Robert B. Von Dreele

A dedicated powder diffraction beamline at the Advanced Photon Source: Commissioning and early operational results

A new dedicated high-resolution high-throughput powder diffraction beamline has been built, fully commissioned, and opened to general users at the Advanced Photon Source. The optical design and commissioning results are presented. Beamline performance was examined using a mixture of the NIST Si and Al(2)O(3) standard reference materials, as well as the LaB6 line-shape standard. Instrumental resolution as high as 1.7 x 10(-4) (DeltaQQ) was observed.

A twelve-analyzer detector system for high-resolution powder diffraction.

A dedicated high-resolution high-throughput X-ray powder diffraction beamline has been constructed at the Advanced Photon Source (APS). In order to achieve the goals of both high resolution and high throughput in a powder instrument, a multi-analyzer detector system is required. The design and performance of the 12-analyzer detector system installed on the powder diffractometer at the 11-BM beamline of APS are presented.

Synchrotron X-ray powder diffraction study of hexagonal turkey egg-white lysozyme.

The structure of turkey egg-white lysozyme (TEWL) has been refined from high-resolution X-ray powder diffraction data. The sample was rapidly obtained as a polycrystalline precipitate at high protein concentration using 0.5 M NaCl solvent pH 6 and was deposited in the PDB with code 1xft. The diffraction data were collected at room temperature. Molecular replacement was shown to give a suitable starting point for refinement, illustrating that powder data can be sufficient for this approach. Crystallographic models were then refined by combined Rietveld and stereochemical restraint analysis of the powder data (d(min) = 3.35 A), resulting in the extraction of reliable lattice parameters and the refinement of the molecular conformation at room temperature. The structure is hexagonal [space group P6(1)22, unit-cell parameters a = 71.0862 (3), c = 85.0276 (5) A] with 12 symmetry-related molecules in the unit cell, in agreement with previous studies. The results of our analysis are indicative of specific amino acids being disordered at this temperature. Upon cooling, a sudden drop in the lattice parameters at approximately 250 K is observed concurrently with the freezing of the mother liquor. The observation of severe peak broadening below this temperature indicates strain effects accompanying the freezing transition, which are found to be reversible. Finally, a correlation between the unit-cell parameters and the pH of the buffer solution is evident, in a similar manner to earlier observations on HEWL.

CIF applications. XIV. Reporting of Rietveld results using pdCIF: GSAS2CIF

A discussion of the process of creating powder diffraction CIF documents (pdCIF) from Rietveld results is presented, with particular focus on the computer program GSAS2CIF. The data structures used within GSAS2CIF are described, as well as how the program implements template files for descriptive information. Two graphical user interface utilities are also discussed.

What's new in GSAS-II

The General Structure and Analysis Software II (GSAS-II) package is an all-new crystallographic analysis package written to replace and extend the capabilities of the universal and widely used GSAS and EXPGUI packages. GSAS-II was described in a 2013 article, but considerable work has been completed since then. This paper describes the advances, which include: rigid body fitting and structure solution modules; improved treatment for parametric refinements and equation of state fitting; and small-angle scattering data reduction and analysis. GSAS-II offers versatile and extensible modules for import and export of data and results. Capabilities are provided for users to select any version of the code. Code documentation has reached 150 pages and 17 web-tutorials are offered.

Application of molecular replacement to protein powder data from image plates.

Macromolecular structures can be solved via molecular replacement from powder diffraction data collected not only on multi-analyzer diffractometers but also on image plates. Diffraction peaks recorded on image plates are generally broader than those collected using an array of crystal analyzer detectors, but the image-plate data often allow the use of powder data to lower d-spacings. Owing to the high incidence of overlaps in powder patterns, which is especially evident for larger structures, a multi-pattern Pawley refinement is necessary in order to distinguish intensity peaks. This work utilized various salt concentrations to produce small lattice distortions, which resulted in shifts of Bragg peak positions, in a suite of five powder patterns. Using reflection structure factors obtained from this combined refinement, the structure of hen egg-white lysozyme was determined by molecular replacement using the 60% identical human lysozyme (PDB code 1lz1) as the search model. This work also expands upon previous work by presenting a full-scale multi-species analysis combined with an investigation of the sensitivity with regard to discrimination between incorrect fold types. To test the limits of this technique, extension to higher molecular-weight structures is ongoing.

Dedicated High‐Resolution Powder Diffraction Beamline at the Advanced Photon Source

A high‐resolution x‐ray powder diffraction beamline that exploits the high flux, high energy resolution, and precise energy tuning of the third‐generation synchrotron source will be built at the Advanced Photon Source (APS). The goal is to establish a high‐resolution high‐throughput dedicated powder instrument at the APS to serve the powder community. We describe design of the instrument that is able to measure a complete high‐resolution powder pattern in one hour or less, uses automation to optimize throughput, has the ability to readily tune over a wide range of x‐ray energies quickly and easily covering important absorption edges for resonant data measurements, and has the ability to accommodate various environmental devices for high‐temperature, low‐temperature or time‐resolved data collection.

Texture – An Overview

Samples that are polycrystalline solids produced by some mechanical process frequently possess a non-random orientation of the crystallites due to deformation of the material during the forming operation. The resulting crystallite orientations (“texture”) can be more complex that those obtained from simple packing of powders. In the course of crystal structure analysis from powder diffraction data, changes in the Bragg intensities resulting from texture / preferred orientation can strongly degrade the quality of a Rietveld refinement or prevent a structure solution. Here, we consider models for describing texture in polycrystalline samples and examine their application to real world examples.