Influence of the Preparation Procedure on the Catalytic Activity of Gold Supported on Diamond Nanoparticles for Phenol Peroxidation

The catalytic activity of diamond‐supported gold nanoparticle (Au/D) samples prepared by the deposition/precipitation method have been correlated as a function of the pH and the reduction treatment. It was found that the most active material is the one prepared at pH 5 followed by subsequent thermal treatment at 300 °C under hydrogen. TEM images show that Au/D prepared under optimal conditions contain very small gold nanoparticles with sizes below 2 nm that are proposed to be responsible for the catalytic activity. Tests of productivity using large phenol (50 g L ^?1) and H₂O₂ excesses (100 g L ^?1) and reuse gives a minimum TON of 458,759 moles of phenol degraded per gold atom. Analysis of the organic compounds extracted from the deactivated solid catalyst indicates that the poisons are mostly hydroxylated dicarboxylic acids arising from the degradative oxidation of the phenyl ring. By determining the efficiency for phenol degradation and the amount of O₂ evolved two different reactions of H₂O₂ decomposition (the Fenton reaction at acidic pH values and spurious O₂ evolution at basic pH values) are proposed for Au/D catalysis. The activation energy of the two processes is very similar (ranging between 30 and 35 kJ mol^?1). By using dimethylsulfoxide as a radical scavenger and N‐tert‐butyl‐α‐phenylnitrone as a spin trap under aerated conditions, the EPR spectrum of the expected PBN? OCH₃ adduct was detected, supporting the generation of HO^., characteristic of Fenton chemistry in the process. Phenol degradation, on the other hand, exhibits the same activation energy as H₂O₂ decomposition at pH 4 (due to the barrierless attack of HO^. to phenol), but increases the activation energy gradually up to about 90 kJ mol^?1 at pH 7 and then undergoes a subsequent reduction as the pH increases reaching another minimum at pH 8.5 (49 kJ mol^?1).     

Mass Spectrometry Studies of the Retro-Cycloaddition Reaction of Pyrrolidino and 2-Pyrazolinofullerene Derivatives Under Negative ESI Conditions

Substituted pyrrolidino- and 3-alkyl-2-pyrazolinofullerenes ionize under ESI and MALDI mass spectrometry conditions and negative mode of detection undergoing mass spectral fragmentations, which can be easily correlated with the reported results for the thermal and electrochemical retro-cycloaddition reactions of these compounds. 2-Pyrazolinofullerenes lead directly to a [60]fullerene product ion formed through a retro-cycloaddition process regardless of the substituents attached at the carbon and nitrogen atoms of the heterocyclic ring. These results are different from whose reported for the thermal and electrochemical processes. In contrast, pyrrolidinofullerenes undergo different fragmentative reactions depending upon the substituents (hydrogen, alkyl, or acyl) attached at the nitrogen atom of the heterocyclic ring leading eventually to the pristine C₆₀ in the last step of the fragmentation pathway.     

Electrorheology of clay particle suspensions. Effects of shape and surface treatment

We investigate the electrorheological (ER) properties of clay (montmorillonite, sepiolite, and laponite®). The selected clays allow to distinguish between planar particles of different sizes (montmorillonite and laponite®), and elongated ones (sepiolite). The effect of coating them with the surfactant CTAB improves dispersibility in the oil medium and favors the ER response, prticularly in the case of laponite®, whereas in the case of montmorillonite, microscopic observations show that the columnar structures are broken in places leading to a reduced yield stress. Both the static yield stress and the storage modulus grow faster with the field in sepiolite suspensions as compared to laponite®. When dealing with mixed systems, it is found that the field-induced montmorillonite structures are reinforced by the addition of either laponite® or sepiolite, whereas when the latter two are combined, it is laponite® that dominates the ER response.

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A theoretical review on the single-impurity electron spin resonance on surfaces

The development of electron spin resonance (ESR) combined with scanning tunneling spectroscopy (STM) is undoubtedly one of the main experimental breakthroughs in surface science of the last decade thanks to joining the extraordinarily high energy resolution of ESR (nano-eV scale) with the single-atom spatial resolution of STM (sub-Ångström scale). While the experimental results have significantly grown with the number of groups that have succeeded in implementing the technique, the physical mechanism behind it is still unclear, with several different mechanisms proposed to explain it. Here, we start by revising the main characteristics of the experimental setups and observed features. Then, we review the main theoretical proposals, with both their strengths and weaknesses. One of our conclusions is that many of the proposed mechanisms share the same basic principles, the time-dependent electric field at the STM junction is modulating the coupling of the spin-polarized transport electrons with the local spin. This explains why these mechanims are essentially equivalent in a broad picture. We analyze the subtle differences between some of them and how they compare with the different experimental observations.     

Expanding the Chemical Space of Non-Proteinogenic N4-Substituted Asparagine: Racemic,Enantioenriched, and Deuterated Derivatives

A site-selective carbamoylation strategy to access non-proteinogenic N⁴-modified asparagines has been described. The protocol is characterized by mild reaction conditions, high functional group compatibility, and a wide diversity of functionalized carbamoyl radicals making possible the access to peptides, pharmaceuticals, and natural N⁴-asparagine conjugates, as well as enantioenriched unnatural N⁴-asparagines. Besides that, deuterated analogues were achieved with the insertion of D₂O and enantioenriched derivatives could be obtained in 15 min in continuous-flow conditions.     

High relative accuracy with some special matrices related to Γ and β functions

For some families of totally positive matrices using $\mathrm{\Gamma }$ and $\beta$ functions, we provide their bidiagonal factorization. Moreover, when these functions are defined over integers, we prove that the bidiagonal factorization can be computed with high relative accuracy and so we can compute with high relative accuracy their eigenvalues, singular values, inverses and the solutions of some associated linear systems. We provide numerical examples illustrating this high relative accuracy.     

Stress And Strain in a Yeast Cell Under High Hydrostatic Pressure

The mechanical effects of the compression of a yeast cell (Saccharomyces cerevisiae) under high hydrostatic pressure (HHP) are modeled and simulated numerically. The deformation of the cell under pressure deviates strongly from isotropic volume reduction. In the cell wall, von‐Mises stress reaches the critical value upon failure at a pressure load between 415Mpa and 460MPa. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Kinetic and thermodynamic aspects of miniemulsion copolymerization

Miniemulsion polymerization involves initiation of polymerization in preformed stable monomer emulsion droplets with average droplet diameter of 50–500 nm. At the end of the polymerization, only a fraction of the initial number of monomer droplets become polymer particles. The emulsifier system used for the preparation of such emulsions comprises a mixture of ionic surfactant and a fatty alcohol or long chain alkane (termed cosurfactant). The cosurfactant is essential for the formation of stable emulsion droplets and in addition it plays an important role in the interparticle monomer transport. Kinetic results are presented on conventional emulsion and miniemulsion copolymerization of different pairs of monomers, showing the main differences for both processes. These differences were related to the particle formation mechanism and the influence of the cosurfactant in the miniemulsion process. A theoretical model was developed, based on mass balances and equilibrium thermodynamics, which was found to describe accurately the experimentally generated data on comonomer distribution during the course of the copolymerization process and the interdroplet mass transport process.     

Numerical simulation of a multi-contact detection technique for foreign particles in closed food containers

In the presented work the basis of a novel method for detecting foreign solid inclusions in closed glass bottles and cans containing liquid food are presented. The new method is based on an automatic recording and analysis of multi-contact oscillatory signals of the food-container-particle (F-C-P) system. In this work, two different active mechanisms for positioning the foreign particles next to the wall of the bottle are studied and relevant numerical simulations are presented. In the first case, a bottle filled with water moves linearly with constant acceleration, while in the second case the bottle rotates around its longitudinal axis at a constant angular velocity. The obtained numerical results permit the selection of optimal locations for the detection system components. (© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)