Biomedical subjects

Tsuguo Sawada

Publications and source records attributed to Tsuguo Sawada.

14 recordsLinked to original sources

PubMed2005

Second harmonic generation-based coherent vibrational spectroscopy for a liquid interface under the nonresonant pump condition.

The molecular dynamics in the low-frequency region (0-500 cm(-1)) sensitively reflects the intermolecular interactions in a liquid. The second harmonic generation-based coherent vibrational spectroscopy (SHG-CVS) was developed to monitor the low-frequency dynamics of molecules at a liquid interface, which was difficult to access by using the present spectroscopic techniques such as sum frequency generation or attenuated total reflection (ATR)-IR. Background-free detection with the transient grating (TG) optical configuration was adopted to obtain the weak signal under the electronically nonresonant pump condition. It was demonstrated that the S/N ratio of the SHG-CVS with the TG configuration was remarkably superior to that with the conventional time-resolved SHG configuration, and the improved detection limit enabled us to detect the low-frequency dynamics of coumarin 314 molecules at the air/water interface under the electronically nonresonant pump condition.

Letter↗

PubMed2005

Local environment and property of water inside the hollow cylinder of a lipid nanotube.

We investigated the local environment of water confined inside the hollow cylinder of lipid nanotubes (LNTs) by time-resolved fluorescent measurements and attenuated-total-reflectance infrared (ATR-IR) spectroscopy. The LNT was obtained by self-assembly of cardanyl glucosides in water at room temperature and had an open-ended cylindrical nanospace with a diameter of 10-15 nm, a length of 10-100 microm, and hydrophilic inner and outer surfaces. We introduced a fluorescent probe of 8-anilinonaphthalene-1-sulfonate into the confined water and observed an extremely slow dynamic Stokes shift with a correlation time of 1.26 ns, which was 2-3 orders of magnitude longer than that of bulk-phase water. From the peak shift of the fluorescent spectrum, the local solvent polarity (ET(30)) of the confined water was estimated as 50 kcal/mol, which is 20% lower than that in bulk water. ATR-IR measurements showed that the hydrogen-bond network of water inside the LNT was more developed than that in bulk water at room temperature, which is in contrast to the water in other self-assembled confined geometries, such as Aerosol-OT (AOT) reversed micelles.

Anilino Naphthalenesulfonates↗

PubMed2004

Hydrodynamically induced chemical oscillation at a water/nitrobenzene interface.

By measuring a time course of interfacial tension and interfacial electrical potential, we successfully observed oscillatory phenomena that were based on alternatively appearing adsorption and desorption processes of anionic surfactant molecules (sodium dodecyl sulfate (SDS)) at the water/nitrobenzene interface. These oscillation patterns were drastically modified by slightly changing the rate of SDS aqueous solution injection into the water phase. When 10 mM of SDS aqueous solution was injected at a low rate, for example, at less than 1 microl/min, abrupt adsorption was repeatedly followed by slow desorption of DS- ions; in other words, the sequence of the oscillation and relaxation processes was repeated. However, when it was injected at a higher rate, no remarkable periodic phenomenon occurred after the first oscillation. In addition, the rapid adsorption process was observed to be accompanied by a flip motion of the liquid/liquid interface and a flow along the interface. This is caused by a Marangoni convection that is brought about by the generation of heterogeneity of interfacial tension. Furthermore, by estimating the flow speed, it was determined that the faster flow tends to quench the periodic oscillation patterns.

Journal Article↗

PubMed2004

Development of a total internal reflection ultrafast transient lens method for studying molecular dynamics on an interface.

We have developed the total internal reflection ultrafast transient lens (TIR-UTL) method to detect nonradiative chemical processes at interfaces and surfaces with subpicosecond time resolution. In the TIR-UTL measurements, the evanescent field of a pump beam irradiated under the TIR condition generates a refractive index change. The refractive index change is attributed to changes of the molecular electronic state, of density by molecular orientation/structure change, and of temperature by vibrational relaxation processes. The refractive index change is detected as a change of the power intensity of the probe beam adjusted coaxially with the pump beam. At first, we discuss a theoretical principle of a coaxial configuration in the TIR-UTL measurement. This configuration has an advantage of versatility over the established TIR configuration. Then, we evaluate time resolution of TIR-UTL and obtain a value of less than 400 fs. We measure the ultrafast molecular dynamics of the cationic chromophore Auramine O (AuO) at a silica/water interface. Two slow time constants originating from AuO adsorbed on the silica surface are detected by TIR-UTL. These are attributed to AuO, whose twisting motion is strongly hindered by adsorption on a silica surface.

Journal Article↗

PubMed2004

Real-time observation for the enzymatic reaction of phospholipid membrane: application of the time-resolved quasi-elastic laser scattering method.

An analytical technique to measure reactions in biological membranes was developed and applied to monitoring the hydrolysis reaction of phospholipids (dipalmitoylphosphatidylcholine, DPPC) by phospholipase A(2). The technique uses the time-resolved quasi-elastic laser scattering (TR-QELS) method to measure an oil/phospholipid monolayer/water membrane system by monitoring the change of interfacial tension under a noncontact condition and in real time. When the TR-QELS method is used with the newly developed oil/phospholipid monolayer/water membrane system, measurement of the hydrolysis reaction of phospholipids with long alkyl chains (C >or=16), which are the major components in biological membranes, becomes possible. The reaction progress is monitored by the increase of interfacial tension at the oil/water interface caused by the decrease of surface-active DPPC molecules due to the reaction. The characteristic phases, namely, lag, burst, and equilibrium, are observed. The relationship between the duration of the lag phase (the rate-limiting step of the reaction) and the concentration of calcium ion (an essential cofactor of the reaction) is also investigated. Increase of calcium ion concentration in the subphase is found to shorten the duration of the lag phase. In addition, the real-time measurement simplifies the estimation process for the reaction activation energy.

1,2-Dipalmitoylphosphatidylcholine↗

PubMed2004

Ultrafast dynamics of a solution in spatially restricted environments studied by photothermal spectroscopies.

The ultrafast dynamics of a solution in spatially restricted environments was studied by using the ultrafast transient lens (UTL) method. The UTL method is used to monitor the molecular dynamics of a solution by means of a change in the refractive index, which is advantageous for investigating the molecular dynamics of restricted systems. We investigated the photoisomerization of azobenzene derivatives in cyclodextrin nanocavities and revealed how the confinement affects the photoisomerization dynamics and yields. We also studied the relaxation dynamics of photo-excited auramine O (AuO) in a water/aerosol-OT/n-heptane reversed micelle. Both the perturbed properties of the included water and the interactions between AuO and the interface of the reversed micelle strongly appeared to affect the relaxation dynamics. At the same time, we observed a change in the refractive index suggesting a structural change of the micelles in the picosecond region that could not be detected by transient absorption spectroscopy. In addition, we developed the total internal reflection UTL (TIR-UTL) method to monitor the ultrafast molecular dynamics at the liquid interface. The relaxation dynamics of photoexcited AuO at the silica/water interface were observed with subpicosecond time resolution, and it was revealed that the interaction with the interface strongly inhibited the relaxation process. These results demonstrated the advantages of the UTL method for investigating the molecular dynamics of a solution in spatially restricted environments.

Azo Compounds↗

PubMed2004

New approaches to liquid interfaces through changes in the refractive index and nonlinear susceptibility utilizing ultrashort laser pulses.

Molecules in inhomogeneous liquid environments, such as air/liquid, liquid/liquid, solid/liquid interfaces interact with each other specifically, and sometimes form characteristic structures and emerge unique properties. Here, we introduce two newly developed spectroscopic techniques, the total-internal-reflection ultrafast transient lens method (TIR-UTL) and second harmonic generation-coherent vibrational spectroscopy (SHG-CVS), to investigate the characteristic behaviors of molecules in such inhomogeneous environments. TIR-UTL probes the refractive-index change with sub-picosecond resolution and provides information on ultrafast changes in the population, density, and thermal properties, such as temperature increase and energy transfer from the solute molecules to the surrounding solvent molecules. On the other hand, SHG-CVS probes nonlinear susceptibility changes at the interfacial areas, and is expected to provide spectroscopic information on the low-frequency vibrational modes that reflect the corrective motion of the molecules in such an inhomogeneous environment. These new approaches are based on pump-probe techniques utilizing (ultra) short laser pulses. They are expected to provide further information on inhomogeneous environments from the viewpoints of solute-solvent interactions, changes in the molecular orientation, and the corrective motion of molecules at liquid interfaces.

Journal Article↗

PubMed2004

Dynamic behaviors of molecular assemblies at liquid/liquid interfaces studied by time-resolved quasi-elastic laser scattering spectroscopy.

The dynamic behaviors of molecular assemblies at two immiscible liquid interfaces are intriguing topics in many fields of science and technology. However, it is generally difficult to investigate the dynamic behaviors of such molecular assemblies because of the buried nature of liquid/liquid interfaces. In the present paper, our recent investigations on dynamic behaviors of various molecular self-assemblies at liquid/liquid interfaces are reviewed. We monitored dynamic behaviors of the molecular assemblies by time-resolved quasi-elastic laser scattering (TR-QELS) and fluorescent spectroscopy. The former method allows us to monitor the change in interfacial tension with millisecond time-resolution. As molecular assemblies, bis(2-ethylhexyl)sulfosuccinate (AOT) microemulsion, phospholipid biomembrane models, and liposome-DNA complexes have all been studied, since they are relevant in material sciences and biological technologies. At liquid/liquid interfaces, these molecular assemblies showed characteristic behaviors. We review the finding of rebound response of the interfacial tension at the liquid/liquid interface induced by the adsorption of the AOT microemulsion. We monitored the hydrolysis reaction of phospholipid biomembrane models formed at oil/water interfaces, observing the different types of behavior of liposome-DNA complexes at biomembrane models with different kinds of phospholipids.

Journal Article↗

PubMed2004

Chemical oscillation with periodic adsorption and desorption of surfactant ions at a water/nitrobenzene interface.

Chemical oscillations with periodic adsorption and desorption of surfactant ions, alkyl sulfate ions, at a water/nitrobenzene interface have been investigated. The interfacial tension was measured with a quasi elastic laser scattering (QELS) method and the interfacial electrical potential was obtained. We found that this oscillation consists of a series of abrupt adsorptions of ions, followed by a gradual desorption. In addition, we observed that each abrupt adsorption was always accompanied by a small waving motion of the liquid interface. From the analysis of the video images of the liquid interface or bulk phase, we could conclude that each abrupt adsorption is caused by nonlinear amplification of mass transfer of ions from the bulk phase to the liquid interface by a Marangoni convection, which was generated due to local adsorption of the surfactant ions at the liquid interface that resulted in the heterogeneity of the interfacial tension. In the present paper, we describe the mechanism of the chemical oscillation in terms of the hydrodynamic effect on the ion adsorption processes, and we also show the interfacial chemical reaction with ion exchange during the ion desorption process.

Journal Article↗

PubMed2004

Adsorption and desorption behaviors of cationic liposome-DNA complexes upon lipofection in inside and outside biomembrane models using a dynamic quasi-elastic laser scattering method.

The dynamic behaviors of cationic liposome-DNA complexes in inside and outside biomembrane models upon lipofection were investigated using the time-resolved quasi-elastic laser scattering (QELS) method. Inside and outside biomembrane models with similar phospholipid compositions to those in living cells were formed at a tetradecane/phosphate buffered saline (TD/PBS) interface. Cationic liposome-DNA complexes were injected into the buffer subphase, and their adsorption/desorption behaviors at the biomembrane models were monitored through changes in the interfacial tension. We found that the adsorption rate of the complexes increased 2.6 times more in the outside model than in the inside one. The adsorption rate of DNA alone did not show a remarkable difference from one side to the other; however, the adsorption rate of the cationic liposome alone showed a similar tendency to that of the liposome-DNA complex. These results indicated that the difference in lipid composition induced a different dynamic behavior of exogenous biomolecules and that the cationic liposomes played an important role in the faster incorporation of DNA into cells upon lipofection.

Adsorption↗

PubMed2004

Self-assembly and subsequent accumulation of lipid nanotubes at oil/water interfaces.

We utilized oil/water interfaces as a new field to produce lipid nanotubes (LNTs), which are formed by the self-assembly of lipid molecules, and possess hollow nanometer-wide cylindrical structures. Compared to the self-assembling field in bulk water, oil/water interfaces produced shorter lipids nanotubes less than 10 microm long more efficiently. In addition, we found that the oil/water interface accumulates lipid nanotubes spontaneously. This methodology is favorable to fabricate LNTs as new nano-fluidic devices, or sensors that require accumulation and alignment in two dimensions.

Journal Article↗

PubMed2004

Development of a new experimental system for monitoring biomembrane reactions: combination of laser spectroscopic techniques and biomembrane models formed at an oil/water interface.

We present a new experimental system to observe reactions in biomembranes by combining laser spectroscopic techniques with phospholipid monolayers formed at oil/water interfaces. The system can monitor reactions through changes in interfacial tension at oil/water interfaces induced by the reactions under non-destructive and non-contact conditions. In addition, oil/water interfaces with defined areas can define the composition of different kinds of phospholipids. Furthermore, the system allows using, as an oil phase, alkanes whose number of carbon atoms is close to the number of the alkyl chains of phospholipids in biomembranes (C > or = 16). We demonstrated the hydrolysis reaction in DPPC (dipalmitoyl phosphatidylcholine)/DPPS (dipalmitoyl phosphatidylserine)-mixed monolayers by phospholipase A2 by using the system.

1,2-Dipalmitoylphosphatidylcholine↗

PubMed2004

Direct observation of chemical oscillation at a water/nitrobenzene interface with a sodium-alkyl-sulfate system.

The oscillation of the interfacial tension and electrical potential at a water/nitrobenzene interface was observed with homologous anionic surfactant molecules, sodium-alkyl-sulfates. Concerning small molecules with a short hydrophobic carbon chain, the oscillation period and amplitude decreased with a decrease of the length of the alkyl chain. On the other hand, when surfactant molecules with a long hydrophobic carbon chain were used, no remarkable periodic oscillation occurred after the first oscillation. In all systems, an interfacial flow by Marangoni convection was observed when the oscillation took place. By monitoring the movement of carbon powder scattered on the liquid/liquid interface with a CCD camera, we could observe that the liquid/liquid interface expanded outward from the area on which the surfactant molecules adsorbed when the oscillation occurred. When the small molecule was used, the speed of expansion of the interface (flow speed) was small and shrinkage followed by expansion of the interface repeatedly occurred. However, when the large molecule was used, the flow speed was large and expansion occurred only one time. These results show that hydrodynamic factors and surface activities are important in chemical oscillation systems.

Journal Article↗

PubMed1998

Production of sound waves by bacterial cells and the response of bacterial cells to sound.

Bacterial cells enhance the proliferation of neighboring cells under stress conditions by emitting a physical signal. Continuous single sine sound waves produced by a speaker at frequencies of 6-10, 18-22, and 28-38 kHz promoted colony formation by Bacillus carboniphilus under non-permissive stress conditions of high KCl concentration and high temperature. Furthermore, sound waves emitted from cells of Bacillus subtilis at frequencies between 8 and 43 kHz with broad peaks at approximately 8.5, 19, 29, and 37 kHz were detected using a sensitive microphone system. The similarity between the frequency of the sound produced by B. subtilis and the frequencies that induced a response in B. carboniphilus and the previously observed growth-promoting effect of B. subtilis cells upon B. carboniphilus through iron barriers, suggest that the detected sound waves function as a growth-regulatory signal between cells.

Journal Article↗