Organic chemistry is the science on the transformation of organic molecules. To elucidate the transformation mechanism is essentially important to construct the basis for new development in this field of science. This paper includes the structural studies on the reaction mechanism in the catalytic system with metal active center, molecular recognition in clathrate compounds and solid state reaction of acetylene compounds. All discussions are based on the molecular structures of the key substances determined by X-ray diffraction method.
Surface superstructures (reconstructed structures) have been observed by many techniques. However, it has not been easy to confirm that a superstructure does exist at an interface between two solid layers. The article reports superstructures at semiconductor interfaces studied by a grazing incidence X-ray diffraction technique with use of synchrotron radiation. At metal-semiconductor interfaces, different superstructures give different Schottky-barrier-height values. Superstructures are also found to exist at insulator-semiconductor interfaces fabricated by the metalorgamc chemical vapor deposition (MOCVD) method. In addition, a boron-induced superstructure is found to exist even at the interface between an epitaxial Si layer and a Si (111) substrate.
A dynamic structure refinement method for protein X-ray crystallography is presented. The Debye-Waller factor is expanded in terms of the low-frequency normal modes whose amplitudes and eigenvectors are experimentally optimized in the process of the crystallographic refinement. Application of the method to human lysozyme showd: (1) Debye-Waller factor consists of two parts, highly anisotropic internal fluctuations and almost isotropic external terms. The former is smaller than the latter. (2) Correlation of fluctuations corresponding to the hinge-bending motion was detected.
Analyses of the X-ray diffraction data of (E) -stilbenes revealed that the X-ray structures of these compounds commonly show an unusually short bond length for the ethylene bond and a strong temperature dependence for the molecular structure. It is concluded that the short ethylene bond is an artifact caused by dynamic averaging originated from the torsional vibration of the C -Ph bonds during which the movement of the benzene rings are restrained minimum. The observed temperature dependence of the molecular structure is ascribed to the slight energy difference between the conformers which are interconverted by the torsinal vibration.
The success in efficiently synthesizing C60 has generated much interest in the physical and chemical properties of this new allotrope of carbon. In this article, methods for producing C60 and other related carbon molecules are first presented, and then studies on crystallized C60 molecules are briefly reviewed.
The CPU benchmark program for crystallographic computing is proposed by Dr.P.E.Bourne. The program consists of a restrained least-squares refinement using the programs PROTIN and PROLSQ for a small (545 atoms, 3590 diffraction maxima) and a large (6864 atoms, 19172 diffraction maxima) problem. The program was tested on more than 50 workstations and summarized. The result is helpful for (protein) crystallographers who will have a plan to buy a workstation. The program is available from the author by postal mail or anonymous ftp.