K5Nd(MoO4)4: a self-tunable laser crystal

We report for the first time to our knowledge an experimental demonstration of wavelength self-tuning in a K5Nd(MoO4)4 broadband-emitting laser crystal (KNM), as well as a theoretical treatment of the system based on its birefringence properties. The self-frequency-tuning of the laser along the full spectral range of the KNM crystal was obtained by rotating a birefringent gain plate in its own plane. The gain plate was placed inside a resonator at Brewster's angle. The tuning characteristics of the spectral filter were obtained by use of the Jones vector formalism. The calculated wavelength-selective tuning precisely matches the experimental observations.     

The determination of kinetic data for the reactions of chromium(VI) with glutathione and other thiols

The equations necessary for the determination of the rate constants corresponding to the opposite elementary steps for formation of the oxidant-reductant ester intermediate, as well as that corresponding to its redox decomposition, in the reduction of chromium(VI) by glutathione and other thiols at physiological pH have been deduced. It is shown that those three rate constants can be obtained with a good reproducibility. © 1994 John Wiley & Sons, Inc.     

Trace Inequalities of Sobolev Type in the Upper Triangle Case

We give a new non-capacitary characterization of positive Borelmeasures µ on Rⁿ such that the potential space I*L^p isimbedded in L^q(dµ) for $1qp+, that is, the trace inequality holds, for Riesz potentials I = (- )². A weak-type trace inequality is also characterized. A non-isotropic version on the unit sphere Sⁿ is studied,as well as the holomorphic case for Hardy–Sobolev spaces in the ball. 1991 MathematicsSubject Classification: primary 31C15, 42B20; secondary 32A35.     

Formation of Superoxochromium(III) by a Novel Mechanism

The reduction of chromate ion by l-cysteine in near-neutral aqueous solutions was studied by u.v.–vis spectroscopy. The rate constants for the formation, decomposition and redox degradation of a Cr^VI thioester intermediate (both in the absence and in the presence of dissolved O₂) were determined by the use of a nonlinear least-squares regression to fit the experimental data to a double-exponential integrated rate law. Superoxochromium(III), CrOO²⁺, could be observed as a long-lived intermediate by the use of u.v. difference spectroscopy (peaks at 238 and 292 nm). The effects of several reaction variables on the yield of the intermediate CrOO²⁺ were studied. A striking result was that the yield decreased as the concentration of dissolved O₂ increased. In the presence of phosphate buffer, the yield showed a maximum at pH 6.8. Formation of CrOO²⁺ was suppressed by the additives Mn²⁺, H₂O₂, d-ribose, 2-deoxy-d-ribose and a high concentration of Ce³⁺, whereas a low concentration of the latter enhanced its appearance. A novel mechanism for the formation of CrOO²⁺ from Cr^VI and l-cysteine (involving the intramolecular formation of an O–O bond) is proposed, and the possible routes for the decay of this intermediate are discussed. This novel mechanism might offer new insights into the redox chemistry of chromate ions.     

Inverted colloidal crystals as three-dimensional cell scaffolds

A new type of three-dimensional scaffold with inverted colloidal crystal geometry for the investigation of topological effects in cell cultures is introduced in this publication. The scaffolds are made by infiltration of the hexagonal crystal lattice of polystyrene spheres with sol-gel formulation and subsequent annealing. It possesses a relatively high degree of order among existing cell scaffolds and affords tight control over the scaffold porosity and tissue organization. The prepared scaffolds can be a convenient system for the investigation of cell-cell and cell-matrix interactions. Their biocompatibility is demonstrated for human hepatocellular carcinoma HEP G2 and human bone marrow HS-5 cell cultures. A preliminary effect of the scaffold topology on cell proliferation is observed. HEP G2 hepatocytes form a large number of 10-15 cell colonies on scaffolds made from 75-microm spheres, while their number diminishes for scaffolds from 10- and 160-microm spheres. Under similar conditions, HS-5 forms smaller colonies consisting of three to four cells in 90-microm cavities.     

Utilisation des plans factoriels fractionnaires pour l'étude de la réaction de bucherer-bergs: Synthèse de la cyclohexane spirohydantoîne

The only sixteen experiments of a fractional factorial design have been necessary to study the influence on the yield of cyclohexanospirohydantoin of the seven following factors: flask volume, cyanide and ammonium carbonate concentrations, quanities of water and ethanol, temperature and reaction time. The experimental strategy and results are compared with a recently published Simplex optimization, showing a better knowledge of the reaction after using a factorial design.     

Supramolecular reagents: versatile tools for non-covalent synthesis

The design and modular synthesis of three ternary co-crystals with desired connectivity, assembled using tailor-made pyridyl/benzimidazol-1-yl-based supramolecular reagents, are described.     

Effect of the substituents on the conformational behavior of five-membered rings: Application to the cis- and trans-2,5-dimethoxytetrahydrofuran

A model is proposed which assumes that the pseudorotational potential in five-membered rings is given by the combination of contributions from the unsubstituted ring, from the individual substituents and from interactions between pairs of substituents. The application of this model to the potentials calculated by the MM2 force field for the cis and trans-2,5-dimethoxytetrahydrofuran shows that the contributions from the individual substituents explain the main features of the potentials of these disubstituted rings. The pseudorotational analysis from vicinal proton spin-spin coupling constants ³J_HH confirms the realibility of the MM2 potentials.     

On the performance of Fe-Cu-ZSM-5 catalyst for the selective catalytic reduction of NO with NH3: the influence of preparation method

Research on Chemical Intermediates - The selective catalytic reduction of NO with ammonia (NH3-SCR) in the presence of H2O was studied over a series of Fe-Cu-ZSM-5 catalysts prepared by solid-state...