Separation of Protein and Water Dynamical Transitions Using Terahertz Spectroscopy*

Terahertz Time Domain spectroscopy (THz TDS) has been used to characterize the protein dynamical transition [1, 2]. The dynamical transition has been considered a manifestation of the slaving of protein motions to thermally activated motions of the solvent, however recently is has been reported that sharp temperature increases in protein dynamics occur independent of the solvent [3]. Potentially terahertz spectroscopy can resolve both the protein and water dynamical transitions using the ~ 5 THz intermolecular water vibrational line and the broad ~ 1.0 THz absorption arising from the protein intramolecular motions. Here we use a combination of THz TDS and FTIR to examine this possibility and resolve the protein and water contributions using a combination of spectral decomposition and concentration dependent measurements. Concentration dependent measurements using hen egg white lysozyme (HEWL) confirm that the transition measured at 1 THz is dominated by the protein dynamics.
1. He, Y.F., et al., Phys. Rev. Lett., 2008. DOI: 10.1103/PhysRevLett.101.178103.
2. Markelz, A.G., et al., Chem. Phys. Lett., 2007. DOI: 10.1016/j.cplett.2007.05,080.
3. Liu, Z., et al., Phys. Rev. Lett., 2017. DOI: 10.1103/PhysRevLett.119.048101.