A Direct Kinematical Derivation of the Relativistic Sagnac Effect for Light or Matter Beams

The Sagnac time delay and the corresponding Sagnac phase shift, for relativistic matter and electromagnetic beams counter-propagating in a rotating interferometer, are deduced on the ground of relativistic kinematics. This purely kinematical approach allows to explain the universality of the effect, namely the fact that the Sagnac time difference does not depend on the physical nature of the interfering beams. The only prime requirement is that the counter-propagating beams have the same velocity with respect to any Einstein synchronized local co-moving inertial frame.     

Organometallic reactions in aqueous media: indium-promoted additions to 2-pyridyl and glyoxylic acid oxime ethers

Oxime ethers derived from 2-pyridinecarboxaldehyde and glyoxylic acid can be effectively allylated in water with five differently functionalized allylic bromides promoted by indium. When the metal is positioned in close proximity of flanking heteroatomic centers, chelation by In is indeed operative and affects both reactivity and stereochemistry. Stereochemical assignments in the addition products were based on X-ray crystallographic measurements and spectral correlations.     

Synthesis and reactivity of (C6F5)3B-N-heterocycle complexes. 1. Generation of highly acidic sp3 carbons in pyrroles and indoles

The reaction of pyrroles and indoles with B(C(6)F(5))(3) and BCl(3) produces 1:1 B-N complexes containing highly acidic sp(3) carbons, for example, N-[tris(pentafluorophenyl)borane]-5H-pyrrole (1) and N-[tris(pentafluorophenyl)borane]-3H-indole (2), that are formed by a new formal N-to-C hydrogen shift, the mechanism of which is discussed. With some derivatives, restricted rotation around the B-N bond and/or the B-C bonds was observed by NMR techniques, and some rotational barriers were calculated from experimental data. The acidity of the sp(3) carbons in these complexes is shown by their ability to protonate NEt(3), with formation of pyrrolyl- and indolyl-borate ammonium salts. The driving force for this reaction is given by the restoration of the aromaticity of the heterocycle.     

Pharmacophore modeling as an efficient tool in the discovery of novel noncompetitive AMPA receptor antagonists

A three-dimensional pharmacophore model for the binding of noncompetitive AMPA receptor antagonists was developed in order to map common structural features of highly active compounds. This hypothesis, which consists of two hydrophobic regions, one hydrogen bond acceptor and one aromatic region, was successfully used as framework for the design of a new class of allosteric modulators containing a tetrahydroisoquinoline skeleton and for in silico screening. The promising biological results suggested that the identified molecules might be useful "lead compounds" for future drug development.     

Cellulose beads: a new versatile solid support for microwave- assisted synthesis. Preparation of pyrazole and isoxazole libraries

The synthesis of libraries of substituted pyrazoles and isoxazoles has been developed via in situ generation of polymer-bound enaminones. The synthetic protocol makes use of commercially available aniline cellulose, a low-cost and versatile biopolymer, under very mild conditions. This new support allowed us to carry out reactions in polar solvents under both conventional heating and MW irradiation without degradation of the polymer. The reaction between cellulose-bound enaminone and hydroxylamine or hydrazines to afford the target heterocycles in high yields directly in solution is the key step. The support can be conveniently recycled.     

Structure of three-interval exchange transformations II: a combinatorial description of the tranjectories

Astract  We describe an algorithm for generating the symbolic sequences which code the orbits of points under an interval exchange transformation on three intervals. The algorithm has two components. The first is an arithmetic division algorithm applied to the lengths of the intervals. This arithmetic construction was originally introduced by the authors in an earlier paper and may be viewed as a two-dimensional generalization of the regular continued fraction. The second component is a combinatorial algorithm which generates the bispecial factors of the associated symbolic subshift as a function of the arithmetic expansion. As a consequence, we obtain a complete characterization of those sequences of block complexity 2n+1 which are natural codings of orbits of three-interval exchange transformations, thereby answering an old question of Rauzy. Partially supported by NSF grant INT-9726708.     

Electrochemical investigation of photooxidation processes promoted by sulfo-polyoxometalates: coupling of photochemical and electrochemical processes into an effective catalytic cycle

Oxidative photocurrents measured upon irradiation by a 7-W visible light (wavelength 312-700 nm) demonstrated that the sulfo-polyoxometalate anion clusters [S2W18O62]4- (1a), [S2Mo18O62]4- (1b), and [SMo12O40]2- (2) may be activated photochemically to oxidize the organic substrates benzyl alcohol, ethanol, and (-)-menthol. In the case of catalytic photooxidation of benzyl alcohol to benzaldehyde in the presence of 1a, quantitative electrochemical methods have identified pathways for the oxidation of reduced forms of 1 generated during the catalysis. More generally, the oxidation pathways P(n+2)- + 2H+ <==> Pn- + H2 and 2P(n+2)- + O2 + 4H+ <==> 2Pn- + 2H2O have been evaluated by monitoring acidified acetonitrile solutions of the 2e(-)-reduced clusters by rotating disk electrode voltammetry under anaerobic and aerobic conditions, respectively. Neither of the reduced forms 1b(2e-) nor 2(2e-) reacted under these conditions. In contrast, 1a(2e-) was oxidized via both pathways, consistent with its more negative redox potential, with the rate of oxidation by air-oxygen being significantly faster than that by H+. The present work demonstrated that the crucial step necessary to oxidize reduced catalyst in photocatalytic reactions involving the anions studied may be achieved or accelerated by application of an external potential more positive than the first redox potential of the polyoxometalate anion. Voltammetric analysis revealed that this in situ electrolytic regeneration of the reduced catalyst is an option that leads to a viable photoelectrocatalytic pathway, even when the H+ and O2 pathways are not available.     

Porphyrin deposition induced by UV irradiation

Simple irradiation by UV light of porphyrin TpyP and its zinc(II) and manganese(III) metal derivatives in chlorinated solvents leads to the deposition on silica of mesoscale aggregates. The process is due to the photochemical decomposition of the solvent with generation of HCl, which causes the precipitation of a protonated form. The morphology of the resulting objects is driven by the nature of the inserted metal ion.     

The Boggess-Polking extension theorem for<Emphasis Type="Italic">CR</Emphasis> functions on manifolds with corners

We give the “boundary version” of the Boggess-PolkingCR extension theorem. LetM andN be real generic submanifolds of ℂ ⁿ withN ⊂M and letV be a “wedge” inM with “edge”N and “profile” Σ ⊂T _NM in a neighborhood of a pointz _o.We identify in natural manner and assume that for a holomorphic vector fieldL tangent toM and verifying we have that the Levi form takes a value . Then we prove thatCR functions onV extend ∀_ω to a wedgeV ₁ “attached” toV in direction of a vector fieldiV such that |pr(iV(z ₀))−iv ₀| < ε (where pr is the projection pr:T _NX →T _MX | _N ).We then prove that when the Levi cone “relative to Σ”iZ _Σ = convex hull is open inT _MX, thenCR functions extend to a “full” wedge with edgeN (that is, with a profile which is an open cone ofT _NX). Finally, we prove that iff is defined in a couple of wedges ±V with profiles ±Σ such thatiZ _Σ =T _MX, and is continuous up toN, thenf is in fact holomorphic atz _o.