Electrorheological toners for electrophotography

The electrorheological (ER) behavior of pigment suspensions dispersed in a nonaqueous solvent was examined for their application as liquid toners for electrophotography. In electric fields, particles can align into chains along the field vector by dielectric polarization forces and the suspensions undergo a rapid transition from Newtonian fluids to Bingham bodies. However, the migration and deposition of particles can take place by the electrophoretic effect, because charge control agents are added to liquid toners for fast development. The combined effects of dielectric polarization forces, electrophoretic forces, and hydrodynamic forces make rheological behavior very complicated. To simulate the ER behavior of liquid toners in reprographic processes, viscosity measurements were carried out in electrodes with a honeycomb pattern. Nonuniform electric fields enhance the dipole-dipole interactions between particles and give rise to a striking ER effect. Based on measurements in honeycomb pattern electrodes, new ER toners were developed which can reproduce images with high quality.     

Selective transformation of N-t-butoxycarbonyl group into n-alkoxy-carbonyl group via n-carboxylate ion equivalent

Reaction of a variety of N-$\text{t}$-butoxycarbonyl compounds with $\text{t}$-butyl-dimethylsilyl trifluoromethanesulfonate afforded the N-$\text{t}$-butyldimethyl-silyloxycarbonyl compounds, chemoselectively, which upon treatment with an alkyl or aryl halide provided the corresponding N-alkoxy- or N-aryl-oxycarbonyl compounds, efficiently.     

Synthesis of novel amino squaric acids via addition of dianion enolates derived from N-Boc amino acid esters

Novel α-amino squaric acid analogs were synthesized by initial addition reaction of a dianion enolate generated from N-Boc amino acid tert-butyl ester to squaric acid diisopropyl ester, and subsequent decarboxylation of the resulting carboxylic acid moiety.     

Synthesis of (+)-galantinic acid,a constituent amino acid in the peptide antibiotic galantin I, via the stereoselective epoxidation of a chiral serine equivalent

Epoxidation of (2$\text{R}$)-$\text{t}$-butoxycarbonylamino-3-butenol afforded, in a highly stereo-selective manner, a $\text{threo}$-3,4-epoxy-2-aminobutanol derivative which was successfully converted to the unusual amino acid (+)-galantinic acid in 8 steps $\text{via}$ regiospecific epoxide ring opening with divinyl cuprate.     

Palladium(II)-catalyzed oxidative transformation of allylic alcohols and vinyl ethers into 2-alkoxytetrahydrofurans: catechol as an activator of catalyst

[chemical reaction: see text]. A highly effective synthesis of 2-alkoxytetrahydrofurans from allylic alcohols and vinyl ethers was achieved by using catalytic amounts of Pd(OAc)2, Cu(OAc)2, and catechol (1:1:2) under O2. The use of catechol as an activator of Pd(II)-Cu(II) catalyst has been unprecedented. The 2-alkoxytetrahydrofurans are formed via oxypalladation of allylic alcohols toward vinyl ethers followed by 5-exo cyclization of the resulting oxypalladation intermediate and subsequent beta-Pd-H elimination. No 6-endo cyclization of the oxypalladation intermediate occurs.     

Total synthesis of dl-mexicanin I and dl-linifolin A

The helenanolides mexicanin I(1) and linifolin A(4) have been synthesized from hydroazulenol 5, thereby confirming the original structural assignments.     

Electrochemical Quantitative Evaluation of the Surface Charge of a Poly(1-Vinylimidazole) Multilayer Film and Application to Nanopore pH Sensor

Nanopore pH sensing is based on the interaction between the surface charge of the nanopore and ions passing through the nanopore. The nanopore surface charge can be derived from the acid-base dissociation equilibrium of the modified polyelectrolyte. Various polyelectrolytes have been selected based on the acid dissociation constant of the monomer units, and various techniques have been applied to modify nanopores. However, they have been developed without clear guidelines for characterizing the surface modification status or surface charge. One reason has been the difficulty in accurately estimating the surface charge of nanopores in solution. Thus, in this study, the dissociation constant (pKa_app) of the surface charge of a modified polyelectrolyte nanopore was quantitatively estimated via electrochemical measurements. Previously, the modification status of nanopores has been evaluated using the ion current response. In addition, we monitored in real-time the polyelectrolyte modification status using a quartz crystal microbalance (QCM). Some polyelectrolytes were difficult to immobilize directly on the nanopore surface, and those polymers could be effectively modified by the layer-by-layer (LbL) technique. Therefore, we produced a guideline for the fabrication of a nanopore sensor for pH measurements under physiological conditions by quantitative evaluation of the pKa_app via electrochemical methods, the monitoring of the modification status by QCM, and the development of an effective modification method via the LbL technique.     

Classification of dynamic vibronic couplings in vibrational real-time spectra of a thiophene derivative by few-cycle pulses

Pump-probe spectroscopy was performed with a few cycle pulses of 6.7 fs duration. The electronic transition intensity modulation was induced by molecular vibration in a quinoid thiophene molecule in solution. The real-time vibrational features were analyzed in terms of dependence of vibrational amplitude and phase on probe photon energy. The electronic transition probability is modulated by molecular vibration via vibronic coupling. Changes in the spectral shape and intensity of the time-resolved spectrum were studied by tracking characteristic spectral features including the peak frequency and intensity, spectral bandwidth, and band-integrated intensity. From the analysis the modulation mechanisms were classified into two groups: (1) Condon type and (2) non-Condon type. The features of the wave packet motions were also classified into zeroth-order derivatives due to quasi-pure non-Condon type and first- and second-order derivative types due to the displacement of the potential minimum and the potential curvature change associated with the relevant vibronic transition, respectively.     

Shear-thickening flow of suspensions of carbon nanofibers in aqueous PVA solutions

The suspensions of carbon nanofibers in aqueous poly(vinyl alcohol) solutions were prepared in the presence of spherical carbon black particles, and the steady-shear viscosity and dynamic viscoelasticity were measured for complex suspensions. Although the single suspensions of carbon black are highly stable, the flocculation of carbon nanofibers is promoted by the addition of carbon black particles. The complex suspensions show remarkable shear thickening in the steady-flow and strain hardening in oscillatory shear with large amplitude. The nonlinear responses strongly depend on the carbon black concentration, whereas the dynamic viscoelasticity at low strains in the linear ranges is not significantly influenced. As the highly elastic effects arise from the long-range motion of particles, the possible mechanism may be the orientation of nanofibers in strong shear fields. The suspensions show the time-dependent behavior of viscosity when the time-scale of measurements is shorter than that of structural recovery to the isotropic states.