Determination of the three-dimensional structures of proteins is one of the key postgenomic research subjects. X-ray crystallography and solution NMR are both used for structural determination; the present paper reviews the process of protein structural determination by NMR. The NMR facility of RIKEN Genomic Sciences Center, constructed in Yokohama in 2000, and the “structural genomics project” being pursued using the NMR facility are briefly described.
NMR spectrometers are considered to be an indispensable tool for structural biology. They are applied to determine the stereoscopic structure of protein molecules and to identify the chemical-reacting part between proteins and candidate medicines. Because the sensitivity and resolution of NMR spectrometers are improved with external magnetic fields, development projects of high-field NMR spectrometers have been carried out worldwide. At the Tsukuba Magnet Laboratory of the National Institute for Materials Science, the development of a high-field NMR magnet has been under way since 1995. The final target is to generate an additional 2.4T with an innermost coil, resulting in a central field of 23.5T corresponding to a 1H NMR frequency of 1GHz in a 54mm diameter room-temperature bore. The magnet was confirmed to operate as a high-resolution NMR magnet at 920MHz, using a Nb3Sn innermost coil. In the case of an NMR magnet, the required conditions of field homogeneity and stability are very strict. In this paper, we introduce the design issues of an NMR magnet by using our developed NMR magnet as an example. The future vision for high-field superconducting NMR magnets generating a field of 23.5T or more is also described.
This paper describes the development of a conductive-cooled superconducting magnet that uses no cryogen, such as liquid helium or liquid nitrogen. First, the history of the development is introduced. A conductive-cooled superconducting magnet was realized in the late 1980s for the first time and was commercialized about 10 years ago. The technical points and construction for the magnet are explained. The important points were a 4K-GM cryocooler and an HTS superconducting current lead. A conventional GM cryocooler had not achieved 4K level, but by using magnetic regenerator material, we realized refrigeration at liquid helium temperature. An HTS current lead was used as a current lead between a thermal shield and a superconducting coil. Heat leakage by a superconducting current lead is less than 1/10th by a conventional copper current lead. Heat leakage to the 4K level was then dramatically reduced, and the total thermal load at 4K level becomes low enough for a 4K-GM cryocooler. In a conductive-cooled superconducting magnet, a superconducting coil is directly cooled by the second stage of a 4K-GM cryocooler at the 4K level via a good thermal conductive pass. The coil is surrounded by a thermal shield, which is cooled by the first cooling stage at around 50K. A conductive-cooled superconducting magnet has such features as simple operation, small size, and easy access to a magnetic field. Several companies have commercialized a conductive-cooled magnet, and the magnets have been applied not only to research, but also to industrial use, such as MRI, silicon crystal growth, and magnetic separation. The latest R & D and future aspects for a conductive-cooled superconducting magnet are also described.