Hydration-Induced Far-Infrared Absorption Increase in Myoglobin

Abstract

The interaction of proteins with an aqueous environment leads to a thin region of "biological water", the molecules of which have properties that differ from those of bulk water, in particular, reduced absorption of far-infrared radiation caused by protein-induced hindrance of the water rotational and vibrational degrees of freedom. New results at terahertz (THz) frequencies, however, show that absorption per protein molecule is increased by the presence of biological water. Absorption measurements were made of the heme protein myoglobin mixed with water from 3.6 to 98 wt % in the frequency range of 0.1-1.2 THz, using THz time-domain spectroscopy. Analysis shows greater THz absorption when compared to a non-interacting protein-water model. Including the suppressed absorption of biological water leads to a substantial hydration-dependent increase in absorption per protein molecule over a wide range of concentration and frequencies, meaning that water increases the protein's polarizability.

Dissecting the THz spectrum of liquid water from first principles via correlations in time and space

“…The intermolecular vibrational modes in the frequency window from 1 THz up to about 10 THz (16,17), corresponding to ≈30-300 cm −1 , have been proven recently to be a unique tool to study the hydration dynamics around solutes (18)(19)(20)(21). Using THz laser spectroscopy, water dynamics has been shown to be influenced within an "extended dynamical hydration shell" (20) of about 6-7 Å for small solutes like carbohydrates (18) by changes in the absolute absorption intensity as probed at 2.4 THz (i.e., ≈80 cm −1 ).…”

Terahertz absorption of lysozyme in solution

“…[13][14][15][16][17][18][19][20][21][22] The absorption of light as the means of probing the solvation structure has a significant advantage compared to broad-band dielectric spectroscopy since the sensitivity of the response is improved by a factor roughly equal to the dielectric constant for the same magnitude of the liquid polarization or by a factor of dielectric constant squared for the same magnitude of the external electric field. 23 The difference is due to the transverse geometry of light absorption compared to the longitudinal geometry of the dielectric experiment.…”

Concentration analysis of breast tissue phantoms with terahertz spectroscopy

“…Considering the biological aspect, proteins often take a hydrated form that enables more engagement with metabolic functions. Analysis of hydrated proteins, such as gelatin in liquid water, provides more accurate understanding of biological protein dynamics than that of dried powder proteins [38,39]. Therefore, the following optimization based on Eq.…”