Synthesis of (+)-trixagol and its enantiomer, the terpenoid side chain of (−)-agelasine E

The naturally occurring γ-cyclogeranylgeraniol called (+)-trixagol has been synthesised for the first time. Trixagol was readily available in five steps from (S)-2,2-dimethyl-6-methylene-1-cyclohexanemethanol. The enantiomer of trixagol, which equates to the terpenoid side chain of the naturally occurring 7,9-dialkylpurinium salt (−)-agelasine E, was prepared from the (R) enantiomer of the cyclohexanemethanol. Both trixagol enantiomers were moderately active against Mycobacterium tuberculosis.     

pH-sensitive Photoluminescence of CdSe/ZnSe/ZnS Quantum Dots in Human Ovarian Cancer Cells

The photoluminescence of mercaptoacetic acid (MAA)-capped CdSe/ZnSe/ZnS semiconductor nanocrystal quantum dots (QDs) in SKOV-3 human ovarian cancer cells is pH-dependent, suggesting applications in which QDs serve as intracellular pH sensors. In both fixed and living cells the fluorescence intensity of intracellular MAA-capped QDs (MAA QDs) increases monotonically with increasing pH. The electrophoretic mobility of MAA QDs also increases with pH, indicating an association between surface charging and fluorescence emission. MAA dissociates from the ZnS outer shell at low pH, resulting in aggregation and loss of solubility, and this may also contribute to the MAA QD fluorescence changes observed in the intracellular environment.     

Dative sigma- and pi-bonding in boron-nitrogen compounds: molecular structures of (CH3)2NB(CH3)N(CH3)B(CH3)2 and [(CH3)2B]2NN(CH3)2 determined by gas electron diffraction and quantum chemical calculations

The molecular structures of dimethylamino[(dimethylboryl)methylamino]methylborane, Me2NBMeNMeBMe2 (1) and 1,1-bis(dimethylboryl)-2,2-dimethylhydrazine, (Me2B)2NNMe2 (2) have been determined by gas electron diffraction (GED), density functional theory calculations at the B3PW91/6-311++G** level and ab initio calculations at the MP2/6-311++G** level. 1 adopts an open structure similar to that of the isoelectronic hydrocarbon molecule permethylbutadiene; the central B-N bond distance at 148.0/149.3(7) pm (MP2/GED) corresponds to a single covalent N--B bond distance, the two terminal distances, 140.9/140.5(4) pm and 141.8/141.3(4) pm, correspond to the distance between N and B atoms joined by a covalent sigma-bond and a dative pi-bond. A closed form where the establishment of a dative bond between the terminal N and B atoms has led to the formation of a four-membered ring also corresponds to a minimum on the potential energy surface, but the energy is calculated to be 14.3 kJ mol(-1) higher at the MP2 level. This structure is also incompatible with the GED data. 2 adopts a structure in which a dative sigma-bond between the dimethylamino N atom and one of the boron atoms has led to the formation of a three-membered N(2)B ring. The dative sigma-bond distance is 165.5/164.0(13) pm, the two other bond distances in the ring are N-B=150.6/148.9(9) pm corresponding to a covalent sigma-bond and N-N=145.1/145.4(3) pm. The terminal B--N distance 139.6/138.9(9) pm is consistent with a covalent sigma-bond augmented by a dative pi-bond. An open Y-shaped structure also corresponds to a minimum on the potential energy surface, but the energy is 18.7 kJ mol(-1) higher (MP2) and it is incompatible with the GED data.     

Synthesis and antimycobacterial activity of agelasine E and analogs

Agelasine E, previously isolated from the marine sponge Agelas nakamurai, has been synthesized for the first time, together with analogs with various terpenoid side chains. Treatment of N6-methoxy-9-methyl-9H-purin-6-amine with allylic bromides gave the desired 7,9-dialkylpurinium salts together with minor amounts of the N6-alkylated isomer. The N6-methoxy group was finally removed reductively. 1H-15N HMBC and 1H-15N HSQC NMR spectroscopy gave additional information on tautomerism and charge delocalization in the purine derivatives studied. The heterocyclic products were screened for activity against Mycobacterium tuberculosis and agelasine analogs carrying a relatively long terpenoid substituent in the purine 7-position and a methoxy group at N-6 were potent inhibitors of bacterial growth. Since agelasine analogs with the geranylgeranyl chain at N-7 exhibited antimicrobial activity, several strategies for synthesis of geometrically pure (2E,6E,10E)-geranylgeranyl bromide from geranyllinalool were evaluated.     

High- and low-molecular-weight lignosulfonates and Kraft lignins as oil/water-emulsion stabilizers studied by means of electrical conductivity

Electrical conductivity measurements were used to study the creaming rates in oil/water emulsions stabilized with five lignosulfonates and one Kraft lignin. The creaming process resulted in a narrow dispersion band separating the water-rich and the oil-rich phases. An electrode was designed to follow this zone in the emulsion as a function of time. This makes it possible to calculate the amount of water separated from the emulsion directly from the creaming profiles. The stability concerning creaming was also evaluated with data obtained from visual inspection. Equivalent creaming profiles indicate that the electrode design used is suitable for stability measurements in the systems examined. Droplet interaction in diluted emulsions was studied with video-enhanced microscopy. Received: 10 September 1998 Accepted in revised form: 18 December 1998     

Synthesis of silicon-based infrared semiconductors in the Ge-Sn system using molecular chemistry methods.

Growth reactions based on a newly developed deuterium-stabilized Sn hydride [(Ph)SnD(3)] with Ge(2)H(6) produce a new family of Ge-Sn semiconductors with tunable band gaps and potential applications in high-speed, high-efficiency infrared optoelectronics. Metastable diamond-cubic films of Ge(1-x)Sn(x) alloys are created by chemical vapor deposition at 350 degrees C on Si(100). These exhibit unprecedented thermal stability and superior crystallinity despite the 17% lattice mismatch between the constituent materials. The composition, crystal structure, electronic structure, and optical properties of these materials are characterized by Rutherford backscattering, high-resolution electron microscopy, and X-ray diffraction, as well as Raman, IR, and spectroscopic ellipsometry. Electron diffraction reveals monocrystalline and perfectly epitaxial layers with lattice constants intermediate between those of Ge and alpha-Sn. X-ray diffraction in the theta-2theta mode shows well-defined peaks corresponding to random alloys, and in-plane rocking scans of the (004) reflection confirm a tightly aligned spread of the crystal mosaics. RBS ion-channeling including angular scans confirm that Sn occupies substitutional lattice sites and also provide evidence of local ordering of the elements with increasing Sn concentration. The Raman spectra show bands corresponding to Ge-Ge and Sn-Ge vibrations with frequencies consistent with random tetrahedral alloys. Resonance Raman and ellipsometry spectra indicate a band-gap reduction relative to Ge. The IR transmission spectra suggest that the band gap decreases monotonically with increasing Sn fraction. The synthesis, characterization, and gas-phase electron diffraction structure of (Ph)SnD(3) are also reported.     

Temperature-Programmed Packed Capillary Liquid Chromatography Separation with Large Volume On-Column Focusing of Retinyl Esters

A non-aqueous isocratic reversed-phase packed capillary high performance liquid chromatography method for the determination of retinyl esters, utilizing temperature programming and on-column focusing large volume injection, has been developed. The stationary phase material was C₃₀, and the mobile phase consisted of acetonitrile-dichloromethane (70 : 30, v/v). A three-step temperature program, starting at 10°C for 10 min, then 1°/min to 30°C, and finally 2.5°/min to 70°C, was found most appropriate. Compared to an isothermal separation at 25°C, this temperature program provided improved peak resolution, enhanced peak shapes of the last eluting compounds, and a reduction of the overall elution time. A mass limit of detection of 27 pg was found with respect to retinyl palmitate, using UV detection with an “U” shaped flow cell at 327 nm. This corresponds to a concentration limit of detection of 2.7 pg/μL, when utilizing an injection volume of 10 μL. The concentration of retinyl palmitate in arctic seal liver samples was estimated to be 62.6 μg/g liver.     

Sodium borohydride mediated reduction of N-Boc protected purines and applications in the synthesis of 7-alkyladenines and tetrahydro[1,4]diazepino-[1,2,3-gh]purines

Electron deficient purines can be reduced to 7,8-dihydropurines when treated with cheap and easy-to-handle sodium borohydride in methanol. The dihydropurine formed by reduction of tris-Boc-protected adenine is a useful intermediate in efficient syntheses of 7-alkyladenines and tetrahydro[1,4]diazepino[1,2,3-gh]purines.