A molecular approach to self-assembly of trimethylsilylacetylene derivatives on gold

We recently discovered that a linear multifunctional trimethylsilylacetylene (TMSA) compound forms long-range and highly stable self-assembled monolayers (SAMs) on reconstructed Au(111). To better understand the interactions governing self-assembly in this new system, we synthesized a series of homologue organosilanes and performed scanning tunneling microscopy (STM) measurements at the Au(111)/n-tetradecane interface. The four TMSA-terminated linear silanes that we synthesized self-assemble in similar ways on gold, with the molecules standing upright on the surface. In contrast, compounds with a slightly modified terminal group but the same polyunsaturated linear chain above the TMSA head do not self-assemble. In particular, substituting a methyl group of TMSA with a more bulky one prevents self-assembly. Removing the C triple bond C triple bond of TMSA or substituting the Si atom by a C atom also hinders self-assembly. Finally, substituting one methyl group of TMSA by a hydrogen atom induces self-assembly but in a different geometry, with the molecules lying flat on the gold surface in a quasi-epitaxy mode. Our molecular approach demonstrates the key role played by the TMSA head in self-assembly, its origin being twofold: 1) the TMSA layers are commensurate to the Au(111) adlattice along the <112> direction, and 2) the C triple bond C triple bond of TMSA activates the Si atom and induces the creation of a surface Si-Au chemical bond. The highly stable TMSA-based SAMs appear then as promising materials for applications in surface modification.     

Chromatographische Trennung und quantitative Bestimmung aller acht Stereoisomeren von α-Tocopherol

Separation and Quantitation of All Eight Stereoisomers of α-Tocopherol by Chromatography The results of the analysis of several derivatives of (all-rac)-α-tocopherol by HPLC on a chiral stationary phase and by capillary GC on a achiral stationary phase are reported. Consecutive application of both methods to the ethyl-ether derivative allows the separation and quantification of all eight possible stereoisomers of (all-rac)-α-tocopherol.     

Versuche zum Nachweis der Strömungsdoppelbrechung von Stärkesubstanzen (Studien über Pflanzenkolloide,L)

Zusammenfassung Lösungen von Kartoffelamylopektin und Kartoffelamylosen zeigen in einer Apparatur, welche die Empfindlichkeit= 1 besitzt, keine Strömungsdoppelbrechung. Durch Vergleich der Rotationsdiffusionskonstante, welche aus der durch die Empfindlichkeit der Apparatur geschätzten Maxwellschen Konstante folgt, und des für kugelige Teilchen berechneten Wertes findet man, daß sowohl das Amylopektin wie auch die Amylose Moleküle besitzen, die nicht wesentlich von der Kugelgestalt abweichen.     

Isolierung und Strukturaufklärung von 36 Diterpenoiden aus Trichomen von Plectranthus edulis (VATKE) T.T. AYE

Isolation and Structure Elucidation of 36 Diterpenoids from Leaf-Glands of Plectranthus edulis (VATKE ) T.T. AYE Analysis of the polar diterpenoids from the yellow glands of the title plant from Kenya and Abyssinia led to the identification of several novel abietanoids. Main compound is the known edulon A ( 40 ), a 5(4→3) abeo-abietane. Minor compounds include 6 different royleanones, 15 spirocoleons, 3 vinylogous quinones, 8 acylhydroquinones (as their 6,7-dioxo compounds or the tautomeric disophenols), 2 naphthaquinones (as the 1,10-seco-abietanoids), and deacetyledulon A. The known coleon-A-lactone (37) now has also been found in Plectranthus edulis. The intermediacy of the γ-enollactol 44 , combined with a leaving group on C(3) is postulted to explain the biogenesis of the unusual 4H-5-oxaaceanthrylen skeleton of edulon A.     

Beitrag zur Analytik und Synthese von 3-Hydroxy-4-oxocarotinoiden

Contribution to the Analytical Separation and the Synthesis of 3-Hydroxy-4-oxocarotenoids (3RS,3′RS)-Astaxanthin (= 3,3′-dihydroxy-β,β-carotene-4,4′-dione, 1:1-mixture of racemate and meso-form; 1 ) can be separated into its optical isomers (3S,3′S)- 1a , (3R,3′R)- 1b and meso-(3R,3′S)- 1c via the corresponding diastereomeric di-(?)-camphanates. Some aspects of the configurational stability of astaxanthin are discussed. - HPLC. analysis of the (?)-camphanates of 3-hydroxy-4-oxocarotenoids provides, in suitable cases and supported by spectroscopic data, an analytical method for the simultaneous determination of constitution and chirality.     

Bottleneck routing with elastic demands

Bottleneck routing games are a well-studied model to investigate the impact of selfish behavior in communication networks. In this model, each user selects a path in a network for routing her fixed demand. The disutility of a user only depends on the most congested link visited. We extend this model by allowing users to continuously vary the demand rate at which data is sent along the chosen path. As our main result we establish tight conditions for the existence of pure strategy Nash equilibria.     

Effects of FeCl3 as oxidizing agent on the conduction mechanisms in polypyrrole (PPy)/pc–ZnO hybrid heterojunctions grown by oxidative chemical vapor deposition

P‐type polypyrrole (PPy) films are deposited on glass and on n‐type polycrystalline ZnO (pc–ZnO) substrates by oxidative chemical vapor deposition under three different amounts of FeCl₃ used as oxidizing agents to form hybrid heterojunctions. Their microstructure, morphology, and electrical characteristics are studied. Particularly, current–voltage characteristics of the PPy/pc–ZnO heterojunctions are analyzed by defining an electrical equivalent circuit. The extracted parameters, together with the estimated heterojunction barrier height and the HOMO energy level of the PPy, indicate that a thermionic emission of holes at the heterojunction determines the saturation current of the diode at low voltage. For larger FeCl₃ amounts, the diode ideality factor increases indicating an increment of recombination by tunneling of charge carriers occurring at the heterojunction. This is attributed to a narrowing of the space charge region due to an increment of the number of charge carriers with a growing amount of FeCl₃. At high voltages, the PPy thickness influences the ohmic and space–charge limited current mechanisms at the bulk region. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 1537–1544