BF3.OEt2-mediated cycloaddition of O-tert-butyldimethylsilyloximes having olefin moieties: intramolecular cycloaddition of N-borano-nitrones

Treatment of O-tert-butyldimethylsilyloximes having olefin moieties in the molecules with BF3.OEt2 results in efficient generation of N-borano-nitrones, which undergo intramolecular cycloaddition at room temperature to afford N-nonsubstituted cycloadducts after work-up.     

Radical cascade reaction with 1,4-dienes and 1,4-enynes using 2-(iodomethyl)cyclopropane-1,1-dicarboxylate as a homoallyl radical precursor: one-step synthesis of bicyclo[3.3.0]octane derivatives

[reaction: see text] Radical cascade reaction with various 1,4-dienes and 1,4-enynes using dimethyl 2-(iodomethyl)cyclopropane-1,1-dicarboxylate as a homoallyl radical precursor smoothly proceeds through an iodine atom transfer mechanism to give functionalized bicyclo[3.3.0]octane derivatives in good yields.     

Practical carbonyl-ene reactions of alpha-methylstyrenes with paraformaldehyde promoted by a combined system of boron trifluoride and molecular sieves 4A

[reaction: see text] A combined system of boron trifluoride and molecular sieves is an efficient promoter for the carbonyl-ene reaction of alpha-methylsyrenes with paraformaldehyde. The coexistence of BF3 x OEt2 and molecular sieves 4A is essential for obtaining high yields of ene products.     

Control of light pulse propagation with only a few cold atoms in a high-finesse microcavity

Propagation of a light pulse through a high-Q optical microcavity containing a few cold atoms (N<10) in its cavity mode is investigated experimentally. With less than ten cold rubidium atoms launched into an optical microcavity, up to 170 ns propagation lead time ("superluminal"), and 440 ns propagation delay time (subluminal) are observed. Comparison of the experimental data with numerical simulations as well as future experiments are discussed.     

Multiple reflections of Lamb waves at a delamination

Wave propagation in laminated plates with delaminations was calculated using the semi-analytical finite element method. The visualization results and deeper numerical analyses revealed the following phenomena on the fundamental Lamb modes at delamination regions of laminated plates. First, Lamb wave propagates toward the delamination, and then splits into two independent waves at the "Entrance" of the delamination with no significant reflections. These two waves reach the "Exit" of the delamination with the different phases and arrival time. Thus reflected and transmitted waves are excited at the Exit. The repetition of such reflections at the Exit causes the multiple reflections at regular intervals corresponding to the delamination size.     

Masking effect of potassium iodide on the interferences in the atomic-absorption spectrophotometric determination of antimony utilizing stibine generation by sodium borohydride tablet reduction

Summary The masking effect of potassium iodide with or without hydroxylamine on the interferences in the atomic-absorption spectrophotometric determination of antimony via its hydride by sodium borohydride tablet reduction has been studied. It has been well known in the conventional colorimetric method [21] that both potassium iodide and stannous chloride completely suppress the evolution of stibine. However, in this sodium borohydride tablet reduction, potassium iodide plays a role in masking the interferences of not only stannous chloride but also other numerous ions. By the procedure established here, the calibration curve was linear up to a concentration of 0.04g/ml of antimony with the coefficient of variation of 2.4 %. The method was successfully applied to the determination of antimony in a river sediment.

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Maskierende Wirkung von Kaliumiodid auf Störungen bei der AAS-Bestimmung von Antimon durch Stibinerzeugung mit Hilfe der Natriumborhydridreduktion

Zusammenfassung Es ist bekannt, daß bei der colorimetrischen Bestimmungsmethode [21] sowohl KI als auch SnCl₂ die Entwicklung von Stibin vollständig verhindern. Bei der hier beschriebenen Reduktion mit Hilfe einer NaBH₄-Tablette maskiert jedoch KI (mit oder ohne Hydroxylaminzusatz) Störungen durch SnCl₂ sowie durch zahlreiche andere Ionen. Die Eichkurve verläuft bis zu 0,04 g Sb/ml linear. Der Variationskoeffizient beträgt 2,4 %. Als Anwendungsbeispiel wird die Antimonbestimmung in Flußsedimenten erwähnt.

     

Anodic a.c. polarography of methylthymol blue

The anodic a.c. polarographic properties of methylthymol blue (MTB) were investigated in the supporting electrolyte of potassium nitrate containing buffer. The difference in the peak potentials of MTB and EDTA is a good measure of the difference in the stabilities of both chelates. The stability constant of mercury(II)-MTB complex was successfully determined on the basis of that reported for the mercury(II)-EDTA complex.     

Synthetic macrocyclic ligands. III. Synthesis of a quinone-hydroquinone redox system incorporated with complexing ability toward cations

Two quinones bridged with a polyether chain and the corresponding hydroquinones were synthesized, and their redox reaction and complexations with sodium and potassium ions were observed.     

Selective pH gradient formation across a capsule membrane corked with charged synthetic bilayers

Ultrathin, large nylon capsules whose porous membranes were corked with charged, synthetic bilayer-forming amphiphiles (cationic, anionic, zwitterionic bilayers) were prepared. The chemically stable, bilayer-corked capsules can selectively retain 0.1 M aqueous acidic (HCl, HNO₃, H₂SO₄, HClO₄ and p-toluenesulfonic acid) and alkaline solutions (NaOH, Ba(OH)₂, NH₄ OH, and N(Et)₄OH) in the inner aqueous phase depending on the surface charge of corking bilayers: the capsule corked with positively and negatively charged bilayers could selectively store alkalies and acids, respectively, and could keep a selective pH-gradient across the membrane. The zwitterionic bilayer-corking could retain neither acids nor alkalies in the inner aqueous phase. The permeation of these acids and alkalies to the outer phase (pH gradient decreasing across the capsule membrane) could be reversibly controlled by the phase transition of corking bilayers from gel to liquid crystalline state. The selective storage and permeation of acids and alkalies could be explained by the process of permeation of H⁺ or OH^- counter ions across the charged bilayer-corking.