Hiroyuki Tagawa

Temperature dependence of the structure of aggregates of tobacco mosaic virus protein at pH 7.2. Static synchrotron small-angle X-ray scattering.

The small-angle X-ray scattering (SAXS) method using a synchrotron radiation source was applied to the study of the self-aggregation process of tobacco mosaic virus protein (TMVP) at a concentration of 5.0 or 12.0 mg ml-1 in 50 mM or 100 mM-phosphate buffer (ionic strengths approx. 0.1 and 0.2, respectively) at pH 7.2 in the temperature region of 4.8 to 25.0 degrees C. This paper presents the results of static measurements of SAXS. Sedimentation velocity experiments were performed simultaneously under the same conditions. These results are qualitatively parallel to those of the SAXS measurements, although the size of stacked disks derived from the SAXS measurements is larger than that derived from the sedimentation experiments, suggesting a change in the equilibrium conditions in the centrifugal field. Qualitative analysis of the SAXS data with model simulation calculations implies that the aggregation of TMVP consists of two steps: (1) the aggregation of A-protein comprising a few subunits to form double-layered disks; and (2) the random polymerization of double-layered disks by disk-stacking. Increase in temperature, ionic strength or protein concentration induced TMVP to polymerize to form a double-layered disk or a quadruple-layered short rod with consumption of A-proteins, accompanied by a small number of multi-layered short rods. The SAXS results indicate that the A-protein and the multilayered short rods are polydisperse with respect to size and shape, i.e. the mixture of A-protein, double-layered disks and multi-layered short rods coexists in the equilibrium state without pressure-induced partial dissociation of TMPV as observed during normal ultracentrifugation, and even under solution conditions in which the formation of double-layered disks or higher-order aggregates is favored.

Soft X-Ray Small-Angle Scattering by Polystyrene Latexes Using Synchrotron Radiation

Small-angle scattering of soft X-rays by polystyrene latex spheres was studied using the synchrotron radiation from the electron synchrotron operated at about 1 GeV at the Institute for Nuclear Study, University of Tokyo. The exposure time required to make three smallest-angle diffraction peaks visible on a photographic plate was 2 min with the soft X-rays (46.8 A) of the synchrotron radiation, compared to 400 min with the CKα radiation (44.8 A) from the X-ray tube operated at 3 kV ×50 mA. The diffraction patterns were so distinct that inter-particle interference functions could be derived with four diffraction peaks. Experimental results as a whole suggest that soft X-rays in the synchrotron radiation will be very useful in studying two-dimensional structures of thin organic materials with the thickness of microns or submicrons.

Structure of oligourethanes: 6. Fine structure of melt crystallized oligourethanes

Abstract The structure and the structure change of the melt crystallized oligourethanes, CH 3 CO (CH 2 ) 5 NHCO n OCH 3 , having strictly homogeneous molecular weight, were studied. The crystal system of every melt crystallized oligourethane was similar to that of the single crystal of n = 2. In the case of n = 2, crystalline rearrangement by annealing does not occur, although the number of hydrogen bonds increases. On the other hand, rearrangement occurs for n = 3 and higher oligomers. It was considered that the rearrangement for n = 3 was the transformation from the spherulite to the plate-like crystal, whilst for those of n = 6 and 8 the growth of the new spherulitic type of crystal by secondary crystallization occurs. For n = 10 and the polymer crystal the thickening was accompanied by an increase of ordered regions.