Me2Zn‐Mediated Catalytic Enantio‐ and Diastereoselective Addition of TosMIC to Ketones

The first catalytic asymmetric addition of TosMIC to unactivated ketones is presented. A combination of Me₂Zn and aminoalcohol catalyst promoted the aldol addition/cyclization reaction to render oxazolines possessing a fully substituted stereocenter with excellent yields (up to 92 %), high enantioselectivities (up to 96 %), and complete diastereoselectivity. The chiral oxazolines were then used to give, after a straightforward acid hydrolysis, enantioenriched building blocks bearing tertiary alcohol motifs such as hydroxylaldehydes, hydroxylacids, and hydroxylesters without racemization.     

Spontaneous waveguide Raman spectroscopy of self-assembled monolayers in silica micropores

Advances in nanoscience are critically dependent on the ability to control and probe chemical and physical phenomena in confined geometries. A key challenge is to identify confinement structures with high surface area to volume ratios and controlled surface boundaries that can be probed quantitatively at the molecular level. Herein we report an approach for probing molecular structures within nano- to microscale pores by the application of spontaneous Raman spectroscopy. We demonstrate the method by characterization of the structural features of picomole quantities of well-organized octadecyltrichlorosilane (OTS) monolayers self-assembled on the interior pore surfaces of high aspect ratio (1 μm diameter × 1-10 cm length), near-atomically smooth silica microstructured optical fibers (MOFs). The simple Raman backscattering collection geometry employed is well suited for a wide variety of diagnostic applications as demonstrated by tracking the combustion of the hydrocarbon chains of the OTS self-assembled monolayer (SAM) and spectral confirmation of the formation of an adsorbed monolayer of human serum albumin (HSA) protein. Using this MOF Raman approach, molecular processes in precisely defined, highly confined geometries can be probed at high pressures and temperatures, with a wide range of excitation wavelengths from the visible to the near-IR, and under other external perturbations such as electric and magnetic fields.     

Thiazolium-catalyzed intermolecular Stetter reaction of linear and cyclic alkyl α-diketones

An efficient method for the N-heterocyclic carbene (NHC)-catalyzed conjugate addition of acetyl anions to various α,β-unsaturated acceptors (Stetter reaction) has been optimized by using 2,3-butandione (biacetyl) as an alternative surrogate of acetaldehyde. The disclosed procedure proved to be compatible with microwave dielectric heating for reaction time reduction and with the use of different linear α-diketones as acyl anion donors (e.g. 3,4-hexanedione for propionyl anion additions). Moreover, the unprecedented umpolung reactivity of cyclic α-diketones in the atom economic nucleophilic acylation of chalcones is herein presented. Mechanistic aspects of the thiazolium-based catalysis involving linear and cyclic α-diketone substrates are also discussed.     

In situ microbial fuel cell-based biosensor for organic carbon

The biological oxygen demand (BOD) may be the most used test to assess the amount of pollutant organic matter in water; however, it is time and labor consuming, and is done ex-situ. A BOD biosensor based on the microbial fuel cell principle was tested for online and in situ monitoring of biodegradable organic content of domestic wastewater. A stable current density of 282±23mA/m(2) was obtained with domestic wastewater containing a BOD(5) of 317±15mg O(2)/L at 22±2°C, 1.53±0.04mS/cm and pH 6.9±0.1. The current density showed a linear relationship with BOD(5) concentration ranging from 17±0.5mg O(2)/L to 78±7.6mg O(2)/L. The current generation from the BOD biosensor was dependent on the measurement conditions such as temperature, conductivity, and pH. Thus, a correction factor should be applied to measurements done under different environmental conditions from the ones used in the calibration. These results provide useful information for the development of a biosensor for real-time in situ monitoring of wastewater quality.     

Enantio and diastereoselective addition of phenylacetylene to racemic α-chloroketones

In this report, we have presented the first diastereoselective addition of phenylacetylene to chiral racemic chloroketones. The addition is controlled by the reactivity of the chloroketones that allowed the stereoselective reaction to be performed at -20 °C. Chiral racemic chloroketones are used in the reaction. By carefully controlling the temperature and the reaction time we were able to isolate the corresponding products in moderate yields and with good, simple and predictable facial stereoselection. Our reaction is a rare example of the use of chiral ketones in an enantioselective alkynylation reaction and opens new perspectives for the formation of chiral quaternary stereocenters.     

Persistence of Eigenvalues and Multiplicity in the Dirichlet Problem for the Laplace Operator on Nonsmooth Domains

We consider the Dirichlet eigenvalue problem for the Laplace operator on a variable nonsmooth domain. We extend a result of Lupo and Micheletti concerning the structure of the set of domain perturbations which leave the multiplicity of an eigenvalue unchanged, and we study the set of perturbations which leave a certain eigenvalue unchanged.     

Micellar Solubilization of Proteins in Aprotic Solvents and their Spectroscopic Characterisation

The quaternary ammonium salt methyl-trioctylammonium chloride enables the transfer of α-chymotrypsin, trypsin, pepsin and glucagone from water to cyclohexane. Reversed micelles, whose polar core solubilizes both protein and water, are probably formed in the apolar phase. The influence of various parameters on the phase transfer (concentration, pH, solvent, temperature, etc.) has been investigated. Absorption, fluorescence and circular dichroism studies of the biopolymers in the cyclohexane system have been carried out. For trypsin and chymotrypsin, the CD. signal in the 200 nm region is very similar in water and in cyclohexane, which suggests that the polypeptide folding is not substantially different in the two phases. The fluorescence quantum yield is always much larger in the cyclohexane phase than in water. The longer wavelength region of the UV. absorption spectrum is slightly red-shifted relative to water, and a band at 225 nm, probably arising from the aromatic chromophore, is apparent in the organic phase. Reasons for these spectral perturbations are discussed. The enzymes transferred from water into cyclohexane phases can be continuously retransferred into a second water phase. The possible relevance of this ‘double transfer’ as a model for the vectorial transport of biopolymers or a separation technique is discussed.