研究者業績

岩田 耕一

イワタ コウイチ  (Koichi Iwata)

基本情報

所属
学習院大学 理学部 化学科 教授
学位
理学博士(東京大学)

J-GLOBAL ID
200901030161773730
researchmap会員ID
1000255661

外部リンク

受賞

 3

論文

 20
  • Shunnosuke Okino, Tomohisa Takaya, Koichi Iwata
    CHEMISTRY LETTERS 44(8) 1059-1061 2015年8月  査読有り
    The energies of low-lying singlet excited states of oligothiophenes, xT's (x = 3 to 8), and polythiophene are determined using femtosecond time-resolved near-infrared spectroscopy. The energies are linearly correlated with the reciprocal number of the thiophene rings for the oligomers 3T to 7T. The linear relation is not observed for 8T, indicating that the effective conjugation is formed over no more than seven rings in the excited states. Transient absorption spectra of polythiophene show that its thiophene chains are composed of planar segments with five or six thiophene rings.
  • Ashok Zachariah Samuel, Sohshi Yabumoto, Kenichi Kawamura, Koichi Iwata
    ANALYST 140(6) 1847-1851 2015年  査読有り
    Raman imaging is one of the very informative methods for the characterization of chemically and structurally heterogeneous materials without employing specific molecular labels. Multifocus Raman imaging is one of the fast-imaging alternatives to the conventional single point mapping technique. Since multiple focal points probe the sample simultaneously, this imaging methodology is faster compared to single point mapping. We have further demonstrated the efficiency of this methodology by investigating the morphological features of a porous PMMA film. A Raman image of a 50 x 50 mu m(2) area was obtained in less than 4 minutes (with a 10 x 10 multifocus configuration). Importantly, a 100 x 100 mu m(2) area could now be analyzed in minutes while a similar Raman image by single point mapping would take hours to days. Optical sectioning using multifocus Raman imaging reveals unique hierarchical features of the porous polymer thin film. Larger pores are limited to the surface and the inner bulk exhibits characteristic small-pores and an interconnected highly porous morphology. The fast multifocal Raman imaging would be advantageous to the diverse field of scientific disciplines where the speed of image acquisition remains a challenge despite the unparalleled specificity and sensitivity of Raman spectroscopy.
  • Yuki Nojima, Koichi Iwata
    JOURNAL OF PHYSICAL CHEMISTRY B 118(29) 8631-8641 2014年7月  査読有り
    A number of biochemical reactions proceed inside biomembranes. Because the rate of a chemical reaction is influenced by chemical properties of the reaction field, it is important to examine the chemical properties inside the biomembranes, or lipid bilayer membranes, for understanding biochemical reactions. In this study, we estimate viscosity inside the lipid bilayers of liposomes with picosecond time-resolved fluorescence spectroscopy. trans-Stilbene is solubilized in the lipid bilayers formed by phosphatidylcholines, DSPC, DOPC, DPPC, DMPC, and DLPC, with 18, 18, 16, 14, and 12 carbon atoms in their alkyl chains, respectively, and egg-PC. Viscosity inside the lipid bilayer is estimated from the photoisomerization rate constant and from the rotational relaxation time of the first excited singlet state of trans-stilbene. The effect of the hydrocarbon chain length and temperature on viscosity is examined. The presence of two solvation environments within the lipid bilayer is indicated from the two independent estimations. One environment is 30 to 290 times more viscous than the other. Even single-component lipid bilayers are likely to have heterogeneous structures.
  • Tomohisa Takaya, Koichi Iwata
    JOURNAL OF PHYSICAL CHEMISTRY A 118(23) 4071-4078 2014年6月  査読有り
    Carotenoids have two major low-lying excited states, the second lowest (S-2 (1B(u)(+))) and the lowest (S-1 (2A(g)(-))) excited singlet states, both of which are suggested to be involved in the energy transfer processes in light-harvesting complexes. Studying vibrational dynamics of S-2 carotenoids requires ultrafast time-resolved near-IR Raman spectroscopy, although it has much less sensitivity than visible Raman spectroscopy. In this study, the relaxation mechanism of beta-carotene from the S-2 state to the S-1 state is investigated by femtosecond time-resolved multiplex near-IR absorption and stimulated Raman spectroscopy. The energy gap between the S-2 and S-1 states is estimated to be 6780 cm(-1) from near-IR transient absorption spectra. The near-IR stimulated Raman spectrum of S-2 beta-carotene show three bands at 1580, 1240, and 1050 cm(-1). When excess energy of 4000 cm-' is added, the S-1 C=C stretch band shows a large upshift with a time constant of 0.2 ps. The fast upshift is explained by a model that excess energy generated by internal conversion from the S-2 state to the 5, state is selectively accepted by one of the vibronic levels of the S-1 state and is redistributed among all the vibrational modes.
  • Koichi Iwata
    JOURNAL OF RAMAN SPECTROSCOPY 39(11) 1512-1517 2008年11月  査読有り
    Ultrafast bimolecular radical reaction proceeds between photoexcited p-terphenyl and carbon tetrachloride. The lifetime of the first excited singlet (Si) state of p-terphenyl in carbon tetrachloride measured with picosecond time-resolved fluorescence spectroscopy is 5.6 ps, shorter than the typical lifetime in ordinary solvents, 0.95-2.8 ns, by a factor of 170 or more. Time-resolved infrared spectroscopy reveals the generation of the trichloromethyl (CCl(3)) radical as a reaction intermediate. The decay kinetics of the CCl(3) radical indicates that the CCl(3) radical and the p-terphenyl-Cl radical adduct, both of which are produced simultaneously by a radical reaction between S(1) p-terphenyl and carbon tetrachloride, recombine to form the product. The picosecond time-resolved Raman spectrum of the reactant S(1) p-terphenyl shows that the dephasing process for the four vibrational modes at 1640, 1497, 1180, and 1017 cm(-1) is selectively accelerated in carbon tetrachloride. The four vibrational modes probably have a large contribution from the motion of a specific atom or atoms where the intermolecular interaction that induces the bimolecular reaction is present. Copyright (C) 2008 John Wiley & Sons, Ltd.

MISC

 25
  • Wenjuan Xiong, Lili Du, Kin Cheung Lo, Haiting Shi, Tomohisa Takaya, Koichi Iwata, Wai Kin Chan, David Lee Phillips
    JOURNAL OF PHYSICAL CHEMISTRY LETTERS 9(14) 3819-3824 2018年7月  
    Conjugated polymers incorporated with cycloplatinated complexes (P1-Pt and P2-Pt) were used as dispersants for single-walled carbon nanotubes (SWCNTs). Significant changes in the UV-vis absorption spectra were observed after the formation of the polymer/SWCNT hybrids. Molecular dynamics (MD) simulations revealed the presence of a strong interaction between the cycloplatinated complex moieties and the SWCNT surface. The photoinduced electron transfer processes in these hybrids were strongly dependent on the type of the comonomer unit. Upon photoexcitation, the excited P1-Pt donates electrons to the SWCNT, while P2-Pt accepts electrons from the photoexcited SWCNT. These observations were supported by results from Raman and femtosecond time-resolved transient absorption spectroscopy experiments. The strong electronic interaction between the Pt complexes and the SWCNT gives rise to a new hybrid system that has a controllable photoinduced electron transfer flow, which are important in regulating the charge transport processes in SWCNT-based optoelectronic devices.
  • Tomohisa Takaya, Tatsuya Oda, Yuki Shibazaki, Yumiko Hayashi, Hiroaki Shimomoto, Eiji Ihara, Yukihide Ishibashi, Tsuyoshi Asahi, Koichi Iwata
    MACROMOLECULES 51(14) 5430-5439 2018年7月  
    The excited-state dynamics of pyrene incorporated into poly(substituted methylene)s is investigated by picosecond time-resolved fluorescence spectroscopy and femtosecond time-resolved near-IR absorption spectroscopy in the 900-1400 nm region. The pyrene rings in poly (substituted methylene)s are photoexcited to the monomer excited state immediately after UV irradiation, followed by prompt excimer formation with time constants of a few picoseconds to a few hundred picoseconds. The excimer formation in poly(substituted methylene)s proceeds with much shorter time constants than that in pyrene-incorporated polyacrylates, vinyl polymer counterparts with the same side-chain structures, indicating the presence of stronger electronic interaction between the pyrene rings in poly(substituted methylene)s. The effects of every methylene substitution hold when each pyrene ring is connected to the polymer backbone with a monomethylene linker, while the effects are observed only weakly when a tetramethylene linker is employed. The results demonstrate the effectiveness of every methylene substitution in the prompt excimer formation of pyrene connected to the polymer backbone either directly or with the monomethylene linker.
  • B. Narayan, K. Nagura, T. Takaya, K. Iwata, A. Shinohara, H. Shinmori, H. Wang, Q. Li, X. Sun, H. Li, S. Ishihara, T. Nakanishi
    Physical Chemistry Chemical Physics 20(5) 2970-2975 2018年2月7日  
    Novel regioisomeric alkylated-naphthalene liquids were designed and synthesized. In the solvent-free liquid state, 1-alkyloxy regioisomers showed excimeric luminescence, whereas 2-alkyloxy analogues exhibited monomer-rich luminescence features. Correlations among the molecular structures and the photophysical, calorimetric, and rheological properties are presented, demonstrating the impact of regioisomerism on the alkylated-chromophore liquid systems.
  • Koichi Iwata, Masahide Terazima, Hiroshi Masuhara
    Biochimica et Biophysica Acta - General Subjects 1862(2) 335-357 2018年2月1日  
    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.
  • Tomohisa Takaya, Masato Anan, Koichi Iwata
    Physical Chemistry Chemical Physics 20(5) 3320-3327 2018年2月  
    © 2018 the Owner Societies. The electronic and vibrational relaxation of carotenoids is one of the key processes in the protection of living cells as well as in the functions of proteins involved in photosynthesis. In this study, the electronic and vibrational relaxation dynamics of β-carotene and its derivatives with substituents on the terminal rings is investigated using femtosecond time-resolved absorption and stimulated Raman spectroscopy in the near-IR region. The carbonyl substituent induces low-frequency shifts of the steady-state and transient absorption bands, decreases of the excited-state lifetimes and the acceleration of vibrational relaxation of the conjugated main chain, whereas the hydroxyl substituent only slightly affects them. The effects of the carbonyl group in the electronic relaxation dynamics are explained well by the lengthening of effective conjugation by the carbonyl group through a partial conjugation between the main chain and the terminal ring. Time-resolved near-IR stimulated Raman spectroscopy demonstrates the significance of the peripheral substitution with the carbonyl group for the vibrational energy relaxation of β-carotene derivatives in the lowest excited singlet state.
  • Fengniu Lu, Naoki Kitamura, Tomohisa Takaya, Koichi Iwata, Takashi Nakanishi, Yuki Kurashige
    PHYSICAL CHEMISTRY CHEMICAL PHYSICS 20(5) 3258-3264 2018年2月  
    We investigated the fluorescence properties of dialkoxyphenyl-pyrene molecules experimentally as well as theoretically. Our experiments confirmed fluorescence solvatochromism in 2,5-dimethoxyphenylpyrene and, in contrast there was no significant solvent-effect on the emission properties of the isomers, 3,5-and 2,6-dimethoxyphenyl-pyrene. This clear difference in the solvent-dependence would reflect the difference in character of the excited-state between the isomers, which differ only in the substitution positions of the two methoxy groups. The positional effects of the di-substituted molecules are successfully explained theoretically by the topologies of the highest occupied molecular orbital of the phenyl group that are governed by the relative positions of the two substituents, though it is somewhat contradictory to the meta-effect for the mono-substituted molecules. Theoretical calculations were also used to analyze the character of the excited states; 2,5-dimethoxyphenyl-pyrene alone exhibited an intramolecular charge transfer character for the excited state, which was responsible for the solvatochromism effect. The dynamics of the excited states were analyzed using time-resolved fluorescence measurements, in which a characteristic increase of the fluorescence intensity was observed for 2,5-dialkoxyphenyl-pyrene; this observation was supported by the theoretical calculations as well.
  • Ryo Ohtani, Tsukasa Tokita, Tomohisa Takaya, Koichi Iwata, Masanao Kinoshita, Nobuaki Matsumori, Masaaki Nakamura, Leonard F. Lindoy, Shinya Hayami
    CHEMICAL COMMUNICATIONS 53(99) 13249-13252 2017年12月  
    A morphology transformation of hybrid liposomes was shown to occur from spherical vesicles to tubular micelles when increasing the ratio of the metal complex lipid present. Phase transition temperatures increased while viscosities decreased, indicating that the hybrids exhibit stronger interaction between heads but weaker interaction between alkyl chains than occurs in pristine liposomes.
  • Nidhi Dwivedi, Sumit K. Panja, Abhineet Verma, Tomohisa Takaya, Koichi Iwata, Sailaja S. Sunkari, Satyen Saha
    JOURNAL OF LUMINESCENCE 192 156-165 2017年12月  
    Two series of new 3d-4f heterodinuclear [Zn(II)Ln(III)] Schiff base complexes of general formula [Zn(mu-L1)(mu-CH3COO)Ln(NO3)(2)(S)] [Ln = Pr (1), Nd (2), Sm (3), Gd (4); S = MeOH; H(2)L1 = N,N-bis(3-methoxysalicylidene)-1,4-diaminobutane] and [Zn(mu-L-2)(-CH3COO)Ln(NO3)(2)(S)] [Ln = Pr (5), Nd (6), Sm (7), Gd (8), S= MeOH; H(2)L2 = N,N-bis(3-ethoxysalicylidene)-1,4-diaminobutane] are synthesized and fully characterized. Complexes 1, 2, 3, 4, 5 &7 are structurally characterized by single crystal X-ray crystallography. The crystallographic investigation indicates that the complexes contain 9 and 10-coordinated Ln(III) ions, while the Zn-II ions always display a distorted square-pyramidal geometry. The crystal structure of the complexes are stabilized by inter molecular extended hydrogen bonding and C-H....pi interactions resulting in supramolecular frameworks. Luminescence studies for the heterodinuclear compounds containing Nd-III & Sm-III reveal that the Zn-complex moiety acts as antenna for the emission from Ln(III) ions. In addition to the ligand-centered emission in the UV-Vis region, complex 2 (having Nd-III) exhibits emission in NIR region also, thus resulting a new NIR emitting material.
  • Fengniu Lu, Tomohisa Takaya, Koichi Iwata, Izuru Kawamura, Akinori Saeki, Masashi Ishii, Kazuhiko Nagura, Takashi Nakanishi
    SCIENTIFIC REPORTS 7 2017年6月  
    Solvent-free, nonvolatile, room-temperature alkylated-pi functional molecular liquids (FMLs) are rapidly emerging as a new generation of fluid matter. However, precision design to tune their physicochemical properties remains a serious challenge because the properties are governed by subtle pi-pi interactions among functional pi-units, which are very hard to control and characterize. Herein, we address the issue by probing pi-pi interactions with highly sensitive pyrene-fluorescence. A series of alkylated pyrene FMLs were synthesized. The photophysical properties were artfully engineered with rational modulation of the number, length, and substituent motif of alkyl chains attached to the pyrene unit. The different emission from the excimer to uncommon intermediate to the monomer scaled the pyrene-pyrene interactions in a clear trend, from stronger to weaker to negligible. Synchronously, the physical nature of these FMLs was regulated from inhomogeneous to isotropic. The inhomogeneity, unexplored before, was thoroughly investigated by ultrafast time-resolved spectroscopy techniques. The result provides a clearer image of liquid matter. Our methodology demonstrates a potential to unambiguously determine local molecular organizations of amorphous materials, which cannot be achieved by conventional structural analysis. Therefore this study provides a guide to design alkylated-pi FMLs with tailorable physicochemical properties.
  • Tomohisa Takaya, Koichi Iwata
    ANALYST 141(14) 4283-4292 2016年  
    Charge transfer and charge delocalisation processes play key roles in the functions of large biomolecular systems and organic/inorganic devices. Many of the short-lived transients involved in these processes can be sensitively detected by monitoring their low-energy electronic transitions in the near-IR region. Ultrafast time-resolved near-IR Raman spectroscopy is a promising tool for investigating the structural dynamics of the short-lived transients as well as their electronic dynamics. In this study, we have developed a femtosecond time-resolved near-IR multiplex stimulated Raman spectrometer using the Raman pump pulse at 1190 nm and a broadband probe pulse covering the 900-1550 nm region. Spectral and temporal instrument responses of the spectrometer are estimated to be 5 cm(-1) and 120 fs, respectively. Time-resolved near-IR stimulated Raman spectra of poly(3-dodecylthiophene) (P3DDT) are recorded in toluene solution for investigating its structural changes following the photoexcitation. The spectra strongly indicate conformational changes of P3DDT in excited states associated with the elongation of its effective conjugation length. The results on P3DDT fully demonstrate the effectiveness of the newly developed femtosecond time-resolved near-IR stimulated Raman spectrometer.
  • Sandor Kunsagi-Mate, Koichi Iwata
    JOURNAL OF SOLUTION CHEMISTRY 42(1) 165-171 2013年1月  
    The dynamic motions of solvent molecules in the solvation shell of phenols in binary water-ethanol solutions have been examined experimentally by measuring the solvent relaxation times using phase-fluorometry. The results show that the mono-exponential character of the solvent relaxation changes to bi-exponential just after the ethanol content of the bulk solution exceeds a critical value. This value depends on the electron density of the aromatic rings of the phenolic molecules. Above the critical values much higher ethanol content is observed in the solvation shell compared to the bulk solutions. This observation is applicable in wide scale of chemical processes in condensed phase and indicates that further research is needed towards development of a picture at the atomic scale.
  • Nobuyuki Asami, Sohshi Yabumoto, Shinsuke Shigeto, Tomohisa Takaya, Hiro-o Hamaguchi, Koichi Iwata
    CHEMISTRY LETTERS 41(6) 654-656 2012年6月  
    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.
  • Kyousuke Yoshida, Koichi Iwata, Yoshio Nishiyama, Yoshifumi Kimura, Hiro-o Hamaguchi
    JOURNAL OF CHEMICAL PHYSICS 136(10) 104504-1 - 104504-8 2012年3月  
    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]
  • Hiroko Miki, Kyousuke Yoshida, Chieko Kawate, Rintaro Shimada, Tomohisa Takaya, Koichi Iwata, Hiro-o Hamaguchi
    CHEMICAL PHYSICS LETTERS 527 27-30 2012年2月  
    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.
  • Yin Li, Zsolt Csok, Laszlo Kollar, Koichi Iwata, Erzsebet Szasz, Sandor Kunsagi-Mate
    SUPRAMOLECULAR CHEMISTRY 24(6) 374-378 2012年  
    2-Methylresorcinarene and its methylene-bridged cavitand derivative as host compounds were investigated in selective complexation of alkali metal ions as guests in methanol media by photoluminescence measurements. These host molecules possess either flexible (2-methylresorcinarene) or rigid (cavitand) molecular skeleton. The Benesi-Hildebrand method and the van't Hoff theory have been applied to determine the stability constants and the thermodynamic parameters, respectively. Considerable interactions between 2-methylresorcinarene and Li+ or Na+ ions have been observed while the rigid cavitand derivative can interact only with K+ or Cs+ ions. Neither the complexes of 2-methylresorcinarene with K+ or Cs+ nor those of the cavitand derivative with Li+ or Na+ ions are stable at room temperature in methanol media. Quantum-chemical investigations justified that only solvated Li+ and Na+ ions can form stable complexes with 2-methylresorcinarene while unsolvated K+ and Cs+ ions form stable complexes with the methylene-bridged cavitand. These results highlight that the stability of the guest solvation shell and its size could play a key role in the selectivity behaviour of host molecules.
  • Yuki Nojima, Koichi Iwata
    CHEMISTRY-AN ASIAN JOURNAL 6(7) 1817-1824 2011年7月  
    Viscosity inside the lipid bilayer of egg-PC (egg yolk phosphatidylcholine) liposome with a diameter of 100 nm is examined with picosecond time-resolved fluorescence spectroscopy. The viscosity is estimated independently from the photoisomerization rate and from the rotational relaxation time of the first excited singlet state of trans-stilbene solubilized within the lipid bilayer. The presence of two solvation environments within the bilayer is suggested from both of the methods. One environment is 50 to 100 times more viscous than the other. The use of trans-stilbene as a probe provides valuable information on the solvation environments inside the lipid bilayer of liposome, which serves as a field for a number of biochemical reactions.
  • Sandor Kunsagi-Mate, Zsolt Csok, Koichi Iwata, Erzsebet Szasz, Laszlo Kollar
    JOURNAL OF PHYSICAL CHEMISTRY B 115(13) 3339-3343 2011年4月  
    The interaction of phenol guest molecules with 2-methylresorcinarene and its methylene-bridged cavitand derivative has been investigated in methanol. The host molecules were selected according to the flexibility of their cavities by varying the conformational freedom of the molecular skeleton prior to molecular association. The results show stronger host-phenol interactions when the host molecule possesses a rigid molecular skeleton (i.e., cavitand) compared to that of the flexible resorcinarene with phenol. Although the enthalpy change associated with the molecular interactions was found to be the same in both cases, higher negative entropy change was obtained when the resorcinarene interacted with the phenol molecules at room temperature. As a result, stronger host-guest complexes are formed at room temperature when the host molecules, possessing a rigid molecular skeleton, participated in the complex formation. Furthermore, since the higher entropy change results in higher temperature-dependence of the interactions, the stability of the complexes formed with the flexible resorcinarene is smaller at higher temperature. These results highlight that the decreasing flexibility of the host molecular skeleton itself can determine the entropy change during the complexation process; therefore, the temperature dependence of the complex stabilities highly depends on the flexibility of the host's molecular skeleton. This information might contribute to the development of selective and sensitive sensor molecules toward phenol derivatives.
  • Nobuyuki Asami, Tomohisa Takaya, Soshi Yabumoto, Shinsuke Shigeto, Hiro-o Hamaguchi, Koichi Iwata
    JOURNAL OF PHYSICAL CHEMISTRY A 114(22) 6351-6355 2010年6月  
    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.
  • Sandor Kunsagi-Mate, Koichi Iwata
    CHEMICAL PHYSICS LETTERS 473(4-6) 284-287 2009年5月  
    The formation of the solvatation shell of anthracene molecule was investigated in binary mixtures of protic alcoholic solvents by solvent-relaxation measurements, anisotropy decay studies and quantum-chemical modeling. Results show significant change of the solvatation shell of anthracene dissolved in binary solutions of methanol, ethanol or n-propanol with n-butanol when the molar fraction of n-butanol in the bulk solution exceeds a critical value. Both the solvent relaxation and anisotropy decay data suggest clusterization process in the solvatation shell of the anthracene probe. Quantum chemical calculation supports formation of energetically preferred heteromolecular (X(2)(BuOH)(2), X = MeOH, EtOH or PrOH) clusters around the solute. (c) 2009 Elsevier B.V. All rights reserved.
  • Motohiro Banno, Koichi Iwata, Hiro-o Hamaguchi
    JOURNAL OF PHYSICAL CHEMISTRY A 113(6) 1007-1011 2009年2月  
    The rate of vibrational energy relaxation (VER) is a valuable probe of microscopic intermolecular interaction. In the present article, the VER rate of the T-1u CO stretch of W(CO)(6) is measured in binary solutions composed of ail alkane (hexane, decane, tetradecane) and cyclohexane or CCl4, with seven mixing volume ratios. The volume ratio dependence indicates that, among the three alkane-cyclohexane solutions, only decane shows ail exceptionally strong contribution to the VER process. It is strongly suggested that decane forms a specific solute-solvent complex with W(CO)(6). The "V-shaped" dependence of the VER rate on the number of carbons in alkane solvents (Banno, M.; Sato, S.; Iwata, K.; Hamaguchi, H. Client. Phys. Lett. 2005, 412, 464.) is explained by the solute-solvent complex model. There are no experimental results that suggest the formation of the specific solute-solvent complex in alkane-CCl4 solutions.
  • Tomohisa Takaya, Hiro-o Hamaguchi, Koichi Iwata
    JOURNAL OF CHEMICAL PHYSICS 130(1) 014501-1-014501-9 2009年1月  
    Femtosecond time-resolved absorption anisotropy spectroscopy by multichannel detection has been developed. The charge transfer (CT) character and dynamics of the UV-photoexcited 9,9(')-bianthryl (BA) in heptane, acetonitrile, and ethanol are revealed with this method. The transient absorption spectra are decomposed into two absorption components with different anisotropy values by the absorption anisotropy spectra. The decomposition results show two absorption bands having different anisotropy values or different directions of the transition dipole moment. One band that has the transition dipole perpendicular to the central C-C bond has almost an identical spectral shape with transient absorption of anthracene in the singlet excited state. This band is assigned to a transition in a locally excited anthracene ring. The other band is broad and structureless. This band is assigned to partial charge transfer (PCT) absorption because its transition dipole moment is parallel to the central C-C bond. Because the PCT band is observed in a nonpolar solvent heptane as well as in polar solvents, the PCT occurs in both nonpolar and polar solvents. The PCT band rises within the instrumental response, indicating that the PCT takes place immediately after the photoexcitation. In acetonitrile, the CT component shows a significant blueshift, indicating the formation of the stabilized CT state from the PCT state. In ethanol, the CT band does not show a spectral shift, suggesting that the stabilization is smaller than in acetonitrile. From these results, a new kinetic model on the intramolecular CT in BA is discussed.
  • IWATA KOICHI
    Reniew of Scientific Instrnments 64 2140 1993年  
  • K IWATA, H HAMAGUCHI
    APPLIED SPECTROSCOPY 44(9) 1431-1437 1990年11月  

講演・口頭発表等

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