Biology Reference
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that the effects of magnetic fields on diamagnetic substances have attracted
attention. This is due partly to the development of superconducting materi-
als that have enabled strong and stable magnetic fields to be generated with-
out much difficulty in many laboratories in addition to those specializing in
low temperature physics with sophisticated techniques. Various effects and
interactions have been recognized, and as a consequence of these effects the
term “non-magnetic” began to be considered to be not entirely correct, “fee-
bly magnetic” being a better description. Among protein molecules, some
(perhaps 10% or a little more) are classified into metal proteins, which
means that they require metal ions for stability and function, in addition to
the usual atoms of C, N, O, H and S as in the majority of proteins. The metal
ions can be Fe, Co, Ni, Mn, and so on, and of various valencies. Since a
metal ion can be paramagnetic, and its absolute value is two to three orders
of magnitude larger than the diamagnetism, a protein molecule can be para-
magnetic if they contain (a) metal ion(s). In other cases, protein molecules
are diamagnetic, like the majority of substances. In any case, protein mole-
cules are feeble magnetic substances.
Our second point is that there are two independent actions of a mag-
netic field interacting with feeble magnetic substances. One is magnetic
orientation. As long as feeble magnetic substances have magnetic
anisotropy, they have an easy axis or axes (an easy axis means an axis that
is magnetically easy to orient along the magnetic field) that tend to align
along the magnetic field. In many cases, this orientation tendency can be
disordered by thermal agitation or hindered by adherence or fixation to an
environment. However, if the magnetic field is strong enough so as to
overcome thermal fluctuation and if the substances can rotate freely with-
out interference from adhesion to an environment, their easy axis will
align along the magnetic field. This magnetic orientation can be observed
both in homogeneous and inhomogeneous magnetic fields.
Magnetic force
The other action is a magnetic force that is observed only in an inhomo-
geneous magnetic field, both for diamagnetic and paramagnetic substances.
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