Tetsuhito Suzuki

Quantitative characterization of hydration state and destructuring effect of monosaccharides and disaccharides on water hydrogen bond network

Terahertz time-domain attenuated total reflection measurements of monosaccharide (glucose and fructose) and disaccharide (sucrose and trehalose) solutions from 0.146 M to 1.462 M were performed to evaluate (1) the hydration state and (2) the destructuring effect of saccharide solutes on the hydrogen bond (HB) network. Firstly, the extent of hydration water was determined by the decreased amount of bulk water with picosecond relaxation time that was replaced by that with much longer orientational relaxation time. As a result, we found glucose and trehalose exhibits stronger hydration capacity than fructose and sucrose, respectively, despite of the same number of the hydroxyl groups. For each saccharide, the hydration number tended to decrease with solute concentration. Secondly, the destructuring effect of these saccharide solutes on the HB network of the surrounding bulk water was discussed from the perspective of the fraction of non-hydrogen-bonded (NHB) water isolated from the HB network. We found the fraction of NHB water molecules that are not engaged in the HB network monotonously increased with saccharide concentration, indicating saccharide solutes promote the disruption of the water HB network. However, no noticeable differences were confirmed in the fraction of NHB water between glucose and fructose or between sucrose and trehalose. In contrast to hydration number, the number of NHB water produced by a single saccharide solute was less dependent on solute concentration, and three monosaccharide/disaccharide solutes were found to produce one/two NHB water molecules.

Hydration and Hydrogen Bond Network of Water during the Coil-to-Globule Transition in Poly(N-isopropylacrylamide) Aqueous Solution at Cloud Point Temperature

Aqueous solutions of poly(N-isopropylacrylamide), P-NIPAAm, exhibit a noticeable temperature responsive change in molecular conformation at a cloud point temperature (Tcp). As the temperature rises above Tcp, the extended coil-like P-NIPAAm structure changes into a swollen globule-like conformation as hydration levels decrease and hydrophobic interactions increase. Though water plays an important role in this coil-to-globule transition of P-NIPAAm, the behavior of water molecules and the associated hydrogen-bond (HB) network of the surrounding bulk water are still veiled in uncertainty. In this study, we elucidate changes in the hydration state and the dynamical structure of the water HB network of P-NIPAAm aqueous solutions during the coil-to-globule transition by analyzing the complex dielectric constant in the terahertz region (0.25-12 THz), where bulk water reorientations and intermolecular vibrations of water can be selectively probed. The structural properties of the water HB network were examined in terms of the population of the non-HB water molecules (not directly engaged in the HB network or hydrated to P-NIPAAm) and the tetrahedral coordination of the water molecules engaged in the HB network. We found the hydration number below Tcp (≈10) was decreased to approximately 6.5 as temperature increased, in line with previous studies. The HB network of bulk water becomes more structured as the coil-to-globule phase transition takes place, via decreases in non-HB water and reduction in the orderliness of the tetrahedral HB architecture. Together these results indicate that the coil-to-globule transition is associated with a shift to hydrophobic-dominated interactions that drive thermoresponsive structural changes in the surrounding water molecules.

Hydration and hydrogen bond network of water around hydrophobic surface investigated by terahertz spectroscopy

Water conformation around hydrophobic side chains of four amino acids (glycine, L-alanine, L-aminobutyric acid, and L-norvaline) was investigated via changes in complex dielectric constant in the terahertz (THz) region. Each of these amino acids has the same hydrophilic backbone, with successive additions of hydrophobic straight methylene groups (-CH2-) to the side chain. Changes in the degree of hydration (number of dynamically retarded water molecules relative to bulk water) and the structural conformation of the water hydrogen bond (HB) network related to the number of methylene groups were quantitatively measured. Since dielectric responses in the THz region represent water relaxations and water HB vibrations at a sub-picosecond and picosecond timescale, these measurements characterized the water relaxations and HB vibrations perturbed by the methylene apolar groups. We found each successive straight -CH2- group on the side chain restrained approximately two hydrophobic hydration water molecules. Additionally, the number of non-hydrogen-bonded (NHB) water molecules increased slightly around these hydrophobic side chains. The latter result seems to contradict the iceberg model proposed by Frank and Evans, where water molecules are said to be more ordered around apolar surfaces. Furthermore, we compared the water-hydrophilic interactions of the hydrophilic amino acid backbone with those with the water-hydrophobic interactions around the side chains. As the hydrophobicity of the side chain increased, the ordering of the surrounding water HB network was altered from that surrounding the hydrophilic amino acid backbone, thereby diminishing the fraction of NHB water and ordering the surrounding tetrahedral water HB network.

Determination of the complex dielectric constant of an epithelial cell monolayer in the terahertz region

We present a method to determine the complex dielectric constant of a cell monolayer using terahertz time-domain attenuated total reflection spectroscopy combined with a two-interface model. The imaginary part of the dielectric constant of the cell monolayer shows a lower absorption of slow relaxation mode than that of the liquid medium. This result allows us to estimate the intracellular water dynamics on a picosecond time scale, and the existence of weakly hydrated water molecules inside the cell monolayer was indicated. This method will provide a perspective to investigate the intracellular water dynamics in detail.

A Quantitative Study for Determination of Glucose Concentration Using Attenuated Total Reflectance Terahertz (ATR-THz) Spectroscopy*

In this work, a quantitative study for glucose concentration determination was conducted using ATR-THz spectroscopy. Glucose solutions with different concentrations were prepared and their absorbance spectra between wavenumber 19.285 cm−1 and 451.261 cm−1 were acquired using a terahertz-based Fourier transform spectrometer. The spectra of glucose solutions in different concentrations were compared and discussed. The results showed that increasing glucose concentration caused decreasing absorbance. Calibration models for glucose determination were developed using partial least squares (PLS) regression for original and pre-processing spectra. The calibration model using Savitzky-Golay second derivative spectra gave satisfactory results. The use of ATR-THz spectroscopy combined with an appropriate chemometric method has potential for a rapid determination of glucose concentrations in aqueous solution.

Hydration state inside HeLa cell monolayer investigated with terahertz spectroscopy

The hydration state in living cells is believed to be associated with various cellular activities. Nevertheless, in vivo characterization of intracellular hydration state under physiological condition has not been well documented to date. In this study, the hydration state of an intact HeLa cell monolayer was investigated by terahertz time-domain attenuated total reflection spectroscopy. Combined with the extended theory of Onsager, we found 23.8 ± 7.4% of HeLa intracellular water was hydrated to biomolecules (corresponding to 1.25 g H2O/g solute); exhibiting slower relaxation dynamics than bulk water.

CMOS Biosensor IC Focusing on Dielectric Relaxations of Biological Water With 120 and 60 GHz Oscillator Arrays

In this paper, a CMOS biosensor integrated circuit (IC) focusing on dielectric relaxations of biological water with 120 and 60 GHz oscillator arrays is proposed. To realize label-free biosensing, we focus on frequencies around 100 GHz where changes in the dielectric constant of water become prominent as many a water molecule is bound to biomolecules. To detect the state of the biological water, sensing elements based on LC-oscillators operating at 120 and 60 GHz are realized using the 65 nm CMOS process. The sizes of the sensing elements are significantly smaller than the wavelengths of the operating frequencies, therefore 2-D arrays can be implemented in a chip. The trial chip enables us to obtain spatial distributions of the targets. In this paper, the cultivated bacterial colony growth is monitored and other biosensing applications are explained, which showcase possibilities for using the biosensor IC.

28.3 CMOS biosensor IC focusing on dielectric relaxations of biological water with 120GHz and 60GHz oscillator arrays

The water present in the close vicinity of biomolecules is particularly relevant to the function of the biomolecules and is termed “biological water” in contrast to ordinary “bulk water” that fills the region beyond this vicinity (Fig. 28.3.1). Many studies have revealed that these two types of water exhibit clear differences in their dielectric relaxations. First, bulk water has two major relaxation modes: (i) the first mode represents the dielectric relaxation of the cooperative organization of hydrogen-bonded water molecules with a time constant τd (≈8ps), and (ii) the second mode exhibits a faster relaxation time constant τf (≈0.27ps) and is usually attributed to the rotation of the water molecules that are not involved in hydrogen bonding. On the other hand, a slower relaxation (τs) appears in biological water because of “bound water” that is strongly bonded to biomolecules and less movable compared with bulk water. Owing to the presence of τs-mode water, the fractions of τd- and τf-mode waters in biological water are smaller than those in bulk water. In this manner, the existence and status of biological water is reflected in the complex dielectric constant at a frequency around 100GHz. Because the ionic polarization of electrolytes (e.g., Na, K, Ca) strongly affects the dielectric loss in the frequency range lower than 50GHz, a difficulty arises in differentiating the dielectric relaxations of water from that of the ionic polarization [2]. By limiting the observation frequency to higher than 50GHz, we can eliminate this difficulty. By focusing on the dielectric relaxations of biological water, we present a CMOS biosensor IC that can detect and visualize the target biomolecules by using biological water as a label.

Prediction of K value for fish flesh based on ultraviolet-visible spectroscopy of fish eye fluid using partial least squares regression

HighlightsUV-VIS spectra of fish eye fluid are used to predict K value of fish flesh.A regression model is developed using partial least squares (PLS) regression technique.Predict the K value of fish flesh with Rpred2 of 0.87 and RMSEP of 7.87% is observed. A method to predict K value of fish flesh using ultraviolet-visible (UV-VIS) spectral properties (250-600nm) of its eye fluid and a partial least squares (PLS) regression method is investigated. UV-VIS absorbance of eye fluid was monitored for 240 fresh fish (Japanese dace) while simultaneously measuring the K value of the fish flesh by a paper electrophoresis technique. Several spectral pre-processing techniques, such as moving average smoothing, normalization, multiplicative scatter correction (MSC), Savitzky-Golay first-order derivative and Savitzky-Golay second-order derivatives were compared. The results showed that the regression model developed by PLS based on MSC preprocessed spectra resulted in better performance compared to models developed by other preprocessing methods, with a determination coefficient of prediction (Rpred2) of 0.87 and a root mean square error of prediction (RMSEP) of 7.87%. Therefore, the use of UV-VIS spectroscopy combined with appropriate multivariate analysis has the potential to accurately predict K value of fish flesh.

Detection of

The effectiveness of metallic mesh sensors to quantitatively measure thickness was evaluated by transmission spectra of sub- μm-thick SiO2 layers deposited on a 6-μm-thick metallic mesh. Initially, we simulated the transmission spectra and the localized electric field distribution of different-sized periodic structures using the finite difference time domain method. Both the wavelength of the resonance peak and the decay distance of the localized electric field changed linearly with the size of the geometric parameters of the metallic meshes. These electro-magnetic properties enabled smaller-sized periodic structures to acquire exponentially higher sensitivity for the thin dielectric layer. The experiment resulted in distinct and systematic frequency shifts over 100-nm-thick SiO2 (101 GHz of shift and 61% of CV). Potential of the metallic meshes as label-free and frequency-flexible biosensors was performed, which have high sensitivity for thin target using small size of periodic structures.