Hiroharu Yui

High-capacity Si–graphite composite electrodes with a self-formed porous structure by a partially neutralized polyacrylate for Li-ion batteries

NaOH-neutralized poly(acrylic acid) is examined as a binder for Si-based negative electrodes in rechargeable Li-ion batteries. To better understand the influence of polymer binder characteristics, the impact of neutralization degree (ND) of poly(acrylic acid) (PAH) on electrode performance of a Si–graphite composite is studied. The electrode performance of the Si-based composites is remarkably improved by appropriate neutralization of PAH because the NDs highly influence rheological properties of a slurry and thus the electrode morphology, such as porosity. It is found that 80% neutralized PAH provides the moderate porous structure inside the composite electrode with 10 wt% binder content because of a unique rheological property during the drying process after casting the slurry onto a current collector. The self-formed porous structure by the partially neutralized PAH is beneficial to buffer volume expansion caused by lithiation of Si. Therefore, an excellent capacity retention for a 100 cycle test with a high reversible capacity of approximately 1000 mA h g−1 is achieved with the 80% neutralized PAH as a binder for Si-based composite electrodes.

Polyacrylate modifier for graphite anode of lithium-ion batteries

Polyacrylates were applied as a binder of graphite electrode in a lithium-ion cell to modify the interface. Compared to a conventional binder, poly(vinylidene fluoride), the efficiency at the initial cycle was improved by poly(acrylic acid) and alkali polyacrylates in an ethylene carbonate (EC)-based electrolyte with highly reversible lithium intercalation. In a LiClO 4 propylene carbonate (PC) solution, the poly(vinylidene fluoride) electrode showed a huge irreversible capacity as is generally known. However, the polyacrylate-modified graphite demonstrated highly reversible lithium intercalation in the PC electrolyte containing no film-forming additives as well as in the EC electrolyte due to the interfacial modification with polyacrylates.

Confinement Effect of Organic Nanotubes Toward Green Fluorescent Protein (GFP) Depending on the Inner Diameter Size

Transportation, release behavior, and stability of a green fluorescent protein (GFP, 3x4 nm) in self-assembled organic nanotubes with three different inner diameters (10, 20, and 80 nm) have been studied in terms of novel nanocontainers. Selective immobilization of a fluorescent acceptor dye on the inner surface enabled us to not only visualize the transportation of GFP in the nanochannels but to also detect release of the encapsulated GFP to the bulk solution in real time, based on fluorescence resonance energy transfer (FRET). Obtained diffusion constants and release rates of GFP markedly decreased as the inner diameter of the nanotubes was decreased. An endo-sensing procedure also clarified the dependence of the thermal and chemical stabilities of the GFP on the inner diameters. The GFP encapsulated in the 10 nm nanochannel showed strong resistance to heat and to a denaturant. On the other hand, the 20 nm nanochannel accelerated the denaturation of the encapsulated GFP compared with the rate of denaturation of the free GFP in bulk and the encapsulated GFP in the 80 nm nanochannels. The confinement effect based on rational fitting of the inner diameter to the size of GFP allowed us to store it stably and without denaturation under high temperatures and high denaturant concentrations.

Organocatalytic, Enantioselective Intramolecular [6 + 2] Cycloaddition Reaction for the Formation of Tricyclopentanoids and Insight on Its Mechanism from a Computational Study

Diphenylprolinol silyl ether was found to be an effective organocatalyst for promoting the asymmetric, catalytic, intramolecular [6 + 2] cycloaddition reactions of fulvenes substituted at the exocyclic 6-position with a δ-formylalkyl group to afford synthetically useful linear triquinane derivatives in good yields and excellent enantioselectivities. The cis-fused triquinane derivatives were obtained exclusively; the trans-fused isomers were not detected among the reaction products. The intramolecular [6 + 2] cycloaddition occurs between the fulvene functionality (6π) and the enamine double bond (2π) generated from the formyl group in the substrates and the diphenylprolinol silyl ether. The absolute configuration of the reaction products was determined by vibrational circular dichroism. The reaction mechanism was investigated using molecular orbital calculations, B3LYP and MP2 geometry optimizations, and subsequent single-point energy evaluations on model reaction sequences. These calculations revealed the following: (i) The intermolecular [6 + 2] cycloaddition of a fulvene and an enamine double bond proceeds in a stepwise mechanism via a zwitterionic intermediate. (ii) On the other hand, the intramolecular [6 + 2] cycloaddition leading to the cis-fused triquinane skeleton proceeds in a concerted mechanism via a highly asynchronous transition state. (iii) The fulvene functionality and the enamine double bond adopt the gauche-syn conformation during the C-C bond formation processes in the [6 + 2] cycloaddition. (iv) The energy profiles calculated for the intramolecular reaction explain the observed exclusive formation of the cis-fused triquinane derivatives in the [6 + 2] cycloaddition reactions. The reasons for the enantioselectivity seen in these [6 + 2] cycloaddition reactions are also discussed.

Fluorescence lifetime probe for solvent microviscosity utilizing anilinonaphthalene sulfonate.

The correlation between the fluorescent dynamics of excited anilinonaphthalene sulfonate (ANS) and the microviscosity of solvent molecules surrounding ANS is investigated by time-resolved fluorescence spectroscopy. ANS has been widely used to probe the local hydrophobicity due to the drastic change in its intensity. It is revealed that the fluorescence lifetime from the charge transfer (CT) state of ANS sensitively reflects the microviscosity. The higher sensitivity of 2,6-ANS than of 1,8-ANS demonstrates that the spatial freedom of the rotating phenylamino group in the photoexcited ANS is an important factor that determines the sensitivity. As an application, the measurements of the microviscosity of water in biologically important systems, such as hyaluronan, gellan gum, and gelatin aqueous solutions are also presented. The present results suggest that the fluorescence lifetime of ANS enables the estimation of the solvent microviscosity and provide a useful probe molecule for fluorescence lifetime imaging microscopy.

Spectroscopic analysis of total-internal-reflection stimulated Raman scattering from the air/water interface under the strong focusing condition

Abstract Anomalous enhancement of stimulated Raman scattering (SRS) derived from the OH stretching vibration of interfacial water molecules is observed when excess electrons are generated at an air/water interface by focusing an intense pulsed beam under a total internal reflection configuration. The characteristic SRS peak appears at 3200 cm −1 and is attributed to the water molecules being in an ice-like hydrogen-bonding environment at the interface. The mechanism of the SRS enhancement is discussed in terms of the enhancement of the nonlinear polarizability of the interfacial water by the large electrostatic fields induced by the transiently generated excess electrons at the interface.

Single bilayered organic nanotubes: anchors for production of a reusable catalyst with nickel ions

Organic nanotubes self-assembled from lipid compounds facilitate the synthesis of a new nano-catalyst with nickel ions. The nickel ions were fixed on the surface of the organic nanotubes through coordination. The nanotubes catalyzed oxidation of a wide range of organic compounds with hydrogen peroxide without organic solvent, and are reusable in at least five cycles without loss of activity.

Electron-enhanced Raman scattering: a history of its discovery and spectroscopic applications to solution and interfacial chemistry.

AbstractRaman scattering spectroscopy can be used to distinguish highly similar molecules and obtain useful information on local physical and chemical environments at their functional group levels. However, obtaining a high-quality Raman spectrum requires high-power excitation and a long acquisition time owing to the inherently small Raman scattering cross section, which is problematic in the analyses of living cells and real-time environmental monitoring. Herein, a new Raman enhancement technique, electron-enhanced Raman scattering (EERS), is described in which artificially generated electrons affect the polarizability of target molecular systems and enhance their inherent Raman cross sections. The EERS technique stands in contrast to the well-known SERS technique, which requires roughened metal surfaces. The history of EERS and its spectroscopic applications to aqueous solutions are presented. FigureA mechanism of electron-enhanced Raman scattering. Left: Polarizability change in a molecular system induced by an electron attachment. An example of hydrogen-bonded water molecules is shown. Right: Resultant transient enhancement of Raman scattering.

Ultrafast transient lens spectroscopy of photoisomerization dynamics of azocompounds in confined nanospace of cyclodextrins

The ultrafast photoisomerization dynamics of azocompounds encapsulated in the cavity of α-, β-, and γ-cyclodextrin (CD) was investigated by the ultrafast transient lens method regarding effects of special restriction and intermolecular interactions. As expected, the spatial restriction reduced the yield of photoisomerization, but the effect was not so remarkable, indicating that the host and guest were relatively freely bounded. This effect was more prominent in azo: γ-CD=2:2 system, where the two guest molecules were packed in parallel as a dimer. From the viewpoint of the confined nanospace as a new reaction field, we found that the azo: γ-CD=2:2 system induced a specific intermediate having a long lifetime, which was not observed in free solutions. We also found that the formation of hydrogen-bonding between CD and guest remarkably elongated the trans–cis transformation of guest molecules in Orange II/CD systems.

Raman spectroscopy of reaction fields induced by plasma in supercritical CO2

The characteristic microstructures of supercritical fluids, such as density fluctuation near the critical point, in reaction fields induced by low-temperature plasma were investigated by using Raman spectroscopy. It was found that the decrease in the density of CO2 during plasma generation was less than 0.02 g/cm3 (critical density of CO2:0.467 g/cm3), when compared to the decrease in density of pure CO2 for a wide pressure range from gaseous to supercritical conditions. Moreover, it was experimentally verified that the density fluctuation observed near the critical point persists in the reaction field.