Solute-induced retardation of water dynamics probed directly by terahertz spectroscopy (original) (raw)
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Probing Biological Water Using Terahertz Absorption Spectroscopy
Terahertz Technology [Working Title], 2021
Hydrogen bonding properties of water molecules, which are confined in microcavities of biological interfaces, are significantly different from those of bulk water and drive most of the complex biological processes. While NMR, X-ray and UV–vis-IR spectroscopic techniques have been found inadequate for describing the dynamics of the thick (20–40 Å) sheath of hydration layer around biomolecules, recently developed THz spectroscopy has emerged as a powerful technique to directly probe the collective dynamics of hydrogen bonds in the hydration layer, which control all important functions of the biomolecules in life. Both laser and accelerator-based THz sources are intense enough to penetrate up to about 100 μm thick water samples, which makes THz transmission and/or dielectric relaxation measurements possible in aqueous solutions. These measurements provide valuable information about the rattling and rotational motions of hydrated ions, making, breaking and rearrangement of hydrogen bond...
Biophysical Journal, 2011
We investigate the thermal denaturation of human serum albumin and the associated solvation using terahertz (THz) spectroscopy in aqueous buffer solution. Far-and near-ultraviolet circular dichroism spectroscopy reveal that the protein undergoes a native (N) to extended (E) state transition at temperature %55 C with a marginal change in the secondary and tertiary structure. At 70 C, the protein transforms into an unfolded (U) state with significant irreversible disruption of its structures. We measure the concentration-and temperature-dependent THz absorption coefficient (a) of the protein solution using a p-Ge THz difference spectrometer (2.1-2.8 THz frequency range), thereby probing the collective protein-water network dynamics. When the solvated protein is heated up to 55 C and cooled down again, a reversible change in THz absorption is observed. When increasing the temperature up to 70 C, we find a dramatic irreversible change of THz absorption. The increase in THz absorption compared to bulk water is attributed to a blue shift in the spectrum of the solvated protein compared to bulk water. This is supported by measurements of THz absorption coefficients using THz time-domain spectroscopy (0.1-1.2 THz frequency range). We also use picosecond-resolved fluorescence spectroscopy of the tryptophan 214 moiety of human serum albumin. All experimental observations can be explained by a change in the hydration dynamics of the solvated protein due to the additional exposure of hydrophobic residues upon unfolding.
The Journal of chemical physics, 2015
Terahertz (THz) spectroscopy has turned out to be a powerful tool which is able to shed new light on the role of water in biomolecular processes. The low frequency spectrum of the solvated biomolecule in combination with MD simulations provides deep insights into the collective hydrogen bond dynamics on the sub-ps time scale. The absorption spectrum between 1 THz and 10 THz of solvated biomolecules is sensitive to changes in the fast fluctuations of the water network. Systematic studies on mutants of antifreeze proteins indicate a direct correlation between biological activity and a retardation of the (sub)-ps hydration dynamics at the protein binding site, i.e., a "hydration funnel." Kinetic THz absorption studies probe the temporal changes of THz absorption during a biological process, and give access to the kinetics of the coupled protein-hydration dynamics. When combined with simulations, the observed results can be explained in terms of a two-tier model involving a lo...
Long-Range Hydration Effect of Lipid Membrane Studied by Terahertz Time-Domain Spectroscopy
Physical Review Letters, 2011
The hydration state of biomolecules is believed to affect their self-assembly. The hydration state of phospholipid bilayers is studied precisely by terahertz spectroscopy, by which water perturbed by a lipid membrane is detected sensitively from the observation of the relaxation dynamics of water molecules in the subpicosecond time scale. Combined with x-ray observation of the lamellar structure of the lipid, a long-range hydration effect on up to 4-5 layers of water is confirmed. Most water molecules in the lamellae fall into the hydration water, and condensation of them is also indicated.
Terahertz spectroscopic techniques for the study of proteins in aqueous solutions
Terahertz Technology and Applications II, 2009
Liquid water is a very strong absorber in the THz frequency range. We have set-up a unique germanium laser spectrometer consisting of a Ge:Be laser, tunable from 1 to 4 THz, and a sensitive Ge photoconductor detector. The spectrometer uses a measurement scheme alternating sample and reference signal while placed in an environmentally controlled housing for high stability of temperature and humidity. The laser system leads to a very small statistical error in the absolute absorption coefficient (400-500 cm −1 ) of less than 0.1% corresponding to 0.3 cm −1 while systematic errors due to filling of the sample cells become dominant. The high accuracy allows us to systematically investigate the effects of different solvates on water dynamics. Even a single point mutation in a protein can be measured in the THz absorption coefficient in the spectral range from 2 to 3 THz. The system has been recently used to study various solvates in liquid water like sugars and prototype proteins in aqueous buffer solutions in dependence of temperature, pH values, and denaturants. These studies are now augmented by time-resolved measurements using THz time-domain spectroscopy to analyze the kinetics of protein folding. We also discuss other THz sources and detection methods including the investigation of coherent synchrotron radiation at the synchrotron ANKA in Karlsruhe.
The Journal of Physical Chemistry B, 2012
The relaxation properties of hydration water around fructose, glucose, sucrose, and trehalose molecules have been studied by means of extended frequency range depolarized light scattering and molecular dynamics simulations. Evidence is given of hydration dynamics retarded by a factor ξ = 5−6 for all the analyzed solutes. A dynamical hydration shell is defined based on the solute-induced slowing down of water mobility at picosecond time scales. The number of dynamically perturbed water molecules N h and its concentration dependence have been determined in glucose and trehalose aqueous solutions up to high solute weight fractions (ca. 45%). For highly dilute solutions, about 3.3 water molecules per sugar hydroxyl group are found to be part of the hydration shell of mono-and disaccharide. For increasing concentrations, a noticeable solute-dependent reduction of hydration number occurs, which has been attributed, in addition to simple statistical shells overlapping, to aggregation of solute molecules. A scaling law based on the number of hydroxyl groups collapses the N h concentration dependence of glucose and trehalose into a single master plot, suggesting hydration and aggregation properties independent of the size of the sugar. As a whole, the present results point to the concentration of hydroxyl groups as the parameter guiding both sugar−water and sugar−sugar interactions, without appreciable difference between mono-and disaccharides.
Terahertz spectroscopy of bound water in nano suspensions
Biomedical Applications of Micro- and Nanoengineering, 2002
The study of enzymatic protein molecules using terahertz time-domain spectroscopy (THz-TDS) has the potential to reveal molecular activity in real time without the use of labelling. Molecular hydration, or bound water, is a critical parameter in enzyme activity and THz-TDS measurements. For the first time we experimentally measure the terahertz-frequency response of nano-sized particles of protein and their level of molecular hydration. These measurements are valuable in understanding the terahertz response of biological systems and in studying the interaction between bound water and proteins.
Protein Science, 2006
Biological polymers are expected to exhibit functionally relevant, global, and subglobal collective modes in the terahertz (THz) frequency range (i.e., picosecond timescale). In an effort to monitor these collective motions, we have experimentally determined the absorption spectrum of solvated bovine serum albumin (BSA) from 0.3 to 3.72 THz (10-124 cm ÿ1). We successfully extract the terahertz molar absorption of the solvated BSA from the much stronger attenuation of water and observe in the solvated protein a dense, overlapping spectrum of vibrational modes that increases monotonically with increasing frequency. We see no evidence of distinct, strong, spectral features, suggesting that no specific collective vibrations dominate the protein's spectrum of motions, consistent with the predictions of molecular dynamics simulations and normal mode analyses of a range of small proteins. The shape of the observed spectrum resembles the ideal quadratic spectral density expected for a disordered ionic solid, indicating that the terahertz normal mode density of the solvated BSA may be modeled, to first order, as that of a three-dimensional elastic nanoparticle with an aperiodic charge distribution. Nevertheless, there are important detailed departures from that of a disordered inorganic solid or the normal mode densities predicted for several smaller proteins. These departures are presumably the spectral features arising from the unique molecular details of the solvated BSA. The techniques used here and measurements have the potential to experimentally confront theoretical calculations on a frequency scale that is important for macromolecular motions in a biologically relevant water environment.
Terahertz spectroscopy of proteins in aqueous solution
Terahertz Time-Domain Spectroscopy (THz-TDS) is one of the key techniques in investigating solid-state materials as well as the study of biomolecules in the THz frequency region. THz waves are very sensitive to the strong absorption of water that makes THz-TDS a useful tool in probing water-biomolecule coupled interaction. In this study, a pure water or guanidine hydrochloride (GuHCl) solvent was mixed with Ascorbic Acid Oxidase (AAO) protein to make native or denatured solutions, respectively. Results revealed that the native and the denatured solution samples both absorb THz weakly although the denatured sample, when compared to the native, showed a higher absorbance. The reason could be the catalyzing effect of AAO.