Probing Local Electrostatics of Glycine in Aqueous Solution by THz Spectroscopy.

Based upon precise terahertz (THz) measurements of the solvated amino acid glycine and accompanying ab-initio molecular-dynamics simulations, we show that the N-C-C-O open/close mode at 315 cm serves as a sensitive, label-free probe for the local protonation of the amide group. Experimentally, we can show that this holds not only for glycine but also for diglycine and valine. The approach is more general, since the changes due to protonation result in intensity changes which can be probed by THz time domain (0-50 cm ) as well as by precise THz-FT spectroscopy (50-400 cm ).

A THz/FTIR fingerprint of the solvated proton: evidence for Eigen structure and Zundel dynamics.

In continuation of earlier work on La(III), Ni(II) and Mn(II) halides, we present low frequency (30-400 cm(-1)) spectra of solvated HCl and HBr as a function of solute concentration. This frequency range provides direct access to water network modes and changes induced by solvated solutes. We were able to dissect the spectra into components associated to solvated ions and ion pairs using a chemical equilibrium model in combination with principal component analysis.

Understanding THz spectra of aqueous solutions: glycine in light and heavy water.

THz spectroscopy of aqueous solutions has been established as of recently to be a valuable and complementary experimental tool to provide direct insights into the solute-solvent coupling due to hydrogen-bond dynamics involving interfacial water. Despite much experimental progress, understanding THz spectra in terms of molecular motions, akin to mid-infrared spectra, still remains elusive. Here, using the osmoprotectant glycine as a showcase, we demonstrate how this can be achieved by combining THz absorption spectroscopy and ab initio molecular dynamics.