Circular dichroism of optically active poly(dialkylsilane) aggregates in microcapsules

Poly[n-hexyl-(S)-3-methylpentylsilane] aggregates confined in microcapsules to keep the aggregation number and ranging in average polymer mass m(p) in a microcapsule from 2 x 10(-)(16) to 2 x 10(-)(14) g were studied by circular dichroism measurements in ethanol (a nonsolvent) and tetrahydrofuran (an associative solvent at low temperature) at various temperatures. The weight-average molecular weight M(w) and the polydispersity index (the ratio of M(w) to the number-average molecular weight) of the polysilane sample were 6.6 x 10(4) and 1.07, respectively, and the average number of polymer molecules in each capsule was estimated to be 1.9 x 10(3) for m(p) = 2 x 10(-)(16) g and 1.7 x 10(5) for m(p) = 2 x 10(-)(14) g. The size of each aggregate did not affect the optical activity because the circular dichroism thus obtained was proportional to m(p) under the same conditions in the investigated m(p) range; on the other hand, the peak height of the circular dichroism in tetrahydrofuran had a significant hysteresis between 0 and 25 degrees C. Moreover, the circular dichroism appreciably reflected the prepared method, that is, the temperature and solvent; in other words, the aggregates memorized the initial conditions in their stacking structures.     

Immobilization of liposomes onto quartz crystal microbalance to detect interaction between liposomes and proteins

To study the interaction between liposomes and proteins, intact liposomes were immobilized on a metal planar support by chemical binding and/or bioaffinity using a quartz crystal microbalance (QCM). A large decrease in the resonance frequency of quartz crystal was observed when the QCM, modified by a self-assembled monolayer (SAM) of carboxythiol, was added to liposome solutions. The stable chemical immobilization of intact liposomes onto SAM was judged according to the degree with which adsorbed mass depended on the prepared size of liposomes, as well as on the activation time of SAMs when amino-coupling was introduced, where the liposome coverage of electrodes was 69+/-8% in optimal conditions. When avidin-biotin binding was used on amino-coupling liposome layers, liposome immobilization finally reached 168% coverage of the electrode surface. Denatured protein was also successfully detected according to the change in the frequency of the liposome-immobilized QCM. The adsorbed mass of denatured carbonic anhydrase from bovine onto immobilized liposomes showed a characteristic peak at a concentration of guanidine hydrochloride that corresponded to a molten globule-like state of the protein, although the mass adsorbed onto deactivated SAM increased monotonously.     

Aerobic oxidation of methanol to formic acid on Au20-: a theoretical study on the reaction mechanism

The aerobic oxidation of methanol to formic acid catalyzed by Au(20)(-) has been investigated quantum chemically using density functional theory with the M06 functional. Possible reaction pathways are examined taking account of full structure relaxation of the Au(20)(-) cluster. The proposed reaction mechanism consists of three elementary steps: (1) formation of formaldehyde from methoxy species activated by a superoxo-like anion on the gold cluster; (2) nucleophilic addition by the hydroxyl group of a hydroperoxyl-like complex to formaldehyde resulting in a hemiacetal intermediate; and (3) formation of formic acid by hydrogen transfer from the hemiacetal intermediate to atomic oxygen attached to the gold cluster. A comparison of the computed energetics of various elementary steps indicates that C-H bond dissociation of the methoxy species leading to formation of formaldehyde is the rate-determining step. A possible reaction pathway involving single-step hydrogen abstraction, a concerted mechanism, is also discussed. The stabilities of reactants, intermediates and transition state structures are governed by the coordination number of the gold atoms, charge distribution, cooperative effect and structural distortion, which are the key parameters for understanding the relationship between the structure of the gold cluster and catalytic activity in the aerobic oxidation of alcohols.     

Can a meso-type dinuclear complex be chiral?: dinuclear β-diketonato Ru(III) complexes

Dinuclear Ru(III) complexes, [Ru(III)(acac)(2)(dabe)Ru(III)(acac)(2)] (acacH = acetylacetone; dabeH(2) = 1, 2-diacetyl-1,2-dibenzoylethane) and [Ru(III)(acac)(2)(tbet)Ru(III)(acac)(2)] (tbetH(2) = 1,1,2,2-tetrabenzoylethane) were synthesized by reacting [Ru(acac)(2)(CH(3)CN)(2)]PF(6) with dabeH(2) and tbetH(2) respectively, in toluene. The X-ray structural analysis of a meso-type dinuclear Ru(III) complex, ΔΛ-[Ru(III)(acac)(2)(dabe)Ru(III)(acac)(2)], showed that the bridging part became chiral due to the orthogonal twisting of two non-symmetrical β-diketonato moieties. To confirm this conclusion, the complex was resolved chromatographically to provide a pair of optical antipodes. Such chirality in the bridging part was not generated for [Ru(III)(acac)(2)(tbet)Ru(III)(acac)(2)], because the β-diketonato moieties in tbet(2-) are symmetrical.     

Quantitative imaging of ion transport through single nanopores by high-resolution scanning electrochemical microscopy

Here we report on the unprecedentedly high resolution imaging of ion transport through single nanopores by scanning electrochemical microscopy (SECM). The quantitative SECM image of single nanopores allows for the determination of their structural properties, including their density, shape, and size, which are essential for understanding the permeability of the entire nanoporous membrane. Nanoscale spatial resolution was achieved by scanning a 17 nm radius pipet tip at a distance as low as 1.3 nm from a highly porous nanocrystalline silicon membrane in order to obtain the peak current response controlled by the nanopore-mediated diffusional transport of tetrabutylammonium ions to the nanopipet-supported liquid-liquid interface. A 280 nm × 500 nm image resolved 13 nanopores, which corresponds to a high density of 93 nanopores/μm(2). A finite element simulation of the SECM image was performed to assess quantitatively the spatial resolution limited by the tip diameter in resolving two adjacent pores and to determine the actual size of a nanopore, which was approximated as an elliptical cylinder with a depth of 30 nm and major and minor axes of 53 and 41 nm, respectively. These structural parameters were consistent with those determined by transmission electron microscopy, thereby confirming the reliability of quantitative SECM imaging at the nanoscale level.     

Relevance of continuously self-imaging gratings for noise robust imagery

We have designed miniaturized, simple, and robust cameras composed of a single diffractive optical element (DOE) that generates a continuously self-imaging (CSI) beam. Two different DOEs are explored: the J₀ Bessel transmittance, characterized by a continuous optical transfer function (OTF) and the CSI grating (CSIG), characterized by a sparse OTF. In this Letter, we will analyze the properties of both DOEs in terms of radiometric performances. We will demonstrate that the noise robustness is enhanced for a CSIG, thanks to the sparsity of its OTF. A camera using this DOE has been made and experimental images are presented to illustrate the noise robustness.     

Excited states and electronic spectra of annulated dinuclear free-base phthalocyanines: a theoretical study on near-infrared-absorbing dyes

The electronic excited states and electronic absorption spectra of annulated dinuclear free-base phthalocyanine (C(58)H(30)N(16)) are studied through quantum chemical calculations using the symmetry-adapted cluster-configuration interaction (SAC-CI) method. Three tautomers are possible with respect to the position of the pyrrole protons; therefore, the SAC-CI calculations for these tautomers were performed. The structures of the Q-band states are discussed based on the character of their molecular orbitals. The lower energy shift of the Q-bands because of dimerization is explained by the decrease in the HOMO-LUMO gaps resulting from the bonding and antibonding interactions between the monomer units. The electronic dipole moments of the nonsymmetric tautomer were calculated, and the possibility of charge-separated excited states is discussed. The relative energies of these tautomers are examined using density functional theory (DFT) calculations for several peripheral substituents. The relative energies of these tautomers significantly depend on the substituents, and therefore, the abundance ratios of the three tautomers were affected by the substituents. The absorption spectra were simulated from the SAC-CI results weighted by the Boltzmann factors obtained from the DFT calculations. The SAC-CI spectra reproduce the experimental findings well. The thermal-averaged SAC-CI spectra could explain the observed substituent effect on the structure of the Q-bands in terms of the relative stabilities and the abundance ratios of the tautomers. The SAC-CI and time-dependent density functional theory calculations are also compared. The CAM-B3LYP results agreed with the trends of the SAC-CI results; however, the CAM-B3LYP calculation overestimated the excitation energies in comparison with the SAC-CI and experimental results.     

An analytical solution to non-axisymmetric heat transfer with viscous dissipation for non-Newtonian fluids in laminar forced flow

Forced convection heat transfer in a non-Newtonian fluid flow inside a pipe whose external surface is subjected to non-axisymmetric heat loads is investigated analytically. Fully developed laminar velocity distributions obtained by a power-law fluid rheology model are used, and viscous dissipation is taken into account. The effect of axial heat conduction is considered negligible. The physical properties are assumed to be constant. We consider that the smooth change in the velocity distribution inside the pipe is piecewise constant. The theoretical analysis of the heat transfer is performed by using an integral transform technique – Vodicka’s method. An important feature of this approach is that it permits an arbitrary distribution of the surrounding medium temperature and an arbitrary velocity distribution of the fluid. This technique is verified by a comparison with the existing results. The effects of the Brinkman number and rheological properties on the distribution of the local Nusselt number are shown.     

Experimental study on effect of relative humidity on heat transfer of an evaporating water droplet in air flow

Dispersed water droplets are often seen in environmental air flows in rain, cloud, mist, sea spray and so on. It is therefore of great importance to precisely estimate heat transfer between water droplets and atmospheric air in developing a reliable climate model. The purpose of this study is to fabricate the measurement system for the temperature of a small water droplet in air flow under the controlled relative humidity condition and to investigate the effect of relative humidity on heat transfer across the surface of an evaporating water droplet in air flow. The results show that the droplet temperature decreases in the low-relative-humidity condition, whereas it increases in the high-relative-humidity condition. Nusselt number on the droplet surface is not affected by the relative humidity.     

Preprocessed visualization of large scale unsteady flow simulations

In some cases, conventional CFD visualization techniques do not give us sufficient information of the flowfield, especially when the flowfield is unsteady, and there is a need for a new postprocessing technique. In the present paper, one of such new post-processing techniques is proposed. In the present technique, raw result of CFD simulation is pre-processed by frequency filters, and then processed secondary data set is visualized. The idea is applied to two examples. The examples show that the present method visualizes each frequency mode separately, and gives clear view of the temporal variation of the whole flowfield. The results indicate that the present method improves the understandings of the flow mechanism.