Browsing by Author "Iwata, Koichi"

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Energy Transfer Characteristics of Lipid Bilayer Membrane in Liposome Studied with Picosecond Time-Resolved Raman Spectroscopy
(2010)
Nojima, Yuki
;
Yoshida, Kyousuke
;
Hamaguchi, Hiro-o
;
Iwata, Koichi
;
應用化學系
Local Structure and Microscopic Thermal Diffusion in Ionic Liquids Studied with Picosecond Time-resolved Raman Spectroscopy
(2010)
Yoshida, Kyousuke
;
Iwata, Koichi
;
Hamaguchi, Hiro-o
;
應用化學系
;
應用化學系分子科學碩博班
Local structure formation in alkyl-imidazolium-based ionic liquids as revealed by linear and nonlinear Raman spectroscopy
(2007-11-01)
Iwata, Koichi
;
Okajima, Hajime
;
Saha, Satyen
;
Hamaguchi, Hiro-O
;
應用化學系
We show several pieces of Raman spectroscopic evidence that are indicative of local structure formation in imidazolium-based ionic liquids. Low-frequency Raman spectra of C(n)mimX, where C(n)mim stands for 1-alkyl(CnH2n+1)-3-methylimidazolium cation and X represents the anion, exhibit broad bands assignable to collective modes of local structures. Spatial distributions of coherent anti-Stokes Raman scattering (CARS) signals from C(n)mim[PF(6)l are consistent with local structures whose size increases with increasing n. Picosecond Raman spectra of S, trans-stilbene as a "picosecond Raman thermometer" show microscopic thermal inhomogeneity ascribable to local structure formation in C(2)mimTf(2)N and C(4)mimTf(2)N. We also describe two novel phenomena that we believe are relevant to extraordinary nanoenvironments generated by local structures in a magnetic ionic liquid C(4)mim[FeCl4].
Local structures in ionic liquids probed and characterized by microscopic thermal diffusion monitored with picosecond time-resolved Raman spectroscopy
(2012-03-14)
Yoshida, Kyousuke
;
Iwata, Koichi
;
Nishiyama, Yoshio
;
Kimura, Yoshifumi
;
Hamaguchi, Hiro-o
Vibrational cooling rate of the first excited singlet (S1) state of trans-stilbene and bulk thermal diffusivity are measured for seven room temperature ionic liquids, C2mimTf2N, C4mimTf2N, C4mimPF6, C5mimTf2N, C6mimTf2N, C8mimTf2N, and bmpyTf2N. Vibrational cooling rate measured with picosecond time-resolved Raman spectroscopy reflects solute-solvent and solvent-solvent energy transfer in a microscopic solvent environment. Thermal diffusivity measured with the transient grating method indicates macroscopic heat conduction capability. Vibrational cooling rate of S1 transstilbene is known to have a good correlation with bulk thermal diffusivity in ordinary molecular liquids. In the seven ionic liquids studied, however, vibrational cooling rate shows no correlation with thermal diffusivity; the observed rates are similar (0.082 to 0.12 ps-1 in the seven ionic liquids and 0.08 to 0.14 ps-1 in molecular liquids) despite large differences in thermal diffusivity (5.4-7.5 x 10-8 m2 s-1 in ionic liquids and 8.0-10 x 10-8 m2 s-1 in molecular liquids). This finding is consistent with our working hypothesis that there are local structures characteristically formed in ionic liquids. Vibrational cooling rate is determined by energy transfer among solvent ions in a local structure, while macroscopic thermal diffusion is controlled by heat transfer over boundaries of local structures. By using " local" thermal diffusivity, we are able to simulate the vibrational cooling kinetics observed in ionic liquids with a model assuming thermal diffusion in continuous media. The lower limit of the size of local structure is estimated with vibrational cooling process observed with and without the excess energy. A quantitative discussion with a numerical simulation shows that the diameter of local structure is larger than 10 nm. If we combine this lower limit, 10 nm, with the upper limit, 100 nm, which is estimated from the transparency (no light scattering) of ionic liquids, an order of magnitude estimate of local structure is obtained as 10 nm < L < 100 nm, where L is the length or the diameter of the domain of local structure. c 2012 American Institute of Physics. [ http:// dx. doi. org/ 10.1063/ 1.3691839]
Nanosecond Time-resolved Infrared Spectra and Structure of the Charge-transfer State of 9,9 '-Bianthryl in Acetonitrile
(2012-06-05)
Asami, Nobuyuki
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Yabumoto, Sohshi
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Shigeto, Shinsuke
;
Takaya, Tomohisa
;
Hamaguchi, Hiro-o
Nanosecond time-resolved infrared spectra of photoexcited 9,9'-bianthryl (BA) and its deuterated derivative (BA-d(18)) were recorded in acetonitrile-d(3) and cyclohexane-d(12). The charge-transfer (CT) bands observed at the 1200-1400 cm(-1) region are contributed mostly by the intra- and inter-ring CC stretch vibrations. The intrinsic frequency of the inter-ring CC stretch falls within the 1200-1400 cm(-1) region, which is consistent more with a twisted structure than with a fully conjugated planar structure of the CT state.
Novel physical chemistry approaches in biophysical researches with advanced application of lasers: Detection and manipulation
(2018-02-01)
Iwata, Koichi
;
Terazima, Masahide
;
Masuhara, Hiroshi
;
應用化學系
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Department of Applied Chemistry
Novel methodologies utilizing pulsed or intense CW irradiation obtained from lasers have a major impact on biological sciences. In this article, recent development in biophysical researches fully utilizing the laser irradiation is described for three topics, time-resolved fluorescence spectroscopy, time-resolved thermodynamics, and manipulation of the biological assemblies by intense laser irradiation. First, experimental techniques for time-resolved fluorescence spectroscopy are concisely explained in Section 2. As an example of the recent application of time-resolved fluorescence spectroscopy to biological systems, evaluation of the viscosity of lipid bilayer membranes is described. The results of the spectroscopic experiments strongly suggest the presence of heterogeneous membrane structure with two different viscosity values in liposomes formed by a single phospholipid. Section 3 covers the time-resolved thermodynamics. Thermodynamical properties are important to characterize biomolecules. However, measurement of these quantities for short-lived intermediate species has been impossible by traditional thermodynamical techniques. Recently, development of a spectroscopic method based on the transient grating method enables us to measure these quantities and also to elucidate reaction kinetics which cannot be detected by other spectroscopic methods. The principle of the measurements and applications to some protein reactions are reviewed. Manipulation and fabrication of supramolecues, amino acids, proteins, and living cells by intense laser irradiation are described in Section 4. Unconventional assembly, crystallization and growth, amyloid fibril formation, and living cell manipulation are achieved by CW laser trapping and femtosecond laser-induced cavitation bubbling. Their spatio-temporal controllability is opening a new avenue in the relevant molecular and bioscience research fields. This article is part of a Special Issue entitled "Biophysical Exploration of Dynamical Ordering of Biomolecular Systems" edited by Dr. Koichi Kato.
Two Different Charge Transfer States of Photoexcited 9,9 '-Bianthryl in Polar and Nonpolar Solvents Characterized by Nanosecond Time-Resolved Near-IR Spectroscopy in the 4500-10 500 cm(-1) Region
(2010-06-10)
Asami, Nobuyuki
;
Takaya, Tomohisa
;
Yabumoto, Soshi
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Shigeto, Shinsuke
;
Hamaguchi, Hiro-o
Transient absorption spectra of 9,9'-bianthryl (BA) in heptane, in acetonitrile, and in 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (bmimTf(2)N) are observed with a nanosecond time-resolved near-IR absorption spectrometer for the wavenumber range of 4500-10 500 cm(-1) (2200-950 nm). In nonpolar heptane solution, a broad absorption band is observed at 6700 cm(-1)(1500 urn), in addition to a strong absorption band of the locally excited (LE) state centered at 9800 cm(-1) (1020 nm). The broad band is assigned to a partial charge transfer (PCT) band. The decay time constants of the PCT band and the LE band are both (13 +/- 1) ns. The agreement of the two decay constants strongly suggests that the PCT state is in equilibrium with the LE state in heptane. In acetonitrile, an absorption band of the charge transfer (CT) state is observed at 8000 cm(-1) (1250 nm). This band decays in (41 +/- 2) ns. In bmimTf(2)N, the CT band appears at 8500 cm(-1) (1180 nm) and decays in (34 +/- 1) ns. The difference in peak position for the CT bands in acetonitrile and in bmimTf(2)N, and the PCT bands in heptane, is explained well by the model based on the charge resonance between the two equivalent electronic structures of the CT state.
Two-step photoionization of trans-stilbene in acetonitrile via an ion-pair precursor studied with picosecond time-resolved absorption and Raman spectroscopies
(2012-02-27)
Miki, Hiroko
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Yoshida, Kyousuke
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Kawate, Chieko
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Shimada, Rintaro
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Takaya, Tomohisa
Picosecond time-resolved visible absorption and Raman spectra of trans-stilbene in acetonitrile have been measured. A new transient absorption band is observed at 440 nm, whose decay time constant coincides with that of the rise of the radical cation. In addition to the known Raman bands of the radical cation, a new Raman feature showing a fast decay is found at 1599 cm(-1). We assign the 440 nm absorption band and the 1599 cm(-1) Raman band to a precursor of the radical cation. The precursor may well be an ion pair that holds an ejected electron still around the cation. (C) 2012 Elsevier B. V. All rights reserved.