Browsing by Author "Shigeto, Shinsuke"

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Anharmonic coupling of the CH-stretch and CH-bend vibrations of chloroform as studied by near-infrared electroabsorption spectroscopy
(2012-12-21)
Nishida, Jun
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Shigeto, Shinsuke
;
Yabumoto, Sohshi
;
Hamaguchi, Hiro-o
;
應用化學系
Combination bands that involve CH- or OH-stretch vibrations appear in the near-infrared (NIR) region (4000-10 000 cm(-1)). Because they arise from anharmonic coupling between the component fundamentals, detailed analysis of the frequency and intensity of NIR combination bands allows one to elucidate the mechanisms behind the vibrational coupling in the condensed phase in terms of mechanical and electrical anharmonicities. Nevertheless, little has been studied, in particular experimentally, on the origin of the combination band intensity. Here, we show that NIR electroabsorption (EA) spectroscopy, which directly probes the effects of an externally applied electric field on a combination band, can shed new light on anharmonic vibrational coupling through determination of the direction of the transition moment for the combination band. We studied the combination band of the CH-stretch (nu(1)) and CH-bend (nu(4)) modes of liquid chloroform. The electric-field induced absorbance change of the nu(1) + nu(4) combination band caused by reorientation of the chloroform molecule was measured at various chi angles, where chi is the angle between the direction of the applied electric field and the polarization of the incident IR light. We were able to detect an absorbance change as small as 5 x 10(-8) for the combination band. Using the NIR EA spectra of the combination band together with those of the CH-stretch and bend fundamentals, the angle between the transition moment for the combination band and the permanent dipole moment was determined experimentally for the first time to be (79 +/- 14)degrees. The present investigation indicates that the contribution of the CH-stretch mode to the mechanical anharmonicity is minor and that the CH-bend mode plays a dominant role in the mechanical part of the vibrational coupling between the two fundamentals. Furthermore, density functional theory calculations show that both the mechanical anharmonicity of the CH-bend mode and the electrical anharmonicity may contribute equally to the anharmonic coupling. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4770264]
Biothiol-triggered, self-disassembled silica nanobeads for intracellular drug delivery
(2015-09-01)
Huang, Xin-Chun
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Wu, Li-Bang
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Hsu, Jen-Fang
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Shigeto, Shinsuke
;
Hsu, Hsin-Yun
Silica-based nanomaterials have demonstrated great potential in biomedical applications due to their chemical inertness. However, the degradability and endosomal trapping issues remain as rate-limiting barriers during their innovation. In this study, we provide a simple yet novel sol-gel approach to construct the redox-responsive silica nanobeads (ReSiNs), which could be rapidly disassembled upon redox gradient for intracellular drug delivery. The disulfide-linked scaffold of the nanobead was synthesized by employing the dithiobis-(succinimidyl propionate) to bridge (3-aminopropyI)-trimethoxysilane. Such silica matrix could be efficiently disrupted in response to intracellular glutathione, resulting in drug release and collapse of entire nanocarrier. Moreover, the ReSiNs exhibited insignificant cytotoxicity before and after the degradation. These results indicated the potential of using ReSiNs as a novel silica-based, biothiol-degradable nanoplatform for future drug delivery. (C) 2015 Acts Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Complementing Crystallography with Ultralow-Frequency Raman Spectroscopy: Structural Insights into Nitrile-Functionalized Ionic Liquids
(2016-01-04)
Chen, Hong-Kai
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Srivastava, Nitin
;
Saha, Satyen
;
Shigeto, Shinsuke
;
應用化學系
Functionalized ionic liquids are a subclass of ionic liquids that are tailored for a specific application. Structural characterization in both solid and liquid phases is central to understanding their physical properties. Here, we used ultralow-frequency Raman spectroscopy, which can measure Raman spectra down to approximately 5cm(-1), to study the structures and physical properties of 1-(4-cyanobenzyl)-3-methylimidazolium salts with five different anions. A comparison of the observed low-frequency Raman spectral patterns enabled us to predict the crystal symmetry of one of the synthesized salts for which single-crystal X-ray diffraction data were unobtainable. Real-time tracking of the low-frequency Raman spectral changes during melting revealed peak shifts indicative of different degrees of microscopic heterogeneity in the ionic liquids. The results show that our method provides a facile means that is complementary to X-ray crystallography, for obtaining structural information of ionic liquids.
Correlation of Carotenoid Accumulation with Aggregation and Biofilm Development in Rhodococcus sp SD-74
(2013-08-06)
Zheng, Yi-Ting
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Toyofuku, Masanori
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Nomura, Nobuhiko
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Shigeto, Shinsuke
;
應用化學系
Aggregation of bacterial populations substantially influences their characteristic properties and functions compared with the planktonic counterpart. It is also involved in the initial stages of biofilm development. Many studies have revealed important roles of bacterial aggregation in microbial production and biodegradation. Nevertheless, mechanistic understanding of bacterial aggregation in vivo and at the molecular level is far from complete. Here, we present a noninvasive, label-free Raman microspectroscopic approach to investigate the aggregation and biofilm development of the biotechnologically important Rhodococcus sp. SD-74. We found that the concentration of intracellular carotenoids increases more than 3-fold within 1 week as the biofilm develops. Raman imaging experiments confirmed that the carotenoid accumulation occurs throughout the Rhodococcus sp. SD-74 biofilm. The correlation between the carotenoid Raman intensities and biofilm development found in the present study provides a new means for quantitative, molecular-level assessment of the level of biofilm development, which is not possible with dye staining assay or electron microscopy. Moreover, our results suggest that microbial production of carotenoids in pigmented bacteria such as Rhodococcus sp. SD-74 may potentially be controlled via bacterial aggregation and biofilm formation.
Direct Observation of the Solvent Effects on the Low-Lying ne and pi pi* Excited Triplet States of Acetophenone Derivatives in Thermal Equilibrium
(2015-03-05)
Narra, Sudhakar
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Shigeto, Shinsuke
;
應用化學系
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應用化學系分子科學碩博班
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Department of Applied Chemistry
Low-lying excited triplet states of aromatic carbonyl compounds exhibit diverse photophysical and photochemical properties of fundamental importance. Despite tremendous effort in studying those triplet states, the effects of substituents and solvents on the energetics of the triplet manifold and on photoreactivity remain to be fully understood. We have recently studied the ordering of the low-lying n pi* and pi pi* excited triplet states and its substituent dependence in acetophenone derivatives using nanosecond time-resolved near-IR (NIR) spectroscopy. Here we address the other important issue, the solvent effects, by directly observing the electronic bands in the NIR that originate from the lowest n pi* and pi pi* states of acetophenone derivatives in four solvents of different polarity (n-heptane, benzene, acetonitrile, and methanol). The two transient NIR bands decay synchronously in all the solvents, indicating that the lowest n pi* and pi pi* states are in thermal equilibrium irrespective of the solvent polarity studied here. We found that the pi pi* band increases in intensity relative to the n pi* band as solvent polarity increases. These results are compared with the photoreduction rate constant for the acetophenone derivatives in the solvents to which 2-propanol was added as a hydrogen-atom donor. Based on the present findings, we present a comprehensive, solvent- and substituent-dependent energy level diagram of the low-lying n pi* and pi pi* excited triplet states.
Directly Probing Intermolecular Structural Change of a Core Fragment of beta(2)-Microglobulin Amyloid Fibrils with Low-Frequency Raman Spectroscopy
(2017-01-26)
Shigeto, Shinsuke
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Chang, Chun-Fu
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Hiramatsu, Hirotsugu
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應用化學系
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Department of Applied Chemistry
Amyloid fibrils, which are ordered aggregates of proteins or peptides, have attracted keen interest because their deposition causes serious human diseases. Despite many studies utilizing X-ray crystallography, solid-state NMR, and other methods, intermolecular interactions governing the fibril formation remain largely unclear. Here, we used low-frequency Raman (LFR) spectroscopy to investigate the intermolecular beta-sheet structure of a core fragment of beta(2)-microglobulin amyloid fibrils, beta(2)m(21-29), in aqueous buffer solutions. The LFR spectra (approximately 10-200 cm(-1)) of beta(2)m(21-29) amyloid fibrils measured at different pH values (ranging from 6.8 to 8.0) revealed a broad-spectral pattern with a maximum at similar to 80 cm(-1) below pH 7.2 and at similar to 110 cm(-1) above pH 7.4. This observation is attributed to a pH-dependent structural change from an antiparallel to a parallel intermolecular beta-sheet structure. Multivariate curve resolution-alternating least-squares (MCR-ALS) analysis enabled us to decompose the apparently monotonous LFR spectra into three distinctly different contributions: intermolecular vibrations of the parallel and antiparallel beta-sheets and intramolecular vibrations of the peptide backbone. Peak positions of the obtained LFR bands not only exhibit a much more pronounced difference between the two beta-sheets than the conventional amide I band, but they also suggest stronger intermolecular interaction, due presumably to the hydrophobic effect, in the parallel beta-sheet than in the antiparallel beta-sheet. The present results show that LFR spectroscopy in combination with the MCR-ALS analysis holds promise for real-time tracking of the intermolecular dynamics of amyloid fibril formation under physiological conditions.
Disentangling Dynamic Changes of Multiple Cellular Components during the Yeast Cell Cycle by in Vivo Multivariate Raman Imaging
(2012-07-03)
Huang, Chuan-Keng
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Ando, Masahiro
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Harnaguchi, Hiro-o
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Shigeto, Shinsuke
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應用化學系
Cellular processes are intrinsically complex and dynamic, in which a myriad of cellular components including nucleic acids, proteins, membranes, and organelles are involved and undergo spatiotemporal changes. Label-free Raman imaging has proven powerful for studying such dynamic behaviors in vivo and at the molecular level. To construct Raman images, univariate data analysis has been commonly employed, but it cannot be free from uncertainties due to severely overlapped spectral information. Here, we demonstrate multivariate curve resolution analysis for time-lapse Raman imaging of a single dividing yeast cell. A four-dimensional (spectral variable, spatial positions in the two-dimensional image plane, and time sequence) Raman data "hypercube" is unfolded. to a two-way array and then analyzed globally using multivariate curve resolution. The multivariate Raman imaging thus accomplished successfully disentangles dynamic changes of both concentrations and distributions of major cellular components (lipids, proteins, and polysaccharides) during the cell cycle of the yeast cell. The results show a drastic decrease in the amount of lipids by similar to 50% after cell division and uncover a protein-associated component that has not been detected with previous univariate approaches.
Evidence of C-F-P and aromatic pi-F-P weak interactions in imidazolium ionic liquids and its consequences
(2018-04-05)
Panja, Sumit Kumar
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Srivastava, Nitin
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Srivastava, Jyoti
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Prasad, Namburi Eswara
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Noothalapati, Hemanth
A simple change from alkyl group to alkene in side chain of imidazolium cation with same anion resulted in a drastic impact on physical properties (e.g., melting point) from bmimPF(6) IL to cmimPF(6) IL The underlying reasons have been elucidated by structural and interaction studies with the help of DSC, SCXRD, vibrational and multi-nuclear NMR spectroscopic techniques. Experiments reveal existence of new weak interactions involving the carbon and pi cloud of the imidazolium aromatic ring with fluoride of PF6 anion (i.e., C-2-F-P and pi-F-P) in cmimPF(6) but are absent in structurally similar prototype IL bmimPF(6). Though weak, these interactions helped to form ladder type supramolecular arrangement, resulting in quite high melting point for cmimPF(6) IL compared to bmimPF(6) IL These findings emphasize that an IL system can behave uniquely because of the existence of uncommon weak interactions. (C) 2017 Elsevier B.V. All rights reserved.
Exploring Metabolic Pathways in Vivo by a Combined Approach of Mixed Stable Isotope-Labeled Raman Microspectroscopy and Multivariate Curve Resolution Analysis
(2014-08-05)
Noothalapati, Hemanth
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Shigeto, Shinsuke
;
應用化學系
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應用化學系分子科學碩博班
;
Department of Applied Chemistry
Understanding cellular metabolism is a major challenge in current systems biology and has triggered extensive metabolomics research, which in most cases involves destructive analysis. However, the information obtainable only in a nondestructive manner will be required for accurately mapping the global structure of the organism's metabolic network at a given instant. Here we report that metabolic pathways can be explored in vivo by mixed stable isotope-labeled Raman microspectroscopy in conjunction with multivariate curve resolution analysis. As a model system, we studied ergosterol biosynthesis in single living fission yeast cells grown in mixtures of normal and C-13-labeled glucose as the sole carbon source. The multivariate spectral data analysis of space-resolved Raman spectra revealed the intrinsic spectra and relative abundances of all isotopomers of ergosterol whose carbon atoms in the 5,7-diene moiety of the sterol skeleton are either partly or fully substituted with C-13. Our approach is applicable to other metabolites and will earn a place in the toolbox of metabolomic analysis.
Exploring Metabolic Pathways in Vivo by a Combined Approach of Mixed Stable Isotope-Labeled Raman Microspectroscopy and Multivariate Curve Resolution Analysis
(2014-08-05)
Noothalapati, Hemanth
;
Shigeto, Shinsuke
;
應用化學系
;
應用化學系分子科學碩博班
;
Department of Applied Chemistry
Understanding cellular metabolism is a major challenge in current systems biology and has triggered extensive metabolomics research, which in most cases involves destructive analysis. However, the information obtainable only in a nondestructive manner will be required for accurately mapping the global structure of the organism\'s metabolic network at a given instant. Here we report that metabolic pathways can be explored in vivo by mixed stable isotope-labeled Raman microspectroscopy in conjunction with multivariate curve resolution analysis. As a model system, we studied ergosterol biosynthesis in single living fission yeast cells grown in mixtures of normal and C-13-labeled glucose as the sole carbon source. The multivariate spectral data analysis of space-resolved Raman spectra revealed the intrinsic spectra and relative abundances of all isotopomers of ergosterol whose carbon atoms in the 5,7-diene moiety of the sterol skeleton are either partly or fully substituted with C-13. Our approach is applicable to other metabolites and will earn a place in the toolbox of metabolomic analysis.
Imaging molecular crystal polymorphs and their polycrystalline microstructures in situ by ultralow-frequency Raman spectroscopy
(2014-01-01)
Chang, Chun-Fu
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Okajima, Hajime
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Hamaguchi, Hiro-o
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Shigeto, Shinsuke
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應用化學系
Ultralow-frequency Raman spectroscopy that can measure vibrational bands at as low as +/- 10 cm(-1) has enabled facile in situ imaging of polycrystalline microstructures such as grains and grain boundaries with high polymorph specificity. We demonstrate this method by investigating microcrystals of two distinct polymorphs of 1,1\'-binaphthyl using a microscope.
Importance of weak interactions and conformational equilibrium in N-butyl-N-methylpiperidinium bis(trifluromethanesulfonyl) imide room temperature ionic liquids: Vibrational and theoretical studies
(2014-11-01)
Shukla, Madhulata
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Noothalapati, Hemanth
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Shigeto, Shinsuke
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Saha, Satyen
;
應用化學系
Piperidinium cation-based room temperature ionic liquids (RTILs) constitute an important class of ILs because of their unique electrochemical properties as well as non-aromatic nature of the cation. However, detailed structural studies are yet to be done. In this paper, we discuss the molecular structure and vibrational spectra of N-butyl-N-methylpiperidinium bis(trifluromethanesulfonyl) imide, (PIP14NTf2; where, PIP14 is N-butyl-N-methylpiperidinium and NTf2 is bis(trifluromethanesulfonyl) imide), obtained with a combined approach of infrared (IR) and Raman spectroscopies in the liquid state and density functional theory (DFT) and Hartree-Fock (H-F) based theoretical calculations. DFT calculations, which are found to produce the most stable geometry compared to other two methods (MP2 and H-F), reproduce the experimental IR and Raman spectra reasonably well. Our findings reveal structural properties that profoundly influence intermolecular interactions and melting point. There exists a large variation in the melting point of the ILs studied. While the bromide salt of the piperidinium derivative (PIP14Br) is solid with very high melting point (241 degrees C), the corresponding NTf2 salt is low viscous liquid at room temperature (mp: -25 degrees C). bmimBr (bmim = 1-butyl-1-methylimidazolium) exhibits a substantially lower melting point of 79 degrees C than PIP14Br, suggesting that more number of strong classical hydrogen bonding interactions in the latter is primarily responsible for the much higher melting point. In addition, involvement of the alkyl group in PIP14 in H-bonding interaction provides additional rigidity in n-butyl chain which is otherwise absent in bmimBr. Interaction energy for PIP14Br is found to be higher than PIP14NTf2, showing a positive correlation between interaction energy and melting point. A blue shift in C-H stretching wavenumber as evident from IR and Raman spectra of PIP14Br IL is a clear indication of the stronger hydrogen bonding as compared to PIP14NTf2 IL. Furthermore, we experimentally observe the existence of cisoid-transoid conformational equilibrium of NTf2- anion in the Raman spectrum of PIP14NTf2 for the first time and determined that transoid NTf2- anion to be more stable than the corresponding cisoid conformer by 1.04 kcal/mol using DFT. Examination of various conformational possibilities of the cation shows that the butyl group preferentially exists in gauche conformation. (C) 2014 Elsevier B.V. All rights reserved.
In Situ Ultralow-Frequency Raman Tracking of the Polymorphic Transformation of Crystalline 1,1 '-Binaphthyl
(2014-02-06)
Chang, Chun-Fu
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Wang, Szu-Cheng
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Shigeto, Shinsuke
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應用化學系
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Department of Applied Chemistry
Extremely low-frequency (LF) Raman spectroscopy that allows for fast access to lattice vibrations with little hindrance of immense Rayleigh scattering was used to track in situ thermally induced polymorphic transformation of crystalline 1,1'-binaphthyl (BN), a fundamental structural unit of specific chiral ligands. BN occurs in two conformational polymorphs, cisoid and transoid forms, with the former being a racemate and the latter being a conglomerate of chiral crystals. Observed LF Raman spectra (from 200 cm(-1) down to similar to 5 cm(-1), equivalent to 0.15 THz), which arise predominantly from lattice vibrations, show markedly different features between the cisoid and transoid forms, making it possible to study their phase transition. A series of LF Raman spectra measured with slow heating of microcrystalline BN reveal that, in contrast to previous studies, the monoclinic cisoid form transforms directly to the tetragonal transoid form in the solid state without formation of any intermediate phase. The present approach is applicable to various phase transition systems, including pharmaceutical compounds, liquid crystals, and polymer films, which conventional X-ray diffraction analysis may not be able to investigate.
In vivo multimode Raman imaging reveals concerted molecular composition and distribution changes during yeast cell cycle
(2011)
Huang, Chuan-Keng
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Hamaguchi, Hiro-o
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Shigeto, Shinsuke
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應用化學系
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應用化學系分子科學碩博班
In vivo time-lapse Raman imaging reveals highly dynamic and concerted changes in concentration and distribution of phospholipids and proteins during and after cell division of a single living Schizosaccharomyces pombe cell.
In Vivo Probing of the Temperature Responses of Intracellular Biomolecules in Yeast Cells by Label-Free Raman Microspectroscopy
(2013-05-27)
Chiu, Yu-Fang
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Huang, Chuan-Keng
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Shigeto, Shinsuke
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應用化學系
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應用化學系分子科學碩博班
Environmental temperature is an essential physical quantity that substantially influences cell physiology by changing the equilibria and kinetics of biochemical reactions occurring in cells. Although it has been extensively used as a readily controllable parameter in genetic and biochemical research, much remains to be explored about the temperature responses of intracellular biomolecules in vivo and at the molecular level. Here we report in vivo probing, achieved with label-free Raman microspectroscopy, of the temperature responses of major intracellular components such as lipids and proteins in living fission yeast cells. The characteristic Raman band at 1602 cm1, which has been attributed mainly to ergosterol, showed a significant decrease (approximate to 47%) in intensity at elevated temperatures above 35 degrees C. In contrast to this high temperature sensitivity of the ergosterol Raman band, the phospholipid and protein Raman bands did not vary much with increasing culture temperature in the 2638 degrees C range. This finding agrees with a previous biochemical study that showed that the initial stages of ergosterol biosynthesis in yeast are hindered by temperature elevation. Moreover, our result demonstrates that Raman microspectroscopy holds promise for elucidation of temperature-dependent cellular activities in living cells, with a high molecular specificity that the commonly used fluorescence microscopy cannot offer.
Infrared Electroabsorption Spectroscopy of N,N-Dimethyl-p-nitroaniline in Acetonitrile/C(2)Cl(4): Solvation of the Solute and Self-Association of Acetonitrile
(2011-05-05)
Wang, Wei-Chieh
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Shigeto, Shinsuke
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應用化學系
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應用化學系分子科學碩博班
;
Department of Applied Chemistry
Solvated structures of N,N-dimethyl-p-nitroaniline (DMPNA), an analog of p-nitroaniline (PNA), and self-associated structures of acetonitrile (ACN) in mixed solvents of ACN and C(2)Cl(4) were studied using infrared (IR) electroabsorption and FTIR spectroscopies. IR electroabsorption spectroscopy measures changes in IR absorption intensity upon application of external electric field modulation, which are a sensitive probe for permanent dipole moments. In ACN/CCl(4), PNA has been shown to occur as two distinct solvated forms, namely, 1:1 and 1:2 forms, which have one and two ACN molecule(s), respectively, associated with PNA. The IR electroabsorption and FTIR measurements on DMPNA show that, unlike PNA, DMPNA occurs as a monomer in ACN/C(2)Cl(4) rather than as specific solvated structures analogous to the 1:1 and 1:2 forms because of the substitution effect. Not only does the N, N-dimethyl substitution in DMPNA hamper solvation of ACN at the N(CH(3))(2) group, but it also indirectly blocks strong interactions with ACN at the NO(2) group. Furthermore, by using the AA signal of DMPNA as an internal intensity standard, it was found that the dipole moment of ACN in the DMPNA/ACN/C(2)Cl(4) system is about 1.5 times larger than that of the ACN monomer in dilute CCl(4) solution. This large value of the dipole moment in the solution studied here is attributable to the formation of a head-to-tail linear dimer of ACN, whereas the antiparallel dimer is energetically more favorable in the gas phase.
Infrared Electroabsorption Spectroscopy of N,N-Dimethyl-p-nitroaniline in Acetonitrile/C2Cl4: Solvation of the Solute and Self-Association of Acetonitrile
(2011-05-05)
Wang, Wei-Chieh
;
Shigeto, Shinsuke
;
應用化學系
;
應用化學系分子科學碩博班
;
Department of Applied Chemistry
Solvated structures of N,N-dimethyl-p-nitroaniline (DMPNA), an analog of p-nitroaniline (PNA), and self-associated structures of acetonitrile (ACN) in mixed solvents of ACN and C2Cl4 were studied using infrared (IR) electroabsorption and FTIR spectroscopies. IR electroabsorption spectroscopy measures changes in IR absorption intensity upon application of external electric field modulation, which are a sensitive probe for permanent dipole moments. In ACN/CCl4, PNA has been shown to occur as two distinct solvated forms, namely, 1:1 and 1:2 forms, which have one and two ACN molecule(s), respectively, associated with PNA. The IR electroabsorption and FTIR measurements on DMPNA show that, unlike PNA, DMPNA occurs as a monomer in ACN/C2Cl4 rather than as specific solvated structures analogous to the 1:1 and 1:2 forms because of the substitution effect. Not only does the N, N-dimethyl substitution in DMPNA hamper solvation of ACN at the N(CH3)(2) group, but it also indirectly blocks strong interactions with ACN at the NO2 group. Furthermore, by using the AA signal of DMPNA as an internal intensity standard, it was found that the dipole moment of ACN in the DMPNA/ACN/C2Cl4 system is about 1.5 times larger than that of the ACN monomer in dilute CCl4 solution. This large value of the dipole moment in the solution studied here is attributable to the formation of a head-to-tail linear dimer of ACN, whereas the antiparallel dimer is energetically more favorable in the gas phase.
Inter- and Intragrain Inhomogeneity in 2D Perovskite Thin Films Revealed by Relative Grain Orientation Imaging Using Low-Frequency Polarized Raman Microspectroscopy
(2020-05-21)
Toda, Shogo
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Yanagita, Naoya
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Jokar, Effat
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Diau, Eric Wei-Guang
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Shigeto, Shinsuke
Two-dimensional (2D) organic-inorganic hybrid lead halide perovskites make up an emerging class of semiconductor materials for optoelectronic applications such as solar cells. The grain structure of polycrystalline 2D perovskites is one of the key factors that dictate their functionality in the devices, but currently available methods for in situ, chemically specific characterization of 2D perovskite grains are scarce. Here we show that ultra-low-frequency polarized Raman microspectroscopy is a facile yet powerful tool for visualizing relative grain orientations within 2D perovskite thin films. We demonstrate this method on the simplest 2D perovskite, (CH3(CH2)(3)NH3)(2)PbI4. Hierarchical clustering and detailed band decomposition analysis of the low-frequency polarized Raman imaging data reveal not only relative grain orientations but also intragrain inhomogeneity. We envisage that with high chemical specificity, this method will find broad applications ranging from other 2D perovskites to perovskite-based optoelectronic devices.
Is Our Way of Thinking about Excited States Correct? Time-Resolved Dispersive IR Study on p-Nitroaniline
(2012-02-01)
Narra, Sudhakar
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Chang, Shu-Wei
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Witek, Henryk A.
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Shigeto, Shinsuke
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應用化學系
Low-lying excited electronic states of an important class of molecules known as pushpull chromophores are central to understanding their potential nonlinear optical properties. Here we report that a combination of high-sensitivity nanosecond time-resolved dispersive IR spectroscopy and DFT calculations on p-nitroaniline (PNA), a prototypical pushpull molecule, reveals that PNA in the lowest excited triplet state has a partial quinoid structure. In this structure, the quinoid configuration is restricted to a part of the phenyl ring adjacent to the NO2 group. The partial quinoid structure of PNA cannot be explained by a commonly used hybrid of a neutral form and a zwitterionic charge-transfer form. Our findings not only cast doubt on the general applicability of the classical way of looking at excited states, based exclusively on characteristic resonance structures, but also provide deeper insights into excited-state structure of highly polarizable molecular systems.
Leucine pools in Escherichia coli biofilm discovered by Raman imaging
(2011-11-01)
Venkata, Hemanth Nag Noothalapati
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Nomura, Nobuhiko
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Shigeto, Shinsuke
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應用化學系
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應用化學系分子科學碩博班
In structured communities of bacteria known as biofilms, a variety of biomolecules have been shown to play a unique role as signals and/or regulators in biofilm formation. Here, we report that high levels of the amino acid leucine ( leucine pool) were detected, for the first time, within microcolonies in a 30-h-old Escherichia coli biofilm by Raman imaging. Localization of leucine revealed by multifrequency Raman images indicates leucine accumulation during the early stage of the E. coli biofilm formation, which may have resulted from physiological environment-specific metabolic adaptation. We demonstrate that our label-free Raman imaging method provides a useful platform for directly identifying still unknown natural products produced in biofilms as well as for visualizing heterogeneous distributions of biofilm constituents in situ. Copyright (C) 2011 John Wiley & Sons, Ltd.