Density functional theory studies of conformational stabilities and rotational barriers of 2- and 3-thiophenecarboxaldehydes

The molecular structures, conformational stabilities, and infrared vibrational wavenumbers of 2-thiophenecarboxaldehyde and 3-thiophenecarboxaldehyde are computed using Becke-3–Lee–Yang–Parr (B3LYP) with the 6-311++G** basis set. From the computations, cis-2-thiophenecarboxaldehyde is found to be more stable than the transfer conformer with an energy difference of 1.22 kcal/mol, while trans-3-thiophenecarboxaldehyde is found to be more stable than the cis conformer by 0.89 kcal/mol. The computed dipole moments, structural parameters, relative stabilities of the conformers and infrared vibrational wavenumbers of the two molecules coherently support the experimental data in the literature. The normal vibrational wavenumbers are characterized in terms of the potential energy distribution using the VEDA4 program. The effect of solvents on the conformational stability of the molecules in nine different solvents is investigated using the polarizable continuum model.     

On the decay rates of Timoshenko system with second sound

In this work, we study the well‐posedness and the asymptotic stability of a one‐dimensional linear thermoelastic Timoshenko system, where the heat conduction is given by Cattaneo's law and the coupling is via the displacement equation. We prove that the system is exponentially stable provided that the stability number χ_τ=0. Otherwise, we show that the system lacks exponential stability. Furthermore, in the latter case, we show that the solution decays polynomially. Copyright © 2015 John Wiley & Sons, Ltd.     

Sea water desalination by dynamic layer melt crystallization: Parametric study of the freezing and sweating steps

This work aims at developing a dynamic layer crystallizer operated batchwise, for freezing desalination of sea water. The experiments were performed with water/NaCl solutions and with samples of sea water from Nice, Rabat and Marseille. The pilot crystallizer consists of a cooled tube immersed in a cylindrical double jacketed tank. The solution is poured into the tank and the crystallization takes place on the external surface of the tube, by applying a cooling ramp in the tube. The solution is agitated by air bubbling. The whole process involves the freezing step, leading to the crystallization of the ice layer and the sweating step, which consists of purifying in depth the ice layer by melting the impure zones. A parametric study on the effect of the operating parameters has allowed quantifying the role of the different key parameters of the freezing and sweating steps. Three experiments allowed reaching salinities lower than 0.5 g/kg, satisfying the standards of drinking water. The duration of the whole process dropped to only 8 h (5 h for freezing and 3 h for sweating), with a yield of sweating equal to about 50%, provided severe conditions were applied for sweating. Higher yields required longer times. Overall, the results show the feasibility of the technique.     

Density functional theory study of the rotational barriers,conformational preference,and vibrational spectra of 2-formylfuran and 3-formylfuran

The torsional potentials, molecular structures, conformational stability, and vibrational wavenumbers for the rotational isomers of 2-formylfuran and 3-formylfuran are computed using the density functional theory (B3LYP) method with the 6-31+G* basis set. All structures are fully optimized and the optimized geometries, rotational constants, dipole moments, and energies are presented. From the computations, both 2-formylfuran and 3-formylfuran are predicted to exist predominantly in trans conformation with a cis–trans rotational barrier of 11.19 kcal/mol and 8.10 kcal/mol, respectively. The vibrational wavenumbers and the corresponding vibrational assignments of the molecules in the C _s symmetry are examined and the infrared spectra of the molecules are simulated using the wavenumbers and the corresponding intensities obtained from the computations. The effect of solvents on the conformational stability of all the molecules in nine different solvents (heptane, chloroform, tetrahydrofuran, dichloroethane, acetone, ethanol, methanol, dimethylsulfoxide, and water) is investigated. The integral equation formalism in the polarizable continuum model (IEF-PCM) is used for all solution phase computations.     

Incorporation of carbon nanotubes in a silica HPLC column to enhance the chromatographic separation of peptides: theoretical and practical aspects

The retention mechanism of a series of peptides on a single-wall carbon nanotube (SWCNT) stationary phase inside an HPLC column was investigated over a wide range of mobile phase compositions. While the similar size C18 column exhibited an efficiency of 11.5 μm, the SWCNT column increased the efficiency, i.e. 7.10 μm at a flow rate of 0.8 mL/min, and significantly affected the separation quality of the peptides. The values of enthalpy (ΔH) and entropy (ΔS(*)) of transfer of the peptides from the mobile to the SWCNT stationary phase were determined. The method studied each factor, i.e. ACN fraction x in the ACN/water mixture and column temperature. The changes in retention factor, ΔH and ΔS(*) as a function of the ACN fraction in the mobile phase were examined. These variations are explained using the organization of ACN in clusters in the ACN/water mixture and on the steric and electronic forces implied in the retention process. The information obtained in this work makes this SWCNT stationary phase useful for peptide research and demonstrated the role of ACN to improve the separation quality.     

General stability of memory-type thermoelastic Timoshenko beam acting on shear force

In this paper, we consider a linear thermoelastic Timoshenko system with memory effects where the thermoelastic coupling is acting on shear force under Neumann–Dirichlet–Dirichlet boundary conditions. The same system with fully Dirichlet boundary conditions was considered by Messaoudi and Fareh (Nonlinear Anal TMA 74(18):6895–6906, 2011, Acta Math Sci 33(1):23–40, 2013), but they obtained a general stability result which depends on the speeds of wave propagation. In our case, we obtained a general stability result irrespective of the wave speeds of the system.     

Safety assessments of subcutaneous doses of aragonite calcium carbonate nanocrystals in rats

Calcium carbonate nanoparticles have shown promising potentials in the delivery of drugs and metabolites. There is however, a paucity of information on the safety of their intentional or accidental over exposures to biological systems and general health safety. To this end, this study aims at documenting information on the safety of subcutaneous doses of biogenic nanocrystals of aragonite polymorph of calcium carbonate derived from cockle shells (ANC) in Sprague-Dawley (SD) rats. ANC was synthesized using the top-down method, characterized using the transmission electron microscopy and field emission scanning electron microscope and its acute and repeated dose 28-day trial toxicities were evaluated in SD rats. The results showed that the homogenous 30 ± 5 nm-sized spherical pure aragonite nanocrystals were not associated with mortality in the rats. Severe clinical signs and gross and histopathological lesions, indicating organ toxicities, were recorded in the acute toxicity (29,500 mg/m²) group and the high dose (5900 mg/m²) group of the repeated dose 28-day trial. However, the medium- (590 mg/m² body weight) and low (59 mg/m²)-dose groups showed moderate to mild lesions. The relatively mild lesions observed in the low toxicity dosage group marked the safety margin of ANC in SD rats. It was concluded from this study that the toxicity of CaCO₃ was dependent on the particulate size (30 ± 5 nm) and concentration and the route of administration used.     

Selective hydroformylation–acetalization of aryl alkenes in methanol catalyzed by RhCl3·3H2O–P(OPh)3 system

Acetals were formed under hydroformylation conditions of alkenes in alcohols as solvents. The hydroformylation process is combined with acetalization in a one-pot reaction leading to acetals as final products. These reactions sequences were catalyzed by the simple rhodium catalyst RhCl₃·3H₂O. The effects of the addition of different types and amounts of phosphine and phosphite ligands were carefully studied in order to improve the regioselectivity of the reaction.     

Heteropolyacids enhanced the catalytic activity of Rh6(CO)16 in the hydroformylation of alkenes

Active homogeneous catalytic systems based on Rh₆(CO)₁₆‐heteropolyacids for the regioselective hydroformylation of styrene and 1‐octene and their derivatives have been developed. The effects of the amount and the type of the heteropolyacid have been studied and showed a significant improvement of the conversion of styrene and the selectivity towards branched aldehydes. Other rhodium complexes were also considered in the study and the results showed the advantages of the rhodium cluster Rh₆(CO)₁₆ associated with the heteropolyacid H₃PW₁₂O₄₀,25H₂O (HPA‐W₁₂). The effects of temperature, type of solvent and CO/H₂ pressure have also been considered in order to optimize the reaction conditions. Copyright © 2004 John Wiley & Sons, Ltd.