BIODIFF

Diffractometer for large unit cells

BIODIFF

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 (d_min < 2.5 Å).

BIODIFF is the first instrument along the cold neutron guide NL1 and is positioned in a distance of about 32.5 m from the cold source. Using a pyrolytic graphite monochromator PG(002) the diffractometer covers a tunable 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 sample crystal’s unit cell 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/accessibility/flexibility

Sample Environment

Besides standard sample environment BIODIFF provides:

Oxford Cryosystems Cryostream 700 plus with a temperature range of 90 K to 500 K
Closed cycle cryostat 3.5 – 325 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 between 1 – 4 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): 5 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: andreas.ostermann@frm2.tum.de

Dr. Tobias Schrader
Phone: +49 (0)89 289-10743
E-Mail: t.schrader@fz-juelich.de

BIODIFF
Phone: +49 (0)89 289-14565

Operated by

Publications

Find the latest publications regarding BIODIFF in our publication database iMPULSE:

impulse.mlz-garching.de

Citation of the instrument

Heinz Maier-Leibnitz Zentrum. (2015). BIODIFF: Diffractometer for large unit cells. Journal of large-scale research facilities, 1, A2. http://dx.doi.org/10.17815/jlsrf-1-19

For citation please always include the DOI.