Probing Temperature-Dependent Dynamics of Hemoglobin and Water Molecules in the Hydration Shells Using High Sensitivity Dielectric Spectroscopy*

Hemoglobin, an iron-containing protein in red blood cells, has diverse biological functions including oxygen/carbon-dioxide transport and storage. The functions and behaviors of hemoglobin proteins strongly depend on environmental conditions and temperatures. The complicated quaternary structure of hemoglobin and the hydrogen-bond network in aqueous environments make it a challenge of identifying the conformational dynamics. Employing high-sensitivity dielectric megahertz-to-terahertz frequency-domain spectroscopy, we have systematically examined the dynamics of hemoglobin and the water molecules in their hydration shells as a function of temperature at the molecular level. Combining experiments with molecular dynamics simulations, we have determined the conformational dynamics of hemoglobin and water in aqueous solutions. The results help us identify hemoglobin dynamics and hemoglobin-water interactions that determine the biochemical functions and reactivity of hemoglobin proteins.