Physics Procedia 36 ( 2012 ) 953 – 957

1875-3892 © 2012 Published by Elsevier B.V. Selection and/or peer-review under responsibility of the Guest Editors. doi: 10.1016/j.phpro.2012.06.236

Superconductivity Centennial Conference

Application of High-Field Superconducting Magnet to Protein Crystallization

Hitoshi Wadaa*, Noriyuki Hirotaa, Shinji Matsumotoa, Hidehiko Okadaa, Motosuke Kiyoharab, Takahiro Odeb, Masaru Tanokurac, Akira Nakamurac, Jun Ohtsukac,Akiko Kitad, Nobutaka Numotod, Tatsuki Kashiwagie and Ei-ichiro Suzukie

aNational Institute for Materials Science, Sengen, Tsukuba, 305-0047 Japan bKiyohara Optics Inc., Shinjuku, Tokyo, 160-0022 Japan

cDept. Applied Biological Chemistry, University of Tokyo, Yayoi, Tokyo, 113-8657 Japan dResearch Reactor Institute, Kyoto University, Asashiro-nishi, Sennan, 590-0494 Japan

eInstitute for Innovation, Ajinomoto Co., Inc., Suzuki-cho, Kawasaki, 210-8681 Japan

Abstract

A quasi-microgravity environment appears in a high-field superconducting magnet bore where a large magnetic force counterbalances gravity acting on a diamagnetic substance. This suppresses convection of the diamagnetic solution in the crystallization cell placed in the bore from which protein crystals precipitate. A 16 T class superconducting magnet has been developed with a special coil configuration; one of the component coils produces a magnetic field the direction of which is opposite to that of the other coils. Thus, a large magnetic field gradient occurs, creating a magnetic force large enough to levitate water and hinder convection. This magnet system is operated in persistent mode, which is adequate for a rather time-requesting crystallization process of proteins. Preliminary experiments have shown that the protein crystallization process is substantially retarded in the magnetic force field.

© 2011 Published by Elsevier Ltd. Selection and/or peer-review under responsibility of Horst Rogalla and Peter Kes. Keywords: Superconducting magnet; Magnetic force; Diamagnetism; Protein crystals.

* Corresponding author. E-mail address: WADA.Hitoshi@nims.go.jp

Available online at www.sciencedirect.com

© 2012 Published by Elsevier B.V. Selection and/or peer-review under responsibility of the Guest Editors.Open access under CC BY-NC-ND license.

Open access under CC BY-NC-ND license.

954 Hitoshi Wada et al. / Physics Procedia 36 ( 2012 ) 953 – 957

1. Introduction

A number of biological and medical products, such as drugs and enzymes, are designed and synthesizedon the basis of 3-D structures of protein crystals determined by X-ray diffraction. Thus, high qualityprotein crystals are a crucial key for innovative biotechnologies. However, obtaining high quality proteincrystals to date is like a gamble leaving everything to chance and regarded as a serious bottleneck in thecourse of development.One of the major factors disturbing the formation of protein crystals of high integrity is convection ofprotein solution that incorporates different defects into growing crystals. If convection is somehowsuppressed, crystallization proceeds in purely diffusional manner and crystals of high integrity shouldprecipitate from solution. Thus, space is an excellent environment for protein crystallization, sincegravity-induced convection disappears. In fact, protein crystallization has always been among major subjects of space experiments. Improved integrity has been reported on those protein crystals grown inspace [1]. A quasi-microgravity environment can appear in a high-field superconducting magnet bore where largemagnetic force counterbalances gravity acting on a diamagnetic substance. Levitation of diamagneticsubstances by magnetic force is now a popular scientific playground where improved integrity has beenreported on protein crystals grown in magnetic fields [2].Magnetic force is proportional to the product of magnetic field and magnetic field gradient, as given inthe following equation:

dz

dBBFm

0

(1)

where Fm is magnetic force per unit volume (N/m3), volume magnetic susceptibility (-), 0 permeabilityof vacuum, B magnetic field (T) and dB/dz magnetic field gradient in vertical direction (T/m). Adiamagnetic substance is fully levitated when Fm is equal to gravity, Fg. To levitate water, BdB/dzamounts to ca. 1,360 T2/m. Thus, this approach to protein crystallization by diamagnetic levitationrequires high magnetic field and large magnetic field gradient. Taking into account the fact that proteincrystallization from solution is a rather time requesting process, sometimes weeks or months long,superconducting magnets operated in persistent mode will be the first choice.A superconducting magnet system has been developed which can generate magnetic force large enoughto levitate water and suppress convection; the magnet has superconducting joints and is operated inpersistent mode. Preliminary protein crystallization experiments have been carried out using this system.The results of these are described below.

2. Fabrication of superconducting magnet for diamagnetic levitation

The superconducting magnet system developed is illustrated in Fig. 1. The design of the system is featured by its coil configuration; the magnetic field direction of the upper Nb3Sn coil is opposite to that of the lower NbTi and Nb3Sn coils. The maximum magnetic field generated by the lower coils is 16 T.Between the two groups of coils Fm becomes large enough to levitate water, creating a quasi-microgravityzone where gravity-induced convection is suppressed. The crystallization cell is placed in this zone. A serious problem with this asymmetric coil configuration is the electromagnetic, repulsive force inducedbetween the upper and the lower coils. This problem has been solved by shifting the relative position ofthe lower NbTi coil to the lower Nb3Sn coil along the magnet axis; the electromagnetic force is thenreduced effectively.In order to generate a magnetic field of 16 T in persistent mode operation, a high performance Nb3Sn

Hitoshi Wada et al. / Physics Procedia 36 ( 2012 ) 953 – 957 955

Fig. 2 Crystallization of protein in and outside magnetic force field.

Fig.1. Superconducting magnet system developed.

superconductor is required. The magnet has been fabricated by using the Nb3Sn superconductor whichwas originally developed for over 900 MHz NMR magnets [3].Prior to the crystallization experiments on different proteins, water was levitated in the magnet bore.

3. Crystallization experiments

The crystallization cell consists of a well and a reservoir, and is placed in the microgravity zone in themagnet bore. The sitting drop vapour diffusion method has been adopted for crystallization [4]. Fig. 2

956 Hitoshi Wada et al. / Physics Procedia 36 ( 2012 ) 953 – 957

shows results of a otein is mixed

crystals

4. Discussion

It is known that crystallization of protein of high quality is difficult. Some proteins cannot even be n

t

parallel been carried out to clarify effects of magnetic field, magnetic

5. Summary

A superconducting magnet system has been developed which is operated in persistent mode and generates

Acknowledgements

This work is supported by “Development of Systems and Technology for Advanced Measurement and

References

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