VISUAL PIGMENTS—10. SPECTROSCOPY AND PHOTOPHYSICAL DYNAMICS OF RETINOL AND RETINYL ETHER

Abstract— The absorption and emission spectra, lifetimes and quantum yields of all-trans retinol have been examined as a function of solvent and temperature. In addition, the spectroscopy of retinyl ether and 2 other polyene alcohols have been determined. Based on the results obtained, we conclude that the singlet excited state of retinol and retinyl cther is of a forbidden character and of the type loosely called ¹A^-_g. Retinol forms a dimer in an alkane solvent when cooling from 298 to 77 K. A general structure for the dimer is proposed.     

Use of transition elements to enhance sensitivity for selenium determination by graphite-furnace atomic-absorption spectrophotometry combined with solvent extraction with the APDC-MIBK system

A microanalytical method for the measurement of selenium in waters and biological materials by a flameless atomic-absorption technique has been developed. The ammonium pyrrolidinedithiocarbamate-methyl isobutyl ketone extraction system is used for separation from interfering materials such as large amounts of alkali and alkaline earth metal salts and mineral acids. The atomic-absorption sensitivity for selenium is found to be enhanced to a large extent by co-extraction of some transition metal ions. Copper(II) has been used successfully as such an additive to diminish the volatility of selenium in the graphite furnace during the ashing step of the atomization cycle. When the aqueous phase/organic solvent volume ratio is 5 and the volume injected into the graphite furnace is 20 mul, the sensitivity for selenium is 0.3 ng/ml for 1% absorption. The relative standard deviation is ca. 2%. Interference by other metal ions is prevented by masking with EDTA. The method has been applied satisfactorily for the determination of minute amounts of selenium in waters and various biological materials.     

Cu(I) catalyst in DMF: an efficient catalytic system for the synthesis of furans from 2-(1-alkynyl)-2-alken-1-ones

The cyclization of 2-(1-alkynyl)-2-alken-1-ones 1 proceeded very smoothly in the presence of alcohols 2 with a catalytic amount of Cu(I)Br in DMF at 80 degrees C, leading to the formation of highly substituted furans 3. The catalytic system reported herein is easy to handle, compared to the previously known system wherein the reaction between 1 and 2 needed to use moisture sensitive gold(III) chloride.     

Stereocontrolled approaches to 9(0)-methanoprostacyclin

A stable PGI₂ analog (methanoprostacyclin $\text{2}$) was synthesized starting from 5-norbornene-2,3-dicarboxylic anhydride.