Molecular hybrids of azobenzene polymer and liquid crystal molecule. A new approach for understanding the command surface system

Langmuir-Blodgett (LB) films consisting of the hybrid of a polymer having the azobenzene (Az) side chain and 4î-pentyl-4-cyanobiphenyl (5CB) are prepared. Microscopic observations and spectroscopic data both indicate that the Az side chain and 5CB are homogeneously mixed at a molecular level without phase separation in the layer. This provides a satisfactory model of the command surface system. Time course accumulation of spectroscopic data for multilayered hybrid films reveals the cooperative nature of the photo-motivated molecular motions.     

Observation of 18O/16O isotope effects at the cathode of a polymer electrolyte membrane fuel cell

¹⁸O/¹⁶O isotope effects were observed at the cathode of a polymer electrolyte membrane fuel cell at 25 and 35°C. Results of experiments in which the ¹⁸O/¹⁶O isotope ratios of the oxygen gases supplied to and exhausted from the cell were measured revealed that the lighter isotope ¹⁶O reacted more preferentially to form water molecules at the cathode than the heavier one, ¹⁸O. The value of the oxygen isotope separation factor, S₁, defined as the ratio of the ¹⁸O/¹⁶O isotope ratios of the oxygen gases supplied to and exhausted from the cell, ranged from 1.0030 to 1.0139, and tended to decrease with decreasing rate of oxygen utilisation (θ) and with increasing flow rate of the feed oxygen gas (D_F). The value of another separation factor, S₂, defined as the ratio of the ¹⁸O/¹⁶O isotope ratios of the exhausted oxygen gas and oxygen having reacted to form water molecules at the cathode, ranged from 1.0049 to 1.0304. The S₂ value was much less affected by the change in θ and D_F than the S₁ value with the majority of the S₂ value being in the range of 1.0240–1.0304.     

Electronic structures of imidazolium-based ionic liquids

Electronic structures of ionic liquids formed by 1-buthyl-3-alkylimidazolium ion [C_nmim]⁺ (n = 4 and 8) with various inorganic and organic anions have been investigated by ultraviolet photoemission, X-ray photoemission, inverse photoemission and soft X-ray emission spectroscopies (SXES). The comparison of the calculated density of states with the observed spectra revealed that the molecular orbital energies of these ionic liquids are significantly affected by the electrostatic Madelung potential among the ions. The SXES results clearly show that the both highest occupied and lowest unoccupied states of [C₄mim]⁺PF₆⁻ are derived from the cation as a result of strong Madelung potential. On the other hand, the SXES results show the valence electronic structures of ionic liquids with larger anion molecules, [C_nmim]⁺Tf₂N⁻ and [C_nmim]⁺OTf⁻ are contributed from the both cation and anion.     

Matrix-free high-resolution imaging mass spectrometry with high-energy ion projectiles

The importance of imaging mass spectrometry (MS) for visualizing the spatial distribution of molecular species in biological tissues and cells is growing. We have developed a new system for imaging MS using MeV ion beams, termed MeV-secondary ion mass spectrometry (MeV-SIMS) here, and demonstrated more than 1000-fold increase in molecular ion yield from a peptide sample (1154 Da), compared to keV ion irradiation. This significant enhancement of the molecular ion yield is attributed to electronic excitation induced in the near-surface region by the impact of high energy ions. In addition, the secondary ion efficiency for biologically important compounds (>1 kDa) increased to more than 10(10) cm(-2), demonstrating that the current technique could, in principle, achieve micrometer lateral resolution. In addition to MeV-SIMS, peptide compounds were also analyzed with cluster-SIMS and the results indicated that in the former method the molecular ion yields increased substantially compared to the latter. To assess the capability of MeV-SIMS to acquire heavy-ion images, we have prepared a micropatterned peptide surface and successfully obtained mass spectrometric imaging of the deprotonated peptides (m/z 1153) without any matrix enhancement. The results obtained in this study indicate that the MeV-SIMS technique can be a powerful tool for high-resolution imaging in the mass range from 100 to over 1000 Da.     

Experimental probe for hyperconjugative resonance contribution in stabilizing the singlet state of 2,2-dialkoxy-1,3-diyls: Regioselective 1,2-oxygen migration

A detailed study of the regioselectivity of 1,2-oxygen migration was conducted using the unsymmetrically substituted singlet 2,2-dialkoxy-1,3-diarylcyclopentane-1,3-diyls 5. The alkoxy group selectively migrates to the electron-donating p-methoxyphenyl-substituted carbon. The regioselective migration of oxygen clearly indicates a hyperconjugative resonance structure, that is, zwitterionic characteristics, in singlet 2,2-dialkoxy-1,3-diyls. This represents the first attempt to experimentally probe the contribution of hyperconjugation to stabilizing the singlet state.     

Continuous separation of particles using a microfluidic device equipped with flow rate control valves

We propose herein an improved microfluidic system for continuous and precise particle separation. We have previously proposed a method for particle separation called "pinched flow fractionation." Using the previously reported method, particles can be continuously separated according to differences in their diameters, simply by introducing liquid flows with and without particles into a specific microchannel structure. In this study, we incorporated PDMS membrane microvalves for flow rate control into the microfluidic device to improve the separation accuracy. By adjusting the flow rates distributed to each outlet, target particles could be precisely collected from the desired outlet. We succeeded in separating micron and submicron-size polymer particles. This method can be used widely for continuous and precise separation of various kinds of particles, and can function as an important part of microfluidic systems.     

Evaluation of intrinsic compressibility of proteins by molecular dynamics simulation

Molecular dynamics simulation has been performed on five native proteins in water to evaluate their intrinsic isothermal compressibilities beta(T,int). To identify physical factors contributing to protein compressibility, a general method is presented for analyzing the compressibility of mechanically inhomogeneous systems. The value of beta(T,int) varies with protein species considerably: beta-lactoglobulin (14.15 x 10(-2) GPa(-1)) is more than twice as compressible as ribonuclease A (6.77 x 10(-2) GPa(-1)). Beta-lactoglobulin and myoglobin (13.95 x 10(-2) GPa(-1)) have similar values of beta(T,int), but the mechanisms responsible for them are significantly different. The volume fluctuations of internal cavities and the magnitudes of the crosscorrelation between them are the key factors determining beta(T,int) of proteins. Though the volume fractions of internal cavity for the five studied proteins are nearly equal to one another, the mean cavity compressibilities beta(T,cav) vary considerably with protein species and range from 0.35 to 0.69 GPa(-1), which are much smaller than those of normal organic liquids such as methanol, ethanol, and benzene and close to that of glycerol (0.55 GPa(-1)), a strongly associated liquid.     

Visualizing conformations of subchains by creating optical wavelength-sized periodically ordered structure in hydrogel

Thick single-crystalline fcc colloidal crystals exhibiting structural color are obtained by a solvent evaporation method from silica colloidal particle suspensions. A periodically ordered interconnecting porous structure can be imprinted in thermosensitive N-isopropylacrylamide (NIPA) gels by using the colloidal crystals as templates. The porous structure endows a structural color to the NIPA gels. We find that the peak position of the reflection spectra from the porous gels (lamdamax') is expressed as a function of the swelling degree and is synchronized with the change in the swelling degree. The color can be precisely tuned by simply changing the amount of the monomer and the cross-linker in the pre-gel solutions. We can estimate the linear expansion factor (> or =1) of the subchains by comparing the peak position at a given situation (lamdamax') and the reference state (lamdamax,0'), in which the subchains behave as Gaussian coils. Creating the periodically ordered structure, which is similar in size to the wavelength of optical light, in the gels allows us to determine the behavior of polymer chains by observing the structural color.