Cooperative hydrogen-bonding effects in silanediol catalysis

The importance of cooperative hydrogen-bonding effects and SiOH-acidification is described for silanediol catalysis. NMR binding, X-ray, and computational studies provide support for a unique dimer resulting from silanediol self-recognition. The significance of this cooperative hydrogen-bonding is demonstrated using novel fluorinated silanediol catalysts for the addition of indoles and N,N-dimethyl-m-anisidine to trans-β-nitrostyrene.     

Boric acid: a highly efficient catalyst for transamidation of carboxamides with amines

A novel method of transamidation of carboxamides with amines using catalytic amounts of readily available boric acid under solvent-free conditions has been developed. The scope of the methodology has been demonstrated with (i) primary, secondary, and tertiary amides and phthalimide and (ii) aliphatic, aromatic, cyclic, acyclic, primary, and secondary amines.     

Remarkable stereoselectivity in intramolecular Borono-Mannich reactions: synthesis of conduramines

An unprecedented intramolecular Petasis condensation provides a novel approach to biologically important conduramines. The compounds are produced with an exclusive anti stereoselectivity for the newly created β-amino alcohol motif. The stereochemical outcome of the reaction is opposite to the one usually observed in the intermolecular reaction.     

Effect of ion adsorption on CEC separation of small molecules using hypercrosslinked porous polymer monolithic capillary columns

Both poly(styrene-co-vinylbenzyl chloride-co-divinylbenzene) and poly(4-methylstyrene-co-vinylbenzyl chloride-co-divinylbenzene) monolithic columns have been hypercrosslinked and for the first time used to achieve capillary electrochromatographic separations. Although these columns do not contain ionizable functionalities, electroosmotic flow was observed due to adsorption of ions from a buffer solution contained in the mobile phase on the surface of the hydrophobic polymer. An increase of more than one order of magnitude was observed with the use of both monolithic polymers. The hypercrosslinking reaction creates a large surface area thus enabling adsorption of a much larger number of ions. Alkylbenzenes were successfully separated using the hypercrosslinked monolithic columns.     

Novel flavanes from Livistona halongensis

A study of the chemical constituents of a methanolic extract of the roots of Livistona halongensis (Arecaceae) led to the isolation of two new flavanes, 2S,3S-3,5,7,3'-tetrahydroxy-5'-methoxyflavane (1) and 3,7,3'-trihydroxy-5'-methoxyflavane 5-O-beta-glucopyranoside (2), together with trans-3,5,3',5'-tetrahydroxy-4-methoxystilbene, saccharose and beta-sitosterol-3-O-beta-glucopyranoside. The structures of these compounds were elucidated on the basis of spectroscopic data.     

Line mixing in the QQ sub branches of the ν1 band of methyl chloride

Line-mixing effects have been studied in the ν₁ ^QQ_K (K from 0 to 10) sub branches of methyl chloride (CH₃Cl) perturbed by nitrogen (N₂). Laboratory Fourier transform spectra have been recorded at room temperature for various pressures of atmospheric interest. In order to accurately model these spectra, a theoretical approach accounting for line-mixing effects is necessary and proposed in this study. The common model used in this work is based on the state-to-state rotational cross-sections calculated by a statistical modified exponential-gap fitting law depending on few empirical parameters. These parameters have been deduced by least-squares fitting a sum rule to the N₂-broadening coefficients modeled previously. Comparisons between experimental and calculated spectra for various ^QQ sub branches at various pressures of N₂ demonstrate the adequacy of the model as compared to the use of the Voigt profile.     

Ultrasonic measurements of particle retention by a porous medium

Ultrasound transmission and reflection are utilized to characterize the particle retention in depth of fluid-saturated porous samples under a flow of silt solution. The effect of the concentration of particles in the fluid is investigated via measurements of “comparison coefficients” which are the ratio of the Fourier transforms of the reflected (transmitted) signals before and after the particle flow. Numerical computations of the latter coefficients using Biot-Stoll’s theory are compared to the experimental data. The frequential evolution of physical parameters such as bulk and shear moduli are sought. To this end, a gradient descent algorithm is utilized to minimize the differences between the experimental and calculated comparison coefficients. Several concentrations of suspended particles are investigated to check the validity of this inversion method and a good agreement between theory and experiments is observed.     

Electrochemical synthesis of polyaniline nanowires on Pt interdigitated microelectrode for room temperature NH3 gas sensor application

In this work, we have successfully developed a facile and effective electrochemical route for directly growing polyaniline (PANI) nanowires (NWs) on platinum interdigitated microelectrode. The as-prepared NWs were characterized by field-emission scanning electron microscopy, transmission electron microscopy and Fourier-transform infrared spectroscopy. They revealed that the PANI NWs were obtained with diameters ranging from 50 to 200 nm and length up to hundreds of micro meters, depending on growth time. The as-obtained PANI NWs on the electrode exhibited a porous nature and the conducting emeraldine type structure. The gas sensing properties of PNAI NWs were explored by monitoring NH₃ in synthetic air in the concentration range of 25–500 ppm at room temperature. The results obtained demonstrated that PANI NWs have good potential as novel room temperature sensors for practical applications.