Investigating Hydration and Dynamics of Biomolecules in Solutions using High Precision Terahertz Spectroscopy

Biomolecules function only in aqueous environments and their dynamics are strongly influenced by physiological conditions including the temperature and the presence of co-solutes. The presence of biomolecules in aqueous solutions will change the dynamics and structure of water, and as a response, water will form hydration layers around biomolecules. The dynamics of hydration water, as well as hydrated proteins, lead to translation, rotation, and oscillating dipoles that, in turn, give rise to absorption in the megahertz-to-terahertz frequencies. However, the strong absorption of water in this frequency range leads to a significant challenge in obtaining terahertz dielectric spectra of aqueous biomolecular solutions. In response, I have employed a high sensitivity terahertz frequency-domain spectroscopy to overcome these issues on a large range of frequencies from 10 MHz to 1.12 THz. The high dynamical range of the system combined with a variable-path-length cell allows precise measurement of the complex dielectric response of the solutions. Employing Debye and Lorentzian approximations, I have decomposed contributions of the dielectric response of the solutions. The structure and dynamics of hydration shells and hydrated biomolecules have been identified. Performing experiments on a number of biomolecules have verified the certainty of the methods, thus, enriching the knowledge of the biological science of dynamics and functions of biomolecules.