Single-wall carbon nanotubes modified with organic dyes: Synthesis, characterization and potential cytotoxic effects

This work deals with the covalent functionalization of single-wall carbon nanotubes (SWNTs) with phenosafranine (PS) and Nile Blue (NB) dyes. These dyes can act as photosensitizers in energy and electron transfer reactions, with a potential to be applied in photodynamic therapy. Several changes in the characteristic Raman vibrational features of the dyes suggest that a covalent modification of the nanotubes with the organic dyes occurs. Specifically, the vibrational modes assigned to the NH(2) moieties of the dyes are seen to disappear in the SWNT-dye nanocomposites, corroborating the bond formation between amine groups in the dyes and carboxyl groups in the oxidized nanotubes. The X-ray absorption (XANES) data also show, that the intense band at 398.6 eV attributed to 1s -> 2p pi* transition of the nitrogen of the aromatic PS ring, is shifted due to the bonding with the carbonic structure of the SWNTs. The cytotoxicity data of dyes-modified SWNT composites in the presence and absence of light shows that the SWNT-NB (4 mu g/mL) composite presents a good photodynamic effect, namely a low toxicity in the dark, higher toxicity in the presence of light and also a reduced dye photobleaching by auto-oxidation. (C) 2010 Elsevier B.V. All rights reserved.

Selective Oxidations of Organoboron Compounds Catalyzed by Baeyer-Villiger Monooxygenases

The applicability of Baeyer-Villiger monooxygenases (BVMOs) in organoboron chemistry has been explored through testing chemo-and enantioselective oxidations of a variety of boron-containing aromatic and vinylic compounds. Several BVMOs, namely: phenylacetone monooxygenase (PAMO), M446G PAMO mutant, 4-hydroxyacetophenone monooxygenase (HAPMO) and cyclohexanone monooxygenase (CHMO) were used in this study. The degree of chemoselectivity depends on the type of BVMO employed, in which the biocatalysts prefer boron-carbon oxidation over Baeyer-Villiger oxidation or epoxidation. Interestingly, it was discovered that PAMO can be used to perform kinetic resolution of boron-containing compounds with good enantioselectivities. These findings extend the known biocatalytic repertoire of BVMOs by showing a new family of compounds that can be oxidized by these enzymes.

Kinetic and mechanistic investigation of the ozonolysis of 2,4-xylidine (2,4-dimethyl-aniline) in acidic aqueous solution

The ozonolysis of 2,4-xylidine (2,4-dimethyl-aniline) in acidic aqueous solution was investigated by determining the major reaction products and their evolution as a function of the reaction time and their dependence on the pH of the reaction system. 2,4-Dimethyl-nitrobenzene and 2,4-dimethyl-phenol were found to be primary reaction products; their formation might be explained by electron transfer and substitution reactions. 2,4-Dimethyl-phenol was further oxidized yielding 2,4-dimethyl- and/or 4,6-dimethyl-resorcinol by electrophilic addition of HO(center dot) radicals. The best fitting phenomenological kinetic model and the good convergence of calculated and experimentally determined rate constants imply two additional competitive pathways of substrate oxidation: (i) electrophilic addition of HO(center dot) radicals and fast subsequent substitution would also yield the resorcinol derivatives. (ii) Substrate and isolated products are thought to be oxidized by hydrogen abstraction at the benzylic sites, but the corresponding products (alcohols, aldehydes, and carboxylic acids) could not be identified. Fe(II) was added to probe for the presence of H(2)O(2), but had no or only a minor effect on the kinetics of the ozonolysis. (c) 2009 Elsevier B.V. All rights reserved.

Spectroscopic evidences of the presence of hydrogenated species on the surface of copper during CO(2) electroreduction at low cathodic potentials

Carbon dioxide electroreduction on copper electrode was studied by surface enhanced Raman scattering (SERS) in K(2)SO(4) aqueous solutions with different pH values. CO(2) was bubbled into the solution at 0 V vs. Ag/AgCl, i.e., on an oxidized copper surface. In acidic solutions (pH around 2.5), at -0.2 V, bands indicative of the presence of ethylene on the electrode surface were detected. Although ethylene is knowledgably a product of CO(2) electroreduction on copper, it was not experimentally identified on the electrode`s surface at such a low cathodic potential in prior works. In solutions with pH around 2.5, CO bands were not observed, suggesting that hydrocarbons could be formed by a pathway that does not occur via adsorbed CO. In solutions with higher pHs, a complex spectral pattern, between 800 and 1700 cm(-1), was observed at approximately -0.4 V. The observed spectrum closely resembles those reported in the literature for adsorption of monocarboxylic acids with small chains. The spectral features indicate the presence of a structure containing a double C=C bond. a carboxyl group, and C-H bonds on the electrode`s surface. SERS spectra obtained in CO-saturated solution are also presented. However, in this case, no SERS bands were observed in the region between 800 and 1700 cm(-1) at low cathodic potentials. (c) 2009 Elsevier B.V. All rights reserved.

Thin films of xyloglucans for BSA adsorption

In this work. XG extracted from Tamarindus indica (XGT) and Copaifera langsdorffii (XGC) seeds were deposited onto Si wafers as thin films. The characteristics of XGT and XGC adsorbed layers were compared with a commercial XG sample (TKP, Tamarind kernel powder) by ellipsometry, and atomic force microscopy (AFM). Moreover, the adsorption of oxidized derivative of XGT (To60) onto amino-terminated Si wafers and the immobilization of bovine serum albumin (BSA) onto polysaccharides covered wafers, as a function of pH, were also investigated. The XG samples presented molar ratios Glc:Xyl:Gal of 2.4:2.1:1 (XGC) 2.8: 23: 1 (XGT) and 1.91.91 (TKP). The structure of XGT and XGC was determined by O-methy alditol acetate derivatization and showed similar features, but XGC confirmed the presence of more alpha-D-Xyl branches due to more beta-D-Gal ends. XGT deposited onto Si adsorbed as fibers and small entities uniformly distributed, as evidenced by AFM, while TPK and XGC formed larger aggregates. The thickness of To60 onto amino-terminated surface was similar to that determined for XGT onto Si wafers. A maximum in the adsorbed amount of BSA occurred close to its isoelectric point (5.5). These findings indicate that XGT and To60 are potential materials for the development of biomaterials and biotechnological devices. (C) 2008 Elsevier B.V. All rights reserved.

Raman, IR, UV-vis and EPR characterization of two copper dioxolene complexes derived from L-dopa and dopamine

The anionic complexes [Cu(L(1-))(3)](1-), L(-) = dopasemiquinone or L-dopasemiqui none, were prepared and characterized. The complexes are stable in aqueous solution showing intense absorption bands at ca. 605 nm for Cu(II)-L-dopasemiquinone and at ca. 595 nm for Cu(II)-dopasemiquinone in the UV-vis spectra, that can be assigned to intraligand transitions. Noradrenaline and adrenaline, under the same reaction conditions, did not yield Cu-complexes, despite the bands in the UV region showing that noradrenaline and adrenaline were oxidized during the process. The complexes display a resonance Raman effect, and the most enhanced bands involve ring modes and particularly the vCC + vCO stretching mode at ca. 1384 cm(-1). The free radical nature of the ligands and the oxidation state of the Cu(II) were confirmed by the EPR spectra that display absorptions assigned to organic radicals with g= 2.0005 and g = 2.0923, and for Cu(II) with g = 2.008 and g = 2.0897 for L-dopasemiquinone and dopasemiquinone, respectively. The possibility that dopamine and L-dopa can form stable and aqueous-soluble copper complexes at neutral pH, whereas noradrenaline and adrenaline cannot, may be important in understanding how Cu(II)-dopamine crosses the cellular membrane as proposed in the literature to explain the role of copper in Wilson disease. (c) 2008 Elsevier B.V. All rights reserved.

Oxidation of anilinium ions intercalated in montmorillonite clay by electrochemical route

Resonance Raman, FTIR, X-ray diffraction, UV-vis-NIR, electron paramagnetic resonance, X-ray absorption at Si K-edge and electron microscopy were employed for characterizing the products formed through electrochemical oxidation of intercalated anilinium ions inside the cationic montmorillonite (MMT) clay. The layer silicate structure was not affected by the anilinium oxidation between the layers. The intercalated products present only an electronic absorption band at 400 nm, very low conductivity (ca. 10(-7) S cm(-1)) and their Raman spectrum displays bands, with high relative intensities, assigned to the benzidine dication, indicating that this product was formed in high amount. Nevertheless, bands that can be correlated to phenazine-like segments and 1,4-phenylenediamine repeat units (PANI like segments) are also observed. The very low EPR signal indicates that diamagnetic species are predominant. All results are compared to those obtained by anilinium-MMT chemically oxidized by persulfate and the differences are pointed out. (C) 2008 Elsevier B.V. All rights reserved.

Spectroscopic Characterization of Oligoaniline Microspheres Obtained by an Aniline-Persulfate Approach

This paper investigates the structure of the pro; ducts obtained from the polymerization of aniline with ammonium persulfate in a citrate/phosphate buffer solution at pH 3 by resonance Raman, NMR, FTIR, and UV-vis-NIR spectroscopies. All the spectroscopic data showed that the major product presented segments that were formed by a 1,4-Michael reaction between aniline and p-benzoquinone monoimine, ruling out the formation of polyazane structure that has been recently proposed. The characterization of samples obtained at different stages of the reaction indicated that, as the reaction progressed, phenazine units were formed and 1,4-Michael-type adducts were hydrolyzed/oxidized to yield benzoquinone. Raman mapping data suggested that phenazine-like segments could be related to the formation of the microspheres morphology.

Charge-transfer behavior of polyaniline single wall carbon nanotubes nanocomposites monitored by resonance Raman spectroscopy

Highly dispersed nanocomposites of polyaniline(PANI) and oxidized single wall carbon nanotubes(SWNTs) have been prepared using dodecylbenzenesulfonic acid as dispersant. The materials were characterized via resonance Raman and electronic absorption spectroscopies. The behavior of the composites as a function of the applied potential was also investigated using in situ Raman electrochemical measurements. The results obtained at E(laser) = 1.17 eV suggest that a charge-transfer process occur between PANI and semiconducting nanotubes for samples where the metallic tubes are previously oxidized. The spectroelectrochemical data show that the presence of SWNTs prevents the oxidation of PANI rings. Copyright (C) 2010 John Wiley & Sons, Ltd.

The role of oxygen in the interaction of emeraldine base polyaniline with Cu(II) or Fe(III) ions in NMP solution

The influence of molecular oxygen in the interactions of emeraldine base form of polyaniline (EB-PANI) with Fe(III) or Cu(II) ions in 1-methyl-2-pyrrolidinone (NMP) solutions has been investigated by UV-vis-NIR, resonance Raman and electron paramagnetic resonance (EPR) spectroscopies. Through the set of spectroscopic results it was possible to rationalize the role Of O(2) and to construct a scheme of preferential routes occurring in the interaction of EB-PANI with Fe(III) or Cu(II). Solutions of 4.0 mmol L(-1) EB-PANI with 0.8, 2.0 and 20 mmol L(-1) Fe(III) or Cu(II) ions in NMP were investigated and the main observed reactions were EB-PANI oxidation to pernigraniline (PB-PANI) and EB-PANI doping process by pseudo-protonation, or by a two-step redox process. In the presence Of O(2), PB-PANI is observed in all Fe(III)/EB solutions and EB-PANI doping only occurs in solutions with high Fe(III) concentrations through pseudo-protonation. On the other hand, emeraldine salt (ES-PANI) is formed in all Fe(III)/EB solutions under N(2) atmosphere and, in this case, doping occurs both by the pseudo-protonation and two-step redox mechanisms. In all Cu(II)/EB solutions PB-PANI is formed both in the presence and absence of O(2), and only for solutions with high Cu(II) concentrations doping process occurs in a very low degree. The most important result from EPR spectra was providing evidence for redox steps. The determined Cu(II) signal areas under oxygen are higher than under N(2) and, further. the initial metal proportions (1:2:20) are maintained in these spectra, indicating that Cu(I) formed are re-oxidized by O(2) and. so, Cu(II) ions are being recycled. Consistently, for the solutions prepared under nitrogen, the corresponding areas and proportions in the spectra are much lower, confirming that a partial reduction of Cu(II) ions actually occurs. (C) 2009 Elsevier B.V. All rights reserved.

Electroanalytical determination of promethazine hydrochloride in pharmaceutical formulations on highly boron-doped diamond electrodes using square-wave adsorptive voltammetry

The electrochemical oxidation of promethazine hydrochloride was made on highly boron-doped diamond electrodes. Cyclic voltammetry experiments showed that the oxidation mechanisms involved the formation of an adsorbed product that is more readily oxidized, producing a new peak with lower potential values whose intensity can be increased by applying the accumulation potential for given times. The parameters were optimized and the highest current intensities were obtained by applying +0.78 V for 30 seconds. The square-wave adsorptive voltammetry results obtained in BR buffer showed two well-defined peaks, dependent on the pH and on the voltammetric parameters. The best responses were obtained at pH 4.0, frequency of 50 s(-1), step of 2 mV, and amplitude of 50 mV. Under these conditions, linear responses were obtained for concentrations from 5.96 x 10(-7) to 4.76 x 10(-6) mol L-1, and calculated detection limits of 2.66 x 10(-8) mol L-1 (8.51 mu g L-1) for peak 1 and of 4.61 x 10(-8) mol L-1 (14.77 mu g L-1) for peak 2. The precision and accuracy were evaluated by repeatability and reproducibility experiments, which yielded values of less than 5.00% for both voltammetric peaks. ne applicability of this procedure was tested on commercial formulations of promethazine hydrochloride by observing the stability, specificity, recovery and precision of the procedure in complex samples. All results obtained were compared to recommended procedure by British Pharmacopeia. The voltammetric results indicate that the proposed procedure is stable and sensitive, with good reproducibility even when the accumulation steps involve short times. It is therefore very suitable for the development of the electroanalytical procedure, providing adequate sensitivity and a reliable method.

The processes involved in the Se electrodeposition and dissolution on Au electrode: the H2Se formation

The processes involved in the Se electrodeposition, mainly the one related to the formation of H2Se species on Au electrode in perchloric acid solutions, have been investigated through cyclic voltammetry, electrochemical quartz crystal microbalance (EQCM), rotating ring-disc electrode (RRDE), and atomic force microscopy (AFM) techniques. In the experiments performed with the EQCM, with the potential sweep in the negative direction, the responses for the mass variation were divided in three well-defined potential regions: A (from 1.55 to 0.35 V), B (from 0.35 to -0.37 V), and C (from -0.37 to -0.49 V). It was verified that the following processes can occur, respectively: the species (AuO)(2)H2SeO3 was desorbed during the AuO reduction, the reduction of Se(IV) to Se(0), and the formation of H2Se. When the potential was swept in the positive direction, the responses for the mass variation were divided in four well-defined potential regions: D (from -0.49 to 0.66 V), E (from 0.66 to 0.99 V), F (from 0.99 to 1.26 V), and G (from 1.26 to 1.55 V), and the described processes in these regions were, respectively: the Se deposition and adsorption of water molecules and/or perchlorate ions, the Se dissolution, the Se incorporating mass in the form of HO-Se, and the Au oxidation (all potentials are referred to the Ag/AgCl electrode). Making use of the RRDE, using the collection technique, the formation of H2Se species during the Se electrodeposition was investigated. Therefore, it was confirmed that this species is formed on the disc electrode between -0.3 and -0.55 V vs the Ag/AgCl potential range (collecting the oxidized compound onto the ring electrode). AFM images also indicated that the surface topography of the Se-massive deposit on Au is different from the images registered after the formation of H2Se species, confirming the cathodic stripping of Se.

Hydrogen purification for fuel cell using CuO/CeO(2)-Al(2)O(3) catalyst

CuO/CeO(2), CuO/Al(2)O(3) and CuO/CeO(2)-Al(2)O(3) catalysts, with CuO loading varying from 1 to 5 wt.%, were prepared by the citrate method and applied to the preferential oxidation of carbon monoxide in a reaction medium containing large amounts of hydrogen (PROX-CO). The compounds were characterized ex situ by X-ray diffraction, specific surface area measurements, temperature-programmed reduction and temperature-programmed reduction of oxidized surfaces; XANES-PROX in situ experiments were also carried out to study the copper oxidation state under PROX-CO conditions. These analyses showed that in the reaction medium the Cu(0) is present as dispersed particles. On the ceria, these metallic particles are smaller and more finely dispersed, resulting in a stronger metal-support interaction than in CuO/Al(2)O(3) or CuO/CeO(2)-Al(2)O(3) catalysts, providing higher PROX-CO activity and better selectivity in the conversion of CO to CO(2) despite the greater BET area presented by samples supported on alumina. It is also shown that the lower CuO content, the higher metal dispersion and consequently the catalytic activity. The redox properties of the ceria support also contributed to catalytic performance. (C) 2010 Elsevier B.V. All rights reserved.

Mass transport effects in the borohydride oxidation reaction-Influence of the residence time on the reaction onset and faradaic efficiency

The borohydride oxidation reaction (BOR) was studied on Pt and Au electrodes by cyclic voltammetry in dilute alkaline borohydride solutions (0.1 M NaOH + 10(-3) mol L(-1) NaBH(4)). More specifically, the electrodes were considered as either Vulcan XC72-supported Pt or Au (noted as Pt/C and Au/C, respectively) active layers or smooth Pt or Au surfaces, the latter possibly being covered by a layer of (non-metalized) Vulcan XC72 carbon powder. The BOR onset potential and the number of electrons (n(e-)) exchanged per BH(4)(-) anion (faradaic efficiency) were investigated for these electrodes, to determine whether the residence time of reaction intermediates (at the electrode surface or inside the porous layer) does influence the overall reaction pathway/completion. For the carbon-supported platinum, n(e-) strongly depends on the thickness of the active layer. While thin (ca. 0.5 mu m-thick) Pt/C active layers yield n(e-) < 4, thick layers (approximately 3 mu m) yield n(e-)approximate to 8, which can be ascribed to the sufficient residence time of the molecules formed within the active layer (H(2), by heterogeneous hydrolysis, or BOR intermediates) enabling further (near-complete) oxidation. This puts into evidence that not only the nature of the electrocatalyst is important to reach high BOR efficiency, but also the structure/thickness of the active layer. The same trend applies for Au/C active layers and for smooth Pt or Au surfaces covered with a layer of (inactive) Vulcan XC72. In addition, the BOR onset usually shifts negative when the reaction intermediates are trapped, which suggests that some of the intermediates are more easily oxidized than BH(4)(-) itself; based on literature data, BH(3)OH(-) species is a likely candidate. (C) 2011 Elsevier B.V. All rights reserved.

Development of an Analytical Methodology for Quantification of Strong Acid in Diesel Oil

Many factors can affect the quality of diesel oil, in particular the degradation processes that are directly related to some organosulfur compounds. During the degradation process, these compounds are oxidized into their corresponding sulfonic acids, generating a strong acid content during the process. p-Toluene sulfonic acid analysis was performed using the linear sweep voltammetry technique with a platinum ultramicroelectrode in aqueous solution containing 3 mol L(-1) potassium chloride. An extraction step was introduced prior to the voltammetric detection in order to avoid the adsorption of organic molecules, which inhibit the electrochemical response. The extraction step promoted the transference of sulfonic acid from the diesel oil to an aqueous phase. The method was accurate and reproducible, with detection and quantification limits of 5 ppm and 15 ppm, respectively. Recovery of sulfonic acid was around 90%.