Promoter Effect of Potassium on an Iron Catalyst in the Carbon Dioxide Hydrogenation Reaction

Catalysts containing copper, zinc and aluminium oxides are used extensively in hydrogenation reactions, low temperature water-gas shift and low pressure methanol synthesis processes. In the present study, the effects of certain pertinent preparation parameters on catalysts' activity have been studied, applying the saturated fractional factorial experimental design method. The influence of time and temperature of calcination, aging time, the method of mixing of reactant solutions, the nature of the precipitant and the molar ratio of the latter to metal nitrates have been investigated. The catalysts prepared, using sodium carbonate showed higher activities relative to those synthesized by applying sodium hydrogen carbonate. Higher temperatures and longer time of calcination have profound effects on the activity of catalysts prepared, using sodium hydrogen carbonate. Shorter aging times and higher molar ratios of precipitant to metal nitrates promoted the activity of catalysts prepared by sodium carbonate. In case of catalysts synthesized, using sodium hydrogen carbonate as the precipitant, the aging time should be maintained as short as possible in order the catalysts to acquire higher activities.     

Weil Representations of Symplectic Groups Over Rings

We are interested in Weil representations of Sp(2n, R), whereR is the ring Z/p^lZ, p is an odd prime and l is a positive integer,or, more generally, R = O/p^l, where O is the ring of integersof a local field, p is the maximal ideal of O and O/p has oddcharacteristic. One reason for this interest is that a continuousfinite-dimensional complex representation of Sp(2n, O) has tofactor through a representation of Sp(2n, O/p^l) for some l.     

Surface structure and redox chemistry of ceria-containing automotive catalytic systems

A summary is given of recent work done at the authors' laboratory, using several spectroscopies, molecular modeling and catalytic activity tests, to study the surface reactivity of ceriacontaining high surface area solids useful for automotive exhaust depollution catalysis. Issues addressed include the influence of the basicity of the cerium ion ligand environment on its ability for activation of O₂ at the material surface, and its modification by supporting on alumina or doping with Cl⁻ or other anions; the tendency to grouping of oxygen vacancies at the CeO₂ (111) surface; the higher ease for formation of surface reduced centers in mixed (Zr,Ce) oxides; and the effect of electronic transfer and other chemical interactions induced by ceria on the redox reactivity of transition metalcontaining catalysts.     

Packed in-tube SPME–LC–MS/MS for fast and straightforward analysis of cannabinoids and metabolites in human urine

Cannabinoids are pharmacologically active compounds present in cannabis plants, which have become important research topics in the modern toxicological and medical research fields. Not only is cannabis the most used drug globally, but also cannabinoids have a growing use to treat a series of diseases. Therefore, new, fast, and efficient analytical methods for analyzing these substances in different matrices are demanded. This study developed a new packed-in-tube solid-phase microextraction (IT-SPME) method coupled to liquid chromatography with tandem mass spectrometry (LC–MS/MS), for the automated microextraction of seven cannabinoids from human urine. Packed IT-SPME microcolumns were prepared in (508 µm i.d. × 50 mm) stainless-steel hardware; each one required only 12 mg of sorbent phase. Different sorbents were evaluated; fractional factorial design 2⁴⁻¹ and a central composite design were employed for microextraction optimization. Under optimized conditions, the developed method was a fast and straightforward approach. Only 250 µl of urine sample was needed, and no hydrolysis was required. The sample pretreatment included only dilution and centrifugation steps (8 min), whereas the complete IT-SPME–LC–MS/MS method took another 12 min, with a sample throughput of 3 samples h⁻¹. The developed method presented adequate precision, accuracy and linearity; R² values ranged from 0.990 to 0.997, in the range of 10–1000 ng ml⁻¹. The lower limits of quantification varied from 10 to 25 ng ml⁻¹. Finally, the method was successfully applied to analyze 20 actual urine samples, and the IT-SPME microcolumn was reused over 150 times.     

Maytansinol Derivatives: Side Reactions as a Chance for New Tubulin Binders

Maytansinol is a valuable precursor for the preparation of maytansine derivatives (known as maytansinoids). Inspired by the intriguing structure of the macrocycle and the success in targeted cancer therapy of the derivatives, we explored the maytansinol acylation reaction. As a result, we were able to obtain a series of derivatives with novel modifications of the maytansine scaffold. We characterized these molecules by docking studies, by a comprehensive biochemical evaluation, and by determination of their crystal structures in complex with tubulin. The results shed further light on the intriguing chemical behavior of maytansinoids and confirm the relevance of this peculiar scaffold in the scenario of tubulin binders.     

Modification of Landau Levels in a 2D Ring Due to Rotation Effects and Edge States

The properties of a 2D quantum ring under rotating and external magnetic field effects are investigated. The Landau levels and their inertial effects on them are initially analyzed. Among the results obtained, it is emphasized that the rotation lifted the degeneracy of Landau levels. The second part deals with the electronic confinement in a 2D ring modeled by a hard wall potential. The eigenstates are described by Landau states as long as they are not too close to the ring edges. On the other hand, near the ring edges, the energies increase monotonically. These states are known as edge states. Edge states have a significant role in the physical properties of the ring. Thus, the Fermi energy and magnetization are analyzed. In the specific case of magnetization, two approaches are considered. In the first approach, an analytical result for magnetization is obtained but without considering rotation. Numerical results show the de Haas-Van Alphen (dHvA) oscillations. In the second approach, rotating effects are considered. In addition to the dHvA oscillations, the Aharonov–Bohm-type (AB) oscillations are verified, which are associated with the presence of edge states. The effects of rotation on the results are discussed and it is found that rotation is responsible for inducing AB oscillations.     

On the solvability of implicit differential inclusions

In the paper, the set-valued covering mappings are studied. The statements on solvability, solution estimates, and well-posedness of inclusions with conditionally covering mappings are proved. The results obtained are applied to the investigation of differential inclusions unsolved for the unknown function. The statements on solvability, solution estimates, and well-posedness of these inclusions are derived.     

On a paper of Edmunds and Opic on limiting interpolation of compact operators between spaces

We show abstract versions for Banach couples of several limiting compact interpolation theorems established by Edmunds and Opic for couples of spaces.