Fluctuations of the propagating beam field in a lens waveguide

It is well known that light beams propagated through a turbulent medium such as the atmosphere or the air between optical lenses suffer fluctuations of the field in respect of its amplitude and phase. This paper investigates the fluctuation distributions of a laser beam propagating through a lens waveguide which consists of a sequence of optical lenses placed in a randomly inhomogeneous medium. By using a Rytov approximation approach, the mean-square values of fluctuations are obtained in terms of log-amplitude and phase of the beam field. The results show that as the light beam propagates through the lens waveguide, the mean-square fluctuations increase with periodic variations corresponding to a period of lens spacing and that a singular phenomenon of fluctuation reduction at each focus of the beam is evident at larger beam spot sizes.     

Trapping of ammonium sila-ylide with pentaphenylfulvene or dibenzofulvene

The thermolysis of a pentacoordinate fluorodisilane bearing an 8-(dimethylamino)-1-naphthyl group in the presence of 2,3,4,5,6-pentaphenylfulvene or 14-phenyldibenzofulvene affords a silylene-fulvene adduct bearing a zwitterionic structure attributable to the silaylide, but it spontaneously undergoes subsequent intramolecular cyclization reaction between the silicon atom and the aromatic carbon atom in the fulvene moiety followed by a sigmatropic proton migration to form a neutral silicon-containing six- or five-membered ring product.     

QUENCHING OF PHOTOEXCITED 4,4'-DICARBOXY-2,2'-BIPYRIDINEBIS(2,2'-BIPYRIDINE)RUTHENIUM(II) BY OXYGEN IN AQUEOUS SOLUTION AND IN SILK FIBROIN MEMBRANE

Abstract— Photoluminescence and quenching of 4,4'-dicarboxy-2,2'-bipyridinebis(2,2'-bipyridine)-ruthenium(II) complex (Ru(DCbpy)(bpy)²₂⁺) in an aqueous solution as well as in a silk fibroin membrane were studied. Emission quenching by oxygen in an aqueous solution showed a linear relationship with respect to oxygen concentration. When the complex was incorporated into a silk fibroin membrane by adsorption from an aqueous solution into a preformed membrane, the photoexcited state of the complex was not quenched by oxygen in an aqueous phase. However, when the complex was incorporated into a silk fibroin membrane by casting a mixture of the complex and silk fibroin, the photoexcited complex was quenched by oxygen in an aqueous phase. In this case the Stern-Volmer plots showed a downward-deviating curve indicating heterogeneity of the probe site. Emission intensity decreased with an increase of the water content in the silk fibroin membrane.     

Development of a highly sensitive galvanic cell oxygen sensor

A highly sensitive galvanic cell oxygen sensor was successfully developed for determining parts per billion of oxygen in high purity gases such as nitrogen, argon, etc. The response of this improved sensor was proportional in the range of oxygen concentrations from 10.0 ppm to the detection limit. The response speed in this study was improved to within 90 sec for a 90% response. The detection limit was tentatively found to be less than 0.4 ppb corresponding to S N = 2 .     

Phenylselenenyl chloride as a reagent for the facile preparation of cyclic ethers from diolefins

Various cyclic ethers are prepared in good to excellent yields by treating diolefins with phenylselenyl chloride in aqueous acetonitrile. This is the most facile method for organoselenium-induced formation of cyclic ethers from diolefins so far reported.     

Stereochemistry and mechanism of the copper(I) halide cleavage of thallium-carbon bonds

Stereochemical studies on the copper(I) halide cleavage of thallium-carbon bonds in acetonitrile indicate that at 80°C a radical path accounts for approximately $\text{2}\text{3}$ of the product, whereas at 60°C an ionic path predominates. The results are consistent with e.s.r. measurements by a spin trapping technique.     

Stability test and improvement of hydrogen analyzer with trace reduction detector

We previously developed an analyzer able to detect hydrogen concentrations of less than 50 cm3/1000 m3. The analyzer uses a carrier gas purifier and a low temperature separation column to remove impurities preventing measurement of low concentrations from the carrier and sample gases. It uses a trace reduction detector with a mercuric oxide bed to detect the concentration of hydrogen based on the reduction reaction of mercuric oxide with hydrogen. We have now evaluated the performance of the analyzer by carrying out a series of tests that measured the spectrum peak and the retention time. We used three sample gases with hydrogen concentrations of 5, 20, and 50 cm3/1000 m3 in nitrogen dilution gas. The measured peak was stable (it was within a relative standard deviation of less than 10%), and there was a linear relationship between the peak and hydrogen concentration. However, the retention time gradually shortened as the measurements were repeated. The shortening was reduced by warming the low temperature separation column used in the analyzer; it was not observed when we used a hydrogen sample gas diluted by helium instead of nitrogen. Using nitrogen as a dilution gas apparently shortens the retention time. We thus added an MS-5A separation column and a thermal conductivity detector. The nitrogen and hydrogen in the sample/carrier gas are separated, and the nitrogen is efficiently removed by switching the pass line to a release line after the hydrogen has been sent to the low temperature separation column. An analyzer using this "after-cut method" was able to stably measure infinitesimal hydrogen concentrations and was not affected by nitrogen in the sample gas.     

Enzyme-less amperometric biosensor for l-ascorbate using poly-l-histidine-copper complex as an alternative biocatalyst

A poly- -histidine(PLH)-copper(II) complex can be used as an alternative biocatalyst in an O₂ detection-type amperometric enzyme-less -ascorbate (AsA) sensor. The PLH–Cu(II) membrane was simply prepared by entrapping the PLH in polyacrylamide gel and subsequent treatment of the gel with CuCl₂ solution. This enzyme-less biosensor can be used over a relatively wide pH region from 4 to 11 and enables precise determination of AsA (RSD less than 3%, n=10) at pH 7.0. The fundamental performance characteristics (sensitivity, response time, and linear range) of this PLH–Cu(II)-based sensor is comparable to those of a native ascorbate oxidase-based sensor. Unfortunately, the selectivity is inherently rather low and, as a result, the response was degraded in the presence of higher concentrations (more than mM order) of quinones. However, reducing sugars caused no interference and the sensor could be used to detect AsA in some fruits and drinks. This enzyme-less sensor has excellent stability for at least 3 months of repeated analysis (more than 300 samples) without loss of ordinal activity.     

Structural role of tyrosine in Bombyx mori silk fibroin, studied by solid-state NMR and molecular mechanics on a model peptide prepared as silk I and II

The influence of the bulky and H-bonding Tyr side-chain on its Ala- and Gly-rich environment in Bombyx mori silk fibroin was examined by (13)C cross-polarization magic angle spinning (CP/MAS), static (2)H and (19)F NMR and molecular mechanics calculations. Model peptides of the type (AG)(15) were synthesized with Tyr in a number of different positions, precipitated under conditions favoring either of the two characteristic protein conformations, and the resulting structures were assigned from their (13)C chemical shifts. Dialysis of native fibroin or the simple (AG)(15) peptide from a 9 M LiBr solution against water produces silk I (the structure of silk before spinning), whereas drying from formic acid yields silk II (fibrous structure after spinning). We found that the introduction one or more Tyr into (AG)(15) can have a dramatic effect not only on the local backbone conformation but also on the long-range intermolecular chain packing in the samples. The antiparallel beta-sheet conformation of silk II is able readily to accommodate a single Tyr residue. Interestingly, the beta-turn conformation of silk I only remains stable when Tyr is positioned near the chain terminus in (AG)(12)YG(AG)(2), but the conformation is driven towards silk II when Tyr is located in the central region of (AG)(7)YG(AG)(7). The role of H-bonding was tested by replacing Tyr with Phe or 4F-Phe, which are no longer compatible with silk I and fully induced a silk II conformation. In the presence of several Tyr residues a mixture of distorted beta-sheet and beta-turn conformations was obtained, regardless of the precipitation conditions. Static (2)H NMR of ring-deuterated [3',5'-(2)H(2)]Tyr located in the central region of (AG)(7)YG(AG)(7) showed that the side-chain is immobilized in both silk I and II, which was also observed by static (19)F NMR of the 4F-Phe analogue. To visualize the local packing around the Tyr side-chain, molecular mechanics calculations were performed on a mixture of (AG)(4) and AGAGYGAG, starting from either the beta-turn type II or the antiparallel beta-sheet structure. The resulting structures show that the intermolecular chain arrangement is significantly affected by Tyr, thus explaining the long-range packing effects in the semi-crystalline regions of silk fibers compared with the crystalline regions that are devoid of Tyr.     

Diastereoselective arylation of l-proline derivatives at the 5-position

Diastereoselective introduction of nucleophiles into l-proline derivatives at the 5-position was achieved with suitable selection of N-protecting group. N-Methoxycarbonylated or benzyloxycarbonylated l-proline derivatives reacted with arene to give cis-arylated products. On the other hand, N-benzoylated l-proline derivative preferentially gave trans-arylated product, which could be easily transformed into optically active C₂-symmetrical pyrrolidine derivative. Such derivative 5 worked well as an organic activator in the asymmetric reduction of aromatic imines by Cl₃SiH.