A review is given on recent X-ray, neutron diffraction and nuclear magnetic resonance studies of inorganic hydrates. The geometry of water molecules and the interaction with their surroundings are discussed in terms of hydrogen bonding between donors and acceptors and lone pair coordinations to metal cations. Various types of finite or infinite hydrogen bonded water networks are related to their characteristic features. Among these, the static and dynamical structures of hydrogen bonded water layers in tin (II) chloride dihydrate are described in some detail, where the hydrogen atoms play an important role in its phase transition. The molecular motion of water in some f erroelectric hydrates and the static and dynamic structure of hydrated protons are also included in this survey.
There are many globular proteins whose molecules are constructed by association of several polypetide chains and the association of such subunit polypeptides play an essential role in functioning the molecules in biological environment. The molecules are stable and active only in the associated state. As the most of these molecules are constructed by polypeptides having identical or very similar amino acid sequences, they can possess one or more axes of symmetry in the molecule. In many cases, the crystals of these molecules exhibit a true symmetry or a pseudo-symmetry which comes into exist only in low resolutions, since the symmetry of the constituent molecules can provide a local symmetry in the crystal lattices. Crystallographically, it is informative to find the pseudo-symmetry at an early stage of structural investigations and to see how the symmetry varies with the binding of the co-enzymes or other reagents to the protein molecules. Symmetrical arrangement of the oligomer proteins in protein molecules seems to be closely related to the origin of the allosteric or co-operative phenomena.
Principles and applicatons of Weak Beam Image (WBI) by Cockayne et al. (Phil. Mag. 20 1256 (1969) ) and Multi Beam Image (MBI) by Hashimoto (Jernkont Ann 155 480 (1971) ) have been introduced. Contrast mechanism of the images taken by WBI method is illustrated by a simple model and the application to the accurate determination of dislocation position and shape of G. P. zone is discussed. Contrast of high voltage (-1 Mev) electron microscopic images by WBI method and its applicability are discussed. Contrast mechanism of dislocation images in higher order Bragg reflections by Osiecki et al. (Proc EMSA Conference 178 (1971) Boston) is also discussed in terms of the extinction distance at high voltages. Image contrast at high voltage by MBI method is discussed and the applications of this method to the determination of the nature of imperfection such as stacking faults and dislocations are discussed.