Ultrabroadband terahertz spectroscopies of biomolecules and water

Abstract

We describe the use of a range of modern spectroscopic techniques—from terahertz time-domain spectroscopy (THz- TDS) to high dynamic-range femtosecond optical Kerr-effect (OKE) spectroscopy—to study the interaction of proteins, peptides, and other biomolecules with the aqueous solvent. Chemical reactivity in proteins requires fast picosecond fluctuations to reach the transition state, to dissipate energy, and (possibly) to reduce the width and height of energy barriers along the reaction coordinate. Such motions are linked with the structure and dynamics of the aqueous solvent making hydration critical to function. These dynamics take place over a huge range of timescales: from the nanosecond timescale of diffusion of water molecules in the first solvation shell of proteins, picosecond motions of amino-acid side chains, and sub-picosecond librational and phonon-like motions of water. It is shown that a large range of frequencies from MHz to THz is accessible directly using OKE resulting in the reduced anisotropic Raman spectrum and by using a combination of techniques including THz-TDS resulting in the dielectric spectrum. Using these techniques, we can now observe very significant differences in the spectra of proteins in aqueous solvent in the 3-30 THz range and more subtle differences at lower frequencies (10 GHz-3 THz

Terahertz Time-Domain and Low-Frequency Raman Spectroscopy of Organic Materials

“…95,96 More detailed reviews of these topics have been published. 97–101 This work complemented very nicely similar studies using low-frequency Raman spectroscopy and light-scattering techniques. 102–108…”

Study of the dielectric function of aqueous solutions of glucose and albumin by THz time-domain spectroscopy

“…When the dissolved substances appear in water, the degree of a becomes less than unity (the Cole - Cole model) [16], and the salt solutions (including the buffer) also acquire the conductivity s [12,20]. There is another new broadband measurement method in this frequency range, based on the optical Kerr effect [21,22]. This method can be employed to simultaneously measure the parameters of the two above-mentioned relaxation processes, but the resulting values of t 2 turn out overestimated compared with data obtained by means of THz time-domain spectroscopy.…”