scholarly journals The Crystal Structure of Fe4S4 Quinolinate Synthase Unravels an Enzymatic Dehydration Mechanism That Uses Tyrosine and a Hydrolase-Type Triad

2014 ◽  
Vol 136 (14) ◽  
pp. 5253-5256 ◽  
Author(s):  
Mickaël V. Cherrier ◽  
Alice Chan ◽  
Claudine Darnault ◽  
Debora Reichmann ◽  
Patricia Amara ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Dehydration Mechanism ◽  
Quinolinate Synthase

Re-investigation of the crystal structure of whewellite [Ca(C2O4)·H2O] and the dehydration mechanism of caoxite [Ca(C2O4)·3H2O]

2005 ◽  
Vol 69 (1) ◽  
pp. 77-88 ◽  
Author(s):  
T. Echigo ◽  
M. Kimata ◽  
A. Kyono ◽  
M. Shimizu ◽  
T. Hatta
Keyword(s):  
Crystal Structure ◽  
Hydrogen Bonds ◽  
Structure Refinement ◽  
Structural Features ◽  
Infrared Analysis ◽  
Water Molecules ◽  
Hydrogen Atoms ◽  
Direct Transformation ◽  
Dehydration Mechanism ◽  
The Difference

AbstractThe crystal structure of whewellite [Ca(C2O4)·H2O] and the dehydration mechanism of caoxite [Ca(C2O4)·3H2O] have been studied by means of differential thermal analysis, X-ray diffraction (powder and single-crystal) analysis and infrared analysis. The first and second analyses confirmed the direct transformation of caoxite into whewellite without an intermediate weddellite [Ca(C2O4)·2H2O] stage. Infrared spectra obtained from caoxite, weddellite and whewellite emphasize the similarity of the O–H-stretching band and O–C–O-stretching band in whewellite and caoxite and the unique bands of weddellite. The structure refinement at low temperature (123 K) reveals that all the hydrogen atoms of whewellite form hydrogen bonds and the two water molecules prop up the crystal structure by the hydrogen bonds that cause a strong anisotropy of the displacement parameter.Comparing the structural features of whewellite with those of weddellite and caoxite suggests that caoxite and whewellite have a sheet structure consisting of Ca2+ ions and oxalate ions although weddellite does not. It is additionally confirmed that the sheets of caoxite are corrugated by hydrogen bonds but whewellite has flat sheets. The corrugated sheets of caoxite would be flattened by dehydration so the direct transformation of caoxite into whewellite would not occur via weddellite. Essential for this transformation is the dehydration of interlayered water molecules in caoxite leading to the building of the crystal structure of whewellite on its intralayered water molecules. The difference in conformation of water molecules between those two crystal structures may explain the more common occurrence of whewellite than of caoxite in nature.

TEM characterization of synthetic hillebrandite: Structure, microstructure, and dehydration

1993 ◽  
Vol 51 ◽  
pp. 932-933
Author(s):  
Y. J. Kim ◽  
W. M. Kriven
Keyword(s):  
Crystal Structure ◽  
Room Temperature ◽  
Dark Field ◽  
Fiber Axis ◽  
Data Space ◽  
Tem Characterization ◽  
Dehydration Mechanism ◽  
Fibrous Mineral

Hillebrandite (Ca2SiO4•H2O) occurs in nature as a white, fibrous mineral. Synthetic hillebrandite was prepared hydrothemally from calcia and silica. On heating, hillebrandite dehydrated to β-Ca2SiO4 which is stable at room temperature. The crystal structure, microstructures and the dehydration mechanism of the synthetic hillebrandite prepared by Ishida et. al were investigated by conventional TEM, HREM, and in situ hot-stage TEM.Most hillebrandite fibers showed their fiber axis to be parallel to the b axis and tended to lie on {001} cleavage planes. SADP’s frequently displayed continuous streaking, and corresponding dark field images revealed stacking disorders perpendicular to the fiber axis (Fig. 1). The observed [001] SADP (Fig. 2) was very different from the expected [001] SADP based on published XRD data (space group, P21/a). For all hk0 reflections, (i) if k = odd, no individual spots are shown but weak continuous streaking exists, (ii) if k = 2, reflections of h = even are extinct, and (iii) if k = 4, reflections of h = odd are extinct.

scholarly journals 2P048 Crystal structure of the NAD biosynthetic enzyme quinolinate synthase

2005 ◽  
Vol 45 (supplement) ◽  
pp. S131
Author(s):  
H. Sakuraba ◽  
K. Yoneda ◽  
T. Ohshima ◽  
H. Tsuge ◽  
N. Katunuma
Keyword(s):  
Crystal Structure ◽  
Biosynthetic Enzyme ◽  
Quinolinate Synthase

scholarly journals Crystal Structure of the NAD Biosynthetic Enzyme Quinolinate Synthase

2005 ◽  
Vol 280 (29) ◽  
pp. 26645-26648 ◽  
Author(s):  
Haruhiko Sakuraba ◽  
Hideaki Tsuge ◽  
Kazunari Yoneda ◽  
Nobuhiko Katunuma ◽  
Toshihisa Ohshima
Keyword(s):  
Crystal Structure ◽  
Biosynthetic Enzyme ◽  
Quinolinate Synthase

Crystal Structure Determination of Glycerol-Containing Lipids from Electron Diffraction Data. Use of Analog Compounds Based upon Configurational Isomers of Cyclopentane-1, 2, 3-TRIOL

1977 ◽  
Vol 35 ◽  
pp. 24-25
Author(s):  
Douglas L. Dorset ◽  
Anthony J. Hancock
Keyword(s):  
Crystal Structure ◽  
Electron Diffraction ◽  
Diffraction Data ◽  
Structure Determination ◽  
Crystal Surface ◽  
Coherent Scattering ◽  
Crystal Structure Determination ◽  
Electron Diffraction Data ◽  
Polar Group ◽  
Axis Orientation

Lipids containing long polymethylene chains were among the first compounds subjected to electron diffraction structure analysis. It was only recently realized, however, that various distortions of thin lipid microcrystal plates, e.g. bends, polar group and methyl end plane disorders, etc. (1-3), restrict coherent scattering to the methylene subcell alone, particularly if undistorted molecular layers have well-defined end planes. Thus, ab initio crystal structure determination on a given single uncharacterized natural lipid using electron diffraction data can only hope to identify the subcell packing and the chain axis orientation with respect to the crystal surface. In lipids based on glycerol, for example, conformations of long chains and polar groups about the C-C bonds of this moiety still would remain unknown.One possible means of surmounting this difficulty is to investigate structural analogs of the material of interest in conjunction with the natural compound itself. Suitable analogs to the glycerol lipids are compounds based on the three configurational isomers of cyclopentane-1,2,3-triol shown in Fig. 1, in which three rotameric forms of the natural glycerol derivatives are fixed by the ring structure (4-7).

Spherulitic crystal growth in the prodissoconch larval of Crassostrea virginica

1983 ◽  
Vol 41 ◽  
pp. 518-519
Author(s):  
George G. Cocks ◽  
Louis Leibovitz ◽  
DoSuk D. Lee
Keyword(s):  
Crystal Structure ◽  
Crassostrea Virginica ◽  
Crystal Orientation ◽  
Developmental Changes ◽  
Gastrula Stage ◽  
Orthorhombic Crystal ◽  
Orthorhombic Crystal Structure ◽  
Stages Of Growth ◽  
Early Stages ◽  
Initial Deposition

Our understanding of the structure and the formation of inorganic minerals in the bivalve shells has been considerably advanced by the use of electron microscope. However, very little is known about the ultrastructure of valves in the larval stage of the oysters. The present study examines the developmental changes which occur between the time of conception to the early stages of Dissoconch in the Crassostrea virginica(Gmelin), focusing on the initial deposition of inorganic crystals by the oysters.The spawning was induced by elevating the temperature of the seawater where the adult oysters were conditioned. The eggs and sperm were collected separately, then immediately mixed for the fertilizations to occur. Fertilized animals were kept in the incubator where various stages of development were stopped and observed. The detailed analysis of the early stages of growth showed that CaCO3 crystals(aragonite), with orthorhombic crystal structure, are deposited as early as gastrula stage(Figuresla-b). The next stage in development, the prodissoconch, revealed that the crystal orientation is in the form of spherulites.

Transmission Electron Microscopy studies of the vacancy ordering in YSI2-X thin films

1991 ◽  
Vol 49 ◽  
pp. 562-563
Author(s):  
F.-R. Chen ◽  
T. L. Lee ◽  
L. J. Chen
Keyword(s):  
Crystal Structure ◽  
Electron Microscopy ◽  
Thin Films ◽  
Diffraction Pattern ◽  
Annealing Temperature ◽  
Lattice Mismatch ◽  
Si Substrate ◽  
Metal Thin Films ◽  
Transmission Electron ◽  
Vacancy Ordering

YSi2-x thin films were grown by depositing the yttrium metal thin films on (111)Si substrate followed by a rapid thermal annealing (RTA) at 450 to 1100°C. The x value of the YSi2-x films ranges from 0 to 0.3. The (0001) plane of the YSi2-x films have an ideal zero lattice mismatch relative to (111)Si surface lattice. The YSi2 has the hexagonal AlB2 crystal structure. The orientation relationship with Si was determined from the diffraction pattern shown in figure 1(a) to be and . The diffraction pattern in figure 1(a) was taken from a specimen annealed at 500°C for 15 second. As the annealing temperature was increased to 600°C, superlattice diffraction spots appear at position as seen in figure 1(b) which may be due to vacancy ordering in the YSi2-x films. The ordered vacancies in YSi2-x form a mesh in Si plane suggested by a LEED experiment.

Crystal Structure Analysis of Cu-Zr Alloys by Convergent Beam Diffraction

1981 ◽  
Vol 39 ◽  
pp. 354-355
Author(s):  
A. F. Marshall ◽  
J. W. Steeds ◽  
D. Bouchet ◽  
S. L. Shinde ◽  
R. G. Walmsley
Keyword(s):  
Crystal Structure ◽  
Point Group ◽  
Intermetallic Phase ◽  
Three Dimensional ◽  
Crystal Structure Analysis ◽  
Ion Milling ◽  
Composition And Structure ◽  
Unit Cells ◽  
Sputter Deposited ◽  
Convergent Beam

Convergent beam electron diffraction is a powerful technique for determining the crystal structure of a material in TEM. In this paper we have applied it to the study of the intermetallic phases in the Cu-rich end of the Cu-Zr system. These phases are highly ordered. Their composition and structure has been previously studied by microprobe and x-ray diffraction with sometimes conflicting results.The crystalline phases were obtained by annealing amorphous sputter-deposited Cu-Zr. Specimens were thinned for TEM by ion milling and observed in a Philips EM 400. Due to the large unit cells involved, a small convergence angle of diffraction was used; however, the three-dimensional lattice and symmetry information of convergent beam microdiffraction patterns is still present. The results are as follows:1) 21 at% Zr in Cu: annealed at 500°C for 5 hours. An intermetallic phase, Cu3.6Zr (21.7% Zr), space group P6/m has been proposed near this composition (2). The major phase of our annealed material was hexagonal with a point group determined as 6/m.

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