Cis-stereoselective SmI2-promoted reductive coupling of keto-nitrones: first synthesis of 1-epitrehazolamine

An expeditious synthesis of 1-epitrehazolamine is presented from readily available 2,3,4,6-tetra-O-benzyl-D-glucose. The key step involves a samarium diiodide-promoted reductive cyclization of a masked keto-nitrone to form a five-membered ring aminocyclitol. The excellent cis selectivity observed in this nitrone-ketone reductive coupling contrasts surprisingly with the trans selectivity of ketone-oxime reductive couplings.     

Comparison of direct and indirect methods of measuring the precursors of beta-methyl-gamma-octalactone and their application to the analysis of Sessile oak wood

A new indirect method for measuring the level of beta-methyl-gamma-octalactone precursors in oak wood by GC-MS is described. This level is calculated from the difference between the amount of free beta-methyl-gamma-octalactone and the amount formed after hydrolysis and lactonization. It is compared to the level of a precursor of cis-beta-methyl-gamma-octalactone, a 6'-O-gallate derivative of (3S,4S)-4-[3-beta-glucopyranosyloxy-3-methyloctanoic acid, determined directly by HPLC. These two methods are applied to 12 powdered samples of Sessile oak wood and the results show that the 6'-O-gallate derivative of (3S,4S)-4-beta-D-glucopyranosyloxy-3-methyloctanoic acid is by far the most abundant precursor of beta-methyl-gamma-octalactone in this wood.     

Designs and Representation of the Symmetric Group

We study (generalized) designs supported by words of given composition. We characterize them in terms of orthogonality relations with Specht modules; we define some zonal functions for the symmetric group and we give a closed formula for them, indexed on ordered pair of semi-standard generalized tableaux: Hahn polynomials are a particular case. We derive an algorithm to test if a set is a design. We use it to search designs in some ternary self-dual codes.     

Size-dependent grain-growth kinetics observed in nanocrystalline Fe

Measurements of grain growth in nanocrystalline Fe reveal a linear dependence of the grain size on annealing time, contradicting studies in coarser-grained materials, which find a parabolic (or power-law) dependence. When the grain size exceeds approximately 150 nm, a smooth transition from linear to nonlinear growth kinetics occurs, suggesting that the rate-controlling mechanism for grain growth depends on the grain size. The linear-stage growth rate agrees quantitatively with a model in which boundary migration is controlled by the redistribution of excess volume localized in the boundary cores.     

Investigation of active structural intensity control in finite beams: theory and experiment

An investigation of structural intensity control is presented in this paper. As opposed to previous work, the instantaneous intensity is completely taken into account in the control algorithm, i.e., all the terms are considered in the real-time control process and, in particular, the evanescent waves are considered in this approach. A finite difference approach using five accelerometers is used as the sensing scheme. A feedforward filtered-X least mean square algorithm is adapted to this energy-based control problem, involving a nonpositive definite quadratic form in general. In this respect, the approach is limited to cases where the geometry is such that the intensity component will have the same sign for the control source and the primary disturbance. Results from numerical simulations are first presented to illustrate the benefit of using a cost function based on structural intensity. Experimental validation of the approach is conducted on a free-free beam covered with viscoelastic material. A comparison is made between classical acceleration control and structural intensity control and the performance of both approaches is presented. These results confirm that using intensity control allows the error sensors to be placed closer to the control source and the primary disturbance, while preserving a good control performance.     

Analysis of insecticidal proteins from Bacillus thuringiensis and recombinant Escherichia coli by capillary electrokinetic chromatography

Bacillus thuringiensis and recombinant Escherichia coli proteinaceous protoxins were subject to proteolysis and analyzed by capillary electrokinetic chromatography. Three resulting toxins (65 kDa) were baseline-resolved within 22 min using a 10 mM borate, pH 11 separation buffer consisting of 25 mM sodium dodecyl sulfate (SDS) and 30 mM phytic acid. The toxins displayed differential interactions with the SDS and phytic acid phases to effect their separation. The ion-pairing interaction between the analyte and phytic acid was also useful in preventing adsorption to the capillary walls and thus enhanced separation resolution and efficiency. The use of electrokinetic chromatography allows achievement of the separation in a significantly shorter time than conventional high-performance liquid chromatography (HPLC) using a diethylaminoethyl (DEAE) weak-anion exchanger.     

Electroformation of peptide self-assembled monolayers on gold

The application of a potential to deposit a monolayer of 3-mercaptopropionic acid-histidinyl-histidinyl-histidinyl-aspartyl-aspartyl (3-MPA-HHHDD-OH) controls the density and molecular structure of the peptide monolayer, which results in different wettabilities of the surface, surface density, orientation of the molecule (extended or bent), and nonspecific adsorption of serum proteins. 3-MPA-HHHDD-OH must be deposited at 200 mV to maintain an extended configuration, which promoted low biofouling properties.     

"Supramolecular circuitry": three chemiluminescent, Cucurbit[7]uril-controlled on/off switches

Three Cucurbit[7]uril-controlled chemiluminescent on/off switches based on the lucigenin motif have been synthesized. Light emission is triggered upon addition of sodium peroxide, interrupted or dimmed in the presence of Cucurbit[7]uril, and restored upon injection of a competitive guest. The process, which can be mimicked by a simple resistor-capacitor circuit, is rationalized by examining the role of the macrocyclic host on the network of equilibria involved in the chemiluminescent process.