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.

Manganese(II) Amides: The Synthesis and X-Ray Crystal Structures of Mn[N(SiMe3)(2,6-Pri2C6H3)]2[THF] and Mn3[N(H)2,6-Pri2C6H3]4[N(SiMe3)2]2

Abstract: A series of manganese(II) am ides (1-4), derived from 2,6-diisopropylaniline (H2NAr; where Ar = 2,6-Pri2C6H3) and its N-silylated derivative H(SiMe3)NAr, has been prepared and characterized. The crystal structure of Mn[N(SiMe3)Ar]2[THF] (2) reveals a monomeric species with a planar three-coordinate Mn(II) center. Crystal data for 2: trigonal (hexagonal axes), a = 30.119(2) Å, c = 10.589(1) Å, V = 8319(1) Å3, T = 153 K, space group P31 (No. 144), Z = 9 (R/Rw = 0.053/0.050). In contrast, Mn3[N(H)Ar]4[N (SiMe3)2]2 · C7H8 (4) is shown to be a novel trinuclear compound held together by nitrogen-bridges. The two terminal Mn(II) atoms have a distorted trigonal planar arrangement of nitrogen donors whereas the central Mn(II) is surrounded by a distorted tetrahedral array of nitrogen donors. Crystal data for 4: orthorhombic, a = 21.301(5) Å, b = 17.021(6) Å, c = 20.519(7) Å, V = 7439(4) Å3, T = 153 K, space group Pbcn (No. 60), Z = 4 (R/Rw = 0.050/0.070).

Structure of a highly NADP+-specific isocitrate dehydrogenase.

Abstract: Isocitrate dehydrogenase catalyzes the first oxidative and decarboxylation steps in the citric acid cycle. It also lies at a crucial bifurcation point between CO2-generating steps in the cycle and carbon-conserving steps in the glyoxylate bypass. Hence, the enzyme is a focus of regulation. The bacterial enzyme is typically dependent on the coenzyme nicotinamide adenine dinucleotide phosphate. The monomeric enzyme from Corynebacterium glutamicum is highly specific towards this coenzyme and the substrate isocitrate while retaining a high overall efficiency. Here, a 1.9 A resolution crystal structure of the enzyme in complex with its coenzyme and the cofactor Mg2+ is reported. Coenzyme specificity is mediated by interactions with the negatively charged 2′-­phosphate group, which is surrounded by the side chains of two arginines, one histidine and, via a water, one lysine residue, forming ion pairs and hydrogen bonds. Comparison with a previous apoenzyme structure indicates that the binding site is essentially pre­configured for coenzyme binding. In a second enzyme molecule in the asymmetric unit negatively charged aspartate and glutamate residues from a symmetry-related enzyme molecule interact with the positively charged arginines, abolishing coenzyme binding. The holoenzyme from C. glutamicum displays a 36° interdomain hinge-opening movement relative to the only previous holoenzyme structure of the monomeric enzyme: that from Azotobacter vinelandii. As a result, the active site is not blocked by the bound coenzyme as in the closed conformation of the latter, but is accessible to the substrate isocitrate. However, the substrate-binding site is disrupted in the open conformation. Hinge points could be pinpointed for the two molecules in the same crystal, which show a 13° hinge-bending movement relative to each other. One of the two pairs of hinge residues is intimately flanked on both sides by the isocitrate-binding site. This suggests that binding of a relatively small substrate (or its competitive inhibitors) in tight proximity to a hinge point could lead to large conformational changes leading to a closed, presumably catalytically active (or inactive), conformation. It is possible that the small-molecule concerted inhibitors glyoxylate and oxaloacetate similarly bind close to the hinge, leading to an inactive conformation of the enzyme.

Zwei Wege zu Si‐funktionellen Cyclosilazanen – Kristallstruktur des 1,3,6,8,10,12‐Hexa‐aza‐2,4,5,7,9,11‐hexasila‐dispiro[4.1.4.1]dodecan

Abstract: Aminochlorsilane [RSiCl2NHCMe3, R Cl (1), H (2)] werden durch die Reaktion der Chlorsilane mit LiNHCMe3 erhalten. HSiCl2N(iso-Bu)SiMe3 (3) entsteht in der Reaktion von HSiCl3 mit LiN(iso-Bu)SiMe3. HSiCl3 reagiert mit LiN(CMe3)SiMe3 unter LiCl- und Me3SCl-Abspaltung zum Cyclodisilazan [(HSiClNCMe3)2 (4)]. Neben C6H5SiCl2N(CMe3)SiMe3 (5) ist C6H5SiCl2NHCMe3 (6) das Hauptprodukt der Reaktion von Trichlorphenylsilan mit LiN(CMe3)SiMe3. 3 verliert thermisch Me3SiCl. Es entsteht das Cyclotrisilazan [(HSiClNiso-Bu)3 (7)]. 5 verliert thermisch iso-Butan unter Bildung von C6H5SiCl2NHSiMe3 (8). 1, 2 und 6 reagieren mit n-C6H9Li unter Butan- und LiCl-Abspaltung zu den Cyclodisilazanen [(RSiClNCMe3)2, R H (4), Cl (9), C6H5 (10)]. 4 wird durch NaF zu (HFSiNCMe3)2 (11) fluoriert. Die Alkoholyse von 4 fuhrt zur Bildung von [(H(RO)SiNCMe3)2, R Me (12), C6H5 (13)], die Aminolyse zu [(H(R2N)SiNCMe3)2, R Me (14), C2H5 (15)]. Nur ein Chloratom von 4 wird in der Reaktion mit H2NCMe3 substituiert (16). Mit Lithium reagiert 4 zum 1,3,6,8,10,12-Hexa-aza-2,4,5,7,9,11-hexasila-dispiro[4.1.4.1]-dodecan (17). Die Kristallstruktur von 17 wird mitgeteilt. Two Ways to Si-functional Cyclosilanes — Crystal Structure of 1,3,6,8,10,12-Hexa-aza-2,4,5,7,9,11-hexasila-dispiro [4.1.4.1]dodecan Aminochlorosilanes [RSiCl2NHCMe3, R Cl (1), H (2)] are obtained in the reaction of the chlorosilanes with LiNHCMe3. HSiCl2N(iso-Bu)SiMe3 (3) is formed in the reaction of HSiCl3 and LiN(iso-Bu)SiMe3. HSiCl3 reacts with LiN(CMe3)SiMe3 under LiCl and Me3SiCl elimination to give the cyclodisilazane [(HSiClNCMe3)2 (4)]. In addition to C6H5SiCl2N(CMe3)SiMe3 (5), the main product of the reaction of trichloro-phenylsilane with LiN(CMe3)SiMe3 is C6H5SiCl2NHCMe3 (6). 3 loses Me3SiCl thermally, giving the cyclotrisilazane [(HSiClNiso-Bu)3 (7)]. 5 loses iso-butane thermally with formation of C6H5SiCl2NHSiMe3 (8). 1, 2 and 6 react with LiC4H9 under butane and LiCl elimination to give the cyclodisilazes [(RSiClNCMe3)2, R H (4), Cl (9), C6H5 (10)]. 4 is fluorinated to (HSiFNCMe3)2 (11) by NaF. The alcoholysis of 4 leads to the formation of [(H(RO)SiNCMe3)2, R Me (12), C6H5 (13)], the aminolysis to [(H(NR2)SiNCMe3)2, R Me (14), C2H5 (15)], only one chloro atom of 4 is substituted in the reaction with H2NCMe3 (16). 4 reacts with lithium to give the 1,3,6,8,10,12-hexa-aza-2,4,5,7,9,11-hexasila-dispiro[4.1.4.1]dodecan (17), for which the crystal structure is reported.

Darstellung und Kristallstrukturen von [Ph4As+][PS2(N3)2] und [(n-C3H7)4N+]2[(NCPS2)2S2-]/ Preparation and Crystal Structures of [Ph4As+][PS2(N3)2–] and [(n-C3H7)4N+]2 [(NCPS2)2S2–]

Abstract: The diazidodithiophosphate anion [PS₂(N₃)₂⁻] can be isolated with a large cation as (Ph₄As⁺][PS₂(N₃)₂⁻] (1). [PS₂(N₃)₂⁻] is formed by the reaction of P₄S₁₀ with NaN₃ in acetonitrile as a solvent. [(NCPS₂)₂S₂⁻] results from the reaction of P₄S₁₀ with NaCN in acetonitrile and is isolated as [(n-C₃H₇)₄N⁺H(NCPS₂)₂S²⁻] (2). 1 crystallizes in the triclinic space group P1 with a - 1329.3(3), b = 1419.1(3),c = 2182.3(5) pm, α = 71.71(2), β = 87.21(2), γ = 84.97(2)° and Z = 6. Crystals of 2 are monoclinic, space group P2₁/n, a - 1899.0(3), b - 949.0(2), c = 2128.4(5) pm, β = 112.90(2)°, Z = 4.

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.