Abstract
Hydration and dehydration of bio-macromolecules result in changes in the physical
properties and thus in the structural stabilization and biological functionality. The structure and
dynamics of the vicinity of water molecules with biomolecules, which is so-called hydration water,
are essential to understand the hydration and dehydration processes of a biosystem, such as cell and
organisms. Because neutrons have a wavelength on the order of Å and thermal energy (order of
meV), we can use them to observe the structures and dynamics of biomolecules and hydration
water. Neutrons are highly permeable and non-destructive probes. The large difference in neutron
scattering cross sections between hydrogen and deuterium provides a powerful method for
emphasizing the scattering from a biomacromolecule or hydration water via selective deuteration
of hydrated biological materials. Incoherent neutron scattering (INS) and small-angle neutron
scattering (SANS) can be used to examine the dynamics of hydration water in the
pico-to-nanosecond time scale and the density and structure of the hydration shell around
biomolecules. Neutron sources, such as the JRR-3 reactor and J-PARC accelerator, are available in
Japan. The present review aims to provide the readers with brief descriptions of the neutron
scattering methods and their applications to protein hydration.
