Comparison of diffraction intensity using a monocapillary optic and pinhole collimators in a microdiffractometer with a curved image-plate

The performance of a tapered, monocapillary optic was compared to double-pinhole optics by measuring the intensity and widths of powder diffraction peaks generated using Cr Kα and Cu Kα X-rays (46 kV, 46 mA). A microdiffractometer and curved image-plate system was used to collect diffraction patterns displayed by an alumina intensity standard. A monocapillary optic with a 20 μm beam width (measured at half the maximum intensity, FWHM) was compared to collimating pinhole optics with two apertures: one with 30 μm diameter pinholes and another with 50 μm pinholes. The average, integrated intensity of the diffraction peaks in the patterns collected using the 20 μm monocapillary optic was 6 to 7 times greater than the average diffraction intensity obtained with the 50 μm pinhole collimator and 25 times greater than the intensity obtained with the 30 μm collimator. The average increase in the FWHM of the diffraction peaks in the patterns obtained with the monocapillary optic was ∼2 times greater than the pinhole collimators.

Resonant X-ray diffraction using high-resolution image-plate data

The experimental setup for the collection of synchrotron X-ray powder diffraction data from samples with high absorption (μR> 10) is described. It consists of a combination of a vacuum chamber with an image-plate system. A numerical absorption correction for the applied geometry has been derived and the data were corrected accordingly. Values forf ′(Er) andf ′′(Er) were refined from eight measurements on Er5Re2O12above and below the ErLIIIabsorption edge. Successful refinement of the crystallographic data has verified the high quality of the collected intensities.

Crystallization and preliminary structural studies of Scilla campanulata lectin complexed with α1–6 mannobiose

Recent work has shown that Scilla campanulata agglutinin from bluebell bulbs has a strong affinity for α(1,3)- and α(1,6)-linked mannosyl residues and possesses moderate antiretroviral activity. This lectin has been crystallized by the hanging-drop method of vapour diffusion complexed with the disaccharide mannose-α1,6-D-mannose. The crystals are in the space group P21212 with unit-cell dimensions a = 70.63, b = 92.79 and c = 47.25 Å, and with a dimer in the asymmetric unit. The crystals diffract X-rays to beyond 1.5 Å resolution at 277 K and are stable in an X-ray beam. Data to 1.6 Å resolution have been collected using a MAR image-plate system at a synchrotron source and the structure of the complex has been solved by the molecular replacement method.

Two Crystal Structures Towards the Discotic Columnar Mesophase of (1,4,8,11,15,18,22,25-Octahexylphthalocyaninato)nickel

(1,4,8,11,15,18,22,25-Octahexylphthalocyaninato)nickel is a thermotropic liquid crystal, undergoing a transition to a discotic columnar mesophase at 418 K. Its crystals are weakly diffracting needles. Single-crystal X-ray diffraction studies at 103 K, using intense synchrotron radiation of wavelength 0.504 Å at Station F2, CHESS and the `Princeton 1k' CCD area detector, and at 295 K using a Cu Kα rotating anode diffractometer, have respectively shown that the symmetry of the crystals is increased from primitive monoclinic (space group P21/n) to C-centred monoclinic (space group C2/c) when the temperature is raised. Solution of the structure at each temperature shows that the increase in symmetry at 295 K arises from slight movement of the molecules, as well as increased thermal motion of the hexyl groups, and small conformational changes in these groups, indicating the first stage of the transition to the discotic columnar mesophase, when the hexyl groups are thought to become completely mobile. The quality of the refinement of the structure is indicative of what can now be realized by employing multipole wiggler synchrotron radiation and a CCD area detector, as well as cryocooling, for difficult small molecule samples. The temperature of the space group transition was determined at the Daresbury SRS, on Station 7.2, using a CCD detector to monitor an area of the diffraction pattern, whilst varying the temperature systematically. A gradual appearance of spots for h + k = 2n + l occurred between 205 and 195 K. Tests were also made using an image plate system at 195 and 293 K, which confirmed the transition from primitive to C-centred lattice symmetry with temperature. No other changes were apparent on the CCD or IP detectors.