Vertical flow apparatus for enhancement and efficient collection of Raman signal

To improve the signal‐to‐noise (S/N) ratio of Raman spectra, we developed a sample flow system in a vertical flow apparatus (VFA). The VFA consists of a brass plate with a drilled pinhole, cover slip on the brass plate, circulation pump, and reservoir. The sample solution flows through a gap between the brass plate and cover slip, spouts from the pinhole, and forms a laminar flow column. The sample column and surrounding air, respectively, serve as the core and cladding of an optical fiber that confines both excitation beam and scattered light owing to the total reflection at the core–cladding interface. The VFA enabled the enhancement and efficient collection of the Raman signal. The VFA with a 0.2‐mm pinhole produced a 12.0‐fold enhancement of the non‐resonant Raman signal of H₂O compared to that measured using a capillary, and the S/N ratio exhibited a 4.1‐fold enhancement. The signal count was inversely proportional to the square of the pinhole diameter (φ), possibly owing to the dependence on the density of the electromagnetic energy of the excitation beam in the sample column. The S/N ratio was inversely proportional to φ because the signal enhancement was accompanied by an increase in the photon shot noise. The VFA also produced a 4.9‐fold enhancement of the resonance Raman signal of Congo red, although the enhancement factor was smaller than that in the non‐resonant Raman measurement. Copyright © 2014 John Wiley & Sons, Ltd.     

Flow of optical patterns due to small lateral wave-front shifts in a nonlinear optical feedback system

Flow of a spontaneously formed optical pattern in a nonlinear optical feedback system consisting of a liquid crystal optically addressable spatial light modulator with feedback is induced by a lateral wave-front shift of the feedback light. We demonstrate the dependency of the flow speed on the wave-front shift by tilting an optical flat inserted in the feedback loop. We also demonstrate the application to real-time, high-sensitivity detection of small tilt angles of optical components.     

Simultaneous direct determination of aluminum, calcium and iron in silicon carbide and silicon nitride powders by slurry-sampling graphite furnace AAS.

A fast and accurate analytical method was established for the simultaneous direct determination of aluminum, calcium and iron in silicon carbide and silicon nitride powders by graphite furnace atomic absorption spectrometry using a slurry sampling technique and a Hitachi Model Z-9000 atomic absorption spectrometer. The slurry samples were prepared by the ultrasonication of silicon carbide or silicon nitride powders with 0.1 M nitric acid. Calibration curves were prepared by using a mixed standard solution containing aluminum, calcium, iron and 0.1 M nitric acid. The analytical results of the proposed method for aluminum, calcium and iron in silicon carbide and silicon nitride reference materials were in good agreement with the reference values. The detection limits for aluminum, calcium and iron were 0.6 microg/g, 0.15 microg/g and 2.5 microg/g, respectively, in solid samples, when 200 mg of powdered samples were suspended in 20 ml of 0.1 M nitric acid and a 10 microl portion of the slurry sample was then measured. The relative standard deviation of the determination of aluminum, calcium and iron was 5 - 33%.     

An overall mechanism for the deposition of plasma polymers from methane in a low-pressure argon plasma jet

An overall mechanism for plasma polymer deposition from a methane-seeded argon plasma jet was established from experimental measurements and a simplified model of reaction kinetics within the plasma jet. Total mass deposition rates were obtained at various substrate positions and methane flow rates. Methane consumption was estimated from residual gas analysis. The influence of substrate coolant temperature on deposition rate was evaluated. The model was based on particle densities, jet temperature, and jet velocity data published previously, and reaction rate constants from the literature were used. No adjustable parameters were employed in this model. Experimental results for total deposition rate and methane consumption were in good agreement with model predictions. The overall deposition mechanism consists of three steps: Penning ionization of methane by excited argon neutrals, followed by dissociative recombination of CN _x ⁺ to yield CH, followed by incorporation of CH into the growing film upon impact. Contributions of species other than CH to the total deposition rate are minor, and adsorption is not a prerequisite for incorporation into the growing film.     

Novel and stereocontrolled synthesis of (+/-)-tetrodotoxin from myo-inositol

[reactions: see text] The novel and stereocontrolled synthesis of (+/-)-tetrodotoxin from myo-inositol is described. The key steps involve the stepwise oxidation of hydroxyl groups to the carbonyl function, followed by the addition of specific nucleophiles, including the successive spiro alpha-chloroepoxide formation and its ring-opening with the azide anion, to give the desired branched chain structures (5-->6, 17-->18-->19-->20 and 23-->24-->25) with the desired regio- and stereoselectivities in high yields. The stepwise conversion of the alpha-azido aldehyde 25 to the delta-lactone 29, followed by reduction of the azide, introduction of a guanidine moiety, aldehyde formation, and deprotection, produced the (+/-)-tetrodotoxin.     

Aggregation behavior of latex particles in shear flow confined between two parallel plates

In this study, the aggregation and breakup behaviors of latex particles in shear flow confined between two parallel plates were investigated using an in situ observation apparatus with a laser scanning confocal microscope. To investigate the effects of shear rate and the gap width between two parallel plates on the size and structure of the aggregates in the steady state, the distributions of the projected cross-sectional area and perimeter-based fractal dimension of the aggregates were measured. As a result, the average size of the aggregates decreases as shear rate increases and the gap width decreases due to the hydrodynamic effect acting on the aggregates. The size distributions of the aggregates become narrow as the gap width decreases. In addition, the fractal dimension, that is, the structure of the aggregates, was almost independent of shear rate and the gap width and approximately 1.2, which suggests that the aggregates are relatively compact.     

ADSORPTION OF COLLOIDAL MATERIALS ON POLYMER SURFACES

Polypropylene surfaces were rendered cationic by hydrophobic implantation and by grafting a quaternized polyvinyl pyridine onto a plasma treated surface. The polypropylene surface with the grafted polymer showed a strong adsorption of an anionic surfactant, corresponding to about ten monomolecular layers. High concentration of electrolyte caused a reduction of the adsorption at low concentrations of surfactant.     

Copper-Catalyzed Enantioselective Reductive Aldol Reaction of α,β-Unsaturated Carboxylic Acids to Alkyl Aryl Ketones: Silanes as Activator and Transient Protecting Group

The first enantioselective reductive aldol reaction of unprotected α,β-unsaturated carboxylic acids was developed by employing a copper/bisphosphine catalyst. The reaction features in situ protection and activation of an α,β-unsaturated carboxylic acid by a hydrosilane. The copper enolate formed in situ reacts with an alkyl aryl ketone to afford the β-hydroxy carboxylic acid with excellent enantioselectivity (up to 99 % ee). The corresponding gram-scale reaction with a low catalyst loading and the derivatization of the β-hydroxy carboxylic acids highlight the practicality of this transformation.     

A Rare and Exclusive Endoperoxide Photoproduct Derived from a Thiacalix[4]arene Crown‐Shaped Derivative Bearing a 9,10‐Substituted Anthracene Moiety

A rare and exclusive endoperoxide photoproduct was quantitatively obtained from a thiacalix[4]arene crown‐shaped derivative upon irradiation at λ=365 nm; the structure was unambiguously confirmed by ¹H/¹³C NMR spectroscopy and X‐ray crystallography. The prerequisites for the formation of the endoperoxide photoproduct have also been discussed. Furthermore, the photochemical reaction rate could be greatly enhanced in the presence of the thiacalix[4]arene platform because it served as a host to capture oxygen.     

Optimization of blur correction of color images formed with aerial imaging by retro-reflection

Optical Review - We propose a pre-processing method of source image to reduce blur of aerial image that is formed with aerial imaging by retro-reflection (AIRR). In the AIRR optical system,...