) where TMC is the macrocyclic ligand l,4,8,ll-tetramethyl-l,4,8,l 1-tetraazacyclotetradecane. Despite their unstable nature, crystal structures of two of these species, 1 and 3, are available. Further essential structural information about these active intermediates is deduced from UV/vis absorption and Raman spectroscopy, as Fig. 3 shows. 

Fused Grain Refractory. Refractories made from raw material which has been melted, destroying its natural crystal structure solidified crushed to an appropriate particle size and sintered. Fused Quartz. This term is often applied to Transparent Vitreous Silica (See under VITREOUS silica) that has been obtained by the fusion of quartz crystal electrically or in a flame. 

Metal Natural Crystal Structure at Room Temperature Other Crystal Structures at Different Temperatures and Pressures... 

Most chitins and derivatives are extracted from crab shells, lobsters and shrimps or from the waste of fungi fermentation (e.g., Aspergillus sp.) in concentrated NaOH solution. The swelling involves a modification of its natural crystal structure (a or (3). After washing in water, the recovered a structure is chemically resistant due to the hydrogen bonds between the chains. The /3-chitin... 

The question arises as to whether there are any general requirements for an effective nucleating agent. Among the factors that need to be considered are the chemical nature, crystal structure and size of the nucleant and their relation to... 

Graphite exists in two forms alpha and beta. These have identical physical properties, except for their crystal structure. Naturally occurring graphites are reported to contain as much as 30% of the rhombohedral (beta) form, whereas synthetic materials contain only the alpha form. The hexagonal alpha type can be converted to the beta by mechanical treatment, and the beta form reverts to the alpha on heating it above lOOOoC. 

Page 1171 (Figure 28 7) is adapted from crystallograpliic coordinates deposited with The Protein Data Bank PDB ID lAOl Luger A Mader W Richmond R K Sargent D F Richmond T J Crystal Structure of the Nucleosome Core Particle at 2 8 A Resolution Nature 1997 V 389 251... 

In compound materials - in the ceramic sodium chloride, for instance - there are two (sometimes more) species of atoms, packed together. The crystal structures of such compounds can still be simple. Figure 5.8(a) shows that the ceramics NaCl, KCl and MgO, for example, also form a cubic structure. Naturally, when two species of atoms are not in the ratio 1 1, as in compounds like the nuclear fuel UO2 (a ceramic too) the structure is more complicated (it is shown in Fig. 5.8(b)), although this, too, has a cubic unit cell. 

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De Bondt, H.E., et al. Crystal structure of cyclin-depen-dent kinase 2. Nature 363 595-602, 1993. 

Martin, J.E., Bardwell, J.C.A., Kuriyan, J. Crystal structure of the DsbA protein required for disulphide bond formation in vivo. Nature 365 464-468, 1993. 

Zhang, R.-G., et al. The crystal structure of trp aporepressor at 1.8 A shows how binding tryptophan enhances DNA affinity. Nature 327 591-S97, 1987. 

Fairall, L., et al. The crystal structure of a two zinc finger peptide reveals an extension to the rules for zinc finger/DNA recognition. Nature 366 483-487, 1993. 

Glover, J.N.M., Harrison, S.C. Crystal structure of the het-erodimeric bZIP transcription factor c-Fos-c-Jun bound to DNA. Nature 373 257-261, 1995. 

Cowan, S.W., et al. Crystal structures explain functional properties of two E. coli porins. Nature 358 727-733, 1992. 

Picot, D., Loll, P.J., Garavito, R.M. The x-ray crystal structure of the membrane protein prostaglandin H2 synthase-1. Nature 367 243-249, 1994. 

Noel, J.R, Hamm, H.E., Sigler, P.B. The 2.2 A crystal structure of transducin-a complexed with GTPyS. Nature 366 654-663, 1993. 

Rittinger, K. et al. Crystal structure of a small G protein in complex with GTPase-activating protein rhoGAP. Nature 388 693-697, 1997. 

Sondek, J., et al. GTPase mechanism of G proteins from the 1.7 A crystal structure of transducin a.GDP.AlF4 . Nature 372 276-279, 1994. 

Spraggon, G., et al. Crystal structures of fragment D from human fibrinogen and its crosslinked counterpart from fibrin. Nature 389 455-462, 1997. 

Stern, L.J., Brown, J.H., Jardetzky, T.S., Gorga, J.C., Urban, R.G., Strominger, J.L., Wiley, D.C. Crystal structure of the human class 11 MHC protein HLA-DRl complexed with an influenza virus peptide. Nature 368 215-221,... 

The characterisation of materials is a central necessity of modern materials science. Effectively, it signifies making precise distinctions between different specimens of what is nominally the same material. The concept covers qualitative and quantitative analysis of chemical composition and its variation between phases the examination of the spatial distribution of grains, phases and of minor constituents the crystal structures present and the extent, nature and distribution of structural imperfections (including the stereological analysis outlined in Chapter 5). 

The highly hindered alkene adamantylideneadamantane forms a bromonium ion which crystallizes as a tribromide salt. An X-ray crystal structure (Fig. 6.1) has confirmed the cyclic nature of the bromonium ion species. This particular bromonium ion does not react further because of extreme steric hindrance to back-side proach by bromide ion. 

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