Carbonyl-yne reactions of 3,3,3-trifluoropyruvates

An efficient synthesis of trifluoromethyl-containing 2,3-allenols via carbonyl-yne reaction of 3,3,3-trifluoropyruvates with acetylenes is described. In the presence of MgBr₂·Et₂O the reaction of methyl trifluoropyruvate with hex-1-yne proceeds diastereoselectively. Trifluoromethyl-substituted 2,3-allenols can be stereoselectively transformed into trifluoromethyl-substituted 2,5-dihydrofurans on treatment with AgNO₃.     

Solvothermale Synthese und Bestimmung der Kristallstrukturen von AgBiI4 und Ag3BiI6

Solvothermal Synthesis and Crystal Structure Determination of AgBiI₄ and Ag₃BiI₆ AgBiI₄ and Ag₃BiI₆ were synthesized by solvothermal reaction from AgI and BiI₃ in diluted HI‐solution (20 %) at a temperature of 160 °C. The greyish‐black crystals grow as octahedra (AgBiI₄) or hexagonal/trigonal platelets (Ag₃BiI₆). AgBiI₄ crystallizes in space group Fd3¯m with a = 1222.3(1) pm (300 K) and Z = 8 whereas Ag₃BiI₆ shows the space group R3¯m with a = 435.37(6) pm, c = 2081.0(4) pm (300 K) and Z = 1. Both crystal structures show stacking sequence abcabc… of hexagonal layers containing Iodine. Bismuth and silver are sharing octahedral sites with different mass ratio in both structures. The part of silver which could be localized varies with temperature. This behaviour indicates mobility of silver within the crystal structure. The ionic conductivity of AgBiI₄ is explored. AgBiI₄ and Ag₃BiI₆ show close structural relationship, with AgBiI₄ as a variant with a higher degree of order.     

Synthesis of homochiral 2-C-perfluoroalkyl substituted d- and l-riboses

Homochiral 2-C-perfluoroalkyl substituted d- and l-riboses were synthesized via Barbier, Grignard and Ruppert type reactions. The influence of the size of the perfluoroalkyl groups, attached to C-2, on the furanose/pyranose as well as on the α-furanose/β-furanose and α-pyranose/β-pyranose ratio in solution was studied.     

Electrochemical doping of chirality-resolved carbon nanotubes

Raman spectra of electrochemically charged single-wall carbon nanotubes (HiPco) were studied by five different laser photon energies between 1.56 and 1.92 eV. The bands of radial breathing modes (RBM) were assigned to defined chiralities by using the experimental Kataura plot. The particular (n,m) tubes exhibit different sensitivity to electrochemical doping, monitored as the attenuation of the RBM intensities. Tubes which are in good resonance with the exciting laser exhibit strong doping-induced drop of the RBM intensity. On the other hand, tubes whose optical transition energy is larger than the energy of an exciting photon show only small changes of their RBM intensities upon doping. This rule presents a tool for analysis of mixtures of single-walled carbon tubes of unknown chiralities. It also asks for a re-interpretation of some earlier results which were reported on the diameter-selectivity of doping. The radial breathing mode in strongly n- or p-doped nanotubes exhibited a blue-shift. A suggested interpretation follows from the charging-induced structural changes of SWCNTs bundles, which also includes a partial de-bundling of tube ropes.     

Molecular structures and intramolecular interactions in dimethyl cyclohexane isomers

The geometries of ten isomers of dimethyl cyclohexane were determined by ab initio gradient geometry refinement with the 4-21G basis set. It is found that many intramolecular interactions are clearly manifested by correlated structural trends, and that they are consistent with strain energies calculated by employing previously defined ab initio group equivalents. Specifically, non-bonded interactions are found between two adjacent methyl groups in some of the forms, and between axial methyl groups and adjacent axial C? H bonds in others. Unperturbed axial C? H and C? C bonds are consistently longer than equatorial bonds. In general, C? H bonds which are involved in non-bonded repulsive interactions are shortened, i.e., strengthened, and the corresponding H? C? C angles are large, compared to non-interacting parameters.     

Synthesis of (±)-Desmarestene and (±)-Viridiene,the Two Sperm Releasing and Attracting Pheromones from the Brown Algae Desmarestia aculeata and Desmarestia viridis

Desmarestene 1 6-(1Z,3-butadienyl)-1,4-cycloheptadiene and viridiene 3 cis-3-(1Z, 3-butadienyl)-4-vinylcyclopentene are chemical messengers for male gametes of the brown algae Desmarestia aculeate and Desmarestia viridis. Total syntheses of 1 , 3 and their stereoisomers 1a , 3a - c are reported. Gas-chromatographic comparison of synthetic 1 and 3 with the corresponding natural products has established their structural identity.     

Efficient chiral discrimination by 77Se NMR

[reaction: see text] Several (77)Se NMR experiments were performed by titrating a sample of selenides with the chiral shift reagent methylbenzylamine (MBA), followed by acquisition of (77)Se NMR spectra. Eventually, we observed the appearance of two anisochronous resonances, with a relatively large separation, from 37 to 56 Hz, corresponding to the formation of the diastereomeric complexes. This methodology avoids derivatization processes, and the studied compound can be easily recovered from the NMR tube.     

Prediction of the glass transition temperature for compatible polymer blends of varying compositions

Compatible polymer blends have been found to have widespread commercial applications. The simplest criterion for judging polymer—polymer miscibility in the solid state is the glass transition temperature (T_g), which can vary widely according to blend composition for a compatible system.Recently, an equation which predicts the T_g of intimate mixtures of compatible polymers has been derived, based on classical thermodynamics. Only a knowledge of the T_g and heat capacity increment (ΔC_p) of each pure component is required to predict the T_g at any composition.In this paper, the validity of this entropy-based relationship is investigated for a variety of commercial compatible polymer blends, including some based on poly(vinyl chloride), polystyrene, and poly(2,6-dimethyl-,4-phenylene oxide). The T_g and ΔC_p of each pure component are measured with a Perkin-Elmer DSC-2 differential scanning calorimeter, are predicted glass transition temperatures are compared with those observed experimentally.     

Photodynamic actinometry using microspheres: concept, development and responsivity

Photodynamic therapy (PDT) relies on three main ingredients, oxygen, light and photoactivating compounds, although the PDT response is definitively contingent on the site and level of reactive oxygen species (ROS) generation. This study describes the development of a novel, fluorescent-based actinometer microsphere system as a means of discerning spatially resolved dosimetry of total fluence and ROS production. Providing a high resolution, localized, in situ measurement of fluence and ROS generation is critical for developing in vivo PDT protocols. Alginate-poly-L-lysine-alginate microspheres were produced using ionotropic gelation of sodium alginate droplets, ranging from 80 to 200 microm in diameter, incorporating two dyes, ADS680WS (ADS) and Rhodophyta-phycoerythrin (RPE), attached to the spheres' inside and outside layers, respectively. To test the responsivity and dynamic range of RPE for ROS detection, the production of ROS was initiated either chemically using increasing concentrations of potassium perchromate or photochemically using aluminum tetrasulphonated phthalocyanine. The generation of singlet oxygen was confirmed by phosphorescence at 1270 nm. The resulting photodegradation and decrease in fluorescence of RPE was found to correlate with increased perchromate or PDT treatment fluence, respectively. This effect was independent of pH (6.5-8) and could be inhibited using sodium azide. RPE was not susceptible to photobleaching with light alone (670 nm; 150 Jcm(-2)). ADS, which absorbs light between 600 and 750 nm, showed a direct correlation between radiant exposure (670 nm; 0-100 Jcm(-2)) and diminished fluorescence. Photobleaching was independent of irradiance (10-40 mW cm(-2)). We propose that actinometer microspheres may provide a means for obtaining high spatial resolution information regarding delivered PDT dose within model systems during investigational PDT development and dosimetric information for clinical extracorporeal PDT as in the case of ex vivo bone marrow purging.     

Structure Determination of a New Spirobicyclic Triterpenoid from Iris foetidissima

The novel iridal 10 has been isolated from rhizome extracts of Iris foetidissima. Its structure was established by spectroscopic methods and oxidative degradation. Final proof of the spirobicyclic nature of the compound – a new feature in the triterpenoid field – was afforded by the correlations observed in the 2D-HMBC- (¹H-detected multiple-bond heteronuclear multiple-quantum coherence) spectrum. The possible biogenesis of this unusual compound is discussed.