Akansha Sharma

Science and technology based on terahertz (THz) light have been developed and improved widely in the last few decades. THz techniques now give valuable insights into the fields of biophysics, material science, security devices, telecommunication, astronomy, and medical applications. The strong temperature dependence of molecular flexibility near 200 K for proteins hydrated above 0.2 gram of water per gram of protein, dynamical transition, is one of the most significant phenomena of biomolecular dynamics. In this dissertation, I present the use of low temperature terahertz transmission measurements to address two main questions: 1) what is the absolute molar absorptivity of proteins in solution; and 2) how do intramolecular protein dynamics effect the protein dynamical transition (DT). At room temperature, the extraction of protein contributions requires multiple high precisions because the absorbance of the water dominates for protein solutions. Our results of low temperature absorption measurements on chicken egg white lysozyme (CEWL) and myoglobin from equine skeletal muscle, indicate that at lower temperatures protein absorption dominates in the solution at 0.75 THz and 1 THz. By fitting the molar absorptivity model to our concentration dependent data of absorbance, we are able to extract the molar absorptivity of proteins in solution and recover Beer’s law for proteins. Further, we address the concern whether the solution phase dynamical transition measurements are effected by the presence of ice. By using dry glycerol solutions of CEWL and myoglobin for our study, we find that solution phase measurements reproduce the hydration dependence of the DT measured using neutron inelastic scattering. These results enable the use of THz DT for providing a fast measurement of biomacromolecule picosecond flexibility. In the last chapter, I interrogate whether the DT of orange carotenoid protein indicates changes in the intramolecular picosecond dynamics with photo excitations. This is based on the recent results by M Xu. et al. where they have shown the protein DT can be isolated from the solvent DT in THz solution phase measurements, and the protein DT follows the thermal stability of the protein for red fluorescent proteins.