Yuko Amo

Salt-induced volume phase transition of poly(N-isopropylacrylamide) gel

The salt effect on the phase transition of N-isopropylacrylamide (NIPA) gel was studied. The swelling behavior of the NIPA gel strongly depends on the salt concentration and is well described as a function of the chemical potential difference of water molecules in solution from that at the transition. From the analysis of the OH stretching, Raman spectra in water and in various aqueous solutions in terms of collective proton motions reveals that the presence of salts tends to disrupt or distort the water molecules in hydrophobic hydration shell around the NIPA gel. This leads to inducing the growth of the cluster shell around the salts, which leads to gel collapse. The volume phase transitions due to the different types of perturbation (temperature, salt) are induced by the same mechanism, hydrophobic hydration and dehydration, and therefore can be described in a unified manner in terms of the chemical potential and the collective proton motions of water molecules.

Dynamical structure of water by Raman spectroscopy

Abstract Raman spectra of liquid water have a broad background extended to 4000 cm−1 as well as molecular vibrational modes. Depolarized Raman spectra below 250 cm−1 in liquid water are well interpreted with a superposition of two damped harmonic oscillators and one Cole–Cole type relaxation mode. Two damped harmonic oscillators are interpreted as stretching and bending vibration modes of a temporal tetrahedral-like structure of five water molecules. High-frequency Raman spectra between 1600 cm−1 and 4000 cm−1 in liquid water are well explained by molecular vibration modes of a temporal C2v tetrahedral-like structure around oxygen atom. This interpretation of high frequency spectra is consistent with the interpretation of low-frequency vibrational modes below 250 cm−1. Moreover, the high frequency tail of the above Cole–Cole type relaxation mode could explain the broad background spectra in liquid water.

Low-frequency Raman study of water isotopes

Depolarized low-frequency Raman spectra of H2O,D2O,H218O, and D218O are measured from 266 to 350 K. The reduced Raman spectra below 250cm−1 are reproduced by a superposition of one relaxation mode and two damped harmonic oscillators. The multiple random telegraph model, which takes into account the inertia and memory effects is applied to analyze the central relaxation component. The 180cm−1 mode corresponds to vibration of the oxygen atom. The hydrogen isotopes affect the relaxation time causing its variation. The relaxation time is considered to correspond to the duration of fluctuation of the local structure in liquid water. The intensity of the 50cm−1 mode decreases with increasing temperature and finally vanishes above about 300–310 K. The 50cm−1 mode can be distinguished from the relaxation mode when the relaxation time is more than five times longer than the period of the 50cm−1 vibration mode.

Low-frequency Raman study of ethanol–water mixture

Abstract Low-frequency Raman spectra of ethanol–water mixtures as a function of concentration are measured. We reconfirm the isosbectic point at 130 cm−1 in the χ′′(ν) spectra [1] . The χ′′(ν) spectra of the mixtures can be decomposed into the linear combination of pure water and neat ethanol in the frequency range from 40 to 250 cm−1. Below 40 cm−1, the spectra cannot be decomposed into the linear combination and systematic deviations are found. The results indicate that the microscopic aggregation of water and ethanol molecules depends on the mixing ratio.

Dielectric measurements of lysozyme and tri-N-acetyl-D-glucosamine association at radio and microwave frequencies

Time domain dielectric measurements were applied to the monitoring of molecular recognition by proteins. Lysozyme and tri-N-acetyl-D-glucosamine((NAG)3) were selected as a typical lock and key type recognition system. After association of (NAG)3, relaxation related to lysozyme itself was increased and depended on the pH of the solution. No change was detected in hydration of the enzyme before and after association.

Low-frequency Raman scattering of liquid CCl4, CHCl3, and acetone

We report herein depolarized low-frequency Raman scattering measurements of liquid CCl4, CHCl3 and acetone. The reduced Raman spectra were analyzed for the first time using a relaxation function based on the multiple random telegraph (MRT) model of dielectric relaxation which takes into account inertia and memory effects. The imaginary part of the dielectric function of the MRT model reproduces the spectral profile of the low-frequency region of the reduced Raman spectra quite well. This indicates that the origin of the complicated central component of Raman spectra of liquids can be explained by intermolecular dynamics based on the MRT model.

Dynamical structure of XCl (X = Li, Na, K) aqueous solutions by low-frequency Raman scattering: relation between 50 cm−1 vibration mode and relaxation mode

Depolarized low-frequency Raman spectra of LiCl, NaCl and KCl have been measured as a function of temperature from 266 to 350 K. The concentration dependence of the spectra of LiCl solutions from 0.00 to 0.20 molar ratio has been also measured at room temperature. The spectral profiles have been analyzed with a superposition of one relaxation mode and two damped-harmonic oscillator modes. The multiple random telegraph (MRT) model which takes into account the inertia and the non-white effects has been adopted for a relaxation component. The relaxation time is considered as an average lifetime of the vibration unit of intermolecular vibrations. Two damped oscillator modes are observed around 50 and 180 cm−1 which are considered as a bending-like vibration and a stretching-like vibration, respectively. Above 320 K, the bending-like mode disappears in the fitting results of the 0.08 molar ratio solution. This means that strongly disrupted vibrational mode cannot be distinguished from the relaxation described by the MRT model. At high temperature the relaxation time becomes fast, which means the lifetime of the vibration unit of intermolecular vibration becomes short and the bending-like mode can only vibrate several times during the duration time. On the other hand, at low temperature or at high concentration, the 50 cm−1 component definitely appeared in our analysis with MRT model, because the relaxation time becomes large or the relaxation process becomes slow.

Low-frequency Raman scattering of KOH and NaOH aqueous solutions

Depolarized Raman scattering measurements from −50 to 250 cm−1 were performed on KOH and NaOH aqueous solutions at room temperature. The reduced Raman spectra were analyzed with one relaxation mode and two damped harmonic oscillator modes. The Cole–Cole relaxation function and the multiple random telegraph (MRT) model which takes into account the inertia and the memory effects were applied. The intensity of the relaxation mode increased and the relaxation time became longer with increasing solute concentration. The characteristic frequencies at around 50 cm−1 differed with the use of the Cole–Cole function and the MRT model. Copyright

The First Observation of Low-Frequency Raman Spectra of Supercritical Water

Low-frequency Raman spectra of liquid water from -250 to 250 cm -1 towards to and above the supercritical point have been observed and analyzed by using the multiple random telegraph model (MRT) relaxation function. The 180 cm -1 band has vanished with increasing temperature with constant pressure at 25 MPa. This is due to the destruction of hydrogen-bonds. The obtained relaxation time first decreases and then increases from about 260°C (433 K) with increasing temperature toward to the supercritical state. This behavior is consistent with that of the dielectric relaxation time.

BREAKDOWN OF NARROWING LIMIT AND OVERDAMPED LIMIT OF RELAXATION MODE IN LOW-FREQUENCY RAMAN SPECTRA OF ETHYLENE GLYCOL

We report depolarized low-frequency Raman spectra of ethylene glycol in wide frequency range from 0.01 to 300cm−1. The reduced Raman spectrum is reproduced with the use of a fitting function which contains two relaxation modes and three damped harmonic oscillator modes. The slow relaxation mode is characterized by the Gaussian–Markovian process under the narrowing limit. While for the fast relaxation mode the spectral profile cannot be reproduced by the function which is approximated by both narrowing limit and overdamped limit. This is the first report on the breakdown of both narrowing limit and overdamped limit in the relaxation mode of low-frequency Raman spectra.