  Superparamagnetism of tryptophan implying the presence of magnetic domain is
reported. The observation helps us to conceive assembly of proteins as a
physical lattice gas with multidimensional Ising character, each lattice points
assuming discrete spin states. When magnetic field is applied the equilibrium
is lost and the population density of one spin state increases (unidirectional
alignment), resulting in net magnetization. Spatial coherence between the
identical spin states further imparts a ferromagnetic memory. This effect is
observed using direct nanoscale video imaging. Out of the three proteins
ferritin serum albumin and fibrinogen, fibrinogen showed an attenuated
response, the protein being essentially one dimensional. Eventually, Ising
lattice is capable of showing ferromagnetic memory only when it has a higher
dimensional character. The study highlights possible presence of long range
spatial coherence at physiological condition and a plausible microscopic origin
of the same.
