The method to refine crystal structure parameters (atom positions and Debye-Waller factors) using convergent-beam electron diffraction (CBED) is described. The method is powerful for crystal structure analysis of a nm-scale specimen area.
Carbon nanotubes were produced by the do arc-discharge evaporation of graphite electrodes in an atmosphere of rarefied gas of He, Ar or CH4. The co-existence of carbon nanoparticles with the nanotubes was observed by both scanning electron microscopy (SEM) and transmission electron microscopy (TEM) . The growth conditions of the carbon nanotubes were not so limited as those of fullerenes, such as C60.
Relative humidity governs the phase transition of nucleoside and nucleotide crystals. Two typical cases are the crystal transition of disodium adenosine 5'-triphosphate (Na2ATP) between the trihydrate and dihydrate forms and that of guanosine between the dihydrate and anhydrous forms. The transitions are reversible, but the adsorption-desorption hysteresis is observed. Reconstruction of a hydrogen-bonding network induces a conformational change of the molecules. In the case of guanosine, the transition proceeds stepwise. On the contrary, the transition of Na2ATP takes place gradually over the wide relative humidity range, and a mixed-layer structure would be formed in the intermediate state.
A possibility of crystallography to estimate large conformational change of proteins is described. An example is the crystal structure of a mutant T4 lysozyme (Faber & Matthews, 1990), where four independent molecuels show a variety of hinge-bending angles. Another example is human α-lactalbumin (Harata & Muraki, 1992) . The amino acid residues of 104-110 assume α-helix in one crystal and a loop structure in another crystal. These observations demonstrate the large conformational flexibility of proteins and indicate that the X-ray crystallography is a powerful tool for the study of dynamic structure of proteins.
Molecular conformations of cytotoxic ascidiacyclamide (a cyclic peptide from marine ascidian), antitumor swinholide A (a cyclic macrolide from marine sponge), antifimgal eureobasidin E (a cyclic depsipeptide antibiotic) and neurotransmitter achatin-I (a linear tetrapeptide from giant snail) have been determined by X-ray single crystal analyses to discuss possible relationship with their bioactivities.
A new family of oxycarbonate superconductors, the synthesis and their physical properties, has been reviewed. In 1992, Miyazaki et al. have synthesized the new compound Sr2CuO2 (CO3), which opened to the new family of oxycarbonate superconductors. On the basis of“block layers concept”, we have attempted to design a series of oxycarbonate compounds having the new crystal structure and made superconductivity by an appropriate carrier doping and, succeeded to synthsize many new oxycarbonate superconductors.
Crystal structure analyses of biological macromolecular assemblies are being carrying out to understand molecular mechanisms of highly systematized reactions. There are many biologically important supramolecules whose structures should be determined at high resolution. Crystallization, intensity data collection and phase determination for these biological assemblies are described.