BIODIFF

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

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

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 × 2048 pixels
• Pixel size: 13.5 × 13.5 µm²
• Overall spatial resolution: ≈ 300 × 300 µm² (limited by scintillator thickness)
• Minimum readout time: ≈ 1 sec (full resolution); < 1 sec (binning mode)