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.
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)
(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)
(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)
(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)