Manuel Salmón

Effect of the Electrosynthesis Method on the Surface Morphology of the Polypyrrole Film An Atomic Force Microscopy Study

The surface morphology of polypyrrole (ppy) films prepared by potentiostatic and voltammetric methods at the platinum electrode was studied by ex situ atomic force microscopy (AFM). The study was mainly focused on the early stages of polymer film growth up to a film thickness of 30 to 50 nm. AFM analysis revealed that polymer film morphology depends on the electrosynthesis method used. Electrosynthesized films produced by the voltammetric method consisted of nano-size ppy nodules, which during the polymer oxidation process become associated forming larger surface aggregates. However, in thicker films and those prepared using a large anion, this association was not observed. The ppy films formed by the potential step method (potentiostatic) allowed a better control of the early stages of the electropolymerization process. Thus, the AFM study showed that the first ppy nodules grow three-dimensionally during the application of the potential pulse steps, and simultaneously their number increase on the electrode surface according to the progressive nucleation and growth model. Negligible association of ppy nodules was noticed for the film prepared by the potentiostatic method, which suggests that this synthesis method is a better alternative for controlling ppy film growth.

Rapid transesterification of bilirubin glucuronides in methanol

Abstract The current studies present evidence that bilirubin conjugates derived from rat bile undergo rapid transesterification, in vitro , in solutions containing methanol. The conjugates of bilirubin and the methyl esters formed from them by exposure to methanol were isolated by thin layer chromatography. The isolates were chemically quantitated for their bilirubin and glucuronic acid composition. Characterization of the bilirubin methyl esters was performed by mass spectrometric analysis of the trimethylsilyl and phenylazo derivatives.

Route to chemically modified chiral electrodes: synthesis and properties of optically active pyrrole monomers

Abstract The synthesis of stable optically active pyrrole monomers and their electrochemical oxidation to chiral polymers is described. The polymers work as chemically modified electrodes which can be used as asymmetric inductors in redox reactions of prochiral organic molecules.

A SIMPLE METHOD FOR THE SYNTHESIS OF CARBAMATES

Abstract A new method for carbamate synthesis using aryl and alkylamines with sodium hydride and diethylcarbonate in dry benzene is described.

Oxidative Cleavage of Aldo and Keto Oximes with Chromyl Chloride Adsorbed on Silica and Bentonite Earth

Abstract A number of Aldo, Keto and O-Acetyl oximes have been deblocked using chemisorbed Chromyl chloride on Bentonite and Silica Gel. A comparative study between the Chromyl chloride in solution and supported is also given.

Photoproduction of H2O2 and hydroxyl radicals catalysed by natural and super acid-modified montmorillonite and its oxidative role in the peroxidation of lipids

The reactivity of both natural montmorillonite and montmorillonite modified with super acids (CF3SO3H and HClO4) to generate hydrogen peroxide (H2O2) and hydroxyl radicals (˙OH) under both darkness and UV-light irradiation was investigated using EPR spin-trapping spectroscopy. We used the free-radical trapping action of 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) to indicate the production of ˙OH from natural and modified clays. The recognition and characterisation of the formed DMPO–OH adduct established that super acid montmorillonites were able to generate hydroxyl radicals at 25 °C in the presence of O2 and H2O. When natural and acid montmorillonite were irradiated with UV light, hydroxyl radical generation was greater than under dark conditions. In addition, the peroxidation of lipids in biological matrices with natural and super acid montmorillonite was studied using a thiobarbituric acid reactive substances (TBARS) assay, which demonstrated that only ˙OH generated from the super acid montmorillonite induced the oxidative degradation of lipids. This study reports, for the first time, the generation of ˙OH and the peroxidation of lipids by a typical super acid-modified Mexican montmorillonite.

Characterization of a bentonitic clay and its application as catalyst in the preparation of benzyltoluenes and oligotoluenes

Abstract The preparation of oligomeric toluenes catalyzed with a bentonitic clay, using thermal energy and ultrasound, was performed and evaluated. When ortho and para benzyltoluenes were studied, the oligomerization reaction was found to be dependent of the catalyst amount, reaction time, temperature and the presence of pyridine as competitive inhibitor. A proposal for the molecular structure calculation analysis at semiempirical AM1 level was proposed based on the regioselectivity and in the oligomerization pathway. Furthermore, a detailed study to characterize the clay was performed, thus several physicochemical properties of the clay were determinated by means of: 29 Si and 27 Al MAS–NMR, X-ray diffraction, X-ray fluorescence, scanning electron microscopy, IR spectrophotometry, thermal analysis (DTA, TG-DTG), and adsorption techniques (N 2 -BET).

Clay-mediated cyclooligomerization of olefin oxides: a one-pot route to crown ethers

The catalytic synthesis of substituted 1,3-dioxolanes, 1,4-dioxanes, 9-crown-3, 12-crown-4 and 15-crown-5 ethers, from alkyl oxiranes and a montmorillonite type clay is discussed.

1,3-dioxolane formation with a montmorillonite-type clay catalyst

Abstract The coupling reaction of oxiranes with carbonyl compounds to produce 1,3-dioxolanes was promoted by catalytic amounts of a bentonitic clay. The product yield was found to be dependent on the catalyst, the reaction temperature and the reagent concentrations. A kinetic study performed with acetone and ethylene oxide showed a first-order dependence in both reagents. Other experiments made with different epoxides, carbonyl compounds and catalysts are also discussed.

Kaurenic acid derivatives from Stevia eupatoria

Abstract Two kaurene type diterpenes were isolated from the aerial part of Stevia euphoria . Their structures and stereochemistry were established by carbon and 1 H NMR, chemical transformation and correlation with known compounds.