The Stereo Structures of Some Mycophenolic Acid Derivatives

2007 ◽  
Vol 60 (5) ◽  
pp. 354 ◽  
Author(s):  
Paul V. Bernhardt ◽  
Raymond M. Carman ◽  
Tri T. Le
Keyword(s):  
Mycophenolic Acid ◽  
Crystallographic Structure ◽  
X Ray ◽  
X Ray Crystallography

X-Ray crystallography affords the stereochemistry of three iodo compounds derived from mycophenolic acid. These included the crystallographic structure of a tertiary iodide.

scholarly journals Howard Flack and the Flack Parameter

Chemistry ◽  
2020 ◽  
Vol 2 (4) ◽  
pp. 796-804
Author(s):  
David John Watkin ◽  
Richard Ian Cooper
Keyword(s):  
Structure Determination ◽  
Standard Uncertainty ◽  
Crystallographic Structure ◽  
X Ray ◽  
Original Algorithm ◽  
X Ray Crystallography ◽  
Chiral Materials

The Flack Parameter is now almost universally reported for all chiral materials characterized by X-ray crystallography. Its elegant simplicity was an inspired development by Howard Flack, and although the original algorithm for its computation has been strengthened by other workers, it remains an essential outcome for any crystallographic structure determination. As with any one-parameter metric, it needs to be interpreted in the context of its standard uncertainty.

The X-Ray Crystallographic Structure of a 1,2-Dibromo-4,8-epoxy-p-menthane

1996 ◽  
Vol 49 (8) ◽  
pp. 925 ◽  
Author(s):  
RM Carman ◽  
RA Edwards ◽  
AC Rayner ◽  
WT Robinson
Keyword(s):  
Crystallographic Structure ◽  
X Ray ◽  
X Ray Crystallography

The crystalline dibromo epoxide obtained from (R)-α- terpineol is shown by X-ray crystallography to have the (1S,2S,4S)-1,2-dibromo-4,8-epoxy-p-menthane structure (3).

scholarly journals X-ray crystallographic structure of a teixobactin analogue reveals key interactions of the teixobactin pharmacophore

2017 ◽  
Vol 53 (18) ◽  
pp. 2772-2775 ◽  
Author(s):  
H. Yang ◽  
D. R. Du Bois ◽  
J. W. Ziller ◽  
J. S. Nowick
Keyword(s):  
Crystallographic Structure ◽  
X Ray ◽  
X Ray Crystallography

X-ray crystallography reveals key interactions in the pharmacophore of the antibiotic teixobactin.

scholarly journals Electron crystallography: imaging and single-crystal diffraction from powders

2007 ◽  
Vol 64 (1) ◽  
pp. 149-160 ◽  
Author(s):  
Xiaodong Zou ◽  
Sven Hovmöller
Keyword(s):  
Three Dimensional ◽  
Two Dimensions ◽  
Three Dimensions ◽  
Crystallographic Structure ◽  
X Ray Diffraction ◽  
Electron Crystallography ◽  
X Ray ◽  
X Ray Crystallography ◽  
Dimensional Reconstruction ◽  
Recent Developments

The study of crystals at atomic level by electrons – electron crystallography – is an important complement to X-ray crystallography. There are two main advantages of structure determinations by electron crystallography compared to X-ray diffraction: (i) crystals millions of times smaller than those needed for X-ray diffraction can be studied and (ii) the phases of the crystallographic structure factors, which are lost in X-ray diffraction, are present in transmission-electron-microscopy (TEM) images. In this paper, some recent developments of electron crystallography and its applications, mainly on inorganic crystals, are shown. Crystal structures can be solved to atomic resolution in two dimensions as well as in three dimensions from both TEM images and electron diffraction. Different techniques developed for electron crystallography, including three-dimensional reconstruction, the electron precession technique and ultrafast electron crystallography, are reviewed. Examples of electron-crystallography applications are given. There is in principle no limitation to the complexity of the structures that can be solved by electron crystallography.

A novel 1:1 benzenesulfonamide: 18-crown-6 complex as uncovered via 13C solid phase NMR spectroscopy and X-ray crystallography

1989 ◽  
Vol 67 (7) ◽  
pp. 1212-1218 ◽  
Author(s):  
G. W. Buchanan ◽  
C. Morat ◽  
J. P. Charland ◽  
C. I. Ratcliffe ◽  
J. A. Ripmeester
Keyword(s):  
Crown Ether ◽  
Correlation Time ◽  
Molecular Motion ◽  
Solid Phase ◽  
Crystallographic Structure ◽  
Temperature Dependent ◽  
X Ray ◽  
X Ray Crystallography ◽  
Anisotropic Motion ◽  
Motional Correlation Time

A 1:1 complex of 18-crown-6 ether and benzenesulfonamide has been prepared, whose melting point is within 4° of the previously reported 1:2 complex. The X-ray crystallographic structure shows pseudo D3d symmetry in the crown ether portion of this complex, in contrast to the 1:2 complex, which exhibits Ci symmetry in the macrocycle. The temperature dependent 13C CPMAS NMR spectra of these complexes have two regions of broadening for the crown ether carbons. At higher temperatures, a dipolar "washout" mechanism is operative, leading to broadening when molecular motion has a correlation time approximately equal to the inverse of the decoupling field. At lower temperatures broadening occurs when the motional correlation time is equal to the inverse of the chemical shift difference. From application of the Arrhenius equation, the activation energy for the molecular motion in solid 18-crown-6 is found to be approximately 10kcal/mol. Evidence for independent anisotropic motion in the benzenesulfonamide moiety of the 1:1 complex is also presented. Keywords: crown ether, molecular motion, solid phase NMR.

scholarly journals PHENIX: a comprehensive Python-based system for macromolecular structure solution

2010 ◽  
Vol 66 (2) ◽  
pp. 213-221 ◽  
Author(s):  
Paul D. Adams ◽  
Pavel V. Afonine ◽  
Gábor Bunkóczi ◽  
Vincent B. Chen ◽  
Ian W. Davis ◽  
...  
Keyword(s):  
Three Dimensional ◽  
Numerical Data ◽  
Crystallographic Structure ◽  
Biological Processes ◽  
X Ray ◽  
X Ray Crystallography ◽  
Software Packages ◽  
Structure Solution ◽  
Repeated Use ◽  
Subjective Input

Macromolecular X-ray crystallography is routinely applied to understand biological processes at a molecular level. However, significant time and effort are still required to solve and complete many of these structures because of the need for manual interpretation of complex numerical data using many software packages and the repeated use of interactive three-dimensional graphics.PHENIXhas been developed to provide a comprehensive system for macromolecular crystallographic structure solution with an emphasis on the automation of all procedures. This has relied on the development of algorithms that minimize or eliminate subjective input, the development of algorithms that automate procedures that are traditionally performed by hand and, finally, the development of a framework that allows a tight integration between the algorithms.

Bridging the resolution gap between x-ray crystallography and electron microscopy

1994 ◽  
Vol 52 ◽  
pp. 92-93
Author(s):  
P. L. Stewart ◽  
S. D. Fuller ◽  
R. M. Burnett
Keyword(s):  
Electron Microscopy ◽  
Transfer Function ◽  
Electron Micrographs ◽  
Structural Information ◽  
Crystallographic Structure ◽  
Contrast Transfer Function ◽  
X Ray ◽  
X Ray Crystallography ◽  
Intact Virus

While x-ray crystallography provides atomic resolution structures of proteins and small viruses, electron microscopy can provide complementary structural information on larger assemblies. A significant computational challenge is faced in bridging the resolution gap between the two techniques. X-ray crystallographic data is collected in the range of 2-10 Å, while image reconstructions from electron micrographs are at a resolution of 25-35 Å. A further problem is that density derived from cryo-electron micrographs is distorted by the contrast transfer function of the microscope, whichaccentuates certain resolution bands.A novel combination of electron microscopy and x-ray crystallography has revealed the various structural components forming the capsid of human type 2 adenovirus. An image reconstruction of the intact virus (Fig. 1), derived from cryo-electron micrographs, was deconvolved with an approximate contrast transfer function to mitigate microscope distortions (Fig. 2). A model capsid was calculated from 240 copies of the crystallographic structure of the major capsid protein and filtered to the correct resolution (Fig. 3).

Direct phase determination from EM images

1993 ◽  
Vol 51 ◽  
pp. 658-659
Author(s):  
Sven Hovmöller ◽  
Xiaodong Zou ◽  
Lars Eriksson ◽  
Gunnar Svensson
Keyword(s):  
Phase Retrieval ◽  
Processing System ◽  
Crystallographic Structure ◽  
Phase Information ◽  
X Ray ◽  
X Ray Crystallography ◽  
Structure Factors ◽  
Diffraction Patterns ◽  
The Fourier Transform ◽  
Oxide Crystals

EM images contain phase information, in contrast to X-ray and electron diffraction patterns. The phases are extracted from the Fourier transform (FT) of the EM image. However, there has been doubts as to what exactly this phase information is. Are the EM phases the same as those of the crystallographic structure factors F(hkl) as defined in x ray crystallography? Or are the phases so distorted by dynamical scattering that very sophisticated procedures are needed for phase retrieval, as has been suggested.We have investigated this question, by comparing phases obtained from EM-images with those of the x ray structure factors from two accurately refined barium niobium oxide crystals.EM images of Ba4Nb14O23 (orthorhombic Cmmm, a=20.782, b=12.448, c=4.148 Å) and Ba3Nb16O23 (orthorhombic Cmmm, a=20.930, b=12.478, c=4.162 Å) were taken with a Philips CM 30 300kV and a JEOL 200CX 200kV electron microscope. Thin areas near the edge were analyzed by our newly developed image processing system, CRISP.

Current Understanding of the Mechanism of Water Oxidation in Photosystem II and Its Relation to XFEL Data

2020 ◽  
Vol 89 (1) ◽  
pp. 795-820 ◽  
Author(s):  
Nicholas Cox ◽  
Dimitrios A. Pantazis ◽  
Wolfgang Lubitz
Keyword(s):  
Water Oxidation ◽  
Isotope Labeling ◽  
Crystallographic Structure ◽  
Water Molecules ◽  
Spectroscopic Techniques ◽  
Enzymatic Process ◽  
X Ray ◽  
X Ray Crystallography ◽  
Biological Water ◽  
Biochemical Research

The investigation of water oxidation in photosynthesis has remained a central topic in biochemical research for the last few decades due to the importance of this catalytic process for technological applications. Significant progress has been made following the 2011 report of a high-resolution X-ray crystallographic structure resolving the site of catalysis, a protein-bound Mn4CaOx complex, which passes through ≥5 intermediate states in the water-splitting cycle. Spectroscopic techniques complemented by quantum chemical calculations aided in understanding the electronic structure of the cofactor in all (detectable) states of the enzymatic process. Together with isotope labeling, these techniques also revealed the binding of the two substrate water molecules to the cluster. These results are described in the context of recent progress using X-ray crystallography with free-electron lasers on these intermediates. The data are instrumental for developing a model for the biological water oxidation cycle.

The reactions of arenesulphonyl azides with tetrahydropyrido[1,2-a]indoles and the X-ray crystallographic structure determination of a resultant novel zwitterion, 1,2,3,4-tetrahydro-10-methyl-4a-p-tolylsulphonylaminopyrido[1,2-a] indole

1979 ◽  
Vol 57 (5) ◽  
pp. 558-564 ◽  
Author(s):  
T. Stanley Cameron ◽  
Ruth E. Cordes ◽  
Aris Terzis ◽  
A. Sydney Bailey ◽  
Peter W. Scott
Keyword(s):  
Structure Determination ◽  
Crystallographic Structure ◽  
X Ray ◽  
X Ray Crystallography ◽  
Ring Enlargement

The reactions of arenesulphonyl azides with tetrahydropyrido[1,2-a]indoles have been examined. Compounds formed by elimination and by ring enlargement are obtained, including a compound with a novel zwitterion structure. The structure of this compound has been determined by X-ray crystallography.

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