Synthesis and Dimerization of Bicyclo [4.4.1] undec-1 (11)-ene,a Bridged trans-Cycloheptene

The synthesis of bicyclo [4.4.1] undec-1 (11)-ene ( 5 ) by intramolecular Wittig reaction is described. The Bredt olefin could not be isolated, but dimerized rapidly to a novel compound 15 containing a cyclopropane ring. The olefin 5 was trapped in situ by 2,5-diphenylbenzo [c]furan.     

A STUDY OF THE FLASH INDUCED 518 NM ABSORBANCE CHANGE KINETICS UNDER ANAEROBIC CONDITIONS

The preillumination induced acceleration of the flash-induced 518 nm absorbance change (ΔA₅₁₈) decay was studied in lettuce leaves and chloroplasts. In leaves, the acceleration was inhibited by DCMU or reversibly by removal of oxygen. In chloroplasts with added ADP and phosphate and/or reconstructed electron transport, the acceleration was also inhibited by DCMU or the lack of O₂.
Anaerobic inhibition of ΔA₅₁₈ decay acceleration was no longer observed when hydroxylamine replaced water as electron donor to PSII. Anaerobiosis was also shown to reversibly inhibit the initial rate of FeCN reduction in chloroplasts. These results suggest the mechanism of anaerobic inhibition of ΔA₅₁₈ decay acceleration to be associated with the O₂ evolving system.     

Tunable Thermoelastic Anisotropy in Hybrid Bragg Stacks with Extreme Polymer Confinement

Controlling thermomechanical anisotropy is important for emerging heat management applications such as thermal interface and electronic packaging materials. Whereas many studies report on thermal transport in anisotropic nanocomposite materials, a fundamental understanding of the interplay between mechanical and thermal properties is missing, due to the lack of measurements of direction‐dependent mechanical properties. In this work, exceptionally coherent and transparent hybrid Bragg stacks made of strictly alternating mica‐type nanosheets (synthetic hectorite) and polymer layers (polyvinylpyrrolidone) were fabricated at large scale. Distinct from ordinary nanocomposites, these stacks display long‐range periodicity, which is tunable down to angstrom precision. A large thermal transport anisotropy (up to 38) is consequently observed, with the high in‐plane thermal conductivity (up to 5.7 W m^?1 K^?1) exhibiting an effective medium behavior. The unique hybrid material combined with advanced characterization techniques allows correlating the full elastic tensors to the direction‐dependent thermal conductivities. We, therefore, provide a first analysis on how the direction‐dependent Young's and shear moduli influence the flow of heat.     

On-line high-performance liquid chromatography-solvent evaporation - high-performance liquid chromatography - capillary gas chromatography - flame ionisation detection for the analysis of mineral oil polyaromatic hydrocarbons in fatty foods

An automated on-line method is described that involves a first LC separation on a large column, evaporation of a 6-ml fraction in an on-line solvent evaporator, a second LC separation using a different mobile phase, fractionating the components of interest and transfer to GC through the in-line vaporiser/overflow interface. The method is designed for the injection of a large amount of food extract (e.g. up to 200 mg of fat) and is applied to the analysis of mineral oil material in a linseed oil.     

A Facile Synthesis of Optically Pure (−)-(S)-Ipsenol Using a Chiral Titanium Complex

A stereocontrolled synthetic route to optically pure (?)-(S)-ipsenol ( 1 ), the pheromone of Pityokteines curvidens and various other bark-beetle species is described. Key step of the synthesis is an enantioselective aldol reaction using a chiral titanium–carbohydrate complex (Scheme 1). The carboxylate function of the optically pure β-hydroxy acid 5 thus obtained in mol quantities is then elaborated to the diene moiety by standard methodology (Scheme 2).     

Axioms for Euclidean Green's functions II

We give new (necessary and) sufficient conditions for Euclidean Green's functions to have analytic continuations to a relativistic field theory. These results extend and correct a previous paper.with an Appendix by Stephen SummersSupported in part by the National Science Foundation under Grant MPS 73-05037 A01.Alfred P. Sloan Foundation Fellow.     

Total Synthesis of the Biphenyl Alkaloid (−)‐Lythranidine

A sequence comprising a ring‐closing alkyne metathesis of a propargyl alcohol derivative, followed by a ruthenium‐catalyzed redox isomerization of the derived cycloalkyne and a transannular aza‐Michael addition allowed the formation of the distinguishing piperidine‐metacyclophane framework of the Lythraceum alkaloid lythanidine in a few high‐yielding steps. This application attests to the excellent functional‐group tolerance of a molybdenum alkylidyne complex endowed with triphenylsilanolate ligands, which enabled the macrocyclization even in the presence of protic functionalities, and thus illustrates the power of contemporary catalytic acetylene chemistry for target‐oriented synthesis.     

Dihydrazidophosphoric Acid Derivatives as Starting Materials for Inorganic Heterocycles with Unusual Ring Conformations

Abstract

Reported are synthetic routes to inorganic heterocycles of different ring size, containing phosphorus, hydrazine, silicon and other elements as ring components. Steric effects that cause saturated sixmembered rings to adopt an unusual twist conformation are discussed (temperature dependent NMR-spectra, X-ray structures).