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Outline of Our Researches

 Molecules in condensed phases such as liquids are always suffering from the fluctuation by the molecules around them, which plays important roles in chemical reaction dynamics and molecular dynamics.  To reveal the phenomena occurring in pico or femto second time scale, we are making researches in non-linear spectroscopy using ultra-fast lasers. Although various kinds of spectroscopic methods have been applied to the conventional liquids, we have picked up new solvent fluids, which have been paid a lot of attention to, (1) superciritcal fluids (SCFs) and(2) room temperature ionic liuids (RTILs) .  Further by utilizing these newly developed solvents, we are making researches in (3)metal nano-particle synthesis, especially using noble metals.  We have also applied the high-pressure technology to the bio-molecules, and developed several equipments for (4) the spectroscopies under hig pressure for the bio-systems.





(1)Chemical reaction and molecular dynamics in SCFs.

 Science using supercritical fluids (SCFs), which connects gaseous phase and liquid phase continuously, have made a great advance since the latter half of 1980’s, in various flied including the separation and extraction, organic synthesis, surface cleaning, creation of microclusters, and so on.  The most characteristic feature of SCFs is the large density fluctuation near the critical point.  The central problem in physical chemistry of SCFs has been how this density fluctuation is reflected in the various kinds of processes of solute molecules dissolved in SCFs.  In general, there is a tendency that the solvent molecules are close to the solute molecule more densely than the bulk solvent density, which is called local density enhancement.  The effects of the density fluctuation do not simply appear various kinds of observables, besides some exceptions such as the partial molar volume of the solute molecule.  The appearance of the density fluctuation or the local density enhancement is strongly dependent on the typical scale lengths of the observables.

Among SCFs, supercritical water (Tc = 647K) and supercritical alcohols (Tc = ~523K) have been attracting much attention as environmentally benign solvents with unique properties for chemical applications. Their characteristic features are wide tunabilities of dielectric constant and hydrogen bonding ability by changing the temperature and the pressure.  In order to understand chemical processes occurring in these media, knowledge of intermolecular interactions such as the solute-solvent hydrogen bonding is quite important. So far, structures of supercritical water (SCW) and supercritical alcohols (scAlcohols) have been investigated by various kinds of spectroscopic methods including NMR, X-ray, and Raman spectroscopy. On the other hand, studies on the solvation and solute-solvent hydrogen bonding in SCW and scAlcohols are still limited.  Most studies to date have used absorption or fluorescence measurements of solvatochromic probe molecules to examine the local environment of the solute.  Therefore it is an urgent task to do the experiment beyond the solvatochromic shift of the electronic transitions.

Our group has been making research on the solvent effect in the medium-density region of the SCFs, especially following four topics.

1. Resonant and non-resonant Raman spectroscopic study on the solvation in SCW and SCalcohols.

2. Vibrational energy relaxation in complex systems

3. Electron transfer in SCW.





(The details of each topic are now under construction)

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(2) Chemical reactions and molecular dynamics in RTILs

Materials composed of cations and anions such as (NaCl; Na+ and Cl-) are ordinary in a solid phase due to the strong Coulomb interaction between ions.  In order to liquidize these materials, we have to heat them up to very high temperatures above 1000K.  However, recently, by mixing organic cations and inorganic anions, materials composed of ions which are in a liquid phase at room temperature have been developed.


These materials are called room temperature ionic liquids(RTILs) or simply ionic liquids, and  have been extensively studied because of their unique physic-chemical characters.  In our group, the following themes are now under investigation by using the transient grating spectroscopy and Raman spectroscopy.


1. Relaxation of the photo-excited state in RTILs

2. Structure relaxation of RTILs

3. Diffusion dynamics in RTILs

4. Raman spectroscopic study on the solvation in RTILs

5. Study on the dynamics properties of RTILs/CO2 mixtures

6. Proton transfer reaction in RTILs


 (The details of each topic are now under construction)

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(3)Synthesis and characterization of metal nano-particles in designer liquids

 Metal particles of nanometer size are quite interesting objects not only for the application as catalyst but also for the quantum system composed of small number atoms.  The establishment of the synthesis method of nano-particles with size control is an important topic, and there have been reported various kinds of methods.  Among them, the synthesis of noble metal nano-particle such as gold, platinum, or silver, by the reduction of ion under the existence of protective polymer is one of the promising methods.  These chemical reductions are ordinary done with refluxing the solution under the ambient pressure, and the reactions proceed over several hours.  By utilizing the high-pressure and the high-temperature conditions, we are trying to regulate the particle size and to improve the productivity.

The followings are the themes under investigation.

1. Synthesis and characterization of noble metal nano-particles in supercritical alcohols

2. Synthesis and characterization of noble metal nano-particles in RTILs

3. Laser ablation in RTILs

4. Development of high pressure optical cells used for X-ray measurements


(The details of each topic are now under construction)

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(4) Development of high pressure optical cells for bio-material investigations

 The effects of the pressure on proteins and biomaterials are worth to study, since the pressure is a quantity which is coupled to the volume of the system, and the volume fluctuation of bio-materials is directly related to their functionalities.  In our research groups, several kinds of new high pressure optical cells have been developed for the investigation of protein or biomaterials under high pressure.  The followings are examples of the developed systems.


1. High pressure cell for the transient grating (TG) measurement.

 This apparatus has been developed for the investigation of the protein thermodynamics under high pressure.  TG spectroscopy is a quite unique method which can determine the thermodynamic values of the reaction intermediates.  By applying this method for the protein under high pressure, we can also evaluate the pressure response of the system, i.e., volume fluctuations. The cell is specially designed for the use of quantitative measurement of the signal intensity.




2. High pressure cell for the microscope.

 Application of microscope for the molecule or biomaterials under high pressure is a universal tool for the in-situ observation under high pressure.  We are now developing high pressure cells used for the microscope with high NA under pressure up to 200 MPa.



(The details of each topic are now under construction)

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