NMR Studies of Alkaloids. Assignment of the Configuration at C(20) in Tubotaiwine (Dihydrocondylocarpine)

Two-dimensional, high-field NMR methods are employed in confirming the relative configuration at the C(20) ethyl side-chain junction as S* in the natural alkaloid tubotaiwine (dihydrocondylocarpine).     

Total synthesis of (±)-desmethylhexahydrovallesiachotaminelactones

Total synthesis of (±)-desmethylhexahydrovallesiachotaminelactones 1a and 1b, and their isomers 2a and 2b is described. The formation of other epimeric pairs of lactones (1a and 3a, and 1b and 3b) from vallesiachotamine 4 is also described.     

Separation of flavonol-2-O-glycosides from Calendula officinalis and Sambucus nigra by high-performance liquid and micellar electrokinetic capillary chromatography.

Calendula officinalis and Sambucus nigra flowers were analysed by reversed-phase high-performance liquid chromatography (RP-HPLC) and micellar electrokinetic capillary chromatography (MECC). RP-HPLC was performed on C8 Aquapore RP 300 columns with eluents containing 2-propanol and tetrahydrofuran. MECC was carried out on a 72-cm fused-silica capillary using sodium dodecyl sulphate and sodium borate (pH 8.3) as the running buffer. The results obtained by these techniques are compared.     

Electron transport and hot phonons in carbon nanotubes

We demonstrate the key role of phonon occupation in limiting the high-field ballistic transport in metallic carbon nanotubes. In particular, we provide a simple analytic formula for the electron transport scattering length, which we validate by accurate first principles calculations on (6, 6) and (11, 11) nanotubes. The comparison of our results with the scattering lengths fitted from experimental I-V curves indicates the presence of a nonequilibrium optical phonon heating induced by electron transport. We predict an effective temperature for optical phonons of thousands Kelvin.     

Novel applications of the modified polonovski reaction. A biomimetic synthesis of quinuclidines.

Suitably substituted aminoesters can be transformed to the corresponding α-aminonitriles and in the case of piperidino-acetic ester derivatives, into the biochemically important quinuclidine ring system.     

Synthetic studies in the alkaloid field—IV: The sodium dithionite reduction of 1-[2-(3-indolyl)-ethyl]-3-methoxycarbonyl pyridinium bromides

The preparation of racemic indolo[2,3-a]quinolizine derivatives by sodium dithionite reduction of appropriate pyridinium bromides has been studied, A method has been found of influencing with high degree of stereoselectivity the C(12b)-C(2) stereochemical relationship in the products formed. The determination of the stereochemistry of the products by comparative examination of their ¹³C NMR spectra is described. The convenience of the sodium dithionite reduction method for the preparation of vallesiachotamine 1 models is discussed.     

A Clustering Search metaheuristic for the Point-Feature Cartographic Label Placement Problem

The Point-Feature Cartographic Label Placement (PFCLP) problem consists of placing text labels to point features on a map avoiding overlaps to improve map visualization. This paper presents a Clustering Search (CS) metaheuristic as a new alternative to solve the PFCLP problem. Computational experiments were performed over sets of instances with up to 13,206 points. These instances are the same used in several recent and important researches about the PFCLP problem. The results enhance the potential of CS by finding optimal solutions (proven in previous works) and improving the best-known solutions for instances whose optimal solutions are unknown so far.     

Intercalant and intermolecular phonon assisted superconductivity in K-doped picene

K(3) picene is a superconducting molecular crystal with a critical temperature of T(c) = 7 or 18 K, depending on the preparation conditions. Using density functional theory we show that electron-phonon interaction accounts for T(c) 3-8 K. The average electron-phonon coupling, calculated by including the phonon energy scale in the electron-phonon scattering, is λ = 0.73 and ω(log) = 18.0 meV. Intercalant and intermolecular phonon modes contribute substantially (40%) to λ as also shown by the isotope exponents of potassium (0.19) and carbon (0.31). The relevance of these modes makes superconductivity in K-doped picene peculiar and different from that of fullerenes.