Ordered semigroups containing maximal or minimal elements

Communicted by J. S. Ponizovskii     

Anomalous conversion of 127 keV (E3) transition in134Cs

The total conversion coefficient of the 127.49 keV E3 isomeric transition in the decay of^134mCs was measured using the gamma intensity balance method with the help of a high resolution low energy photon detector. Theα _Tvalue was found to be 5.84±0.47 as against the theoretical value of 6.96, thus showing an anomaly of (16.1±6.7)%. TheK-conversion coefficient,α _kwas also measured using the X-ray peak to gamma ray intensity method and found to be 2.24±0.04 as against the theoretical value of 2.72, which shows an anomaly of (17.6±1.4)% consistent with the experimental anomaly inα _T. TheE3 hindrance factor of the isomeric transition was estimated to be (3.44±0.23) ·10⁴.     

A short convergent synthesis of the [3.2.1]dioxabicyclooctane subunit of sorangicin A via regioselective epoxide opening

In this paper, we disclose the synthesis of the dioxabicyclo[3.2.1]octane subunit of the potent antibiotic sorangicin A. The synthesis was achieved in a convergent manner in 8 steps. Regio- and stereoselective intermolecular epoxide opening, ring-closing metathesis and iodo-etherification are key steps. cis-2-Butene diol has been employed as a common staring material.     

Phosphomolybdic acid supported on silica gel: a mild, efficient and reusable catalyst for the synthesis of 2,3-unsaturated glycopyranosides by Ferrier rearrangement

A simple, mild, efficient and environmentally benign method for the synthesis of 2,3-unsaturated allyl C-glycosides and O- and S-glycosides is described using phosphomolybdic acid supported on silica gel as a reusable catalyst with high α-selectivity.     

Enantiospecific synthesis of tricyclo[5.2.1.0]decanes via acid catalysed rearrangement of isotwistanes

An acid catalysed rearrangement was employed for the enantiospecific conversion of isotwistanol to tricyclo[5.2.1.0^4,8]decanes, which provided support for the proposed biosynthesis of allopupukeananes from pupukeananes. The strategy has been further extended to the enantiospecific synthesis of a homobrexane.     

Kinetics and mechanism of the oxidation ofbis(2,4,6-tripyridyl-1,3,5-triazine)iron(II) bytrans-1,2-diaminocyclohexanetetraacetatomanganate(III) in acetate buffer

The rapid oxidation ofbis(2,4,6-tripyridyl-1,3,5-triazine)-iron(II), [Fe(TPTZ)₂]²⁺, bytrans-1,2-diaminocyclohexanetetraacetatomanganate(III), [Mn^III(Y)]⁻, in acetate buffers was monitored using stopped-flow spectrophotometry. The reaction is first order in the substrate and evidence was obtained for pre-complexation between the oxidant and the substrate. The reaction rate increases as the pH increases. Characterisation of the products using the radiotracers⁵⁴Mn and⁵⁹Fe indicated that [Mn^II(Y)]²⁻ and [Fe(TPTZ)₂]³⁺ are the final products. The reaction obeys the rate law:

Studies on the use of salicylaldehyde as a chelating and extracting agent

Summary Salicylaldehyde is proposed as both a chelating and extracting agent. Vanadium(V) can be extracted from aqueous solutions of pH 1.4 using a solvent mixture containing 90% salicylaldehyde and 10% n-butanol. n-Butanol exerts a synergic effect on the extraction of vanadium(V) by salicylaldehyde. Based on this extraction, a spectrophotometric method has been developed for the determination of vanadium, the sensitivity being 0.0168 g of vanadium per cm². The nature of the extracted species and a possible mechanism for the synergic effect of the alcohol are discussed.

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Zusammenfassung Salicalaldehyde wird als chelatbildendes Extraktionsmittel für Vanadium vorgeschlagen. Aus wäßrigen Lösungen vom pH 1,4 kann Vanadium mit einem Lösungsmittelgemisch aus 90% Salicylaldehyd und 10% n-Butanol extrahiert werden, wobei das Butanol eine synergistische Wirkung ausübt. Die anschließende spektrophotometrische Bestimmung kann mit einer Empfindlichkeit von 0,0168 g V/cm² durchgeführt werden. Die Art des gebildeten Komplexes sowie die Wirkung des Alkohols werden diskutiert.

     

In situ NMR spectroscopy of combustion

The first successful in situ studies of free combustion processes by one- and two-dimensional NMR spectroscopy are reported, and the feasibility of this concept is demonstrated. In this proof-of-principle work, methane combustion over a nanoporous material is investigated using hyperpolarized (hp)-xenon-129 NMR spectroscopy. Different inhomogeneous regions within the combustion cell are identified by the xenon chemical shift, and the gas exchange between these regions during combustion is revealed by two-dimensional exchange spectra (EXSY). The development of NMR spectroscopy as an analytical tool for combustion processes is of potential importance for catalyzed reactions within opaque media that are difficult to investigate by other techniques.     

Zinc triflate: A mild and efficient catalyst for deprotection of tetrahydropyranyl ethers

Treatment of tetrahydropyranyl (THP) ethers with zinc triflate in methanol provides a simple and efficient process for deprotection of these ethers and the parent alcohols are obtained in excellent yields.