Chiral synthons from carvone. Part 53. First enantiospecific synthesis of (-)-9-pupukeanone

The first enantiospecific total synthesis of (-)-9-pupukeanone, starting from (R)-carvone employing a combination of Michael-Michael reaction and an intramolecular rhodium carbenoid C H insertion reaction as key steps, is described. (C) 2002 Elsevier Science Ltd. All rights reserved.

First-principles electronic structure of the delafossites ABO(2) (A=Cu, Ag, Au; B=Al, Ga, Sc, In, Y): evolution of d(10)-d(10) interactions

While bonding between d(10) atoms and ions in molecular systems has been well studied, less attention has been paid to interactions between such seemingly closed shell species in extended inorganic solids. In this contribution, we present visualizations of the electronic structures of the delafossites ABO(2) (A = Cu, Ag, Au) with particular emphasis on the nature of d(10)-d(10) interactions in the close packed plane of the coinage metal ion. We find that on going from Cu to Ag to Au, the extent of bonding between A and A increases. However, the structures (in terms of distances) of these compounds are largely determined by the strongly ionic 13,11 0 interaction and for the larger B ions Sc, In and Y, the A atoms are sufficiently well-separated that A-A bonding is almost negligible. We also analyze some interesting differences between Ag and Au, including the larger A-O covalency of the Au. The trends in electronic structure suggest that the Ag and Au compounds are not good candidate transparent conducting oxides. (C) 2002 Editions scientifiques et medicales Elsevier SAS. All rights reserved.

Partial instantiation methods for inference in first-order logic

Satisfiability algorithms for propositional logic have improved enormously in recently years. This improvement increases the attractiveness of satisfiability methods for first-order logic that reduce the problem to a series of ground-level satisfiability problems. R. Jeroslow introduced a partial instantiation method of this kind that differs radically from the standard resolution-based methods. This paper lays the theoretical groundwork for an extension of his method that is general enough and efficient enough for general logic programming with indefinite clauses. In particular we improve Jeroslow's approach by (1) extending it to logic with functions, (2) accelerating it through the use of satisfiers, as introduced by Gallo and Rago, and (3) simplifying it to obtain further speedup. We provide a similar development for a "dual" partial instantiation approach defined by Hooker and suggest a primal-dual strategy. We prove correctness of the primal and dual algorithms for full first-order logic with functions, as well as termination on unsatisfiable formulas. We also report some preliminary computational results.

The first bis(phosphine) monoxide (BPMO) complexes of copper(I)

Copper(l) complexes of bis(phosphine) monoxide ligands, bis(diphenylphosphino)ethane monoxide (dppeo) and bis(diphenylphosphino)methane monoxide (dppmo) have been prepared and characterized. One of the complexes with dppeo was characterized by X-ray crystal structure analysis confirming Cu(I) coordination to hard and soft donors. The stability of these complexes in solution was probed via spectroscopic and electrochemical studies. Copper(I) is more readily oxidized in the presence of the hard 0 donor ligands. In solution, they readily exchange the hard donor O, for soft ligands. Although copper(l) prefers soft ligands and is more stable towards oxidation in their presence, it coordinates to hard donors when there is electrostatic or an entropy driven advantage. (C) 2002 Elsevier Science Ltd. All rights reserved.

DNA recognition by the first tail-to-tail linked distamycin-like oligopeptide dimers

Sequence-specific bidentate binding to double-stranded (ds)-DNA by 'tail-to-tail' linked dimeric, distamycin analogues is described; compared to their monomeric analogues, these dimers exhibit greater affinity and longer binding site size and open up a novel avenue in the design of minor groove binders that overcome the phasing problem.

The first copper(I) complex of tris(hydroxymethyl)phosphine

The first copper(I) complex of tris(hydroxymethyl)phosphine (THP) has been synthesized from a reaction with [Cu(CH3CN)4]ClO4. The crystal structure and spectroscopic properties of this complex showing the tetrahedral coordination around copper and a deprotonated THP coordinated to Cu through P are presented.

A waveguide problem involving a thick iris in the theory of electromagnetism

The problem of electromagnetic wave propagation in a rectangular waveguide containing a thick iris is considered for its complete solution by reducing it to two suitable integral equations, one of which is of the first kind and the other is of the second kind. These integral equations are solved approximately, by using truncated Fourier series for the unknown functions. The reflection coefficient is computed numerically from the two integral equation approaches, and almost the same numerical results are obtained. This is also depicted graphically against the wave number and compared with thin iris results, which are computed by using complementary formulations coupled with Galerkin approximations. While the reflection coefficient for a thin iris steadily increases with the wave number, for a thick iris it fluctuates and zero reflection occurs. The number of zeros of the reflection coefficient for a thick iris increases with the thickness. Thus a thick iris becomes completely transparent for some discrete wave numbers. This phenomenon may be significant in the modelling of rectangular waveguides.

Enantiospecific first total synthesis and assignment of absolute configuration of the sesquiterpene (-)-cucumin H

The first total synthesis of the sesquiterpene (-)-cucumin H, a linear triquinane isolated from Macrocystidia cucumis, has been accomplished starting from (R)-limonene employing two different cyclopentannulation methodologies, which in addition to confirming the structure also established the absolute configuration of the natural product.

A Macroscopic Model for First Return Stroke of Lightning

A lightning return stroke model for a downward flash is proposed. The model includes underlying physical phenomena governing return stroke evolution, namely, electric field due to charge distributed along the leader and cloud, transient enhancement of series channel conductance at the bridging regime, and the nonlinear variation of channel conductance, which supports the return stroke current evolution. Thermal effects of free burning arc at the stroke wave front and its impact on channel conductance are studied. A first-order arc model for determining the dynamic channel conductance along with a field-dependent conductivity for corona sheath is used in the model. The model predicts consistent current propagation along the channel with regard to current amplitude and return stroke velocity. The model is also capable of predicting the remote electromagnetic fields that are consistent with the experimental observations.

Enantiospecific first total synthesis of cucumin-H

Enantiospecific first total synthesis of the linear triquinane sesquiterpene cucumin-H has been described. (R)-Limonene has been employed as the chiral starting material and a combination of Claisen rearrangement, intramolecular cyclopropanation and Nazarov reactions are employed for the regio- and stereospecific construction of the triquinane framework.