Protein crystallography is one of the most powerful methods in structural biology to determine the three-dimensional structures of protein molecules at an atomic resolution. However, it is often difficult and laborious to obtain a welldiffracting crystal suitable for structure determination. Since the gravity is one of factors affecting protein crystallization, the microgravity environment has been used to improve the quality of protein crystals. On the other hand, development of the advanced synchrotron facilities such as SPring-8 enabled us to utilize very strong X-ray beams that have almost ideal character for the use in protein crystallography. Here we describe the recent progress of the synchrotron techniques in protein crystallography and discuss the effective crystallization under microgravity for synchrotron experiments.
It is thought that the protein crystal grows larger and gets better quality under microgravity than the crystal obtained on the ground, since there is neither convection nor sedimentation. We investigated the crystallization conditions in detail about NfsB, an oxygen-sensitive nitroreductase from Escherichia coli, and considered the crystallization mechanism by using phase diagram. This research tends to acquire the high generality knowledge in protein crystallization as research connected to elevate authenticity of the crystallization experiment under microgravity.
Attempts to control sedimentation and convection using a superconducting magnet are introduced. Magneto-Archimedes levitation was applied to protein crystal growth by converting the aqueous protein solution into paramagnetic with the addition of Gd ions. Since the responses of diamagnetic protein crystals and paramagnetic surrounding solution toward a magnetic flux density gradient are opposite to each other, the tendency of the crystals to escape from the magnetic field can be augmented, leading to levitation at the air-solution interface. Navier-Stokes equations were numerically solved in the presence of the magnetic, escaping force. A number of instances were shown in which convection was suppressed by use of a magnetic flux density gradient. Quality improvements of lysozyme crystals grown in a magnetically levitated state were demonstrated by white X-ray topography.
Forsterite Mg2SiO4 exhibits an orthorhombic structure (space group Pbnm) consisted of two kinds of MgO6 octahedra. One of them forms edge-sharing ribbons along the  direction which are linked by the other kind of edge-sharing MgO6 octahedra, resulting in a three-dimensional framework. Given only 33.3 mol% of SiO2 in the material, the SiO4 tetrahedra are isolated within the framework, sharing the O-O bonds with the common edges of the MgO6 octahedra. If forsterite can be vitrified, an interesting question concerning the glass structure arises because there is insufficient glass forming SiO2 to establish the corner-sharing SiO4 tetrahedral network needed in conventional silicate glasses. A bulk Mg2SiO4 glass was synthesized using an aero-acoustic levitation technique and to determine the short- to intermediaterange structure by a combined high-energy X-ray and neutron diffraction and reverse Monte Carlo computer simulation. Interestingly, we found that the role of network former is largely taken on by corner- and edge-sharing ionic magnesium species that adopt 4-, 5- and 6-coordination with oxygen.
Porous media in which deep pores are regularly aligned were fabricated by unidirectional solidification of monotectic alloys and selective dissolution of the rod phase. Unidirectional solidification of Al-In alloys with hyper-monotectic compositions under a high static magnetic field up to 10 T achieved the rod-type eutectic-like structure in which continuous rods were regularly aligned. The static magnetic field exceeding several T reduced movement of the In droplets and enhanced the engulfment of the In droplets into the solidifying front. The coupled growth between the liquid In and the Al occurred and consequently the regular structure was produced even at the hyper-monotectic composition. A selective dissolution of the In rods from the Al matrix was performed to fabricate porous media. A micro X-ray tomography technique using a synchrotron radiation was used to evaluate the solidified structure and the selective dissolution of the In rod during the electrochemical etching.
Precise measurements of density and structure of undercooled molten Si by using synchrotron radiation combined with electromagnetic levitation technique have been performed to investigate the atomic structure of molten Si in a wide temperature range including the undercooling region. The shoulder in the 1 st peak of structure factor S(Q) was slightly changed with decrease of temperature. This suggests that the middle-range order in real space of molten Si is changed with the change of temperature. However, the short-range order of molten Si is not changed in temperature region from 1550 K to 1900 K. From these experimental results, we discuss the temperature dependences of the density and the structure of undercooled molten Si based on the local structure models obtained by analytical methods.
A projection microtomographic system using synchrotron radiation with the spatial resolution of about 1 μm has been developed at SPring-8. The quantitative relation between CT-values and linear attenuation coefficients of materials has been obtained empirically in this system. Materials (minerals) can be estimated from the CT values using this relation. The relation also made possible to obtain three-dimensional concentration distributions of some elements by subtraction method. The microtomographic system was applied to extraterrestrial samples, such as meteorites and cosmic dust. This system is also useful to samples those will be returned by spacecrafts in the Hayabusa mission by JAXA and Stardust mission by NASA.
Development of elemental technology for gauging liquid fuel in a tank under microgravity condition will be required for developing fuel station in space and orbital transfer vehicle. A closed-type Helmholtz resonator had been already developed and worked well for this purpose. However, a microphone used for detecting acoustic response cannot work when it is masked by sloshing liquid, and might be damaged by its frequent contact with liquid. In order to resolve such a problem, a new measurement apparatus was developed without a microphone. The acoustic response was detected by measuring electrical impedance of loudspeaker's voicecoil. The performance of predicting liquid volume by using the electrical impedance method was comparable with the result of the microphone method. Some results of the ground test and the microgravity test with aircraft are summarized in the present report.