Moving from surfactant-stabilized aqueous rhodium (0) colloidal suspension to heterogeneous magnetite-supported rhodium nanocatalysts: Synthesis, characterization and catalytic performance in hydrogenation reactions

Wet impregnation of pre-synthesized surfactant-stabilized aqueous rhodium (0) colloidal suspension on silica was employed in order to prepare supported Rh-0 nanoparticles of well-defined composition, morphology and size. A magnetic core-shell support of silica (Fe(3)O4@SiO2) was used to increase the handling properties of the obtained nanoheterogeneous catalyst. The nanocomposite catalyst Fe3O4@SiO2-Rh-0 NPs was highly active in the solventless hydrogenation of model olefins and aromatic substrates under mild conditions with turnover frequencies up to 143,000 h(-1). The catalyst was characterized by various transmission electron microscopy techniques showing well-dispersed rhodium nanoparticles (similar to 3 nm) mainly located at the periphery of the silica coating. The heterogeneous magnetite-supported nanocatalyst was investigated in the hydrogenation of cyclohexene and compared to the previous surfactant-stabilized aqueous Rh-0 colloidal suspension and various silica-supported Rh-0 nanoparticles. Finally, the composite catalyst could be reused in several runs after magnetic separation. (C) 2011 Elsevier B. V. All rights reserved.

Iron(III) Porphyrin Covalently Supported onto Magnetic Amino-Functionalized Nanospheres as Catalyst for Hydrocarbon and Herbicide Oxidations

This work describes the covalent immobilization of an ironporphyrin, 5,10,15,20-tetrakis(pentafluorophenyl)porphyrin iron(III) chloride (FeTFPP), onto maghemite/silica magnetic nanospheres covered with aminofunctionalized silica. The resulting material (gamma-Fe2O3/SiO2-NHFeP) was characterized by diffuse reflectance infrared spectroscopy (DRIFTS) and UV-Vis absorption spectroscopy. The catalytic activity of this magnetic ironporphyrin was investigated in the oxidation of hydrocarbons (styrene, (Z)-cyclooctene and R-(+)-limonene) and an herbicide (simazine) by hydrogen peroxide or 3-chloroperoxybenzoic acid. Hydrocarbon and simazine oxidation reaction products were analyzed by gas chromatography (GC) and high performance liquid chromatography (HPLC), respectively. This catalytic system proved to be efficient and selective for hydrocarbon oxidation, leading to high product yields from styrene (89%), cyclooctene (71%) and R-(+) -limonene (86%). Simazine oxidation was attained with 100% selectivity for a dechlorinated product (OEAT), while several oxidation products were obtained for the same catalyst in homogeneous media. The catalyst can be easily recovered through application of an external magnetic field and washed after reaction. Catalyst reuse experiments for R-(+)-limonene oxidation have shown that the catalytic activity is kept at 90% after 10 consecutive reactions.

Design of a Dinuclear Nickel(II) Bioinspired Hydrolase to Bind Covalently to Silica Surfaces: Synthesis, Magnetism, and Reactivity Studies

Presented herein is the design of a dinuclear Ni-II synthetic hydrolase [Ni-2(HBPPAMFF)(mu-OAc)(2)(H2O)]-BPh4 (1) (H(2)BPPAMFF = 2-[(N-benzyl-N-2-pyridylmethylamine)]-4-methyl-6-[N-(2-pyridylmethyl)aminomethyl)])-4- methyl-6-formylphenol) to be covalently attached to silica surfaces, while maintaining its catalytic activity. An aldehyde-containing ligand (H(2)BPPAMFF) provides a reactive functional group that can serve as a cross-linking group to bind the complex to an organoalkoxysilane and later to the silica surfaces or directly to amino-modified surfaces. The dinuclear Ni-II complex covalently attached to the silica surfaces was fully characterized by different techniques. The catalytic turnover number (k(cat)) of the immobilized (NiNiII)-Ni-II catalyst in the hydrolysis of 2,4-bis(dinitrophenyl)phosphate is comparable to the homogeneous reaction; however, the catalyst interaction with the support enhanced the substrate to complex association constant, and consequently, the catalytic efficiency (E - k(cat)/K-M) and the supported catalyst can be reused for subsequent diester hydrolysis reactions.

Iron(III) porphyrin covalently supported onto magnetic amino-functionalized nanospheres as catalyst for hydrocarbon and herbicide oxidations

This work describes the covalent immobilization of an ironporphyrin, 5,10,15,20- tetrakis(pentafluorophenyl)porphyrin iron(III) chloride (FeTFPP), onto maghemite/silica magnetic nanospheres covered with aminofunctionalized silica. The resulting material (γ-Fe2O3/SiO2-NHFeP) was characterized by diffuse reflectance infrared spectroscopy (DRIFTS) and UV-Vis absorption spectroscopy. The catalytic activity of this magnetic ironporphyrin was investigated in the oxidation of hydrocarbons (styrene, (Z)-cyclooctene and R-(+)-limonene) and an herbicide (simazine) by hydrogen peroxide or 3-chloroperoxybenzoic acid. Hydrocarbon and simazine oxidation reaction products were analyzed by gas chromatography (GC) and high performance liquid chromatography (HPLC), respectively. This catalytic system proved to be efficient and selective for hydrocarbon oxidation, leading to high product yields from styrene (89%), cyclooctene (71%) and R-(+)-limonene (86%). Simazine oxidation was attained with 100% selectivity for a dechlorinated product (OEAT), while several oxidation products were obtained for the same catalyst in homogeneous media. The catalyst can be easily recovered through application of an external magnetic field and washed after reaction. Catalyst reuse experiments for R-(+)-limonene oxidation have shown that the catalytic activity is kept at 90% after 10 consecutive reactions.

Shape Changes of Pt Nanoparticles Induced by Deposition on Mesoporous Silica

Polyvinylpyrollidone (PVP)-capped platinum nanoparticles (NPs) are found to change shape from spherical to flat when deposited on mesoporous silica substrates (SBA-15). Transmission electron microscopy (TEM), small-angle X-ray scattering (SAXS), and extended X-ray absorption fine structure (EXAFS) analyses are used in these studies. The SAXS results indicate that, after deposition, the 2 nm NPs have an average gyration radius 22% larger than in solution, while the EXAFS measurements indicate a decrease in first neighbor co-ordination number from 9.3 to 7.4. The deformation of these small capped NPs is attributed to interactions with the surface of the SBA-15 support, as evidenced by X-ray absorption near-edge structure (XANES).

The influence of different co-catalysts in Pt-based ternary and quaternary electro-catalysts on the electro-oxidation of methanol and ethanol in acid media

One of the key objectives in fuel cell technology is to reduce Pt loading by the improvement of its catalytic activity towards alcohol oxidation. Here, a sol-gel based method was used to prepare ternary and quaternary carbon supported nanoparticles by combining Pt-Ru with Mo, Ta, Pb, Rh or Ir, which were used as electro-catalysts for the methanol and ethanol oxidation reactions in acid medium. Structural characterization performed by XRD measurements revealed that crystalline structures with crystallites ranging from 2.8 to 4.1 nm in size and with different alloy degrees were produced. Tantalum and lead deposited as a heterogeneous mixture of oxides with different valences resulting in materials with complex structures. The catalysts activities were evaluated by cyclic voltammetry and by Tafel plots and the results showed that the activity towards methanol oxidation was highly dependent of the alloy degree, while for ethanol the presence of a metal capable to promote the break of C-C bond, such as Rh, was necessary for a good performance. Additionally, the catalysts containing of TaOx or PbOx resulted in the best materials due to different effects: the hi-functional mechanism promoted by TaOx and a better dispersion of the catalysts constituents promoted by PbOx. (C) 2012 Elsevier B.V. All rights reserved.

Performance and selectivity of PtxSn/C electro-catalysts for ethanol oxidation prepared by reduction with different formic acid concentrations

Carbon supported Pt-Sn catalysts were prepared by reduction of Pt and Sn precursors with formic acid and characterized in terms of structure, morphology and surface properties. The electrocatalytic activity for ethanol oxidation was studied in a direct ethanol fuel cell (DEFC) at 70 degrees C and 90 degrees C. Electrochemical and physico-chemical data indicated that a proper balance of Pt and Sn species in the near surface region was necessary to maximize the reaction rate. The best atomic surface composition, in terms of electrochemical performance, was Pt:Sn 65:35 corresponding to a bulk composition 75:25 namely Pt3Sn1/C. The reaction products of ethanol electro-oxidation in single cell and their distribution as a function of the nature of catalyst were determined. Essentially, acetaldehyde and acetic acid were detected as the main reaction products; whereas, a lower content of CO2 was formed. The selectivity toward acetic acid vs. acetaldehyde increased with the increase of the Sn content and decreased by decreasing the concentration of the reducing agent used in the catalyst preparation. According to the recent literature, these results have been interpreted on the basis of ethanol adsorption characteristics and ligand effects occurring for Sn-rich electrocatalysts. (C) 2012 Elsevier Ltd. All rights reserved.

Raman spectroscopy and DFT calculations of para-coumaric acid and its deprotonated species

An electronic and vibrational spectroscopic analysis of p-coumaric acid (HCou) and its deprotonated species was performed by UV-vis and Raman, respectively, and the results were supported by density functional theory (OFT) calculations. Electronic UV-vis spectral data of HCou solutions show that the deprotonation of the carboxyl group (Cou(-)) leads to a blue shift of the lowest energy electronic transition in comparison to the neutral species, whereas the subsequent deprotonation of the phenolic moiety (Cou(2-)) carries out to a more delocalized chromophore. The DFT geometric parameters calculations suggest that the variation in the electronic delocalization for the three organic species is due to different contribution of a quinoid structure that is significantly distorted in the case of Cou(2-). The Raman data of HCou and its sodium salts show that the main spectral features that allow to differentiate the three organic species are those involving the styrene nu(C=C)(sty) vibration at 1600cm(-1) region. Even though the Raman spectra of the sodium salts of Cou(-) and Cou(2-) anions show subtle differences, the appearing of a band at ca. 1598cm(-1) in the Na(2)Cou spectrum, assigned to a mode involving the carboxylate asymmetric stretching, nu(as)(COO), and the styrene stretching, nu(C=C)(sty), is quite characteristic, as confirmed by the theoretical Raman spectrum. Considering that p-coumaric acid is an archetypical phenolic compound with several biological activities that essentially depend upon the medium pH, Raman spectroscopy results reported in this work can provide a proper way to characterize such important phytochemical compound in different protonation states. In order to complement the characterization of the sodium salts, X-ray diffraction (XRD) and thermal analysis were performed. (C) 2011 Elsevier B.V. All rights reserved.

Self-Assembly of Poly(4-vynil-N-alkylpyridinium) Bromide onto Silica: Effect of Side-Chain Length on Structural Aspects at a Molecular Level

Self-assembly of poly(4-vynil-N-alkyl)pyridinium bromide with alkyl side chains of 2, 5, 7, 10, or 16 carbons from ethanolic solutions onto flat silica surfaces was studied by means of ellipsometry, atomic force microscopy (AFM), contact angle measurements, and sum-frequency generation (SFG) vibrational spectroscopy in the CH3 and CH2 stretch region. Ab initio quantum-chemical calculations on the N-alkylpyridinium side-group with restricted Hartree-Fock (RHF) method and 6-311G (d,p) basis set were C one to estimate the charge distribution along the pyridinium ring and the alkyl side-chain. SFG results showed that longer side chains promote the disorientation of the alkyl groups at the surface, corroborating with the contact angle values. AFM images revealed film homogeneity, regardless the alkyl side group. However, after 24 h contact with water, ringlike structures appeared on the film surfaces, when the polycation alkyl side chain had 7 or less carbons, and as the alkyl chain increased to 10 or 16 carbons, the films dewetted because the hydrophobic interactions prevailed over the electrostatic interactions between the pyridinium charged groups and the negatively charged SiO2 surface. Under acid conditions (HCl 0.1 mol.L-1), the film mean thickness values decreased up to 50% of original values when the alkyl side chains were ethyl or pentyl groups due to ion-pair disruption, but for longer groups they remained unchanged. Quantum-chemical optimization and Mulliken electron population showed that (i) from C2 to C15 the positive charge at the headgroup (HG) decreased 0.025, while the charge at combined HG + alpha-CH2 increased 0.037; and (ii) for C6 or longer, the alkyl side group presents a tilt in the geometry, moving away from the plane. Such effects summed up over the whole polymer chain give support to suggest that when the side chains are longer than 7 carbons, the hydrophobic interaction decreases film stability and increases acid resistance.

Adsorption of caffeic acid on titanium dioxide: A spectroscopic study

Caffeic acid is an ortho-phenol found in vegetable tissues presenting important properties such as carcinogenesis inhibitor, anti-oxidant, anti-viral, anti-inflammatory and anti-rheumatic actions. It was observed that caffeic acid was not degraded in daylight during the adsorption on TiO2 at pH 4.8. The adsorption fit very well to a Brunauer-Emmett-Teller isotherm equation with a monolayer coverage of 68.15 mg(CA) g(TiO2)(-1) and saturation coverage of 195.4 mg(CA) g(TiO2)(-1). A strong adsorption of caffeic acid was verified on TiO2 for the dry solid obtained from the mixture. The Raman and IR spectroscopies revealed that the adsorption should occur through the interaction of the diphenol oxygens with contribution of CC double bond of the acrylic group, however, the carboxylic acid group did not have participation in the adsorption. (C) 2012 Elsevier B.V. All rights reserved.

Stratum corneum lipids liposomes for the topical delivery of 5-aminolevulinic acid in photodynamic therapy of skin cancer: preparation and in vitro permeation study

Abstract Background Photodynamic therapy (PDT) using 5-aminolevulinic acid (5-ALA) is a skin cancer therapy that still has limitations due to the low penetration of this drug into the skin. We have proposed in this work a delivery system for 5-ALA based on liposomes having lipid composition similar to the mammalian stratum corneum (SCLLs) in order to optimize its skin delivery in Photodynamic Therapy (PDT) of skin cancers. Methods SCLLs were obtained by reverse phase evaporation technique and size distribution of the vesicles was determinated by photon correlation spectroscopy. In vitro permeation profile was characterized using hairless mouse skin mounted in modified Franz diffusion cell. Results Size exclusion chromatography on gel filtration confirmed vesicle formation. SCLLs obtained by presented a degree of encapsulation of 5-ALA around 5.7%. A distribution of vesicle size centering at around 500 nm and 400 nm respectively for SCLLs and SCLLs containing 5-ALA was found. In vitro 5-ALA permeation study showed that SCLLs preparations presented higher skin retention significantly (p < 0.05) on the epidermis without SC + dermis, with a decreasing of skin permeation compared to aqueous solution. Conclusions The in vitro delivery performance provided by SCLLs lead to consider this systems adequate for the 5-ALA-PDT of skin cancer, since SCLLs have delivered 5-ALA to the target skin layers (viable epidermis + dermis) to be treated by topical PDT of skin cancer.

The relationship between training status, blood pressure and uric acid in adults and elderly

Abstract Background Hypertension can be generated by a great number of mechanisms including elevated uric acid (UA) that contribute to the anion superoxide production. However, physical exercise is recommended to prevent and/or control high blood pressure (BP). The purpose of this study was to investigate the relationship between BP and UA and whether this relationship may be mediated by the functional fitness index. Methods All participants (n = 123) performed the following tests: indirect maximal oxygen uptake (VO2max), AAHPERD Functional Fitness Battery Test to determine the general fitness functional index (GFFI), systolic and diastolic blood pressure (SBP and DBP), body mass index (BMI) and blood sample collection to evaluate the total-cholesterol (CHOL), LDL-cholesterol (LDL-c), HDL-cholesterol (HDL-c), triglycerides (TG), uric acid (UA), nitrite (NO2) and thiobarbituric acid reactive substances (T-BARS). After the physical, hemodynamic and metabolic evaluations, all participants were allocated into three groups according to their GFFI: G1 (regular), G2 (good) and G3 (very good). Results Baseline blood pressure was higher in G1 when compared to G3 (+12% and +11%, for SBP and DBP, respectively, p<0.05) and the subjects who had higher values of BP also presented higher values of UA. Although UA was not different among GFFI groups, it presented a significant correlation with GFFI and VO2max. Also, nitrite concentration was elevated in G3 compared to G1 (140±29 μM vs 111± 29 μM, for G3 and G1, respectively, p<0.0001). As far as the lipid profile, participants in G3 presented better values of CHOL and TG when compared to those in G1. Conclusions Taking together the findings that subjects with higher BP had elevated values of UA and lower values of nitrite, it can be suggested that the relationship between blood pressure and the oxidative stress produced by acid uric may be mediated by training status.