Conversion of alpha-haloaldehydes into acylating agents by an internal redox reaction catalyzed by nucleophilic carbenes

Reactivity umpolung allows us to consider nontraditional bond disconnections. We report herein that treatment of an alpha-haloaldehyde with a nucleophile in the presence of catalytic amounts of nucleophilic carbenes results in an internal redox reaction giving rise to a dehalogenated acylating agent as an intermediate by a new reaction manifold. A brief illustration of the scope of this reaction is presented along with evidence supporting the direct intervention of the carbene in the acylation step.     

Effects of temperature and pH on the helicity of a peptide adsorbed to colloidal silica

The conformation of a cationic -helical peptide (DDDDAAAARRRRR) adsorbed to anionic colloidal silica has been investigated by circular dichroism (CD) spectroscopy as a function of temperature and pH in order to examine how the structure of an adsorbed molecule responds to two simultaneous perturbations. Increased temperature destabilizes the helicity of the peptide in solution, while pH changes alter the substrate surface charge and the corresponding strength of the interaction with the peptide. Near neutral pH, the helicity of the adsorbed peptide, which is determined from the intensity of the CD signal at 222 nm, decreases with increasing temperature, similarly to the temperature-dependent behavior observed for the peptide in aqueous solution. By contrast, at basic pH and a strongly negative surface charge, the helicity of the adsorbed peptide increases with temperature. In order to elucidate the origin of the reversal of the temperature dependence of helicity, a statistical model for the conformation of the adsorbed peptide has been formulated based on the Lifson–Roig model for the helix–coil transition of the peptide in solution. The model provides insight into the trends in fractional helicity and reveals that the temperature dependence of the helicity of the adsorbed peptide results from a competition between the intramolecular interactions that promote helicity and the intermolecular interactions with the surface. The statistical model also enables estimation of the free energy contributions from specific aspects of the adsorption process. Through identification of a connection between the conformation of adsorbed peptide and the interactions of the peptide with the surface, this work suggests a route for the control of adsorbate conformation through peptide and surface engineering.     

Quantum hall states and boson triplet condensate for rotating spin-1 bosons

We propose and analyze two series of clustered quantum Hall states for rotating systems of spin-1 bosons. The first series [labeled SU(4)(k)] includes the exact ground states of a model Hamiltonian at large angular momentum L, and also for N=3k particles at L=N. The latter is a spin-singlet boson-triplet condensate. The second series, labeled SO(5)(k), includes exact ground states at large L for different parameter values.     

A highly enantioselective catalytic intramolecular Stetter reaction

A family of chiral triazolium salts has been developed for inducing the asymmetric intramolecular Stetter reaction. The use of an aminoindanol-derived catalyst affords optimal results, with the product keto esters formed in 82-97% ee and very good chemical yield. Aromatic and aliphatic aldehydes are equally competent substrates for this reaction. The reaction conditions are reasonably mild and allow the isolation of the newly formed stereocenter without epimerization, although the presumed carbenic intermediates are strong bases.     

Asymmetric landscapes of early spinodal decomposition

We address the effect of an asymmetric concentration-dependent mobility on the early stages of spinodal decomposition in polymer blends and solutions, and characterise it quantitatively. This is particularly important when one of the components has a slower dynamics than the other, e.g., because it is closer to its glass transition, or is weakly cross-linked. Composition mode coupling is proposed as the underlying physical mechanism, and then investigated by means of numerical simulations of the Cahn-Hilliard equation in one (1d) and two (2d) dimensions. In general, this coupling broadens the peak in the structure factor: in 1d an asymmetric concentration profile is obtained, with sharpened interfaces, whereas in 2d the formation is favoured of sharp peaks of the phase rich in the more mobile component. It is shown how the changing morphology of this phase-separating system can be described with the aid of Minkowski functionals. Received 28 August 2000 and Received in final form 18 July 2001     

Electrostatic lenses

The various types of electrostatic lenses that are used to control beams of ions or electrons are briefly described, together with the computational techniques for evaluating their properties. Particular emphasis is placed on the calculation and minimization of the aberrations of these lenses. In computer-aided designs of lens systems it is convenient to have lens properties available in the form of numerical approximations, and the achievement of this is discussed. Special types of lens, such as the zoom lens, are also discussed.     

Gravitational waves from neutron stars: promises and challenges

We discuss different ways that neutron stars can generate gravitational waves, describe recent improvements in modelling the relevant scenarios in the context of improving detector sensitivity, and show how observations are beginning to test our understanding of fundamental physics. The main purpose of the discussion is to establish promising science goals for third-generation ground-based detectors, like the Einstein Telescope, and identify the various challenges that need to be met if we want to use gravitational-wave data to probe neutron star physics.