The Use of a Magnetic Field and Magnetic Force as a Means to Improve the Quality of Protein Crystals - Molecules: Nucleation, Aggregation and Crystallization - page 205

is observed when the crystals are grown in a horizontal magnetic field pro-
vided by the electromagnet. The strength of the field was about 1 T and the
vessel containing the supersaturated solution was observed from above. The
only crystalline face observed was {110}, and not {101}. These facts can be
explained if the c -axis was parallel with the magnetic field. It was very clear
that the magnetic field orients the crystalline c -axis along the field direction.
In 1989, two undergraduate students, Takashi Imaeda and Yoshio Ohno
participated in the research initiated by Kuroda. The new undergraduates
calculated the magnetic moment of the tetragonal lysozyme crystal, using
the atomic coordinates obtained from the Protein Data Bank (PDB). The
calculation showed that the c -axis was in fact the easy axis. From the ten-
sor representing the magnetic susceptibilities along the three principal axes,
the magnetic anisotropy was calculated to be 1.45-6.75 10 −9 emu/cm 3 .

The range of values comes from a different PDB dataset as well as from
the whole atomic coordinate versus polypeptide main chain atoms. The
main chain atoms were used to exclude possible fluctuations in the
side chain positions as evidenced from NMR measurements. The mag-
netic anisotropy in MKS units was calculated to be about 5

×

10 −27 J/T 2 .
The prediction from calculation was further compared with an experi-
ment, in which a single tetragonal crystal of a certain size, suspended
with a thin thread, was rotated in the presence of a static magnetic field,
and from the oscillatory period an experimental value comparable with
the calculation was obtained. Thus, it was concluded that the magnetic
orientation of the protein crystal used comes from diamagnetic
anisotropy.
Unfortunately, the laboratory to which these three students belonged
was a major research group of liquid crystals. For liquid crystals, i.e. rod-like
anisotropic molecules, magnetic orientation is a well-known phenomenon —
as is evident from the color change of a TV or PC monitor near a strong
magnet. Since the magnetic orientation of the tetragonal lysozyme crys-
tals was regarded as self-evident, the results were not reported further as
a scientific paper. However, the Master's Degree Thesis of Kuroda as well
as the Batchelor's Theses of Imaeda and Ohno, submitted in March of
1990, are kept in a library of the University of Tokyo.

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