Electrochemical oxidation of catechol at poly(indole-5-carboxylic acid) electrode

In this work we examined the electrochemical properties of poly(indole-5-carboxylic acid), PIn₅COOH. The polymer was produced by electrochemical polymerisation using cyclic voltammetry (CV). It was shown that PIn₅COOH is electroactive in aqueous solutions showing two redox processes in acidic solution and one redox process in solutions with pH > 4. The oxidation of catechol (CT) on Pt/In₅COOH modified electrodes was investigated by cyclic voltammetry (CV) and rotating disc electrode (RDE) voltammetry. It was established that CT was oxidised only after the oxidation of polymer film was initiated and that polymer significantly enhanced the oxidation and reduction peak currents in comparison with bare Pt electrode. The variation of peak currents (i _pa, i _pc) as a function of CT concentration was found to be linear up to 6 mM. Experiments with a rotating disk electrode show that the oxidation reaction of catechol occures not only at the polymer/electrolyte interface but also in the polymer film.     

Density functional study on electronic structures and reactivity in methyl‐substituted chelates used in organic light‐emitting diodes

The electronic structure and reactivity trends of a set of tris‐(n‐methyl‐8‐quinolinolato) metal (III) (n = 0, 3, 4, 5; metal = Al⁺³, Ga⁺³) used as electron‐transport layer in organic light‐emitting diodes were studied and compared. All geometries were optimized at B3LYP/6‐31G(d,p) level of theory. The geometries of the ground state (S₀) of unsubstituted molecules AlQ3 and GaQ3 were found to be slightly affected by the methyl group, which is in agreement with previous works. Methyl‐derivatives conserve largely the electronic structures of AlQ3 and GaQ3. The energies of the frontier orbitals highest occupied and lowest unoccupied molecular orbital are raised by the electron‐releasing effect of methyl group. Molecular orbital contribution analysis reveals that the orbital population is essentially the same for both MQ3 and their derivatives. Analyses of the ionization potential and electron affinity showed that MQ3 tend to be better hole‐blockers than methylated analogues and 5Me‐MQ3 have higher hole‐injection capability than the other methyl‐substituted derivatives. The global reactivity analysis showed that the electrophilicity index can be an indicator of electron‐injection capability in these complexes. Local reactivity analysis showed that atomic sites that are prone to nucleophilic/electrophilic attack are atoms C‐4 in L3/C‐5 in L1. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010     

The first total synthesis of the (±)-17-methyl-trans-4,5-methyleneoctadecanoic acid and related analogs with antileishmanial activity

The first total synthesis of the marine cyclopropane fatty acid (±)-17-methyl-trans-4,5-methyleneoctadecanoic acid was accomplished in eight steps and in 9.1% overall yield starting from 1-bromo-12-methyltridecane. The cis analog (±)-17-methyl-cis-4,5-methyleneoctadecanoic acid was also synthesized but in seven steps and in 16.4% overall yield. With the two isomeric cyclopropane fatty acids at hand it was possible to unequivocally corroborate the trans relative configuration of the naturally occurring fatty acid by gas chromatographic co-elution of the corresponding methyl esters. The cis isomer was cytotoxic to Leishmania donovani promastigotes with an IC₅₀ of 300.2 ± 4.2 μM.     

Measuring Submicron-Sized Fractionated Particulate Matter on Aluminum Impactor Disks

Sub-micron sized airborne particulate matter (PM) is not collected well on regular quartz or glass fiber filter papers. We used a micro-orifice uniform deposit impactor (MOUDI) to fractionate PM into six size fractions and deposit it on specially designed high purity thin aluminum disks. The MOUDI separated PM into fractions 56-100 nm, 100-180 nm, 180-320 nm, 320-560 nm, 560-1000 nm, and 1000-1800 nm. Since the MOUDI has a low flow rate (30 L/min), it takes several days to collect sufficient carbon on 47 mm foil disks. The small carbon mass (20-200 microgram C) and large aluminum substrate (~25 mg Al) present several challenges to production of graphite targets for accelerator mass spectrometry (AMS) analysis. The Al foil consumes large amounts of oxygen as it is heated and tends to melt into quartz combustion tubes, causing gas leaks. We describe sample processing techniques to reliably produce graphitic targets for (14)C-AMS analysis of PM deposited on Al impact foils.     

Selective Separation of Oxy-PAH from n-Alkanes and PAH in Complex Organic Mixtures Extracted from Airborne PM2.5

A fast and simple fractionation method was optimized to selectively separate oxy-PAH from polycyclic aromatic hydrocarbons (PAH) and n-alkanes contained in solvent extracted organic matter (SEOM) from atmospheric particles with an aerodynamic diameter ≤2.5 μm (PM_2.5). Samples were collected in Mexico City. Multivariate parameters were adjusted on a standard mixture, and on SEOM spiked with pure standard mixture solutions: type and amount of phase; packing densities; type, proportion and amount of solvents, and elution flow rates were tested under several elution schemes. Cyanopropylsilyl-bonded phase material was the selected stationary phase. The separation method was applied to real samples of SEOM (2.6, 5.6 and 8.5 mg) spiked with n-alkanes, PAH and oxy-PAH. n-Alkanes overlapped with PAH due to an excess of n-alkanes in real samples overloading the capacity of the stationary phase. Oxy-PAH was separated totally from n-alkanes and PAH. Mean recoveries ± confidence intervals (95%) for n-alkanes ranged from 53 ± 17% (n-tetracontane) to 101 ± 11% (n-hexacosane); for PAH from 58 ± 5% (phenanthrene) to 85 ± 9% (benzo[k]fluoranthene); and for oxy-PAH from 68 ± 12% (9,10-dihydrobenzo[a]pyren-7(8H)one) to 108 ± 9% (1,2-benzopyrone). This method is an efficient fractionation procedure to be applied to oxy-PAH, PAH and n-alkanes in complex organic mixtures extracted from PM_2.5.     

Information-theoretic properties of the half-line Coulomb potential

The half-line one-dimensional Coulomb potential is possibly the simplest D-dimensional model with physical solutions which has been proved to be successful to describe the behaviour of Rydberg atoms in external fields and the dynamics of surface-state electrons in liquid helium, with potential applications in constructing analog quantum computers and other fields. Here, we investigate the spreading and uncertaintylike properties for the ground and excited states of this system by means of the logarithmic measure and the information-theoretic lengths of Renyi, Shannon and Fisher types; so, far beyond the Heisenberg measure. In particular, the Fisher length (which is a local quantity of internal disorder) is shown to be the proper measure of uncertainty for our system in both position and momentum spaces. Moreover the position Fisher length of a given physical state turns out to be not only directly proportional to the number of nodes of its associated wavefunction, but also it follows a square-root energy law.     

Technical electrodes catalyzed with PtRu on mesoporous ordered carbons for liquid direct methanol fuel cells

This paper presents the behavior of ordered mesoporous carbon (OMC)-supported catalysts as anodes for direct methanol fuel cells (DMFC), fed with an aqueous methanol solution. OMC samples were prepared by the nanocasting method from a polymerized furan resin using mesoporous silica as a template. Pt and PtRu nanoparticles were supported on OMC with high dispersion, the particle size being 2.4 nm at PtRu loading of 15 wt.%. The resulting catalysts were analyzed using carbon monoxide stripping voltammetry, cyclic voltammetry, and chronoamperometry in three-electrode experiments and recording cell voltage vs. current density curves in practical DMFC. It was found that PtRu-catalyzed technical electrodes exhibited good activity towards methanol electrooxidation in half-cell experiments under fuel-cell-relevant conditions. Specifically, Pt₈₅Ru₁₅/OMC catalyst showed the highest catalytic enhancement compared to Pt/OMC for the steady-state electrooxidation of methanol at 60 °C and 0.5 V, by a factor of 22 in 2-M MeOH solution. DMFC single cells yielded an open-circuit voltage of 0.625 V at 60 °C. Polarization curves indicate that DMFC with OMC-supported Pt₈₅Ru₁₅ catalyst at the anode exhibited the best performance.     

Electrochemical behavior of Ni-Al-Fe alloys in simulated human body solution

An investigation about the corrosion resistance of Ni-Al-Fe intermetallic alloys in simulated human body fluid environments has been carried out using electrochemical techniques. Tested alloys included 57 (wt%) Ni-(20 to 30) Al-(12 to 23) Fe using the Hank's solution because the high corrosion resistance provided by protective Al₂O₃ external layer. For comparison, AISI 316L type stainless steel has also been used. Electrochemical techniques included potentiodynamic polarization curves, electrochemical impedance spectroscopy, and electrochemical noise measurements. The different techniques have shown that these alloys showed a similar or higher corrosion resistance than conventional AISI 316L type stainless steel, and this corrosion resistance decreased as the Al content in the alloy increased. The alloys were susceptible to pitting type of corrosion on the interdendritic Ni-rich phases.     

Label-free voltammetric immunosensor using a nanoporous membrane based platform

A novel device and methodology for the rapid and simple label-free electrochemical detection of proteins based on screen-printed carbon electrodes (SPCEs) modified with nanoporous Al₂O₃ membranes is reported. The nanoporous membranes are functionalized with antibodies and followed by the immunorecognition event that gives rise to the pore blocking. The blockage inside the nanochannels is fast, pore size dependent and easy to be detected by measuring the decrease in the differential pulse voltammetric (DPV) peak current of the [Fe(CN₆)]^4?/3? redox specie used as indicator. The developed nanoporous membrane based device represents a simple biodetection alternative that can be extended in the future to several other immuno and DNA detection systems.