Diffusion Of Molecular Oxygen Research Articles

Stabilization of a Photoradiated Naphthalene Diimide-Based Organic Radical Anion Inside a Peptide-Based Gel Matrix with an Improvement of Optoelectronic Properties.

An amino acid-conjugated naphthalene diimide (NDI)-based highly red fluorescent radical anion has been found in a water medium under the photoradiated condition. This molecule has failed to form the radical anion in the monomeric state; however, the J aggregation in the aqueous medium has ensured the formation of radical anion in the ambient condition after the irradiation of both sunlight and UV light exposure. Electron paramagnetic resonance (EPR) studies clearly suggest the formation of radical anions. Herein, the stability of the radical anion in the aqueous medium is only a few minutes as a small amount of shaking is enough to quench the radical anion in the solution state. Furthermore, the incorporation of this molecule into a peptide-based hydrogel matrix and the consequent photoirradiation have not only helped to develop radical anion in the gel matrix but also increased the enormous stability of the radical anion inside the hydrogel matrix even for 30 days. It is envisaged that the formation of the radical anion within the gel matrix prevents the free movement of the NDI molecules and restricts the diffusion of molecular oxygen in the system, which leads to the stability of the radical anions in the gel. Moreover, the stability of the radical anion within the gel has helped to enhance the conductivity of the hybrid gel to a great extent. Interestingly, the radical anion-containing hybrid hydrogel has shown a potential photoswitching property.

Nanoparticle Shape Influence over Poly(lactic acid) Barrier Properties by Molecular Dynamics Simulations.

Climate change is leading us to search for new materials that allow a more sustainable environmental situation in the long term. Poly(lactic acid) (PLA) has been proposed as a substitute for traditional plastics due to its high biodegradability. Various components have been added to improve their mechanical, thermal, and barrier properties. The modification of the PLA barrier properties by introducing nanoparticles with different shapes is an important aspect to control the molecular diffusion of oxygen and other gas compounds. In this work, we have described changes in oxygen diffusion by introducing nanoparticles of different shapes through molecular dynamics simulations. Our model illustrates that the existence of curved surfaces and the deposition of PLA around them by short chains generate small holes where oxygen accumulates, forming clusters and reducing their mobility. From the several considered shapes, the sphere is the most suitable structure to improve the barrier properties of the PLA.

Redox conditions of bottom sediments and macrozoobenthos characteristics in the Kruglaya and Kazachya bays (Sevastopol)

A lack of systemic and environmentally efficient approach to exploitation of the Kruglaya and Kazachya bays (Sevastopol) resulted in their severe pollution. The conjunction of natural and anthropogenic factors led to deterioration of habitat conditions of benthic communities. The aim of this work was to carry out complex research of Kruglaya and Kazachya bays’ ecosystems to study peculiarities of formation of redox conditions in bottom sediments and bottom water layer, as well as their effect on macrozoobenthos characteristics. Bottom sediments were sampled by diver in plexiglass tubes hermetically sealed at the top and bottom; it helped in preserving a fine structure of bottom sediments and bottom water layer. To study benthic communities, samples were taken in the same spot with a manual sampler. To obtain chemical composition of pore waters with high vertical resolution, the voltammetry analysis was carried out. Calculation of an oxygen flux at the boundary and in the upper layer of bottom sediments was performed according to the vertical profile of oxygen concentration in pore waters and geochemical analysis with applying the equation for the Fick’s first law and considering concentration gradient and molecular diffusion of oxygen in pore waters. Standard hydrobiological methods were applied for the analysis of benthic material. When calculating the values of the Shannon diversity index (H’), the binary logarithm was used. The data analysis showed as follows: a high level of anthropogenic load and restricted water dynamics resulted in siltation of bottom sediments in the studied water areas, which obstructed oxygen penetration; the accumulation of organic carbon contributed to its active consumption. Stratification of a water column due to limited water exchange, high temperature of bottom water, accompanied by a decrease in oxygen solubility, and finely dispersed nature of bottom sediments contributed to the fact that the rate of oxygen input was lower than the rate of oxygen consumption for organic matter oxidation. This was followed by the development of oxygen deficiency zones and emergence of reduced compounds, in particular hydrogen sulfide. Importantly, suboxic conditions prevailed in the upper sediment layer, and anaerobic conditions prevailed below. Due to this, the main forms of macrozoobenthos were species tolerant to oxygen deficiency and organic pollution. Specifically, in some spots of the Kazachya Bay, polychaetes alone were recorded. At the same time, in the Kruglaya Bay mouth area, intense water dynamics and morphological peculiarities of bottom sediments contribute to saturation of the upper sediment layer with oxygen. Based on oxygen concentration data for the surface (0–5 mm) sediment layer (pore waters) and on geochemical peculiarities of bottom sediments (moisture and porosity), the oxygen flux at st. 4 (the Solenaya Bay) was calculated; the value was 0.73 M·m−2·year−1. Considering oxygen concentration in bottom water layer (259 μM), the time for complete depletion of oxygen or its renewal is about 5 months if taking into account biogeochemical processes alone. Hence, it can be assumed that the ecosystems of the Kruglaya and Kazachya bays are in the stage of degradation. Their further exploitation without a developed systemic and rational approach will result in a critical deterioration of the ecosystems – the emergence and spread of environmental risk zones. It will reduce the recreational and socioeconomic attractiveness of these areas.

SOME RESULTS OF SOLVING THE NON-STATIONARY PROBLEM OF GAS DIFFUSION IN POLYETHYLENE

The problems of diffusion of molecular oxygen and ethylene in amorphous-crystalline polyethylene are considered. The temperature of the medium is assumed to be constant, and the diffusion process is described by the classical Fick partial differential equations. It is assumed that the material obtained from the polyethylene granules using the thermomechanical extrusion process is located in a limited sealed container. The impermeability of the container shell leads to the need to take into account the parameters of the gas in the free volume. The problem is nonlinear and non-stationary, and it is assumed that the rate of interphase processes at the gas-polyethylene interface significantly exceeds the rate of diffusion. Using the finite element method, numerical results are obtained describing the process of oxygen evacuation from polyethylene and the process of ethylene diffusion into the material, at different values of the external pressure of the penetrant gas. The main characteristics of these processes are determined. An effective variant of double vacuuming is considered, which makes it possible to obtain a significantly lower concentration of oxygen in polyethylene. The results are of practical significance for evaluating the parameters of the production of high-quality heat-shrinkable polyethylene pipes produced by the technology of gamma-ray radiation exposure in the protective environment of an inert gas.

Features of burning's porous coal coke particles

A comparison of empirical and theoretical dependences of coke particle density on the diameter during its combustion is carried out. In contrast to the established notions that oxygen diffuses inside the particle in the pores mainly by Knudsen diffusion, in comparison with numerical calculations it is shown that mainly bulk diffusion should occur inside the pores. Oxygen does not have time to get inside the transients and micropores. For a certain combustion region (high value of the internal diffusion-kinetic ratio Sev> 5), an analytical expression is obtained that describes the relationship between density and particle diameter under the assumption of molecular diffusion of oxygen within the pores of coke particles. It is shown that when burning particles of coal dust with a diameter of less than 150 μm, the values of Sev could be less than 5.According to a certain degree in the obtained dependence, you can determine the value of the effective specific surface area of the coke pores.

Probing the Folding of Peptide–Polymer Conjugates Using the π-Dimerization of Viologen End-Groups

The synthesis of a foldable viologen-functionalized peptide–polymer conjugate is presented. The ABA-type triblock conjugate with a PEG polymer was capped with a FHFHF pentapeptide sequence and further modified with a viologen building block at both chain ends. The pH-responsive peptide domains fold into an intermediate structure inducing close proximity of the viologen units, which upon a reduction step form π-dimers of the radical cation. Overall the intramolecular folding and intermolecular self-assembly process leads to the formation of supramolecular nanorods. Mixing of viologen-peptide–polymer conjugates with unfunctionalized conjugates leads to crosslinking of the nanorods and hydrogels with a tunable content of viologen end groups. π-Dimerization in the gels induces a deep purple color, which is used as an optical probe to monitor the diffusion of molecular oxygen through the hydrogel matrix.

Analysis of O2 Diffusion Resistance without Cathode Humidification in a PEMFC

Fuel cells are power-generating devices from chemical energy by electrochemical reactions. Especially, proton exchange membrane fuel cells (PEMFCs) have a high-power density, even if they utilize polymer electrolyte and run at a low temperature. It is generally ascribed that oxygen transport to the cathode catalyst layer (CL) greatly affect a PEMFC performance. When molecular oxygen travels from the cathode flow channel to the surface of Pt, it is gradually in three diffusion regimes: molecular diffusion (MD), Knudsen diffusion, and ionomer film diffusion. Recently, much effort has been devoted to understanding oxygen diffusion resistance at the cathode, especially in the CL. Using the Stefan-Maxwell equation, Mashio et al.1 separated total oxygen diffusion resistance into three different oxygen diffusion that includes pressure-dependent resistance and two pressure-independent resistance, and they determined molecular diffusion resistance RMD and non-molecular diffusion resistance Rnon-MD from the experimentally measured limiting current with diluted gaseous oxygen. Similarly, in this study, we measured limiting current to study oxygen diffusion resistance at various RHs of the anode without the cathode humidification. Fig. 1a shows total oxygen diffusion resistance RMD with increasing total pressure Ptot at the cathode. RMD increases with increasing Ptot, while it decreases with higher RH at the anode. Fig. 1b gives Rnon-MD against pressure. The value of Rnon-MD decreases with increasing RH at the anode. It is inferred from the results that i) MD is dominant at the cathode with no humidification, depending on RHs at the anode that affect water content at the cathode and ii) smaller Rnon-MD with higher RH at the anode is associated with increased sites available for oxygen diffusion possibly due to ionomer swelling.2 References T. Mashio, A. Ohma, S. Yamamoto, K. Shinohara, ECS trans., 11(1) 529-540 (2007).M. Schalenbach, T. Hoefner, P. Paciok, M. Carmo, W. Lueke, and D. Stolten, J. Phys. Chem. C, 119, 25145-25155 (2015) Figure caption Fig. 1(a) Molecular oxygen diffusion resistance RMD and (b) non-molecular oxygen diffusion resistance Rnon-MD against total pressure at various relative humidity at the anode (No humidification at the cathode). Figure 1

Analysis of H2/Air Polarization Curves: The Influence of Ionomer/Carbon Ratio and Carbon Supports in Low Pt Loading Catalyst on the Cathode Performance

Significant effort has been devoted to reduce the cathode platinum loading for proton exchange membrane fuel cell (PEMFC). Apart from advanced electrocatalysts, the role of ionomer properties, Pt nanoparticle dispersion and catalyst layer microstructures are of equal significance to achieve low Pt loading [1-3]. The polarization loss due to oxygen transport limitations on reduced Pt loading electrodes was reported to account for ~50% of the total loss at high current density operation [1]. Since ionomer (Nafion ®) is usually incorporated with the Pt/C catalyst, such loss has been attributed to the oxygen transport resistance in the interface between the ionomer and Pt [3,4]. Therefore, it is imperative to have a comprehensive understanding of the polarization behavior for the low-Pt-loading electrodes and reduce the polarization loss due to oxygen transport through optimizing the ionomer-to-carbon (I/C) ratio. In this study, a systematic breakdown of six types of polarization sources [5] is presented to elaborate the effect of I/C ratios and carbon support on the cathode polarization behavior in air-breathing fuel cells. The sources of polarization is summarized in Table I. A novel electrode fabrication method, reactive spray deposition technology (RSDT), was employed to deposit low Pt loading (anode, 0.05 mg cm-2; cathode, 0.1 mg cm-2) catalyst-coated membranes (CCMs) using high-surface-area carbon black (KB) and multi-walled carbon nanotube (MWNT) as catalyst supports. This technique is unique in combining the catalyst synthesis and deposition into one step and allows for independent control of the catalyst, support and ionomer compositions in the electrode. The analysis of the H2/Air polarization distinguished three Tafel regions with different controlling processes for RSDT-derived cathode electrodes. The non-electrode concentration overpotential dominated in the region where the current densities were above 1000 mA cm-2, while the cathode electrode concentration overpotential dominated the current densities from 100 to 1000 mA cm-2. Below 100 mA cm-2, the ORR overpotential following Tafel kinetics is dominant. Non-electrode concentration overpotential (ηcorr3) is controlled by the molecular diffusion of oxygen in the gas diffusion layer (GDL) and mesopores in the catalyst layer. It was reduced with higher back pressure or higher pore volume in the pore range of 10 nm-100 nm. The cathode electrode concentration overpotential (ηcorr4) is related to the oxygen transport in the micropores (Knudsen diffusion) and through ionomer thin film. The I/C ratio for optimal fuel cell performance is related to the lowest ηcorr4. As Pt/KB cathodes exhibited higher microporosity than that of Pt/MWNT cathodes, the ηcorr4 for Pt/KB was also higher. The ORR overpotential (ηcorr5 and ηcorr6) decreased with increasing I/C ratios for both Pt/KB and Pt/MWNT CCMs, suggesting an improved triple-phase boundary between Pt, carbon and ionomer with enhanced ionomer coverage on the carbon. As a result, the ORR activities at 0.9ViR-freeincreased with I/C ratio. Table I. List of fuel cell polarization sources and the technique of separation [5].

High-temperature oxidation behavior of polymer-derived SiHfBCN ceramic nanocomposites

Within this study, the oxidation behavior of SiHfBCN ceramic powders and monoliths was studied at temperatures from 1200 to 1400°C. Both powder and monolithic samples exhibited parabolic oxidation behavior characterized by very low rates (10−9–10−8mg2cm−4h−1). The activation energy of 112.9kJmol−1, which was determined for the SiHfBCN powder, is comparable to that of other silica formers such as silicon or SiC and relates to the diffusion of molecular oxygen through silica scale. Whereas, the values determined for the SiHfBCN ceramic monoliths (174 and 140kJmol−1, depending on the Hf content) indicate the complex nature of their oxidation process, leading at temperatures below 1300°C to a continuous oxide scale consisting of borosilicate, silica, m-and t-HfO2. At higher temperatures, the oxide scale consists of silica, HfSiO4 as well as m-and t-HfO2 and becomes discontinuous, probably due to the evaporation of boria.

Chemical Passivation of In0.53Ga0.47As(100) Using Ammonium Sulfide and Thiols

III-V compound semiconductors have superior electron and hole mobilities compared to silicon, which makes them alternative materials to fabricate transistors that are faster and use less energy. Since the oxides of III-V’s contain many defects and have undesirable electrical properties, aqueous passivation chemistries are needed to incorporate these materials into existing semiconductor processing lines. This study seeks to determine whether a thin (~2-3 nm) layer of sulfur or a sulfur-containing molecule can chemically passivate clean InGaAs surfaces to prevent oxide regrowth upon ambient exposure. The goal is to devise a liquid phase process to remove carbon contamination from the surface, etch the native oxides, and deposit a thin film to prevent the diffusion of molecular oxygen and water vapor to the clean surface of the semiconductor for at least one hour. In0.53Ga0.47As(100) on InP substrates (RMS=0.18 nm by atomic force microscopy) were cleaned in dilute SC1 solutions and etched for 1 min in 0.3 M HF or 1.0 M HCl followed by immersion in dilute solutions of 1-eicosanethiol (ET, 20 carbon atoms in chain) in ethanol or ammonium sulfide ((NH4)2S) in water. The chemical composition of the passivated surfaces was analyzed by x-ray photoelectron spectroscopy (XPS). The presence of InGaAs oxides was evaluated by comparing the In 3d, Ga 2p, As 2p and O 1s region of the XPS spectra of the substrates after different processes. The analysis of InGaAs etched for 1 min in HF or HCl showed that the surface reoxidized completely after only 4 min of ambient exposure (no surface roughening occured after etching). The main oxides present on the surface after the acid etching were the As3+ and Ga3+ states. When clean substrates were etched in HF or HCl and immersed for 20 min 4 mM ET and 0.02% (NH4)2S solutions, oxides were detectable on the surface after 4 min of atmospheric exposure, but the reoxidation of InGaAs was slowed down (after 60 min of ambient exposure, less oxides were present on the surface in comparison with the substrate that was not passivated, as shown in Figure 1). Additional tests showed similar results for 0.02% (NH4)2S passivation for 1 min and for 60 min, or for 20 min in 20% (NH4)2S, suggesting that the passivation is independent of (NH4)2S concentration or deposition time. From the XPS analysis, the passivation layer is bonding to the InGaAs surface in the form of sulfide (As1+ states observed in the passivated samples only). Only when InGaAs was passivated for 20 h in ET or for 20 min in (NH4)2S under a nitrogen atmosphere in a glove box, no detectable oxygen was observed in the O 1s region after exposing to air for a short time (4 min). Oxide regrowth was observed for longer ambient exposure times. To estimate the thickness of the passivation layer deposited, spectroscopic ellipsometry was used to measure the overlayer (ET, S and InGaAs oxides) on InGaAs after the passivation processes. An overlayer thickness of 0.8 nm was measured on InGaAs after passivating for 20 min in 0.02% (NH4)2S. The thickness of the overlayer on InGaAs after passivating for 20 h in 4 mM ET was 2.6 nm (the calculated molecular length of the ET molecule is 2.7 nm). These results show that the sulfur-based chemistries are bonding to the III-V’s but the resulting layer is not thick enough to prevent oxygen or water vapor from diffusing and reacting at the surface. We are working to understand how to densify the ET layer and control the thickness of layers deposited using (NH4)2S. Figure 1. XPS spectra of In0.53Ga0.47As(100) etched in 0.3 M HF and passivated for 20 min in 0.02% (NH4)2S in a nitrogen atmosphere (glove box). A control experiment where a water rinse was done instead of the passivation, exposed for 4 min to atmosphere, is shown in a). The passivated surface was exposed to atmosphere for b) 4 min, c) 8 min, d) 20 min and e) 60 min Figure 1

Opening gates to oxygen reduction reactions on Cu(111) surface.

Electrocatalytic reduction of oxygen is composed of multiple steps, including the diffusion-adsorption-dissociation of molecular oxygen. This study explores the role of electrical double layer in aqueous medium in quantifying the rate of these coupled electrochemical processes at the electrode interface during oxygen reduction. The electronic, energetic, and configurational aspects of molecular oxygen diffusion and adsorption onto Cu(111) in water are identified through density functional theory based computations. The liquid phase on Cu(111) is modeled with hexagonal-ordered water bilayers, at two slightly different structures, with O-H bonds either facing the vacuum or the metal surface. The results indicate that the energetically preferred structure of water bilayers and adsorption configuration of O2 are different in cathodic and anodic potentials. The diffusion of O2 is found to be heavily hindered at the water/metal interface because of the ordering of water molecules in bilayers as compared to the bulk liquid. The unique correlations of diffusion and adsorption kinetics with water structure identified in this work can provide clues for improving oxygen reduction efficiency.

A MATHEMATICAL COUPLED MODEL OF OXYGEN TRANSPORT IN THE MICROCIRCULATION: THE EFFECT OF CONVECTION–DIFFUSION ON OXYGEN TRANSPORT

This paper is aimed at examining the effect of convection–diffusion on oxygen transport at the micro-level. A coupled model of the convection–diffusion and molecular diffusion of oxygen is developed, and the solid deformation resulting from capillary fluctuations and the seepage of tissue fluid are incorporated into this model. The results indicate that (1) the oxygen concentration calculated from this coupled model is higher than that given by molecular diffusion models, both within the capillaries and tissue (maximum difference of 16%); (2) convection–diffusion has the greatest effect in tissue surrounding the middle of the capillary, and enhances the amount of oxygen transported to cells far from the oxygen source; (3) larger permeability coefficients or smaller diffusion coefficients produce a more obvious convection–diffusion effect; (4) a counter-current flow occurs near the inlet and outlet ends of the capillary. This model also provides a foundation for the study of how oxygen affects tumor growth.

X-ray induced mobility of molecular oxygen at extreme conditions

We report an in situ Raman study of KClO4 irradiated with x-rays in a diamond anvil cell. Decomposition via KClO4 + hv → KCl + 2O2 was monitored via the O2 vibron at 2 GPa, 6 GPa, and 9 GPa. For all pressures, the vibron grew in intensity and then diminished after successive irradiation suggesting that O2 was diffusing away from the irradiated region. Surprisingly, the diffusion rate accelerated with pressure increase, indicating that the nonhydrostatic pressure gradient was likely driving molecular diffusion of oxygen. At 9 GPa, the vibron bifurcated suggesting that O2 exists as two forms: interstitial and bulk solid. This method can be employed to study molecular diffusion under extreme conditions.

An interference-free glucose biosensor based on a novel low potential redox polymer mediator

A highly sensitive and interference-free glucose biosensor based on a novel ruthenium complex-tethered redox polymer (Ru-RP) mediated enzymatic oxidation of glucose at −0.15V (vs. Ag/AgCl) is described in this report. Through the co-immobilization of the Ru-RP and glucose oxidase (GOx) on a glassy carbon electrode (GCE) via a simple one-step chemical crosslinking process with glutaraldehyde, the crosslinked membrane displays excellent catalytic activity toward the oxidation of glucose with a current sensitivity of 24.3μAmM−1cm−2 and a linear correlation between the oxidation current and glucose concentration up to 10mM. More importantly, owing to the low operating potential of −0.15V (vs. Ag/AgCl), potential interferences from naturally occurring interfering species in blood such as ascorbic acid, dopamine, uric acid, and common drug acetaminophen are effectively alleviated. Furthermore, the hydrophilic nature of the crosslinked membrane also effectively retards the diffusion of molecular oxygen. This glucose biosensor could be an attractive candidate in the development of miniaturized glucose biosensors.

Exploring the Diffusion of Molecular Oxygen in the Red Fluorescent Protein mCherry Using Explicit Oxygen Molecular Dynamics Simulations

The development of fluorescent proteins (FPs) has revolutionized cell biology research. The monomeric variants of red fluorescent proteins (RFPs), known as mFruits, have been especially valuable for tagging and tracking cellular processes in vivo. Determining oxygen diffusion pathways in FPs can be important for improving photostability and for understanding maturation of the chromophore. We use molecular dynamics (MD) calculations to investigate the diffusion of molecular oxygen in one of the most useful monomeric RFPs, mCherry. We describe a pathway that allows oxygen molecules to enter from the solvent and travel through the protein barrel to the chromophore. We calculate the free-energy of an oxygen molecule at points along the path. The pathway contains several oxygen hosting pockets, which are identified by the amino acid residues that form the pocket. We also investigate an RFP variant known to be significantly less photostable than mCherry and find much easier oxygen access in this variant. The results provide a better understanding of the mechanism of molecular oxygen access into the fully folded mCherry protein barrel and provide insight into the photobleaching process in these proteins.

Microbial Fuel Cell for Sustainable Electricity Production from Seafood Wastewater

To make the treatment of seafood wastewater more economical and sustainable, this study aims to examine electricity generation from seafood wastewater in MFC reactor. By supplying the MFCs with seafood wastewater, the maximum power density of 291.6 mW/m2 and CE of 20.3 % could be obtained. The substrate loss was attributed to diffusion of molecular oxygen from the cathode to the anode, which led to substrate conversion through aerobic respiration rather than electricity-producing pathway. This study provides a conceptual demonstration of seafood wastewater for electricity production using MFC technology.

A redox shuttle to facilitate oxygen reduction in the lithium air battery

A novel design of the non-aqueous lithium air cell is presented with a demonstration of a new reaction concept, involving a soluble redox shuttle to catalyse oxygen reduction. In principle, this can relieve the requirement for fast diffusion of molecular oxygen from the air interface to the positive electrode. To demonstrate this concept, ethyl viologen ditriflate was dissolved in BMPTFSI, reduced at a carbon electrode and regenerated by aspiration with oxygen. Useful shuttle behaviour, confirmed by several reduction–oxidation cycles, was observed in the case where the electrolyte contained at least 0.3M lithium salt. The beneficial effect of the salt was attributed to its critical role in converting superoxide, which would otherwise destroy the shuttle, into the more desirable product of oxygen reduction, lithium peroxide.

Functional layered niobate nanocomposite with cationic manganese porphyrin and its electrocatalytic behavior

Cationic manganese porphyrin 5,10,15,20-tetrakis(N-methylpyridinium-4-yl) porphyrinato manganese(III), MnTMPyP, has been successfully intercalated into both interlayers I and II of layered niobate (K 4Nb 6O 17·3H 2O) through a guest-exchange method using PrNH 3 +-Nb 6O 17 as a precursor. The characterizations for MnTMPyP-Nb 6O 17 were carried out by means of XRD, CHN analysis, SEM and UV–vis absorption spectra. The metalloporphyrin molecules incorporated within the nanocomposite were found to be tilted approximately 52° against the niobate nanosheets. The cyclic voltammetric measurement verified that the glassy carbon electrode (GCE) modified with MnTMPyP-Nb 6O 17 film showed excellent electrocatalytic activity for oxygen reduction in neutral media. Furthermore, the peak currents increased linearly with the square root of scan rates, suggesting that the electrocatalytic processes were controlled by molecular oxygen diffusion.

Lipid peroxidation modifies the picture of membranes from the “Fluid Mosaic Model” to the “Lipid Whisker Model”

The “Fluid Mosaic Model”, described by Singer and Nicolson, explain both how a cell membrane preserves a critical barrier function while it concomitantly facilitates rapid lateral diffusion of proteins and lipids within the planar membrane surface. However, the lipid components of biological plasma membranes are not regularly distributed. They are thought to contain “rafts” – nano-domains enriched in sphingolipids and cholesterol that are distinct from surrounding membranes of unsaturated phospholipids. Cholesterol and fatty acids adjust the transport and diffusion of molecular oxygen in membranes. The presence of cholesterol and saturated phospholipids decreases oxygen permeability across the membrane. Alpha-tocopherol, the main antioxidant in biological membranes, partition into domains that are enriched in polyunsaturated phospholipids increasing the concentration of the vitamin in the place where it is most required. On the basis of these observations, it is possible to assume that non-raft domains enriched in phospholipids containing PUFAs and vitamin E will be more accessible by molecular oxygen than lipid raft domains enriched in sphingolipids and cholesterol. This situation will render some nano-domains more sensitive to lipid peroxidation than others. Phospholipid oxidation products are very likely to alter the properties of biological membranes, because their polarity and shape may differ considerably from the structures of their parent molecules. Addition of a polar oxygen atom to several peroxidized fatty acids reorients the acyl chain whereby it no longer remains buried within the membrane interior, but rather projects into the aqueous environment “Lipid Whisker Model”. This exceptional conformational change facilitates direct physical access of the oxidized fatty acid moiety to cell surface scavenger receptors.

Comparison between hexatriacontane and stearic acid behaviours under late Ar―O2 post-discharge

The transformations undergone in a late Ar―O2 afterglow by the hexatriacontane, a long chain alkane, and the stearic acid, a C18 alkane skeleton with an acid function, are compared. The diffusion of molecular oxygen is found to be the limiting step in the case of the HTC. When the SA is treated, this process is fast, likely because of the high diffusion coefficient of O2 in the SA than in the HTC. Desorption of OH groups produced by the abstraction of one hydrogen from the alkane skeleton by an oxygen atom is proposed as the limiting step. The fragmentation process stands in the core of the material and creates by-products that are responsible for the appearance of bubbles whose mobility and coarsening depend on the viscosity of the treated material. Finally, by resorting to pulse mode, both the HTC and the SA can be etched whereas they are functionalized in the continuous mode where non-linear behaviours are observed.