Rhodium(I) carbonyl complexes with α-diimine ligands containing amino or hydroxy substituents

-Diimines, RN:C(R)C(R):NR(LL) derived from glyoxal, GLL (R=H) abbreviated as GAA (R= R=4-dimethylaminophenyl) or GHA (R= R=4-hydroxyphenyl), and derived from biacetyl, BLL (R=Me) abbreviated as BDH (R=R= NH₂), BOH (R=NH₂, R=OH) react with carbonylrhodium(I) compounds to give different products depending on the imino substituents in the ligand and/or the solvent employed. The reaction of -diimines bearing amino groups, such as GAA or BDH with [RhCl(CO)₂]₂ in acetone yields binuclear [RhCl(CO)₂]₂(-LL) while in CH₂Cl₂ ionic [Rh- (CO)₂(LL)]⁺[RhCl₂(CO)₂]^– species are obtained. In acetone [RhCl(CO)₂]₂(-GAA) exists as an equilibrium mixture between two different neutral binuclear species; [Rh(CO)₂(BDH)]⁺ exists as a mixture of two species containing chelate or monodentate bonded diimine respectively. GAA or BDH react in situ with [RhCl(CO)(C₂H₄)]₂ in benzene to yield tetracoordinated monocarbonylated [RhCl(CO)(LL)] compounds. -Diimines (LL) bearing hydroxy groups, such as GHA or BOH react with [RhCl(CO)₂]₂ or [RhCl(CO)(C₂H₄)]₂ to give pentacoordinated dicarbonylated [RhCl(CO)₂(LL)] compounds.     

On nonhomogeneous singular elliptic equations with cylindrical weights

In this paper, we establish the existence of multiple solutions for nonhomogeneous singular elliptic equations with cylindrical weights, by using Ekeland??s variational principle and mountain pass theorem without Palais?CSmale condition.     

Oxidation of phenol and chlorophenols on platinized titanium anodes in an acidic medium

A comparative study of oxidation of phenol, 3-chlorophenol, 4-chlorophenol, and 2,4-dichlorophenol on Pt/Ti and Ce,Pt/Ti electrocatalysts is performed via cyclic voltammetry. It is shown that the surface morphology and roughness of the anode do not change after modification with cerium. The formal kinetic orders of electrooxidation of all compounds are found to be less than one. It is shown that the β temperature coefficients of the rate of oxidation of chlorophenols grow by 10 to 50% when the Ce,Pt/Ti anode is used at a substrate concentration of 1 mM. A tenfold increase in concentration reduces the effect of cerium additive, except for 3-chlorophenol: the latter exhibits a 250% increase in the β value, compared to the Pt/Ti anode.     

Recent advances in graphite powder-based electrodes

Graphite powder-based electrodes have the electrochemical performance of quasi-noble metal electrodes with intrinsic advantages related to the possibility of modification to enhance selectivity and their easily renewable surface, with no need for hazardous acids or bases for their cleaning. In contrast with commercial electrodes, for example screen-printed or sputtered-chip electrodes, graphite powder-based electrodes can also be fabricated in any laboratory with the form and characteristics desired. They are also readily modified with advanced materials, with relatively high reproducibility. All these characteristics make them a very interesting option for obtaining a large variety of electrodes to resolve different kinds of analytical problems. This review summarizes the state-of-the-art, advantages, and disadvantages of graphite powder-based electrodes in electrochemical analysis in the 21st century. It includes recent trends in carbon paste electrodes, devoting special attention to the use of emergent materials as new binders and to the development of other composite electrodes. The most recent advances in the use of graphite powder-modified sol–gel electrodes are also described. The development of sonogel–carbon electrodes and their use in electrochemical sensors and biosensors is included. These materials extend the possibilities of applications, especially for industrial technology-transfer purposes, and their development could affect not only electroanalytical green chemistry but other interesting areas also, for example catalysis and energy conversion and storage.     

Silver nanoparticles immobilized onto poly(4‐vinylpyridine)‐functionalized magnetic nanoparticles: A robust magnetically recyclable catalyst for oxidant‐free alcohol dehydrogenation

A heterogeneous and recyclable catalyst with a high loading of silver nanoparticles was synthesized via the silver nanoparticles being supported onto the surface of magnetic nanoparticles coated with poly(4‐vinylpyridine). The synthesized catalyst was used in the dehydrogenation of alcohols to corresponding carbonyl compounds. A broad diversity of alcohols was converted into their corresponding carbonyl compounds in excellent yields. The catalyst was easily recovered by applying an external magnetic field and reused for seven reaction cycles without considerable loss of activity. The catalyst was fully characterized using various techniques.     

The impact of time on the heat resistance of self-compacting high-performance concrete incorporated with recycled martials

The influence of time on the mechanical behavior of concrete after exposure to elevated temperatures has been studied. Twenty-one self-compacting high-performance concrete mixtures with different incorporation amounts of coarse recycled concrete aggregate (RCA) and three unprocessed waste powder materials have been tested at age of 270 days for residual compressive and flexural strength after exposure to fire. The results have been compared to the results for the same concrete, which have been studied at age of 90 days. A new parameter has been introduced for comparing the responses of concrete to elevated temperatures at different ages; this parameter was the “heat resistance” which expresses the total area under the curve of the relative residual strength (compressive or flexural) after exposing to six temperature degrees (20, 150, 300, 500, 600, and 800 °C). The results showed that the age of concrete has an influence on the response of concrete to elevated temperatures. The heat resistance of compressive strength enhanced with age but the concrete behaved with a tendency different to that at the age of 90 days. The heat resistance of flexural strength has not been affected or slightly decreased but not with more than 10% to that at the age of 90 days. The used waste powder materials were unprocessed waste fly ash, waste cellular concrete powder and waste perlite powder; they proved that using any of them up to 15% as a replacement for cement with 0% or 25% of RCA enhanced the concrete resistance for the fire with time. The main two reasons for changing of residual strength with the time were the changing of water content and the proceeding of hydration of the binder. In general, long ages testing properties of concrete simulate the real behavior of concrete structures accurately.

     

Use of capillary electrophoresis for characterisation of vinyl‐terminated Au nanoprisms and nanooctahedra

It is described a simple, rapid and efficient methodology to characterise and separate gold nanoprisms and nanooctahedra by capillary electrophoresis. This technique is suitable to distinguish between morphologies and it can be used as a powerful separation tool after a customised synthesis of both structures. This synthesis was carried out by amending two parameters, temperature and pH, and a sharp decrease was found in nanotriangles when temperature was increased from 70 up to 95°C. However, when the synthesis was performed at a given temperature, an increase in pH did not promote an important change in isolation of any structure until pH = 9.5, critical in the final morphology of the nanoparticle. Gold nanoprisms and nanooctahedra were successfully separated by capillary electrophoresis according to differences in charge‐to‐mass ratio of the morphologies. Final particle morphology was confirmed by transmission electron microscopy analysis. Under optimal working conditions, a mixture containing both shapes of gold nanoparticles was initially injected and two major peaks were obtained for each structure. Capillary electrophoresis allowed to study pH and temperature influence on both morphologies. It was inferred that the ratio between triangles and octahedra decreased to a great extent when increasing both temperature and pH.     

On the Rayleigh-Plateau instability

In this paper,we study the surface instability of a cylindrical pore in the absence of stress. This instability is called the Rayleigh-Plateau instabilty. We consider the model developed by Spencer et ...