Quasi-Optical Sub-THz Circular Dichroism Spectroscopy of Solvated Myoglobin

A quasi-optically based, sub-terahertz, circular dichroism (CD) spectrometer is demonstrated on the model protein, myoglobin, over waveguide bands D (110-170 GHz) and H (220-325 GHz). In doing so, an equivalent methodology is propounded for acquiring cross-polar spectra that eliminates the need for having to physically rotate the receive-horn through 90°. A significant source of systematic-error is, thereby, eliminated (and, no less, random-error that follows when cabling is moved). The “zero-crossing” points of CD spectra are characterized as they are correlated with traditional far-ultraviolet CD spectra for given environmental parameter settings of, for example, pH and/or sample concentration.