Basis of neutron inelastic scattering for measurements of dynamics of biological macromolecules

Nakagawa, Hiroshi   ; Fujiwara, Satoru

Proteins are constantly fluctuating under the influence of environment. These thermal fluctuations, or dynamics, of the proteins at a picosecond time scale are known to be indispensable for functions of the proteins. Neutron inelastic scattering provides a unique tool to directly measure dynamics of the proteins. In particular, since the incoherent neutron scattering cross section of hydrogen is significantly larger than any other atoms commonly found in biological materials, the techniques of incoherent neutron scattering is important for the measurements of the dynamics of the protein, a half of the atoms in which are hydrogen atoms. Furthermore, since a distribution of hydrogen atoms is fairly homogeneous in the protein, the neutron scattering spectra arising from hydrogen atoms in the proteins provides a global view of the protein dynamics. Here, various aspects of three techniques of incoherent neutron scattering: elastic incoherent neutron scattering, quasi-elastic neutron scattering, and inelastic neutron scattering, are briefly described as a basis for application to characterization of the protein dynamics.