Asymmetric enamide hydrogenation using phosphinite thioglycosides: synthesis of D- and L-aminoesters using D-sugars as catalyst precursors

Diastereomerically pure cationic Rh(I) complexes derived from phosphinite thioglycosides I were used as catalysts in highly enantioselective hydrogenations of enamides. The conformational similarity of alpha-D-arabinopyranose with beta-L-galactopyranose allows the synthesis of both enantiomers of alpha-amino acid derivatives such as D- and L-DOPA in excellent ee (97% and 98%), using derivatives of the former sugar as catalyst precursors.     

"Sulfolefin": highly modular mixed S/olefin ligands for enantioselective Rh-catalyzed 1,4-addition

Reported is a single high yielding step approximation to mixed olefin/sulfinamide ligands enclosing a chiral sulfur atom as the sole chiral center. The synthetic design is validated by a rapid optimization of the substituent at the sulfinyl sulfur, and by the synthesis of an efficient, highly enantioselective catalyst for the Rh-catalyzed 1,4-addition of boronic acids to both, cyclic and acyclic olefins.     

Theoretical study of the polarized infrared spectra of the hydrogen bond in 2‐furoic acid crystal dimer

This work presents a theoretical simulation of ν_{O? H} and ν_{O? D} band shapes in the polarized infrared spectra of 2‐furoic acid dimer crystals measured at liquid‐nitrogen temperature. The line shapes are studied theoretically within the framework of the anharmonic couplings between low‐frequency hydrogen‐bond vibrations and degenerate excited states of high‐frequency hydrogen vibrations in hydrogen‐bonded dimers and the anharmonic coupling between the first excited state of the fast mode and the harmonics or band combinations of some low‐frequency bending modes, which lead to Fermi resonances.This approach takes into account the adiabatic approximation, the intrinsic anharmonicity of the low‐frequency mode through a Morse potential, Davydov coupling triggered by resonance exchange between the excited states of the fast modes of the two hydrogen bonds involved in the cyclic dimer, and the direct and indirect damping of the fast‐stretching modes of the hydrogen bonds and of the bending modes. The infrared spectral density was calculated within the linear response theory by Fourier transform of the autocorrelation function of the transition dipole moment operator of the fast mode. Numerical results show that mixing of all these effects allows satisfactory reproduction of the main features of the experimental IR line shapes of crystalline H‐ and D‐bonded 2‐furoic acid at liquid‐nitrogen temperature and for different polarizations. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012     

Photochemistry of a naphthalene-thymine dyad in the presence of acetone

Irradiation of dyad 1 in aqueous acetone leads to the introduction of an acetonyl substituent at the naphthalene 5-position, to give photoproduct 2. The proposed reaction mechanism involves electron transfer from the naphthalene excited singlet state to the ketone. Neither thymine dimers, nor acetone photoadducts involving the thymine ring were detected. These photoproducts would arise from the thymine triplet excited state, which in dyad 1 must be efficiently depopulated via a fast intramolecular energy transfer to the naphthalene chromophore, due to the lower energy of its excited triplet state.     

The Relative Reduced Redlich-Kister and Herráez Equations for Correlating Viscosities of 1,4-Dioxane + Water Mixtures at Temperatures from 293.15 K to 323.15 K

Viscosity deviations from ideal mixing for 1,4-dioxane + water mixtures over the entire range of composition at temperatures of (293.15, 303.15 and 313.15) K and atmospheric pressure were calculated from experimental viscosity data presented in a previous work. The temperature range was extended to 323.15 K with data from the literature. This system exhibits very large positive deviations due to strong heteromolecular interactions and also due to size differences of the unlike molecules. The viscosity data as well as their corresponding relative functions were used to test the applicability of two correlative equations: the reduced Redlich-Kister equation and the recently proposed Herráez equation. These relative functions are important to reduce the effect of temperature and, consequently, to reveal the effects of different types of interactions. Their correlation abilities at different temperatures, and using different numbers of parameters, are discussed for the case of limited experimental data. Generally, good agreement between experimental and calculated data was obtained with both equations provided more than three parameters were employed.     

Equivalent formulations for Monge-Kantorovich equation

In this paper, we study some equivalent formulations in divergence form for the optimization problem where and k>0 in Ω. This is the so called dual equation of Monge-Kantorovich problem.     

New Synthetic Route for Reaching Higher Phase Stabilization in LAMOX-Based Electrolyte for Solid Oxide Fuel Cells

S-substituted La₂Mo₂O₉ were synthesized by a solid-state procedure employing ammonium sulfate (NH₄)₂SO₄ as a sulfur source. The synthesized powders were examined using X-ray diffraction (XRD), thermogravimetric analysis (TGA), infrared, and Raman spectroscopies. The results divulged that the stabilization of the β-La₂Mo₂O₉ polymorph occurred in the interval of sulfur composition 0.1≤y≤0.6. This substitution generates a linear dwindling of the unit cell volume. The decomposition of all substituted samples started above 900 °C with a total weight loss linearly dependent on the sulfur content. Electrical studies confirmed that substituting S⁶⁺ for Mo⁶⁺ suppresses the phase transition of La₂Mo₂O₉ and stabilizes the cubic polymorph down to ambient temperature. It was also remarkable that this substitution caused a decrease in the conductivity, and unfortunately, none of the tested compositions allowed exceeding the conductivity of La₂Mo₂O₉. Infrared and Raman spectra confirmed the presence of the characteristic peaks of sulfates and molybdates groups.     

Electrochemical determination of sulfaguanidine using COOH-MWCNT coated GC electrode

The electrochemical behavior of sulfaguanidine was investigated in PBS buffer aqueous solutions. Cyclic voltammograms have shown that (1) the Sg provided a well-defined irreversible oxidation peak (2) the signal-to-background current ratio is 3 times higher at COOH-MWCNT coated GCE than that of bare GCE and (3) the modifying GCE surface by COOH-MWCNT led to a significant improvement (2.7 folds) of the electrochemical response. It has been shown that Sg oxidizes according to a diffusion-controlled mechanism. A linear calibration curve was obtained for the oxidation of Sg at 10–70 μM. The COOH-MWCNT coated GCE has also been successfully used for the determination of Sg in real samples.     

Influence of morphology on electric conductance in poly(ethylene naphthalene-2,6-dicarboxylate)

Polymers find an important field of application in the electrical industry because of their utilization as insulators and dielectrics. The challenge over the last several years has been to make electrical compounds smaller in size. In that way the material morphology is of strategic importance in the performance of new components in relation to their geometry. Therefore, it is important to know the influence of different types of stress on electric properties of the materials. We have studied the influence of the crystallinity on electric conductance of poly(ethylenenaphthalene-2,6-dicarboxylate) (PEN), which is increasingly replacing some dielectrics (polypropylene and PET) in certain electric applications. Starting from an amorphous PEN, samples with various crystallinities were obtained and analyzed using DSC in order to determine their thermal characteristics. Moreover, measurements of charge and discharge currents were carried out on PEN samples to characterize their electric properties. The steady state current observed after 120 min, in response to the electric field, shows an increase in the insulator resistivity with the crystallinity. The increase in the crystallinity favors a decrease in the free volume, so the movement of charges is restricted especially by the species of large sizes.