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.
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:
Besides FRM II standard sample environment BIODIFF provides:
Beam properties at the sample position
Neutron image plate (cylindrical)