Self-potential signals from an analog biogeobattery mode

A tank experiment was conducted to check if self-potential (SP) signals can be generated when buried organic matter is wire-connected to a near-surface, oxygen-rich, sediment layer. This experiment demonstrated that once wired, there was a flux of electrons (hence an electric current) between the lower and upper layers of the sandbox with the system responding as a large-scale microbial fuel cell (a type of bioelectrochemical system). An electric current was generated by this process in the wire and the SP method was used to monitor the associated electric potential distribution at the top of the tank.. The electric field was controlled by the flux of electrons through the wire, the oxidation of the organic matter, the reduction of oxygen used as a terminal electron acceptor, and the distribution of the DC resistivity in the tank. The current density through the wire was limited by the availability of oxygen and not by the oxidation of the organic matter. This laboratory experiment incorporated key elements of the biogeobattery observed in some organic-rich contaminant plumes. This analogy includes the generation of SP signals associated with a flux of electrons, the capacity of buried organic matter in sustaining anodic reactions, network resistance connecting terminal redox reactions spatially separated in space, and the existence of anodic secondary coupled reactions. A resistivity tomogram of the tank, after almost a year in operation, suggests that oxidative processes triggered by this geobattery can be imaged with this method to determine the radius of influence of the bioelectrochemical system.

First- and second-row transition metal oxa-aza macrocyclic complexes: a DFT study of an octahedral conformation

A theoretical study of structures of the 1,7,1 l,17-tetraoxa-2,6,12,16-tetraaza-cycloeicosane ligand ([20]AneN(4)O(4)) coordinated to Fe2+, Co2+, Ni2+, Ru2+, Rh2+, and Pd2+ transition metals ions was carried out with the DFT/B3LYP method. Complexes were fully optimized in C-s symmetry with the metal ions coordinated either to nitrogen (1a) or oxygen atoms (1b). For all the cases performed in this work, 1a was always more stable than 1b. Considering each row it is possible to see that the binding energy increases with the atomic number. The M2+ cation binding energies increase in the following order: Fe2+ < Ru2+ < Co2+ < Ni2+ < Rh2+ < Pd2+. In addition, it was observed the preference of Pd2+ and Rh2+ complexes for a tetrahedral arrangement, while Fe2+, Ru2+, Co2+, Ni2+ complexes had a preference for the octahedral arrangement. From the orbital representation results, it was seen that 1b unsymmetrical orbitals may influence the susceptibility over metal ions orientation toward heteroatoms orbitals.

Inhibitory activity of liposomal flavonoids during oxidative metabolism of human neutrophils upon stimulation with immune complexes and phorbol ester

Context and objective: The massive production of reactive oxygen species by neutrophils during inflammation may cause damage to tissues. Flavonoids act as antioxidants and have anti-inflammatory effects. In this study, liposomes loaded with these compounds were evaluated as potential antioxidant carriers, in attempt to overcome their poor solubility and stability. Materials and methods: Liposomes containing quercetin, myricetin, kaempferol or galangin were prepared by the ethanol injection method and analyzed as inhibitors of immune complex (IC) and phorbol ester-stimulated neutrophil oxidative metabolism by luminol (CLlum) and lucigenin-enhanced (CLluc) chemiluminescence (CL) assays. The mechanisms involved this activity of liposomal flavonoids, such as cytotoxicity and superoxide anion scavenging capacity, and their effect on phagocytosis of ICs were also investigated. Results and discussion: The results showed that the inhibitory effect of liposomal flavonoids on CLlum and CLluc is inversely related to the number of hydroxyl groups in the flavonoid B ring. Moreover, phagocytosis of liposomes by neutrophils does not seem to necessarily promote such activity, as the liposomal flavonoids are also able to reduce CL when the cells are pretreated with cytochalasin B. Under assessed conditions, the antioxidant liposomes are not toxic to the human neutrophils and do not interfere with IC-induced phagocytosis. Conclusion: The studied liposomes can be suitable carriers of flavonoids and be an alternative for the treatment of diseases in which a massive oxidative metabolism of neutrophils is involved.

Surface-enhanced Raman spectroscopy studies of organophosphorous model molecules and pesticides

This work reports the analytical application of surface-enhanced Raman spectroscopy (SERS) in the trace analysis of organophosphorous pesticides (trichlorfon and glyphosate) and model organophosphorous compounds (dimethyl methylphosphonate and o-ethyl methylphosphonothioate) bearing different functional groups. SERS measurements were carried out using Ag nanocubes with an edge square dimension of ca. 100 nm as substrates. Density functional theory (DFT) with the B3LYP functional was used for the optimization of ground state geometries and simulation of Raman spectra of the organophosphorous compounds and their silver complexes. Adsorption geometries and marker bands were identified for each of the investigated compound. Results indicate the usefulness of SERS methodology for the sensitive analyses of organophosphorous compounds through the use of vibrational spectroscopy.

Electrodeposition of PVA-protected PtCo electrocatalysts for the oxygen reduction reaction in H2SO4

In this paper we report the electrosynthesis of PVA-protected PtCo films (PVA = poly(vinylalcohol)) and their activities towards the oxygen reduction reaction (ORR). PtCo electrodeposits were potentiostatically obtained in the presence and absence of PVA at distinct potentials. The film morphology and composition were characterized by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX), which revealed that the use of PVA in the electrodeposition of PtCo films was decisive to achieve better film composition control. Cyclic voltammetry for PVA-protected PtCo films showed that the electrochemical surface area is dependent on the electrodeposition potentials and suggested different adsorption strengths of oxygen-containing species. Films produced in the presence of PVA presented the following activity order towards ORR as a function of the electrodeposition potential (vs. Ag/AgCl): -0.9 V> -0.8 V> -1.0 V> -0.7 V. In contrast, PtCo films electrodeposited in the absence of PVA displayed very similar activities regardless of the electrodeposition potential. The simplicity of the electrodeposition method combined with its effectiveness enabled the production of "model electrodes" for investigating the fundamental aspects of the reactions taking place in the fuel cell cathodes. (C) 2011 Elsevier B.V. All rights reserved.

Oxygen reduction reaction on a Pt/carbon fuel cell catalyst in the presence of trace quantities of ammonium ions: An RRDE study

The effect of trace quantities of ammonia on oxygen reduction reaction (ORR) on carbon-supported platinum catalysts in perchloric acid solutions is assessed using rotating ring disk electrode (RRDE) technique. The study demonstrates that ammonia has detrimental effects on ORR. The most significant effect takes place in the potential region above 0.7 V vs RHE. The effect is explained by the electrochemical oxidation of ammonia, which blocks Pt active sites and increases the formation of H2O2. This leads to losses in the disk currents and increments in the ring currents. The apparent losses in ORR currents may occur in two ways, namely, through the blocking of the active sites for ORR as well as by generating a small anodic current, which is believed to have a lower contribution. In addition, a detrimental effect of sodium cations in the potential range below 0.75 V vs RHE was demonstrated. This effect is most likely due to the co-adsorption of sodium cations and perchlorate anions on the Pt surface. Copyright (C) 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

Synthesis and Characterization of the Europium(III) Pentakis(picrate) Complexes with Imidazolium Countercations: Structural and Photoluminescence Study

Six new lanthanide complexes of stoichiometric formula (C)(2)[Ln(Pic)(5)]-where (C) is a imidazolium cation coming from the ionic liquids 1-butyl-3-methylimidazolium picrate (BMIm-Pic), 1-butyl-3-ethylimidazolium picrate (BEIm-Pic), and 1,3-dibutylimidazolium picrate (BBIm-Pic), and Ln is Eu(III) or Gd(III) ions-have been prepared and characterized. To the best of our knowledge, these are the first cases of Ln(III) pentakis(picrate) complexes. The crystal structures of (BEIm)(2)[Eu(Pic)(5)] and (BBIm)(2)[Eu(Pic)(5)] compounds were determined by single-crystal X-ray diffraction. The [Eu(Pic)(5)](2-) polyhedra have nine oxygen atoms coordinated to the Eu(III) ion, four oxygen atoms from bidentate picrate, and one oxygen atom from monodentate picrate. The structures of the Eu complexes were also calculated using the sparkle model for lanthanide complexes, allowing an analysis of intramolecular energy transfer processes in the coordination compounds. The photoluminescence properties of the Eu(III) complexes were then studied experimentally and theoretically, leading to a rationalization of their emission quantum yields.

Selectivity and Mechanisms Driven by Reaction Dynamics: The Case of the Gas-Phase OH-+CH3ONO2 Reaction

Well-established statistical approaches such as transition-state theory based on high-level calculated potential energy profiles are unable to account for the selectivity observed in the gas-phase OH- + CH3ONO2 reaction. This reaction can undergo bimolecular nucleophilic displacement at either the carbon center (S(N)2@C) or the nitrogen center (S(N)2@N) as well as a proton abstraction followed by dissociation (E(CO)2) pathway. Direct dynamics simulations yield an S(N)2:E(CO)2 product ratio in close agreement with experiment and show that the lack of reactivity at the nitrogen atom is due to the highly negative electrostatic potential generated by the oxygen atoms in the ONO2 group that scatters the incoming OH-. In addition to these dynamical effects, the nonstatistical behavior of these reactions is attributed to the absence of equilibrated reactant complexes and to the large number of recrossings, which might be present in several ion-molecule gas-phase reactions.