Abstract-Spectroscopy and sensing of fluid using terahertz waves

Toshiaki Hattori,  Katsuyoshi Aoki,  Borwen You,  Ja-Yu Lu,  Chin-Ping Yu

https://www.spiedigitallibrary.org/conference-proceedings-of-spie/10826/108260K/Spectroscopy-and-sensing-of-fluid-using-terahertz-waves/10.1117/12.2505842.short?SSO=1

Understanding of terahertz spectroscopic properties of materials is crucially important for applications of terahertz waves in sensing. Spectroscopic properties of water-rich media, such as biological tissues, gels, and aqueous solutions, are strongly affected by the amount and the dynamics of water in them. Terahertz spectroscopical measurements can clarify the dynamical and/or structural characteristics of water molecules in the hydrogen-bond network in these media. We studied the dynamical properties of water around protein molecules and polymers in aqueous solutions using terahertz spectroscopic measurements. Sensing of liquid using a terahertz waveguide composed of a metal rod array will also be described.

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Abstract-Salt effects on the picosecond dynamics of lysozyme hydration water investigated by terahertz time-domain spectroscopy and an insight into the Hofmeister series for protein stability and solubility

Katsuyoshi Aoki,^a   Kentaro Shiraki^b and   Toshiaki Hattori*^a  

http://pubs.rsc.org/en/content/articlelanding/2016/cp/c5cp06324h#!divAbstract

Phys. Chem. Chem. Phys., 2016, Advance Article

DOI: 10.1039/C5CP06324H
Received 18 Oct 2015, Accepted 03 May 2016
First published online 19 May 2016

The addition of salts into protein aqueous solutions causes changes in protein solubility and stability, whose ability is known to be ordered in the Hofmeister series. We investigated the effects of Hofmeister salts on the picosecond dynamics of water around a lysozyme molecule using terahertz time-domain spectroscopy. The change in the absorption coefficient for 200 mg mL⁻¹ lysozyme aqueous solution by the addition of salts was found to depend on the salts used, whereas that for pure water was almost independent of salts. From the difference in the salt concentration dependence for various salts, it has been found that chaotropic anions make the dynamics of water around the lysozyme molecule slower, whereas kosmotropic anions make the dynamics faster. The ability of an anion to slow down the water dynamics was found to have the following order: SCN⁻ > Cl⁻ > H₂PO₄⁻ > NO₃⁻ ≈ SO₄²⁻. This result indicates that the effects of anions on the dynamics of water around the lysozyme molecule are the opposite of those for bulk water. This finding agrees with a prediction from a molecular model proposed by Collins [K. D. Collins, Methods, 2004, 34, 300]. The results presented here are compared with the results from preferential interaction studies and the results from sum frequency generation spectroscopy. These discussions have led to the conclusion that the picosecond dynamics of protein hydration water strongly contributes to protein stability, whereas electrostatic interactions between protein molecules contribute to protein solubility.