Hydration Study on Biomolecules (DNA, Lipid-membrane)
Water plays an important role in our bodies. About 70 percent of our body is made up of water. Water regulates the structure and function of biomolecules such as DNA, proteins, and cell membranes in our bodies. Therefore, it is very important to understand the hydration dynamics of water. Terahertz is a suitable technique for analyzing the hydration dynamics of water.
Uniqueness of Hydration Water Probed through THz Spectroscopy
Using conventional techniques, researchers can access to (sub)nanosecond timescale and find water molecules located in 4~5A in average from biomolecular surface. While, THz spectroscopy can access to sub picosecond timescale, which means that we are able to see faster water. Does biomolecule affect sub-picosecond dynamics of water motion? If does, what is range of hydration effect of faster water?
Hydration Study on DNA
Extraction of Properties of Hydrated DNA (Effective Medium Theory)
To extract properties of biological water only, effective medium theory is applied. We divided DNA solutions into buffer and hydrated DNA. Hydrated DNA is composed of DNA molecule and hydration water. By fitting data into effective medium theory, volume fraction and dielectric constant of hydrated DNA are obtained. The range of hydration water is determined by subtracting size of DNA molecule. And timescale of reorientational motion of hydration water is deduced by Debye model.
Spatiotemporal Property of DNA Hydration Water is Revealed by THz Time-Domain Spectroscopy
We studied spatiotemporal property of DNA hydration water using THz time-domain spectroscopy. Thickness of DNA hydration and timescale of motion of DNA hydration water are determined using effective medium theory and Debye model. It was 57 water molecules and 11.6ps, respectively. This results from Effective medium theory show consistent with absorption coefficient data. From 30mM DNA concentration, nonlinearity behavior occurs. It means inclusions interact each other and hydration water of each DNA overlaps. Therefore, we can assume most water 30mM DNA solution is hydration water. At the 30mM DNA concentration. 57.4 water molecules per nucleotide are affected by DNA and their timescale of reorientaional motion is 12.1ps. The results show a good agreement with those from effective medium theory
<Heyjin Son, Da-Hye Choi, Seonghoon Jung, Jaehun Park and Gun-Sik Park, Dielectric relaxation of hydration water in the Dickerson–Drew duplex solution probed by THz spectroscopy, Chem. Phys. Lett 627 (2015) 134-139>
Hydration Study on Lipid-membrane
Hydration Water Confined in Lipid Structure Resulted Temperature Dependen Behavior of the Lipid Solution
Using three-component model, volume and absorption coefficient of hydration water was calculated. The results shows strong correlation with lipid phase transition (as below).
Hydration water ratio drastically changes during the gel-to-fluid phase transition. Temperature-dependent behavior of Debye relaxation time shows water motion is restricted by lipid molecules and this phenomenon is prominent in biological relevant fluid phases.
<Da-Hye Choi, Heyjin Son, Seonghoon Jung, Jaehun Park, Woong-Yang Park, Oh Sang Kwon and Gun-Sik Park, Dielectric relaxation change of water upon phase transition of a lipid bilayer probed by terahertz time domain spectroscopy, J. Chem. Phys, 2012, 137, 175101-1>
Strong Correlation between Multi-lamellar Spacing Change and the Fast Water Fraction Change Depending on NaCl Concentration
Dielectric constant of hydrated Multi-lamellar vecisle (MLV) can be calculated by effective medium theory (EMT). It is analyzed by double Debye model which has ionic conductivity term.
As NaCl concentration increases, fraction of fast water having few hydrogen bonds increases. This shows strong correlation with the swelling of the lipid multi-lamellar vesicles (MLV). This result suggests that water could be the critical element in nanometer-scale mebrane-membrane communications.
<Da-Hye Choi, Heyjin Son, Jin-Young Jeong and Gun-Sik Park, Correlation between salt-induced change in water structure and lipid structure of multi-lamellar vesicles observed by terahertz time-domain spectroscopy, Chem. Phys. Lett, 2016, 659, 164-168>