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.

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A short history of SHELX

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.

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Crystal structure refinement with SHELXL

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.

OLEX2: a complete structure solution, refinement and analysis program

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。

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

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.

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

Synthesen und Kristallstrukturen der Ag‐S‐Clusterverbindungen [Ag70S16(SPh)34(PhCO2)4(triphos)4] und [Ag188S94(PR3)30]

Crystals of the title compound (I) are orthorhombic, space group Pnma, a= 17·54(3), b= 14·55(2), c= 6·766(10)A, Z= 4. The structure was solved by the heavy-atom method and refined by full-matrix least-squares to R 0·047 for 1018 unique reflections measured by diffractometer. The molecule lies on a crystallographic mirror plane and possesses approximately C3ν(3m) symmetry; principal bond lengths (averaged for C3ν): Ru ⋯ Ru 2·842(6), Ru–C(O) 1·869(15) and 1·956(19), Ru–C(C) 2·083(11), C–O 1·152(16), and C–C 1·511(20)A. The bridging hydrogen atoms were located in symmetrical positions on the opposite side of the Ru3 plane from the CMe moiety; their positions were refined from the X-ray data subject to the constraints that all Ru–H and all (C)C–H distances were respectively equal, leading to Ru–H, 1·72(7)A and Ru–H–Ru, 112(7)°. The nematic-phase proton n.m.r. spectrum has been reinterpreted in the light of the idealised heavy-atom geometry found in the crystal, and used to give calculated values for Ru–H (1·81 A) and Ru–H–Ru (103°), which are probably more accurate than those calculated only from X-ray data.

Crystal structure of nonacarbonyl-µ3-ethylidyne-tri-µ-hydrido-tri-ruthenium

Labyrinthopeptine – eine neue Klasse carbacyclischer Lantibiotika

Diels-alder reactions of malondialdehyde derivatives with reversed electron demand; an easy approach to structurally unique carbohydrates and compounds of the thromboxane type

Untwinned single crystals of the actinomycins D and Z3 that diffracted to atomic resolution could be obtained for the first time. Low-temperature data collection and a new ab initio method for solving the structures led to precise crystal structures which showed, for example, that the unit cell of actinomycin D contains three molecules, two of which are present in the form of a hydrogen-bridged dimer related by a pseudo-twofold axis (see picture).

George M. Sheldrick

Papers

Synthesen und Kristallstrukturen der Ag‐S‐Clusterverbindungen [Ag70S16(SPh)34(PhCO2)4(triphos)4] und [Ag188S94(PR3)30]

Crystal structure of nonacarbonyl-µ3-ethylidyne-tri-µ-hydrido-tri-ruthenium

Labyrinthopeptine – eine neue Klasse carbacyclischer Lantibiotika

Diels-alder reactions of malondialdehyde derivatives with reversed electron demand; an easy approach to structurally unique carbohydrates and compounds of the thromboxane type

Crystal Structures of Actinomycin D and Actinomycin Z3.