Facilities for macromolecular crystallography at the Helmholtz-Zentrum Berlin.

Three macromolecular crystallography (MX) beamlines at the Helmholtz-Zentrum Berlin (HZB) are available for the regional, national and international structural biology user community. The state-of-the-art synchrotron beamlines for MX BL14.1, BL14.2 and BL14.3 are located within the low-ß section of the BESSY II electron storage ring. All beamlines are fed from a superconducting 7 T wavelength-shifter insertion device. BL14.1 and BL14.2 are energy tunable in the range 5-16 keV, while BL14.3 is a fixed-energy side station operated at 13.8 keV. All three beamlines are equipped with CCD detectors. BL14.1 and BL14.2 are in regular user operation providing about 200 beam days per year and about 600 user shifts to approximately 50 research groups across Europe. BL14.3 has initially been used as a test facility and was brought into regular user mode operation during the year 2010. BL14.1 has recently been upgraded with a microdiffractometer including a mini-κ goniometer and an automated sample changer. Additional user facilities include office space adjacent to the beamlines, a sample preparation laboratory, a biology laboratory (safety level 1) and high-end computing resources. In this article the instrumentation of the beamlines is described, and a summary of the experimental possibilities of the beamlines and the provided ancillary equipment for the user community is given.

Ion-beam-induced collective rotation of nanocrystals.

Vapor-deposited nanocrystalline titanium layers have been irradiated at room temperature with 350-MeV-Au ions up to 4x10;{15} Au/cm;{2}. Bombardment-induced texture changes were determined at the BESSY synchrotron light source. During off-normal irradiation, the nanocrystals undergo grain alignment and rotation up to approximately 90 degrees at the highest ion fluence. At the same time, the whole layer exhibits shear flow very similar to that observed previously in amorphous materials. Below 1x10;{15} Au/cm;{2}, a reversal of the ion incidence angle leads to a back rotation of the grains. These effects are absent or immeasurably small in coarse-grained titanium but have also been found in nanocrystalline TiN and NiO. The observations can be modeled by assuming that grain boundaries behave during ion bombardment like amorphous matter or by assuming a generation of disclination dipoles moving along grain boundaries.