On DABAL-Me3 promoted formation of amides

The range and utility of DABAL-Me₃ couplings of methyl esters and free carboxylic acids with primary and secondary amines under a variety of conditions (reflux, sealed tube, microwave) has been compared for a significant range of coupling partners of relevance to the preparation of amides of interest in pharmaceutical chemistry. Commercial microwave reactors promote the fastest couplings and allow the use of significantly sterically hindered amines (primary and secondary) and carboxylic acids derivatives. The influence of microwave energy on the reaction system was shown to be typically related to thermal effects (over-pressuring and superheating).     

Pinnatoxin H: a new pinnatoxin analogue from a South China Sea Vulcanodinium rugosum isolate

Pinnatoxin H was isolated from a culture of the dinoflagellate Vulcanodinium rugosum isolated from the South China Sea. The structure of pinnatoxin H was elucidated by LC–MS/MS and NMR spectroscopy. It was found to have the same macrocyclic structure and substituents as pinnatoxins D, E and F, but the side chain on the cyclohexenyl ring was an ethenyl group, as found in pinnatoxin G and portimine. The observation that this strain of V. rugosum produced only pinnatoxin H and portimine is consistent with previous findings that the profile of pinnatoxins can vary significantly among strains. The acute toxicity of pinnatoxin H to mice was 67 μg/kg (intraperitoneal) and 163 μg/kg (gavage).     

Integrated quantum key distribution system using single sideband detection

We report a new quantum cryptographic system involving single sideband detection and allowing an implementation of the BB84 protocol. The transmitted bits are reliably coded by the phase of a high frequency modulating signal. The principle of operation is described in terms of both classical and quantum optics. The method has been demonstrated experimentally at 1 550 nm using compact and conventional device technology. Single photon interference has been obtained with a fringe visibility greater than 98%, indicating that the system can be used in view of quantum key distribution potentially beyond 50-km-long standard single-mode fiber. Received 13 July 2001 and Received in final form 30 November 2001     

Decidability of complexity one-half for finite semigroups

Resume All semigroups considered are finite. The semigroup C is by definition combinatorial (or group free or aperiodic) iff the maximal subgroups of C are singletons. Let S₂oS₁ denote the wreath product of S₁ by S₂, so P₁: S₂oS₁ → S₁ with P₁ the projection surmorphism. S<T, read S divides T, iff S is a homomorphic image of a subsemigroup of T. In this paper we give necessary and sufficient conditions in terms of a homomorphic image of S (resp. a subsemigroup of S) so that S<GoC (resp. S<CoG), with C a combinatorial semigroup and G a group. This requires an earlier results by Bret Tilson and John Rhodes in [8]. This research was partially supported by a grant from the National Science Foundation.     

Pulse‐shape instabilities and their measurement

Multi‐shot pulse‐shape measurements of trains of ultrashort pulses with unstable pulse shapes are studied. Measurement techniques considered include spectral‐phase interferometry for direct electric‐field reconstruction (SPIDER), second harmonic generation frequency‐resolved optical gating (FROG), polarization gate FROG, and cross‐correlation FROG. An analytical calculation and simulations show that SPIDER cannot see unstable pulse‐shape components and only measures the coherent artifact. Further, the presence of this instability cannot be distinguished from benign misalignment effects in SPIDER. FROG methods yield a better, although necessarily rough, estimate of the pulse shape and also indicate instability by exhibiting disagreement between measured and retrieved traces. Only good agreement between measured and retrieved FROG traces or 100% SPIDER fringe visibility guarantees a stable pulse train.     

The vitamin D debate: translating controlled experiments into reality for human sun exposure times

Exposure to sunlight, specifically the ultraviolet radiation, has both positive and negative health effects. Maximizing the benefits (vitamin D synthesis) while minimizing the damage is a multifaceted problem in which many of the elements are poorly quantified. Here we show how rigorously conducted large sample size laboratory studies of the effect of ultraviolet radiation dose on vitamin D status can be applied to real-life situations. This was achieved by modeling the radiation incident on different surfaces for different solar locations, and equating with the controlled exposures in the laboratory studies. Results from both model and experimental data show that relatively short exposures of a modest amount of unprotected skin to summer sunlight in northern climes, on a regular basis during lunchtime hours, increases vitamin D to sufficiency status (≥20 ng mL(-1) ) in the white Caucasian population. While both sun exposure conditions and human skin responses are variable in real life, these quantitative findings provide a guide for authorities devising sunlight exposure recommendations.     

A radiolabelling study of radicals derived from benzene, toluene and benzaldehyde sorbed in model environmental carbon

Radiolabelled free radicals were formed by the addition of muonium--a radioactive hydrogen atom with a positive muon as its nucleus--to benzene, toluene and benzaldehyde, as sorbed in porous carbon. The activation parameters associated with their reorientational motion were measured using longitudinal-field muon spin relaxation (LF-MuSRx). Two distinct sorbed fractions were detected in each sample, characterised by molecular reorientational activation energies of 5.9/25.8 kJ/mol for benzene, 2.5/5.9 kJ/mol for toluene and 2.9/11.5 kJ/mol for benzaldehyde.     

Limiting laws of supercritical branching random walks

In this Note, we make explicit the limit law of the renormalized supercritical branching random walk, giving credit to a conjecture formulated in Barral et al. (2012) [5] for a continuous analogue of the branching random walk. Also, in the case of a branching random walk on a homogeneous tree, we express the law of the corresponding limiting renormalized Gibbs measures, confirming, in this discrete model, conjectures formulated by physicists (Derrida and Spohn, 1988 [9]) about the Poisson–Dirichlet nature of the jumps in the limit, and precising the conjecture by giving the spatial distribution of these jumps.