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Lichtenbergstr.1
85748 Garching

BIODIFF

Diffractometer for large unit cells

BIODIFF scheme BIODIFF scheme

The monochromatic single crystal diffractometer BIODIFF is a joint project of the FRM II, TUM and JCNS, Forschungszentrum Jülich.

BIODIFF is designed to handle crystals with large unit cells and is dedicated to the structure determination of biological macromolecules. In biological macromolecules, like proteins and nucleic acids, hydrogen atoms play an important role. Hydrogen atoms take part in the substrate binding process and are essential for proton transfer reactions du­ring the catalysis in many enzymes. Therefore the knowledge about the protonation states of amino acid residues in the active centre of proteins is often crucial for the understanding of their reaction mechanisms. However, hydrogen atoms, especially rather flexible ones, are barely detectable in X-ray structure determinations of proteins. On the other hand, hydrogen atoms are clearly visible in neutron crystallography experiments even at moderate resolutions (dmin < 2.0 Å).

BIODIFF is the first instrument along the cold neutron guide NL-1 and is positioned in a distance of about 32.5 m to the cold source. Using a pyrolytic graphite monochromator PG(002) the diffracto­meter covers a wavelength range of 2.4 Å to about 5.6 Å. Higher order wavelength contaminations are removed by a neutron velocity selector. The main detector of the diffractometer consists of a neutron imaging plate system in a cylindrical geometry to cover a large solid angle. A fast LiF/ZnS scintillator CCD ca­mera is foreseen for additional detection abilities. The main advantage of this instrument is the possibility to adapt the wavelength to the size of the unit cell of the sample crystal while operating with a clean monochromatic beam that keeps the background level low.

Typical Applications

The main field of application is the neutron structure analysis of proteins, especially the determination of hydrogen atom positions. Typical questions in this field of interest are:

  • Enzymatic mechanism (protonation states of amino acids)
  • Ligand binding mediated by hydrogen bonds
  • Investigation of the hydration shell of proteins
  • H/D-exchange pattern as a monitor of structural stability/flexibility
Sample Environment

Besides FRM II standard sample environment BIODIFF provides:

  • Oxford Cryosystems Cryostream 700 plus with a temperature range of 90 – 500 K
Technical Data

Primary beam

  • Neutron guide NL-1; supermirror m = 2
  • Monochromator:
    • PG(002) mosaicity: 0.4 – 0.5°
  • Higher order filter:
    • Astrium type velocity selector
    • transmission 87% for 2.4 Å
  • Wavelength range:
    • 2.4 - 5.6 Å with selector
    • 2.4 - 6.1 Å without selector
  • Collimation by adjustable slits down to Ø = 1 mm

Beam properties at the sample position

  • Wavelength resolution at sample position: ∆λ/λ = 2.9 % at 2.4 Å
  • Beam divergence (no slits):
    • 0.8° FWHM horizontal
    • 0.7° FWHM vertical

Main detector

Neutron image plate (cylindrical)

  • BaFBr:Eu2+ mixed with Gd2O3
  • Dimensions:
    • radius: 200 mm
    • angular range:
      • ±152° horizontal
      • ±48° vertical
  • Pixel size (quadratic): 125, 250, 500 µm
  • Readout time (with erasing): 4 min (for 500 µm pixel size)

Auxiliary detector

  • CCD camera with scintillator
  • ZnS mixed with 6LiF
  • Dimensions:
    • Active scintillator area (flat): 200 x 200 mm²
    • Distance to sample: 100 mm
  • 2Θ-angle around sample position 0° - 113°
  • CCD chip with 2048 x 2048 pixels
  • Pixel size: 13.5 x 13.5 µm2
  • Overall spatial resolution: ≈ 300 × 300 µm2 (limited by scintillator thickness)
  • Minimum readout time: ≈ 1 sec (full resolution); < 1 sec (binning mode)

Instrument Scientists

Dr. Andreas Ostermann
Phone: +49.(0)89.289.14702
E-Mail:

Dr. Tobias Schrader
Phone: +49.(0)89.289.10743
E-Mail:

BIODIFF
Phone: +49.(0)89.289.14565

Operated by

Logo FRMII
Logo JCNS

Gallery

BIODIFF
BIODIFF
Beta pattern
Beta pattern
Cryostream
Cryostream

FRM II> FRM IITechnische Universität München> Technische Universität MünchenForschungszentrum Jülich> Forschungszentrum JülichHelmholtz-Zentrum Geesthacht> Helmholtz-Zentrum Geesthacht