Enantioselective organocatalytic Mannich reactions of ferrocenecarbaldehyde

The first examples of highly enantioselective organocatalytic Mannich reactions of ferrocenecarbaldehyde are disclosed. The reaction is catalyzed by simple amino acids and gives access to β-arylamino-β-ferrocenylketones in high yields and with up to 99% ee.     

Linear partial difference equations of hypergeometric type: Orthogonal polynomial solutions in two discrete variables

In this paper a systematic study of the orthogonal polynomial solutions of a second order partial difference equation of hypergeometric type of two variables is done. The Pearson's systems for the orthogonality weight of the solutions and also for the difference derivatives of the solutions are presented. The orthogonality property in subspaces is treated in detail, which leads to an analog of the Rodrigues-type formula for orthogonal polynomials of two discrete variables. A classification of the admissible equations as well as some examples related with bivariate Hahn, Kravchuk, Meixner, and Charlier families, and their algebraic and difference properties are explicitly given.     

New routes to manganese higher-nuclearity topologies: synthesis of the cluster [Mn8(mu4-O)4(phpz)8(thf)4

Reaction of Mn(ClO4)2.6H2O with 3(5)-methyl-5(3)-(2-hydroxyphenyl)pyrazole (H2phpz) affords a highly asymmetric octanuclear manganese(III) cluster resulting from the different bridging coordination modes of the ligand H2phpz.     

Assessment of provitamin A determination by open column chromatography/visible absorption spectrophotometry

Determination of provitamin A content by open column chromatography/visible absorption spectrophotometry is assessed using food samples of varying carotenoid composition. A general method consisting of extraction with acetone, transfer to petroleum ether, saponification (optional), concentration, separation on activated MgO:Hyflo Supercel column developed with 1 to 15% acetone in petroleum ether, and quantitation of individual provitamins spectrophotometrically demonstrates repeatability comparable with that of high-performance liquid chromatographic (HPLC) methods. Overnight saponification (10% methanolic KOH, ambient temperature) does not degrade the provitamins and is unnecessary for kale, tomato, and squash; however, it is required for good separation of papaya carotenoids due to the presence of carotenol esters. The current Association of Official Analytical Chemists (AOAC) method is found to be inappropriate because (1) the volume of extracting solvent is not adjusted to the type of sample; (2) the less active alpha- and gamma-carotene, alpha- and beta-cryptoxanthin, and 5,6-monoepoxy-beta-cryptoxanthin (50% active) are quantified as beta-carotene (100% active); (3) inactive carotenoids such as xi-carotene and zeinoxanthin are also quantified as beta-carotene.     

Computing Green's function of elasticity in a half-plane with impedance boundary condition

This Note presents an effective and accurate method for numerical calculation of the Green's function G associated with the time harmonic elasticity system in a half-plane, where an impedance boundary condition is considered. The need to compute this function arises when studying wave propagation in underground mining and seismological engineering. To theoretically obtain this Green's function, we have drawn our inspiration from the paper by Durán et al. (2005), where the Green's function for the Helmholtz equation has been computed. The method consists in applying a partial Fourier transform, which allows an explicit calculation of the so-called spectral Green's function. In order to compute its inverse Fourier transform, we separate as a sum of two terms. The first is associated with the whole plane, whereas the second takes into account the half-plane and the boundary conditions. The first term corresponds to the Green's function of the well known time-harmonic elasticity system in (cf. J. Dompierre, Thesis). The second term is separated as a sum of three terms, where two of them contain singularities in the spectral variable (pseudo-poles and poles) and the other is regular and decreasing at infinity. The inverse Fourier transform of the singular terms are analytically computed, whereas the regular one is numerically obtained via an FFT algorithm. We present a numerical result. Moreover, we show that, under some conditions, a fourth additional slowness appears and which could produce a new surface wave. To cite this article: M. Durán et al., C. R. Mecanique 334 (2006).     

Degradation studies of quetiapine fumarate by liquid chromatography–diode array detection and tandem mass spectrometry methods

Quetiapine fumarate (QUE) is an antipsychotic agent with a chemical structure that is susceptible to degradation; therefore, it is important to study its stability using appropriate analytical tools. Knowledge of the stability profile of a drug is important because chemical degradation of its active component often results in a loss of potency, affecting its efficacy and safety. This current work reports degradation studies of QUE as drug substance, under different stress conditions such as oxidation, hydrolysis, heat, humidity and photolysis, by a stability‐indicating LC method. The chemical stability was evaluated using a simple HPLC/diode array detection method, with a core‐shell C₁₈ column under isocratic conditions, which allows the separation of all primary degradation products (DPs) in a short run time. QUE was mainly degraded under oxidative and hydrolytic conditions, with the formation of three and two DPs, respectively, which were identified by electrospray ionization–tandem mass spectrometry. The method was properly validated in terms of linearity, accuracy, precision, selectivity, robustness and quantitation limit. Commercial tablets containing 25 mg of QUE were quantified, with results obtained within the United States Pharmacopeia limits. The proposed method is suitable to assess the stability and perform routine analysis of QUE in pharmaceutical samples.     

Quantum Derivation of Ginzburg-Landau Equation. New Formula for Penetration Depth

The Cooper pair (pairon) field operator ψ(r,t) changes in time, following Heisenberg’ s equation of motion. If the system Hamiltonian $\mathcal{H}The Cooper pair (pairon) field operator ?(r,t) changes in time, following Heisenberg's equationof motion. If the system Hamiltonian contains the pairon kineticenergies h ₀, the condensation energy per pairon(< 0) and the repulsive point-like potential(r ₁ –r ₂), > 0, the evolution equation for ?is non-linear, from which we obtain the Ginzburg-Landau equation: for the complex order parameter $$ " align="middle" border="0"> , where denotes thestate of the condensed pairons, and n the pairon densityoperator. The total kinetic energy h ₀ forelectron (1) and hole(2) pairons is where are Fermi velocities, and A thevector potential. A new expression for the penetration depth isobtained: where p and n ₀ are respectively themomentum and density of condensed pairons.     

Synthesis and characterisation of a {Ni21Ag} cage

An unusual {Ni21Ag} cluster is reported and demonstrates the importance of examining the "counter-ion" present in all reactions involving polymetallic complexes.