Etude en RMN 13C de Spiropyrannes Hétérocycliques

A ¹³C n.m.r. study of different heterocyclic spiropyrans has been carried out. We have attempted to describe the specific influence of the heteroatoms on the chemical shift of the neighbouring atoms. Carbon-13 chemical shifts and coupling constants have been also obtained for compounds similar to both parts of the spiropyran molecule: the heterocycle and the benzopyran.     

Sur la mesure de sortie du super mouvement brownien

Summary We study some properties of the exit measure of super Brownian motion from a smooth domainD inR ^d . In particular, we give precise estimates for the probability that the exit measure gives a positive mass to a small ball on the boundary. As an application, we compute the Hausdorff dimension of the support of the exit measure. In dimension 2, we prove that the exit measure is absolutely continuous with respect to the Lebesgue measure on the boundary. In connection with Dynkin's work, our results give some information on the behavior of solutions of u=u ² inD, and are related to the characterization of removable singularities at the boundary. As a consequence of our estimates, we give a sufficient condition for the uniqueness of the positive solution of u=u ² inD that tends to on an open subsetO of D and to 0 on the complement in D of the closure ofO. Our proofs use the path-valued process studied in [L2, L3].

     

On the representation of integers as sums of triangular numbers

Summary In this survey article we discuss the problem of determining the number of representations of an integer as sums of triangular numbers. This study yields several interesting results. Ifn 0 is a non-negative integer, then thenth triangular number isT _n =n(n + 1)/2. Letk be a positive integer. We denote by _k (n) the number of representations ofn as a sum ofk triangular numbers. Here we use the theory of modular forms to calculate _k (n). The case wherek = 24 is particularly interesting. It turns out that, ifn 3 is odd, then the number of points on the 24 dimensional Leech lattice of norm 2n is 2¹²(2¹² – 1) ₂₄(n – 3). Furthermore the formula for ₂₄(n) involves the Ramanujan(n)-function. As a consequence, we get elementary congruences for(n). In a similar vein, whenp is a prime, we demonstrate ₂₄(p ^k – 3) as a Dirichlet convolution of ₁₁(n) and(n). It is also of interest to know that this study produces formulas for the number of lattice points insidek-dimensional spheres.     

Ellagitannin Chemistry. First Total Synthesis of the 2,3- and 4,6-Coupled Ellagitannin Pedunculagin

The biomimetic synthesis of pedunculagin (1) was accomplished through the sequential diastereoselective formation of two biphenyl C-C bonds. The synthesis strategy employed is predicated on extensive conformational modeling and involves initial oxidative coupling of the galloyl moieties at the O(2) and O(3) positions of an appropriately protected glucose-derived core, followed by installation and oxidative coupling of galloyl esters at the O(4) and O(6) positions.     

Application of atomic stereomicroscope to surface science

A stereograph of atomic arrangement was displayed directly on the screen of display-type spherical-mirror analyzer without any computer-aided conversion process for the first time. This stereoscopic photograph enables viewing three-dimensional atomic arrangement. This technique was realized taking advantage of the phenomenon of circular dichroism in photoelectron angular distribution. The azimuthal shifts of forward focusing peaks in a photoelectron angular distribution taken with left and right helicity light in a special arrangement are the same as the parallaxes in a stereo view of atoms. Hence a stereoscopic recognition of three-dimensional atomic arrangement is possible, when the left eye and the right eye respectively view the two images obtained by left and right helicity light simultaneously.     

Discovery and crystal structure of a novel chlorocarbon host: perchlorofluorene-9-spirocyclohexa-2′,5′-diene

Chlorination of triphenylene (1a) employing a mixture of aluminium trichloride and sulphur monochloride in sulphuryl chloride leads to rearrangement with formation of the title chlorocarbon (2), a new host, as main product. X-ray crystal structure analyses of the unsolvated spirocycle (2) as well as of its inclusion compounds with guests benzene and cyclohexa-1,4-diene are described.     

CO-transfer carbonylation reactions. A catalytic Pauson-Khand-type reaction of enynes with aldehydes as a source of carbon monoxide

The reaction of enynes with aldehydes in the presence of a catalytic amount of [RhCl(cod)](2)/dppp results in the Pauson-Khand-type reaction without the use of gaseous carbon monoxide to give bicyclic cyclopentenones in high yields (14 examples). Aldehydes serve as a source of carbon monoxide, and their carbonyl moiety is transferred to enynes, resulting in the formation of the carbonylated products. This reaction represents the first example of a CO-transfer carbonylation.     

Potassium-thiacalix[8]arene assembly: structure and guest sorption profiles

Treatment of thiacalix[8]arene (3.8H) with KH in THF, followed by recrystallization from methanol, affords an adduct of [K4(3.4H)].8MeOH as a pale yellow crystal (4), which shows highly-extensive coordination that gives rise to a zeolitic structure. An adduct of 4 gives apohost [K4(3.4H)] with the loss of methanol, which can adsorb such gaseous organic guest molecules as methanol and benzene. After binding methanol as the guest molecule, the apohost is converted back to the original structure of 4.     

Evaluation of the enzymatic susceptibility of cellulosic substrates using specific hydrolysis rates and enzyme adsorption

Applied Biochemistry and Biotechnology - Adsorption of cellulases to cellulose is a critical step in the hydrolysis of cellulosic substrates. However, the importance of adsorption in determining...     

Lipid phosphate phosphatases dimerise,but this interaction is not required for <Emphasis Type="Italic">in vivo</Emphasis> activity

Background  

Lipid phosphate phosphatases (LPPs) are integral membrane proteins believed to dephosphorylate bioactive lipid messengers, so modifying or attenuating their activities. Wunen, a Drosophila LPP homologue, has been shown to play a pivotal role in primordial germ cell (PGC) migration and survival during embryogenesis. It has been hypothesised that LPPs may form oligomeric complexes, and may even function as hexamers. We were interested in exploring this possibility, to confirm whether LPPs can oligomerise, and if they do, whether oligomerisation is required for either in vitroor in vivoactivity.