MnFeNi-Based Composite as a Case Study of a Bifunctional Oxygen Electrocatalyst under Dynamically Changing Electrode Potentials

High-performance bifunctional electrocatalysts for the oxygen reduction (ORR) and oxygen evolution reaction (OER) are essential components in energy conversion and storage technologies. Yet, their poor reversibility hinders their applicability. A highly active ORR/OER catalyst, consisting of multiwalled carbon nanotubes-supported MnFeNiOx nanoparticles, was subjected to sequences of chronoamperometric steps alternating between the ORR, the OER and highly cathodic potentials (E_c). Rotating ring disk electrode methods revealed that applying E_c leads to a small increase in the current and peroxide species yield during the ORR while enhancing substantially the OER. X-ray absorption spectroscopy showed irreversible changes in the chemical state of MnFeNiOx correlating with its catalytic properties. The complexity of changes that a composite catalyst may undergo under varying potentials, the importance of monitoring product formation, and the convenience of using dynamic electrochemical sequences for the assessment of catalyst reversibility, as well as for the activation and/or restoration of their catalytic properties, are highlighted.     

Synthesis,stereochemistry, and opioid receptor binding activity of heterocyclic analogues of BW373U86

The synthesis of a series of heterocyclic analogues of (±)-4-((αR*)-α-((2S*,5R*)-4-allyl-2,5-dimethyl-1-piperazmyl)-3-hydroxybenzyl)-N,N-diethylbenzarrude (BW373U86) for screening against opioid receptors is described. The intermediate α-heterocyclic benzyl alcohols 24 were synthesized either by low temperature reaction of lithioheterocycles with 3-((tert-butyldimethylsilyl)oxy)benzaldehyde ( 10 ) or by reaction of 3-((tert-butyldimethylsilyl)oxy)phenylmagnesium bromide ( 19 ) with heterocyclic carbaldehydes. The α-heterocyclic benzyl alcohols 24 were converted to chloromethines ( 25 ) with thionyl chloride and used to alkylate with trans-1-allyl-2,5-dimethylpiperazine ( 5 ) to give diastereomeric pairs of the target compounds. The bromoheterocycles were then derivatized to produce amides. Compounds that are potent and selective for the 5 or μ opioid receptors and some mixed δ/μ analogues are reported.     

Study of the Ternary Complex Formation between Vanadium(III)-Cysteine and Small Blood Serum Bioligands

The complex species formed between vanadium(III) cysteine and small blood serum bioligands: lactic, oxalic, citric and phosphoric acids were studied in aqueous solution by means of electromotive force measurements, Emf(H), at 25 °C and 3.0 mol⋅dm⁻³ KCl as the ionic medium. The ternary complexes were studied by potentiometric measurements and the data analyzed using the least-squares computational program LETAGROP to obtain the respective stability constants and stoichiometric coefficients. The UV-Vis spectrophotometric measurements were done in order to make a qualitative characterization of the complexes formed in aqueous solution.     

Simultaneous correction of the influence of skin color and fat on tissue spectroscopy by use of a two-distance fiber-optic probe and orthogonalization technique

We have demonstrated simultaneous correction for the optical interference of skin and fat in tissue spectra by using a two-distance fiber-optic probe. We obtained the correction by orthogonalizing the spectra collected at a long source-detector distance (SD) to the spectra collected at a short SD and mapped to the long SD space. The method was validated in tissuelike three-layer phantoms as well as preliminarily in human tissue. After the correction, a partial-least-squares model of the phantoms showed enhanced prediction performance.     

Assembly intermediates in polyketide biosynthesis: enantioselective syntheses of beta-hydroxycarbonyl compounds

A versatile approach for the enantioselective synthesis of functionalised beta-hydroxy N-acetylcysteamine thiol esters has been developed which allows the facile incorporation of isotopic labels. It has been shown that a remarkable reversal of selectivity occurs in the titanium mediated aldol reaction of acyloxazolidinone using either (S)- or (R)-tert-butyldimethylsilyloxybutanal. The aldol products are valuable intermediates in the synthesis of 4-hydroxy-6-substituted delta-lactones.     

Weyl Type Theorems and Restrictions

In this paper we show that for a bounded linear operator \({T\in L(X)}\) acting on a Banach space X, the study of generalized Weyl’s theorem for T can be reduced to the study of generalized Weyl’s theorem for some restrictions of T.     

Interplay between Riccati,Ermakov, and Schrödinger equations to produce complex‐valued potentials with real energy spectrum

Nonlinear Riccati and Ermakov equations are combined to pair the energy spectrum of 2 different quantum systems via the Darboux method. One of the systems is assumed Hermitian, exactly solvable, with discrete energies in its spectrum. The other system is characterized by a complex‐valued potential that inherits all the energies of the former one and includes an additional real eigenvalue in its discrete spectrum. If such eigenvalue coincides with any discrete energy (or it is located between 2 discrete energies) of the initial system, its presence produces no singularities in the complex‐valued potential. Non‐Hermitian systems with spectrum that includes all the energies of either Morse or trigonometric Pöschl‐Teller potentials are introduced as concrete examples.     

Two‐electron atomic systems confined within spheroidal boxes

The direct variational method is used to estimate some interesting physical properties of the He atom and the Li⁺ ion confined within impenetrable spheroidal boxes. A comparative investigation of the ground‐state energy, pressure, polarizability, dipole, and quadrupole moments with those of the He atom inside boxes with paraboloidal walls is made. The overall results show a similar qualitative behavior. However, for Li⁺ there are quantitative differences on such properties due to its major nuclear charge, as expected. The trial wave function is constructed as a product of two hydrogenic wave functions adapted to the geometry of the confining boxes. © 2000 John Wiley & Sons, Inc. Int J Quant Chem 77: 509–515, 2000     

Crystal structure of trans-dibromobis(triphenylphosphine)platinum(II).

Crystal structure of trans-dibromobis(triphenylphosphine)platinum(II) was determined by X-ray-crystallography. The complex crystallizes on an inversion center in distorted square planar coordination around platinum with triphenylphosphine ligands in trans positions to each other and with two molecules of dichloromethane as solvate.     

Surface P and Al Distribution in P-modified ZSM-5 Zeolites

The surface composition of two commercial ZSM-5 zeolites with and without PO₄ modification was examined by X-ray photoelectron spectroscopy. Both zeolites were slightly enriched in aluminum on the surface. The surface silica/alumina ratio (SAR) was about half of that of the bulk. Calcination at 600^∘C decreased slightly this enrichment. After drying with H₃PO₄ followed by calcination, both zeolites showed surface enrichment of PO₄. The surface of the zeolite with large crystal was more enriched. Steaming resulted in enrichment of aluminum on the surface, in agreement with migration of extra-framework alumina. Increasing phosphate content decreased this enrichment. This paper was presented in the 5th Brazilian Meeting on Adsorption, held at Natal, Brazil, 18-21 July, 2004.