Voltammetric investigation of the complexation equilibria in the presence of a low level of supporting electrolyte Part 1: Steady-state current-potential curves for inert complexes

The use of microelectrodes for voltammetric investigations of the complexation equilibria at very low concentrations of supporting electrolyte allows the risk of competitive complexation or contamination to be avoided, makes the activities of the species involved closer to their concentrations (which facilitates comparisons with the spectroscopic results) and finally, allows the concentrations of the species to be varied over a broader range. This paper presents the calculations of the steady-state currents for a wide range of complexes that are inert on the experimental time scale, and reports the influence of the concentration of the electroinactive ionic species on the limiting currents. Also, for a number of cases the variation of halfwave potential with the ligand concentration, resulting from changes in the ohmic drop, is given. It is assumed that only one species (the complex or the uncomplexed form) is electroactive; if this is the complex, it may or may not change the number of ligands. The theoretical results were obtained either employing the Myland-Oldham theory extended in this paper or by digital simulation. The results of calculations show that the magnitude of the changes in the steady-state limiting current on complexation depends on the type of complexation equilibrium, the type of the change in the reactant charge number in the electrode process, and the complex formation constant. In a number of situations migrational effects are negligibly small and no special treatment is necessary, despite the lack of supporting electrolyte. In other cases, where migration is significant, the relations between the measured steady-state limiting current and the complex formation constant ß are given in the form of fitted equations that can be used to obtain ß from appropriate experimental data

Obesity in Adolescents (Handout)

The handout briefly discusses obesity in the adolescents. It covers possible causes, risk factors, and some simple solutions.https://dune.une.edu/an_studedres/1134/thumbnail.jp

Raman spectra of zinc phthalocyanine monolayers adsorbed on glassy carbon and gold electrodes by application of a confocal Raman microspectrometer

Raman spectra of zinc phthalocyanine monolayers, adsorbed on gold and on glassy carbon surfaces (electrodes), are presented. These spectra have been recorded with the electrodes inside and outside an electrochemical cell filled with an aqueous electrolyte. A confocal Raman microspectrometer was used. It was demonstrated that, because this spectrometer uses low laser intensifies, no damage of the monolayer occurred. The results show that the interaction of the phthalocyanine molecule with gold differs from that with glassy carbon. Because the laser excitation wavelength (660 nm) coincides with a UV-visible absorption band (Q band), a strong resonance- enhanced Raman spectrum was obtained. No signs of surface enhancement (surface-enhanced Raman scattering) effects were detected

Digital simulation of chronopotentiometric and steady-state voltammetric curves at microelectrodes in the presence of a low concentration of supporting electrolyte

A simulation scheme for the calculation of theoretical chronopotentiograms at microelectrodes in solutions containing low amounts of supporting electrolyte is presented. The scheme allows computation of the changes in the concentration profiles of the substrates, products and the supporting electrolyte ions with time. The electrode potentials that are established after reaching the steady-state, together with the appropriate current intensities, can be used for constructing the steady-state voltammograms. The simulation of the mixed diffusional and migrational transport is based on the Crank-Nicolson method with an exponentially expanding time and space grids. The scheme does not impose any limitations on diffusion coefficients and it can be applied both to simple electrode reactions (one reactant-one product) and more complicated reactions under the assumption that the double-layer thickness is small in comparison to the diffusion layer. Five simple types of electrode reactions and an example of a more complicated scheme were considered. The results obtained demonstrate that the dependence of the steady-state limiting current on the support ratio (csupp.el./csubst) depends not only on the charge of the reactant and the product, but also on the diffusion coefficient ratio of the substrate and product. If the difference between diffusion coefficients is large, the predictions based on simpler theories available in literature can become invalid

Effect of axial ligands on the spectroelectrochemical properties of zinc phthalocyanine films. In situ Raman and electroreflection spectra

Electroreflection and Raman spectra (in situ and ex situ) of zinc phthalocyanine (ZnPc) films (80 nm thick) have been studied. Raman spectra were resonantly and preresonantly enhanced. Both electroreflection and Raman experiments reveal the homogeneous inclusion of electrolyte anions upon oxidation of the film. The anions coordinate preferentially axial positions of the ZnPc molecule. This process is accompanied by an out-of-plane deformation of the phthalocyanine macrocycle, which results in the change of both electroreflection and Raman spectra. The ZnPc molecule remains deformed when the film is saturated with anions. The detailed analysis of new bands and altered intensities in the Raman spectrum indicates that the molecular symmetry point group changes from the D4h point group to C2v. The influence of ZnPc oxidation on the Raman excitation mechanism has been also studied. Effects of axial ligands on the molecular geometry have been studied by quantum chemical calculations for the ZnPc+, ZnPc+Cl¿ and ZnPc+(Cl¿)2 species using the unrestricted Hartree¿Fock variant of the MNDO method. Calculation results show that the ZnPc molecule undergoes an out-of-plane deformation when one axial position is coordinated by the anion

Oxygen reduction in acid media: influence of the activity of CoNPc(1,2) bilayer deposits in relation to their attachment to the carbon black support and role of surface groups as a function of heat treatment

O2 reduction was investigated using rotating disk electrode and voltammetry techniques on NPcCo(1,2) impregnations deposited onto two kinds of carbon black support. They were selected on the basis of their similar pH and dibuthylphthalate (DBP) adsorption values. Samples were also characterized by IR and X-ray photoelectron spectroscopy techniques. An optimized thermal treatment yielded an improvement in the O2 reducibility and identical activities (with N = 3.8) on both supports. These spectroscopic methods revealed a bilayer structure and suggested the presence of two sorts of site (active and inactive) which differed in their attachment of the substrate via surface groups which were characterized

A bioinformatics characterization of secondary metabolism and alkyl citric acid pathway reconstruction in Aspergillus niger NRRL3

Secondary metabolites (SMs) from fungi have become an integral part of various scientific and medical fields as well as providing economic benefits. The genes involved in the biosynthesis of fungal and bacterial SMs are often co-localized in closely linked clusters that are generally dormant under laboratory conditions. Genomics technologies are being intensively used to identify SM gene clusters, and suggest methods to promote their expression. These efforts have already been used to discover new natural products, reveal the biosynthetic underpinnings of known products, and establish methods to eliminate toxic substances from industrially relevant organisms. An important aspect of SM gene cluster characterization is the development of methods to overproduce known compounds which are difficult to synthesize in the lab. This thesis presents the annotation of SM gene clusters in the sequenced genome of Aspergillus niger NRRL3. Using our cluster data as a guide to induce production of secondary metabolites through the overproduction of clustered transcription factors, we confirm the identity of the regulators that are involved in the biosynthesis of the fumonisins, TAN-1612/BMS-192548, and the azanigerones which were also used as positive controls. Additionally, we discovered three previously uncharacterized regulators of compounds whose masses correspond to the malformins, pyrophen, and the alkyl citric acids hexylitaconic acid, 2-carboxymethyl-3-hexylmaleic acid and the tensyuic acids. Selecting the alkyl citric acids for further investigation, we obtained a transcriptomic profile to define the genes of the alkyl citric acid gene cluster in A. niger. Using the identified compounds from mass spectrometry and NMR as well as the functional annotations of our defined cluster, I reconstruct a biosynthetic pathway for the alkyl citrates I identified. I then tested the robustness of my reconstruction by successfully predicting the accumulation of two early precursors, 2-hexylcitric acid (log2 fold change = 2.982 ± 0.15, p-value < 0.01) and its anhydride (log2 fold change = 3.792 ± 0.26, p-value < 0.01), as well as the elimination of all downstream compounds

When You\u27re Out, You\u27re Not Really Out: Exiting Strategies Among Gang-Affiliated Chicanas

In recent years there has been an increased focus on gang desistence and exiting strategies, yet little is known at present regarding the experiences of women exiting the gang lifestyle. The current study, based on semi-structured interviews with twenty-four formerly gang-affiliated Chicana women involved with a prominent gang prevention/intervention organization, sought to understand how these women negotiated their disengagement from the gang. Consistent with previous literature, we found that disengagement from the gang lifestyle is neither linear nor immediate. Five primary themes that emerged from the interviews included: (1) the process of identity transition; (2) motherhood and its responsibilities; (3) generational shifts in gang culture; (4) burning bridges; (5) impacts of prison; and (6) support services. The women\u27s narratives offer an alternative lens through which to understand women’s negotiation of their own identities through the process of disengagement from the gang