Lithium Selective Chromogenic Azocrown Ethers

Novel chromogenic crown ethers having an intraannular azo and phenolic hydroxy subunits have been used as complexing reagents for alkali metal cations. The complex formation was studied by visible spectroscopy and formation constants were calculated. The most pronounced spectral changes were observed for lithium ion.     

Porous Molecular Capsules as Non-Polymeric Transducers of Mechanical Forces to Mechanophores

Mechanical grinding/milling can be regarded as historically the first technology for changing the properties of matter. Mechanically activated molecular units (mechanophores) can be present in various structures: polymers, macromolecules, or small molecules. However, only polymers have been reported to effectively transduce energy to mechanophores, which induces breakage of covalent bonds. In this paper, a second possibility is presented—molecular capsules as stress-sensitive units. Mechanochemical encapsulation of fullerenes in cystine-based covalent capsules indicates that complexation takes place in the solid state, despite the fact that the capsules do not possess large enough entrance portals. By using a set of solvent-free MALDI (sf-MALDI) and solid-state NMR (ss-NMR) experiments, it has been proven that encapsulation proceeds during milling and in this process hydrazones and disulfides get activated for breakage, exchange, and re-forming. The capsules are porous and therefore prone to collapse under solvent-free conditions and their conformational rigidity promotes the collapse by the breaking of covalent bonds.     

Photooxygenation of 2-amino-3-cyano-4,5,6,7-tetrahydrobenzo[b]thiophene

The photooxygenation of 2-amino-3-cyano-4,5,6,7-tetrahydro-benzo[b]thiopene1 was carried out in the presence of thiourea in order to reductively trap the intermediate; however, the rearranged compound 3-cyano-7-hydroxy-2-thio-2,4,5,6,7,7a-hexahydroindole2 was isolated. The structure, determined by X-ray crystallography, is described, and the mechanism for the formation of2 is discussed.     

High-pressure (2+2)cycloaddition of toluene-4-sulphonyl isocyanate to glycals

High-pressure (2+2)cycloaddition of toluene-4-sulphonyl isocyanate to glycals is examined. Reactions proceed regiospecifically to afford single products in case of all 3-substituted glycals. Upon heating or even after standing at room temperature adducts undergo retro-addition to give starting glycals. Various aspects of the cycloaddition are discussed, especially ret-ro-reaction and rearrangement of β-lactams to α,β-unsaturated amides.     

Determination of gold in biological materials by radiochemical neutron activation analysis

A radiochemical neutron activation analysis procedure was developed for the determination of trace amounts of gold in biological materials. The procedure was realized with irradiation of reference and test samples in a nuclear reactor, selective and quantitative separation of gold using inorganic MnO₂ Resin and gamma-ray spectrometric measurement of ¹⁹⁸Au. The method is characterized by a low limit of detection of gold at ng g^?1 level. Results shows that the method can be applied to the determination of trace amounts of gold in tissues for medical research.     

Photooxygenation of 2-amino-3-cyano-4,5,6,7-tetrahydrobenzo[b]thiophene

The photooxygenation of 2-amino-3-cyano-4,5,6,7-tetrahydro-benzo[b]thiopene1 was carried out in the presence of thiourea in order to reductively trap the intermediate; however, the rearranged compound 3-cyano-7-hydroxy-2-thio-2,4,5,6,7,7a-hexahydroindole2 was isolated. The structure, determined by X-ray crystallography, is described, and the mechanism for the formation of2 is discussed.     

Energy transfer dynamics of nanocrystal-polymer composites

Steady-state and time-resolved photoluminescence spectroscopy are used to examine the photoluminescent properties of nanocrystal-polymer composites consisting of colloidal PbS nanocrystals blended with poly(2-methoxy-5(2-ethylhexyloxy)-p-phenylene vinylene). Quenching of the emission from the conjugated polymer due to the PbS nanocrystals is observed along with band edge emission from the ligand capped PbS nanocrystals. A decrease in the photoluminescence lifetime of MEH-PPV is also observed in the thin film nanocrystal-polymer composite materials. Photoluminescence excitation spectroscopy of the PbS nanocrystal emission from the composite shows features attributed to MEH-PPV providing evidence of a F?rster transfer process.