Can Terahertz time-domain spectroscopy detect an extended hydration layer around peptides?

A peptide was added to a KF solution and the absorbance measured by Terahertz time-domain spectroscopy (THz-TDS). The absorbance dropped then plateaued at ~25 mM. This is consistent with a hydration layer around 11-17 Å thick with lower absorbance than bulk water. Terahertz spectroscopy using synchrotron light performed on a solution containing the protein bovine serum albumin (BSA) confirmed the rise in absorbance observed using p-germanium spectroscopy and the plateauing observed by THz-TDS in aqueous peptide samples. Using the inflection in the decline of the absorbance, the thickness of the hydration layer around BSA can be estimated at 15A thick.