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.

Preparation and X-ray crystal structure of [(OC)3Mo{P2[MeNC(O)NMe]2}3Mo(CO)3]

Abstract: Two new complexes [(OC)3Mo(µ-L)3Mo(CO)3](1) and [Mo(CO)3L3](2) have been isolated from the reaction of [Mo(CO)3(C7H8)](C7H8= cycloheptatriene) with the diphosphine ligand P2[MeNC(O)NMe]2(L). Crystals of (1) are tetragonal with a=b= 2 271.9(2), c= 3 212.1(4) pm, Z= 16, and space group I41/acd. The structure has been refined to R= 0.038 for 2 309 unique observed diffractomer data. The molecule possesses approximate 32 (D3) symmetry, with a crystallographic two-fold axis perpendicular to the Mo ⋯ Mo vector. Mean Mo–P and P–P bond lengths are 246.2(2) and 221.7(2) pm.

Darstellung und Eigenschaften des Tribrom-cyclo-1λ6-wolfram-3,5-dithia-2,4,6-triazens/Synthesis and Properties of Tribromo-cyclo-1λ6-tungsten-3,5-dithia-2,4,6-triazene

Abstract: The metallacycle [Br₃WS₂N₃] has been obtained from the reaction of S₄N₄ with WBr₅. The salt [Ph₄P⁺][Br₄WS₂N₃⁻] was formed from [Br₃WS₂N₃] by addition of Ph₄PBr. It crystallizes in the orthorhombic space group Pbca with a = 1396.8(4), b = 1961.9(5), c = 2108.0(4) pm, and Z = 8. The following mean bond lengths were observed in the anion: W-N 184.2, W-Br 256.8, N-S 157.8 pm.

Synthese, Eigenschaften und Kristallstruktur von (NH4)NbOBr4/ Synthesis, Properties and Crystal Structure of (NH4)NbOBr4

Abstract: (NH₄)NbOBr₄ is obtained as air sensitive, light red crystals from NH₄Br and NbBr ₅ in a sealed glass ampoule at 420 °C, whereby the oxygen presumably originates from the glass surface. The compound crystallizes in the monoclinic space group C2/m with a = 1269.9(1), b = 1384.7(2). c = 773.0(2) pm, β = 114.44(2)° and Z = 6. The structure is built up by NH⁴⁺ cations and polymeric NbOBr₄ anions. Symmetrical linear oxo bridges with Nb-O = 199 pm connect square planar NbBr₄ units to form endless chains arranged in planes parallel (010). Neighbouring NbBr₄ units are in eclipsed as well as staggered orientations. The NH₄⁺ cations are located between the planes of parallel NbOBr₄ ⁻ chains. The vibrational frequencies of the IR and Raman spectrum are assigned.

Triostin A Derived Cyclopeptide as Architectural Template for the Alignment of Four Recognition Units

Abstract: The DNA bisintercalator triostin A is structurally based on a disulfide-bridged depsipeptide scaffold that provides preorganization of two quinoxaline units in 10.5 A distance. Triostin A analogues are synthesized with nucleobase recognition units replacing the quinoxalines and containing two additional recognition units in between. Thus, four nucleobase recognition units are organized on a rigid template, well suited for DNA double strand interactions. The new tetra-nucleobase binders are synthesized as aza-TANDEM derivatives lacking the N-methylation of triostin A and based on a cyclopeptide backbone. Synthesis of two tetra-nucleobase aza-TANDEM derivatives is established, DNA interaction analyzed by microscale thermophoresis, cytotoxic activity studied and a nucleobase sequence dependent self-aggregation investigated by mass spectrometry.

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.