In single crystal work on small molecule systems, D19 allows the determination of the location of light atoms amongst heavy ones and the accurate characterisation of liganded H and H2 and of hydrogen bonding and hydrogen disorder in studies of organic and inorganic molecules, complexes, solvates, and adducts.

Some larger molecules of biological interest have also been studied on D19, such as vitamin B12 (Jogl et al., in preparation), lysozyme (Bouquiere et al., 1993b), and haemoglobin (Waller, 1989). The interest here is obvious – information on proton positions and hydration is vital for understanding biological processes. Data from monochromatic neutron diffraction studies allows H or D positions to be determined at a much higher level of significance than is obtainable with x-rays. Although it is true that such information can be obtained from high resolution x-ray diffraction when crystals diffract to 1.2Å or better, it is also true that only a small fraction of crystals diffract to this resolution.

The availability of an area detector has also meant that D19 can be used to record high-angle neutron fibre diffraction patterns. The first experiments of this type were on DNA hydration and provided the first information on hydration in polymeric DNA. The studies are also important because fibres allow the study of DNA conformations that have not been observed in oligonucleotide single crystals and also of stereochemical changes that occur during conformational transitions (see Shotton et al., 1997). The same techniques have since been used to study hyaluronic acid, filamentous viruses, and have recently produced some outstanding results from cellulose (Nishiyama et al., 1999; Langan et al., 1999). Similar methods have been used to study hydrogen atoms in aromatic polymers (Mahendrasingam et al., 1992) and are currently being developed for the study of polymers such as Nylon 66. There is increasing interest from industrial collaborators in the use of fibre diffraction methods in combination with specific deuteration to study changes in polymer structure as a function of chemical composition, temperature, and drawing processes. All of the neutron fibre diffraction studies provide information that cannot be obtained from complementary x-ray fibre diffraction studies.

• Neutron diffraction studies of vitamin B12 (Bouquiere et al. 1993b; Langan et al., 1999)
• Structure of oligosaccharides (Lebas et al., 1994; Steiner et al., 1991)
• Structure of modulated phases in TlGaSe2
• Supramolecular organic complexes (Allen et al., 1997)
• Inorganic and organometallic complexes (Bau et al., 1997; Mueller et al., 1998)
  Liquid crystal studies (Richardson et al., 1990)
  Quasicrystals (Frey et al., 1997)

• Hydration patterns in polymeric DNA (Shotton et al., 1997; Forsyth et al., 1998)
• Hydrogen bonding networks in cellulose
• (Nishiyama et al., 1999; Langan et al., 1999)
• Hydration of hyaluronic acid
• Location of hydrogen atoms in industrial polymers
• Filamentous viruses