Lifetime of metastable fluorine atoms

For laser collimation of neutral F atoms, a resonance transition cycle between the metastable and the upper excited states (3s⁴ P _5/2?3p⁴ D ⁰ _7/2) can be used as a two-level closed system. We have determined the lifetime of the metastable state (3s⁴ P _5/2) in F atoms by measuring the decay curve of the fluorescence intensity as a function of distance from the plasma source. Combining the measured velocity of F radicals from the Doppler shift of the fluorescence peak, we have obtained the lifetime of the F metastable state as 3.7±0.5 μs. With this short metastable lifetime of F radicals, the simple Doppler cooling method using spontaneous light force is not practical for laser collimation of F radicals. Use of stimulated light force may be necessary to collimate F radical beams in a short distance. Received: 4 July 2000 / Published online: 13 September 2000     

Velocity spectrometer for a neutral atomic beam

A velocity spectrometer for a neutral atomic beam has been developed to prepare a monovelocity atomic beam. In order to disperse a relatively fast atomic beam according to its longitudinal velocity, a magnetic quadrupole lens with a large magnetic gradient has been used. The device was made using NdFeB permanent magnets. The magnetic gradient in the quadrupole was measured to be sufficiently large (1 T/cm) and uniform along the radial direction. The resonance fluorescence spectra of the Li atomic beam after passing through the magnetic quadrupole lens have been measured by using a single-mode tunable laser. From the peak shift of the fluorescence spectrum, the exerted force on Li atoms by the magnetic lens was 8160 times as large as the acceleration of gravity. Using the present spectrometer, we have measured the longitudinal velocity distribution of the thermal Li beam at 800 °C, which was in good agreement with the result from the fluorescence spectra. It is expected that a monovelocity Li atomic beam of 1000 m/s with a velocity spread narrower than 1% can be easily formed with a compact experimental arrangement using the developed velocity spectrometer. In this case, the available flux given as a fraction of the incident Li flux is estimated to be about 1%. A high-velocity resolution of 0.03% is expected at the available fractional flux of about 0.01%. Received: 5 June 2000 / Revised version: 14 August 2000 / Published online: 8 November 2000     

Catch and Release of DNA in Coacervate‐Dispersed Gels

Summary: We have synthesized novel coacervate‐droplet gels, which were applied to controlling the transportation of DNA in electrophoresis. Coacervate droplets are colloidal particles and they are usually composed of positive and negative polyelectrolytes. However, the polyzwitterion (polyampholyte) PDMAPS can form coacervate droplets in water by itself, since PDMAPS has both positive and negative charges in each side group of main chain. Coacervate droplets have a unique nature and can catch charged macromolecules such as DNA. In order to utilize the nature of the PDMAPS coacervate droplets for the catch and release of DNA, we stabilized PDMAPS droplets in gels. The droplets catch the DNA in electrophoresis and the release of DNA can be controlled by temperature and salt addition.

Electrophoresis of DNA, using coacervate‐dispersed PAAm gels, prepared at various PDMAPS concentrations. The circles indicate the PAAm gels embedded in agarose gels.     

Irradiation of Crosslinked, Poly(Vinyl Alcohol) Blended Hydrogel for Wound Dressing

In order to obtain a more ideal hydrogel wound dressing, crosslinked hydrogel films blended with polyvinyl alcohol (PVA), polyvinyl pyrrolidone, kappa-carrageenan (KC), and powder silk were prepared by electron beam, and their physiochemical properties were investigated as a combination of function factors. The experimental results showed that the gel fraction of the hydrogel films depended mainly on irradiation dose and the monomer concentration of the polymers, the properties of hydrogel could be greatly extended or improved by blending homopolymers. The rate of gel formation of the hydrogel was raised, and the water evaporation from hydrogel could be retarded after mixing with KC, while the tensile strength of hydrogel films were obviously increased after mixing with silk. Toxicity and healing effect of PVA/PVP/KC/silk blended hydrogel films as wound dressings were evaluated. The irradiated blended hydrogel showed satisfactory properties for wound dressing, the hydrogel did not induceany acute general toxic effects, and it is effective for fast healing of wound.     

An Efficient Synthesis of 3-Cyano-1(3H)-Isobehzofuranones

Reaction of o-formyl-N, N-diethylbenzamides (5) with trimethylsilyl cyanide affords the corresponding (0-trimethylsi-lyl)cyanohydrins (6), which on treatment with acetic acid produce 3-cyanophthalides (7) in 80–90% isolated yields.     

Development of a Practical and Scalable Preparation using Sonication of Pd/Fibroin Catalyst for Chemoselective Hydrogenation

A practical and efficient preparation method of palladium‐fibroin (Pd/Fib), silk‐fibroin‐supported Pd(0) by means of sonication, has been developed. The Pd/Fib catalyst could be prepared within 12 h at room temperature starting from commercial silk‐fibroin and Pd(OAc)₂ in MeOH, whereas our previous preparation method required at least 4 days. The present improved process is applicable to a large‐scale preparation of Pd/Fib. The Pd/Fib prepared by the present method also catalyzed chemoselective hydrogenation of acetylenes, olefins, and azides in the presence of aromatic ketones, aldehydes, and halides; N‐Cbz protective groups; and benzyl esters, which are readily hydrogenated under the Pd/C‐ or Pd/C(en)‐catalyzed hydrogenation conditions.