George M. Sheldrick

Bio: George M. Sheldrick is an academic researcher from University of Göttingen. The author has contributed to research in topics: Crystal structure & Bond length. The author has an hindex of 58, co-authored 791 publications receiving 151229 citations. Previous affiliations of George M. Sheldrick include University of Regensburg.

The crystal structure of 2-(4-chlorophenoxy)-tetrahydropyran

Abstract: The crystal structure of the title compound has been determined (space group Ρ J, a = 6.774(3), b = 8.900(4), c = 9.811(4) Α, α = 66.06(2), /3 = 86.67(3), y = 76.87(2)°, Ζ = 2) and refined to R = 0.040. The bond lengths at the acetal centre are consistent with a previously published bond· length/reactivity correlation (Jones and Kirby, 1979). Introduction We have shown recently (Jones and Kirby, 1979) that there is a linear correlation between reactivity and the length of the exocyclic C — Ο bond in a series of three 2-aryloxy-tetrahydropyran acetals. To test the strength of this correlation we have prepared several more acetals in this series, and report here the crystal and molecular structure of one of the simplest such compounds to exist in crystalline form at room temperature, the 4-chlorophenoxy acetal (1). (1) was prepared by the acid-catalysed addition of p-chlorophenol to dihydropyran. The phenol (0.025 mol) and dihydropyran (0.05 mol) were dissolved in dry ether and a few crystals of p-toluenesulphonic acid added. After stirring for 3 h under nitrogen, the solution was allowed to stand 1 Crystal Structures of Acetals, Part 6. Parts 1—5 are the first five references 2 All correspondence to P.G.J, (above address) 266 P. G. Jones et al.: The crystal structure of 2-(4'-chlorophenoxy)-tetrahydropyrran Table 1. Atom coordinates ( χ 10) and temperature factors (Α χ 10 ). The anisotropic termperature factor has the form 7~= — 2π {£/,, h a* + . . . 2 Vi2 hka*b* + ... J

Solution and structure of an alternating D,L-peptide.

Abstract: The crystal structure of H-(l-Tyr-d-Tyr)4-l-Lys-OH has been determined to 1.3 A resolution. The d,l-alternating peptide crystallizes in the tetragonal system, space group P43212, with unit-cell parameters a = b = 27.99 (3), c = 78.93 (8) A. The crystals contain two molecules in the asymmetric unit that form a double-stranded right-handed antiparallel β-helix. The structure has been solved by SIRAS using a crystal soaked in an iodide-containing solution for 1 min. The programs SHELXD and SHELXE were used to determine the iodide substructure and also the experimental electron-density map. Using the coordinates of known d,l-peptides deposited in the PDB, several attempts were made to solve the structure by molecular-replacement techniques. Although the backbone of the MR model selected shows great similarity and was used to trace the actual peptide structure in the map, it was not possible to obtain the correct solution before the experimental phases became available. The correct fragment orientations are easily determined, but the same does not apply to the translation search. Nevertheless, insights into fragment search and expansion were gained from the tests described in this paper. The correlation coefficient calculated with the resolution shell of data around 2.4 A, a distance corresponding to most 1—3 interatomic vectors, is a particularly good discriminator of correct orientations in the rotation search of small fragments.

Crystal Structure of 2-Thiopyrrole-1,2-dicarboximide-(bis-triphenylphosphine)copper(I)chloride, [(Ph3P)2Cu(Cl)C6H4N2OS]

Abstract: Cristallisation dans le systeme monoclinique, groupe C2/c et affinement de la structure jusqu'a R=0,063. Coordination tetraedrique autour des atomes Cu

A short history of SHELX

Abstract: An account is given of the development of the SHELX system of computer programs from SHELX-76 to the present day. In addition to identifying useful innovations that have come into general use through their implementation in SHELX, a critical analysis is presented of the less-successful features, missed opportunities and desirable improvements for future releases of the software. An attempt is made to understand how a program originally designed for photographic intensity data, punched cards and computers over 10000 times slower than an average modern personal computer has managed to survive for so long. SHELXL is the most widely used program for small-molecule refinement and SHELXS and SHELXD are often employed for structure solution despite the availability of objectively superior programs. SHELXL also finds a niche for the refinement of macromolecules against high-resolution or twinned data; SHELXPRO acts as an interface for macromolecular applications. SHELXC, SHELXD and SHELXE are proving useful for the experimental phasing of macromolecules, especially because they are fast and robust and so are often employed in pipelines for high-throughput phasing. This paper could serve as a general literature citation when one or more of the open-source SHELX programs (and the Bruker AXS version SHELXTL) are employed in the course of a crystal-structure determination.

Crystal structure refinement with SHELXL

Abstract: The improvements in the crystal structure refinement program SHELXL have been closely coupled with the development and increasing importance of the CIF (Crystallographic Information Framework) format for validating and archiving crystal structures. An important simplification is that now only one file in CIF format (for convenience, referred to simply as `a CIF') containing embedded reflection data and SHELXL instructions is needed for a complete structure archive; the program SHREDCIF can be used to extract the .hkl and .ins files required for further refinement with SHELXL. Recent developments in SHELXL facilitate refinement against neutron diffraction data, the treatment of H atoms, the determination of absolute structure, the input of partial structure factors and the refinement of twinned and disordered structures. SHELXL is available free to academics for the Windows, Linux and Mac OS X operating systems, and is particularly suitable for multiple-core processors.

OLEX2: a complete structure solution, refinement and analysis program

Abstract: New software, OLEX2, has been developed for the determination, visualization and analysis of molecular crystal structures. The software has a portable mouse-driven workflow-oriented and fully comprehensive graphical user interface for structure solution, refinement and report generation, as well as novel tools for structure analysis. OLEX2 seamlessly links all aspects of the structure solution, refinement and publication process and presents them in a single workflow-driven package, with the ultimate goal of producing an application which will be useful to both chemists and crystallographers.

疟原虫var基因转换速率变化导致抗原变异[英]／Paul H, Robert P, Christodoulou Z, et al//Proc Natl Acad Sci U S A

Abstract: 抗原变异可使得多种致病微生物易于逃避宿主免疫应答。表达在感染红细胞表面的恶性疟原虫红细胞表面蛋白1（PfPMP1）与感染红细胞、内皮细胞、树突状细胞以及胎盘的单个或多个受体作用，在黏附及免疫逃避中起关键的作用。每个单倍体基因组var基因家族编码约60种成员，通过启动转录不同的var基因变异体为抗原变异提供了分子基础。

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

Abstract: 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. PHENIX has 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.