Journal ArticleDOI
Phase annealing in SHELX-90: direct methods for larger structures
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TLDR
In this article, a phase annealing method, related to the simulated-annealing approach in other optimization problems, is proposed and it is shown that it can result in an improvement of up to an order of magnitude in the chances of solving large structures at atomic resolution.Abstract:
A number of extensions to the multisolution approach to the crystallographic phase problem are discussed in which the negative quartet relations play an important role. A phase annealing method, related to the simulated annealing approach in other optimization problems, is proposed and it is shown that it can result in an improvement of up to an order of magnitude in the chances of solving large structures at atomic resolution. The ideas presented here are incorporated in the program system SHELX-90; the philosophical and mathematical background to the direct-methods part (SHELXS) of this system is described.read more
Citations
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Cascade complexation of pseudo-halide by dicopper cryptates: a linear Cu–NNN–Cu unit
TL;DR: An X-ray crystallographic structure determination of a µ-azido azacryptate has confirmed the existence of collinear Cu-NNNN-Cu geometry.
Journal ArticleDOI
para‐Functionalized Aryl‐di‐tert‐butylfluorosilanes as Potential Labeling Synthons for 18F Radiopharmaceuticals
Ljuba Iovkova,Björn Wängler,Esther Schirrmacher,Ralf Schirrmacher,Gabriele Quandt,Guido Boening,Markus Schürmann,Klaus Jurkschat +7 more
TL;DR: Novel para-functionalized aryl-di-tert-butylfluorosilanes, p-(tBu(2)FSi)C(6)H(4)X (X=functional group), have been made available and broaden the spectrum of silicon-based (18)F acceptors (SiFAs) for potential PET applications.
Journal ArticleDOI
Nickel(II) complexes of pentadentate N5 ligands as catalysts for alkane hydroxylation by using m-CPBA as oxidant: a combined experimental and computational study.
Muniyandi Sankaralingam,Mani Balamurugan,Mallayan Palaniandavar,Mallayan Palaniandavar,Prabha Vadivelu,Cherumuttathu H. Suresh +5 more
TL;DR: Both the catalytic activity and the selectivity decrease in the new nickel(II) complexes catalyze the oxidation of cyclohexane in the presence of m-CPBA as oxidant up to a turnover number of 530 with good alcohol selectivity.
Journal ArticleDOI
Accurate Hydrogen Positions in Organic Crystals: Assessing a Quantum-Chemical Aide
TL;DR: In this article, the authors review and evaluate a popular ab initio strategy based on plane-wave density-functional computations, namely, selectively relaxing H positions in an otherwise fixed cell.
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Structural Importance of Secondary Interactions in Molecules: Origin of Unconventional Conformations of Phosphine–Borane Adducts
TL;DR: QC analysis of phosphine-borane adducts revealed the importance of a subtle interplay between competing attractive and repulsive secondary interactions, causing the surprising eclipsed conformational preference for systems of this degree of complexity.
References
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Book
Crystallographic Computing 3: Data Collection, Structure Determination, Proteins and Databases
TL;DR: The latest in a series on crystallographic computing, this collection of 33 papers covers the full spectrum of computer applications in crystallography, including the use of micro-, mini-, and mainframe computers.