| Biopolymers are expected to exhibit broad spectral features in the terahertz frequency range, corresponding to their functionally relevant, global and sub-global collective vibrational modes with approximately picosecond timescales. Recent advances in terahertz source and detection methods have stimulated experimental researchers to employ terahertz absorption spectroscopy to directly probe and confirm these postulated collective vibrational modes. However, these pioneering studies have been limited to dry and, at best, moist samples. Successful isolation of the low frequency vibrational activities of solvated biomolecules in their natural water environment has remained elusive, due to the overwhelming attenuation of the terahertz radiation by water.;In an effort to probe the terahertz dynamics in solvated biopolymers, I have adopted two distinct and complementary techniques: terahertz absorption spectroscopy and terahertz circular dichroism (TCD) spectroscopy. I have developed a terahertz absorption and circular dichroism spectrometer suitable for studying biomolecules in biologically relevant water solutions. The spectrometer combines intense terahertz radiation (UCSB Free-Electron Lasers, harmonic multipliers, and a Gunn oscillator, with an ultra sensitive cryogenic detector, a precision variable path length sample cell, and a polarizing interferometer.;I have isolated, for the first time, the terahertz absorption of solvated prototypical proteins, and have made important direct comparison to the existing theoretical calculations. Using our TCD spectrometer, with current resolution reaching below one part in one thousand, we have successfully demonstrated the magnetic circular dichroism in semiconductors, and placed upper bounds on the TCD signatures of prototypical proteins in aqueous solution. Work remains to achieve the requisite instrumental sensitivity to recover TCD signatures of biological materials in solution phase. |
