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 217

further need for other proteins to be grown and the quality of their crystals
to be evaluated precisely. Yin et al . (2004) reported that the cubic form
of crystals of porcine insulin did not exhibit a quality improvement —
an interesting observation for crystal symmetry lacking in magnetic
anisotropy.
The levitated state has found interesting applications. Santesson et al .
(2003) used acoustic levitation of protein droplets of up to 2.3 microliters
surrounded only by air to screen conditions for amorphous precipitation.
The information was used to determine regions of high supersaturation
and thus to find suitable conditions likely to lead to nucleation and
growth of single crystals. The idea behind this is that amorphous precip-
itation appears rapidly when sufficient supersaturation is provided, and
can likely be used to obtain conditions for crystal growth. Levitation by
other means than acoustic waves has been considered to be appropriate
also, which suggests that magnetic levitation is a possibility, not widely
known at the time when this acoustic levitation was applied in 2003 in
Sweden.
An additional study of ours used the magneto-Archimedes effect to
achieve levitation (Maki et al ., 2004). With a commercial superconduct-
ing magnet with a rather wide bore diameter of 100 mm conventionally
used, only about 30% of gravity can be canceled (Lin et al ., 2000). To
overcome this and achieve complete levitation — 100% cancellation of the
gravity — we considered the use of the magneto-Archimedes effect, first
proposed and coined by Ikezoe et al . (1997). This effect uses, in addition
to the response of a substance to a magnetic field, that of the environment
surrounding the substance. If the substance to be considered is diamag-
netic, its surroundings are intentionally converted into the paramagnetic
kind by addition of a paramagnetic ion. Then, the response toward the
magnetic force will be opposite, enabling superposition of the opposing
tendency in the presence of the magnetic field gradient. Thus, when the
substance experiences an upward force, the environment is pulled down-
ward, and the net upward force is much enhanced. By using this effect,
we could totally levitate the protein crystals within a solution supersatu-
rated with respect to aqueous lysozyme. The crystals thus obtained were