Scaling analysis of bio-molecular dynamics derived from elastic incoherent neutron scattering experiments

Doster, W.*; Nakagawa, Hiroshi   ; Appavou, M. S.*

Numerous neutron scattering studies of bio-molecular dynamics employ a qualitative analysis of elastic scattering data and atomic mean square displacements. We provide a new quantitative approach, showing, that the intensity at zero energy exchange can be a rich source of information of bio-structural fluctuations on a pico- to nano-second time scale. Elastic intensity scans performed either as a function of the temperature and /or by varying the instrumental resolution yield the activation parameters of molecular motions and the approximate structural correlation function in the time domain. The two methods are unified by a scaling function. The complete elastic scattering function versus temperature, momentum exchange and instrumental resolution is analyzed instead of focusing on a single cross-over temperature of mean square displacements at the apparent onset temperature of an-harmonic motions. Our method predicts the protein dynamical transition (PDT) at Td from the collective alpha-structural relaxation rates of the solvation shell as input. By contrast the secondary beta-relaxation enhances the amplitude of fast local motions in the vicinity of the glass temperature Tg.