A quasi-elastic neutron scattering study of hydrogen dynamics in trypsin-deuterium oxide solution (deuterium oxide)
Cao, Hung Duc
Rorschach, Harold E., Jr.
Master of Arts thesis
The quasi-elastic neutron scattering (QNS) method is a useful technique to study biomolecular dynamics. The versatility of the method makes possible motional studies of biomolecules in different forms: powder, crystalline, and solution; and at different temperatures. Thus, it allows investigation of biomolecular dynamics in different states of matter. We have used the QNS method to study the motion of the trypsin chain segments in powder and in D$\sb2$O solution at temperatures of 200K, 280K, and 300K. The scattering spectra S(Q,$\omega$) were measured in constant-Q mode. The S(Q,$\omega$) for trypsin protons in liquid solution exhibits a broadening due to diffusive motion which is absent in the powder and the frozen solution. This diffusive motion has the character of a jump diffusion. The high-frequency thermal motion obtained from the Debye-Waller factor $\langle$u$\sp2\rangle$/3 $\cong$ 0.33A$\sp2$ at T = 300K is consistent with earlier measurements. The DW factor at lower temperatures for trypsin solution shows deviation from theoretical predictions.
Radiation; Molecular physics; Biophysics