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Notes: Crystal structure solution by anomalous dispersion methods has been greatly facilitated using the rapidly tunable station 9.5 at the Daresbury SRS. Both SIROAS and MAD techniques, with IP data, have been used in the phasing of a brominated nucleotide and a seleno deaminase, respectively. The electron density maps in each case are interpretable. Throughput of projects could be improved upon with a better duty cycle detector. Another category of data collection is that at very high resolution. Detailed structure refinement pushes the limits of resolution and data quality. Station 9.5 has been used to collect high resolution (1.4 A(ring)) native data for the protein concanavalin A. This utilized very short wavelengths (0.7 A(ring)), the image plate, and crystal freezing. A total of 155 407 measurements from two crystals benefited from the on-line nature of the IP detector device, but a slow and quick pass are required to capture the full dynamic range of the data. There are data seen to 1.2 A(ring) and beyond for a pure Mn substituted form of the protein, but a higher intensity still is required to actually record these data. By comparison, trials at CHESS, on a multipole wiggler (station A1) with a CCD (without image intensifier) system, yield native concanavalin A data to 0.98 A(ring) and beyond. This demonstrates that the combination of yet higher intensity and the ease of use of a CCD offers worthwhile improvements; in this case an increase in the data by a factor of (1.4/0.98)3, thus at least doubling the data to parameter ratio for protein structure model refinement and potentially opening up direct structure determination of proteins of the size of concanavalin A (25 kDa).Finally, possibilities at ESRF and further detector developments, such as mosaic CCDs and scintillator coatings, offer further impetus for the field. These include more intense rapidly tunable beams for anomalous dispersion-based structure solution and "ideal'' higher resolution data collection and reactivity studies. ESRF BL19 is described; facilities on BL19 will include a system for freezing and storing crystals at cryogenic temperatures, so that data can be recorded from the same crystal on different runs. Overall, there have been tremendous strides made in this field in the last 15 years, and yet further improvements are to come. © 1995 American Institute of Physics.

Notes: A new instrument (Station 9.5) has been established on the wiggler line at the Daresbury Synchrotron Radiation Source (SRS). It extends the experimental capability at Daresbury for macromolecular crystallography beyond what is provided for with Stations 7.2 (Ref. 1), 9.6 (Ref. 2), and 9.7 by providing a point focused white beam (from a Pt-coated toroid mirror) and/or a rapidly tunable monochromatic beam (using a water-cooled double-crystal monochromator (Ref. 3). The design principles of the new Station 9.5 have been published (Ref. 4). A CCD detector for the station is being developed (preliminary work is described in Ref. 5, or see the additional poster at this meeting) to allow time slices of part of a diffraction pattern to be measured. Laue patterns are currently recorded on film, but access to an image plate detector will shortly become available. Shutter speeds down to 50 μs are routinely available using a rotating disk shutter (Ref. 6). Fluorescence detectors are available for optimized anomalous dispersion data collection. The experimental bench is long enough to accommodate a camera system, and downstream from it an "on-line'' image plate scanner. Data collected on the instrument in various modes of operation will be described for a variety of macro and small molecule crystal systems.

Notes: Many years ago the idea of collecting voluminous quantities of weak reflection intensities from a protein crystal, at high resolution, was a particular challenge [J.R. Helliwell (1979) Daresbury Study Weekend DL/SCI R13, pp. 1–6]. The combination of insertion devices with very high x-ray fluxes at short x-ray wavelengths, sensitive CCD detectors, and freezing of crystals have provided the means to certainly match those best hopes. So much so that the data can best be described as ultrahigh resolution, at least as evidenced in our studies of the 25000 molecular weight plant protein concanavalin A. (The intrinsic property of this protein is to bind sugar molecules; it is implicated in cell-to-cell recognition processes and is widely used as a laboratory diagnostic tool.) At CHESS we have used a 0.9 A(ring) wavelength beam on station A1, fed by a 24 pole multipole wiggler. Both an imaging plate system and the Princeton 1k CCD detector [M. Tate et al., J. Appl. Cryst. 28, 196 (1995)] have been used on this experimental setup to collect diffraction data sets from frozen concanavalin A crystals (saccharide-free crystal form). The rapid readout of the CCD was most convenient compared with the image plate and its associated scanning and erasing. Moreover the data processing results towards the edges of the detectors, 0.98 A(ring), show that the CCD is much better than the image plate at recording these weaker data (Rmerge(I) 13% versus 44%, respectively). The poor performance of the image plate with weak signals has of course been documented by the Daresbury detector group [R. Lewis, J. Synchrotron Radiation 1, 43 (1994)]. However, the aperture of the CCD used was limiting here. Very recently, in another run at CHESS with the CCD on A1, we have been able to record diffraction data to 0.94 A(ring) by further offsetting the detector. We again found that the reflections are still strong at the edge. Clearly the use of even shorter wavelengths than 0.9 A(ring) would be very useful in matching the solid angle of the diffraction pattern to the available detector aperture, for a reasonable crystal-to-detector distance. In addition, absorption errors in the data can be simultaneously removed by such a strategy. Indeed, finely focused x-ray beams of, say 0.5 A(ring) wavelength, are especially well suited to high energy, low emittance synchrotron radition (SR) machines. Some initial tests carried out on CHESS station F2 with a 0.5 A(ring) wavelength beam and the CCD detector show an improvement in the R-merge(I) to 2 A(ring) resolution, in comparison to the data collected at 0.9 A(ring) wavelength (i.e., 2.3% versus 3.0%). In conclusion, the diffraction resolution limit (0.94 A(ring)) seen already in our concanavalin A studies can be further enhanced and is important for the most detailed molecular model refinement (and the testing of structure solving strategies), in conjunction with novel spectroscopic and theoretical studies. This paper builds upon the work of Deacon et al. [Rev. Sci. Instrum. 66, 1287 (1995)]. © 1996 American Institute of Physics.

Notes: Single-crystal x-ray diffraction data can be measured very quickly in Laue geometry compared with monochromatic methods. Alternatively, this gain factor can be used instead to reduce the sample volume for a fixed exposure time. In the latter case especially, there is a critical need to control parasitic scatter in the Laue camera. The use of Laue geometry as a means of quantitative data acquisition required the solution of some fundamental problems. The so-called "overlapping orders problem'' has been found not to be limiting. It can be shown that the bulk of the Laue spots are single order, provided dhkl〈2dmin where dhkl is the interplanar spacing and dmin is the resolution limit of the data. In addition, empirical wavelength normalization is required. This can be achieved by using the symmetry of the diffraction pattern. The fact that different equivalents occur at different wavelengths means that the differences in these intensities can be used to establish the "λ curve.'' Successful wavelength normalization to date has used a relatively broad-band pass. The multiplicity distribution is the histogram of the number of spots of a given order. This distribution is determined by the ratio λmax/λmin (λmax =maximum wavelength, λmin =minimum wavelength in the beam). λmax is determined by the use of any filters in the beamline. λmin is determined either by the spectral curve or a critical cutoff if a mirror is used. A mirror can be usefully introduced to enhance the multiplicity distribution in favor of single wavelength spots or to focus the white beam; so far only vertical focussing has been used. The detector options used to date have been photographic film, Fuji image plate (at Photon Factory)/Kodak storage phosphor (at Cornell) and charge coupled device (CCD) (at Daresbury). It is useful to consider the joint theoretical spatial and energy distribution of spots in defining the detector specification and geometry. To date, we have processed Laue film data successfully. The attraction of using the CCD, even to look at a small portion of the Laue pattern, is to view the diffraction in real time.This will allow tight control of parasitic scatter for microcrystal Laue diffraction and real-time monitoring for time-resolved work. We performed initial experiments using a direct detection CCD imager, and have obtained satisfactory diffraction data on a 40 ms time scale. Results of this work will be presented. In order to assess the efficacy of the Laue method for quantitative crystallography, we have used Laue data from the protein pea lectin and compared it in detail with monochromatic pea lectin data. To assess the use of a vertically focussing mirror, we have successfully used a mercury derivative protein crystal to yield isomorphous and anomalous differences suitable for phase determination. In both the pea lectin and mercury derivative cases, doublet Laue spots were deconvoluted. In the latter case, the data were used in a difference Fourier calculation which showed the mercury peak. Future developments and projections based on multipole sources are given.

Notes: Highlights of a workshop on synchrotron radiation intrumentation and macromolecular crystallography, a satellite meeting of the 4th International Conference on Synchrotron Radiation Instrumentation, will be presented. The theme of the meeting was to look towards the developments on the next generation of high brilliance SR sources current under construction. Macromolecular crystallography needs span a very wide range of technical requirments covering the most demanding uses of SR. It is a rapidly expanding field. (AIP)

Notes: There exists considerable promise for the use of charge-coupled device (CCD) imagers in the fast recording of parts of macromolecular crystal Laue diffraction patterns. As part of this development CCD tests have been made with direct detection of Laue patterns from a small molecule test crystal and a protein crystal. Merging R factors (on intensity), for strong reflections, of 3% have been obtained. A time-slicing scheme for a CCD camera is discussed based on the stacking of slices held in storage in the CCD in the submillisecond time resolution range.

Notes: The size and shape of diffraction spots produced by monochromated synchrotron X-radiation from a singly bent triangular monochromator are derived following a simpler more comparative treatment given in earlier work on reflecting range and prediction of partiality for oscillation camera data [Greenhough & Helliwell (1982). J. Appl. Cryst. 15, 493–508]. In that treatment the possibility of a polychromatic experiment {[see Arndt Nucl. Instrum. Methods (1978), 152, 307–311] for an earlier suggestion} was identified and here the energy profile within each diffraction spot is derived along with the spectral resolution ∂E/E at any point in the profile due to experimental conditions and sample characteristics. A firm theoretical basis is established so that experimental problems and procedures can be discussed with a view to optimizing the method in the light of the presentation of the first reported polychromatic experiment [Arndt, Greenhough, Helliwell, Howard, Rule & Thompson (1982). Nature (London), 298, 835–838].

Notes: The correction of intensity data from protein single crystals for sample absorption effects is important for refinement and interpretation of atomic parameters. Synchrotron X-radiation sources are extensively used to provide high-resolution data and their tuneability utilized to collect data with optimized anomalous dispersion. At longer wavelengths the sample absorption effects become increasingly important. Previous methods of determining the absorption correction using the oscillation camera relied upon film methods, which cannot readily take account of the decay in incident-beam intensity of synchrotron sources. The use of a sensitive ion chamber to measure the transmitted intensity and monitoring of the incident intensity allows an empirical absorption correction to be calculated directly.

Notes: The film absorption factors for CEA Reflex 25 X-ray film have been estimated by three different methods as a function of wavelength in the range 0.3 ≤ λ ≤ 2 Å. This wavelength range encompasses many absorption edges of interest in X-ray crystallography to optimize anomalous dispersion, those wavelengths used to reduce protein crystal absorption (λ ≤ 1 Å), and the spectral range utilized for protein crystal Laue diffraction at synchrotron radiation sources. The value of the film factor at a given λ is important to many protein structural projects.