Maximum Surface Concentration Research Articles

Kinetics of Fibrinogen Adsorption on Hydrophilic Substrates

Irreversible side-on adsorption of fibrinogen, modeled as a linear chain of touching beads of various size, was studied theoretically using the random sequential adsorption (RSA) model. Numerical simulation of the Monte Carlo type enabled one to determine the dependence of the surface blocking function (available surface function) on the protein coverage. These numerical results were interpolated using analytical functions based on a polynomial expansion. The dependence of the jamming coverage on the size of the simulation area was also determined. By an extrapolation of these results to the infinite area size, the maximum surface concentration of fibrinogen for the side-on adsorption was determined to be 2.26 x 10(3) microm(-2). This corresponds to a jamming coverage theta(infinity) of 0.29. It was shown that the blocking function can well be approximated in the limit of high coverage by the dependence C(theta(infinity) - theta)(4). Using this interpolating expression, the kinetics of fibrinogen adsorption under convection and diffusion transport conditions were evaluated for various bulk concentrations of the protein. These kinetic curves were derived by numerically solving the mass transport equation in the bulk with the blocking function used as a nonlinear boundary condition at the interface. It was shown that our theoretical results are in agreement with experimental kinetic data obtained by AFM, ellipsometry, and other techniques for hydrophilic surfaces in the limit of low bulk fibrinogen concentration.

Silver nanoparticle monolayers on poly(ethylene imine) covered mica produced by colloidal self-assembly

Monodisperse silver particles were synthesized according to the method of Creighton et al. by reduction of AgNO 3 solutions with NaBH 4 in the presence of polyvinyl alcohol as the stabilizing agent. Bulk characteristics of silver nanoparticles in aqueous solutions were carried out by measuring their extinction spectrum, fluorescence, diffusion coefficients using the PCS method and the electrophoretic mobilities. The average hydrodynamic diameter of PVA covered silver particles was 44 nm, being fairly independent of ionic strength and pH in the range of 3–9. It was also shown that the hydrodynamic radius did not change within prolonged storage of suspensions (up to 75 days), indicating that the sols were quite stable. A similar value of 45 ± 8 nm was determined from SEM measurements. The electrophoretic mobility measurements showed that the zeta potential of silver nanoparticles was insensitive to pH and decreased with the ionic strength, attaining −45 mV for I = 10 −5 M and −25 mV for I = 10 −2 M. Additionally, the kinetics of silver particle deposition on mica modified by adsorption of a saturated layer of poly(ethylene imine) (PEI) was studied. Surface concentration was determined directly by counting the number of particles over various surface areas using the atomic force microscopy working in the semicontact mode. The maximum surface concentration for I = 10 −3 M was 102 μm −2, which corresponds to the coverage degree of 16%. The kinetic run and the maximum coverage value was in a good agreement with theoretical predictions stemming from the random sequential adsorption (RSA) model. This kinetic run allowed one to determine the size of Ag core, which was 20 nm and the thickness of the PVA layer, equal to 12 nm.

Atomic structure of the (3 × 2) Si–GaAs (0 0 1) reconstructed surface: A clue to δ doping mechanism derived from in situ grazing incidence X-ray diffraction data

In view of understanding silicon incorporation in the δ doping process of GaAs (0 0 1), Si atoms have been deposited, under UHV, on a α(2 × 4) arsenic terminated substrate. In the low coverage regime, a transition to a less As rich (3 × 2) reconstructed Si–GaAs (0 0 1) surface was observed whose atomic structure has been investigated by grazing incidence X-ray diffraction performed in situ. Silicon is found to occupy not only a Ga substitutional site, precursor of a donor dopant but also to form nuclei for neutral clusters, on a template made by the (3 × 2) GaAs (0 0 1) reconstructed surface observed by Martrou et al. [Phys. Rev. B 72 (2005) 241307®]. The maximum surface concentration of donor-like silicon is estimated at 1.04 × 10 14 cm −2 (1/6th monolayer).

Adsorption Wave of Vanadium Complex with 2,3–Dihydroxybenzaldehyde

The polarographic behavior of the complex formed by V(V) and 2,3–dihydroxybenzaldehyde (2,3–DHBA) in the solution containing acetate buffer (pH 5,2) has been investigated. By means of a.c. polarography, chronovoltammetry and other techniques, it has been shown that the electrode process is complicated by the adsorption of 2,3-DHBA and its vanadium complex. The kinetic and adsorption parameters of the electrode process have been determined: adsorption equilibrium constant B= 1,32⋅105 mol-1⋅dm3, the attraction constant γ = 1,2, the maximum surface concentration Гmax = 9,10⋅10-11 mol⋅ cm-2; the share of the electrode surface occupied by one particle of the adsorbed complex S = 1,81 nm2 and the free adsorption energy ΔG = - 39,1 kJ· mol-1.

Perfluorinated Surfactant Chain-Length Effects on Sonochemical Kinetics

The sonochemical degradation kinetics of the aqueous perfluorochemicals (PFCs) perfluorobutanoate (PFBA), perfluorobutanesulfonate (PFBS), perfluorohexanoate (PFHA), and perfluorohexanesulfonate (PFHS) have been investigated. Surface tension measurements were used to evaluate chain-length effects on equilibrium air-water interface partitioning. The PFC air-water interface partitioning coefficients, KeqPF, and maximum surface concentrations, Gamma(max)PF, were determined from the surface pressure equation of state for PFBA, PFBS, PFHA, and PFHS. Relative KeqPF values were dependent upon chain length KeqPFHS approximately equal to 2.1KeqPFHA approximately equal to 3.9KeqPFBS approximately equal to 5.0KeqPFBA, whereas relative GammamaxPF values had minimal chain length dependence Gamma(max)PFHS approximately equal to Gamma(max)PFHA approximately equal to Gamma(max)PFBS approximately equal to 2.2Gamma(max)PFBA. The rates of sonolytic degradation were determined over a range of frequencies from 202 to 1060 kHz at dilute (<1 microM) initial PFC concentrations and are compared to previously reported results for their C8 analogs: perfluorooctanesulfonate (PFOS) and perfluorooctanoate (PFOA). Under all conditions, the time-dependent PFC sonolytic degradation was observed to follow pseudo-first-order kinetics, i.e., below kinetic saturation, suggesting bubble-water interface populations were significantly below the adsorption maximum. The PFHX (where X = A or S) sonolysis rate constant was observed to peak at an ultrasonic frequency of 358 kHz, similar to that for PFOX. In contrast, the PFBX degradation rate constants had an apparent maximum at 610 kHz. Degradation rates observed for PFHX are similar to previously determined PFOX rates, kapp,358PFOX approximately equal to kapp,358PFHX. PFOX is sonolytically pyrolyzed at the transiently cavitating bubble-water interface, suggesting that rates should be proportional to equilibrium interfacial partitioning. However, relative equilibrium air-water interfacial partitioning predicts that KeqPFOX 5KeqPFHX. This suggests that at dilute PFC concentrations, adsorption to the bubble-water interface is ultrasonically enhanced due to high-velocity radial bubble oscillations. PFC sonochemical kinetics are slower for PFBS and further diminished for PFBA as compared to longer analogs, suggesting that PFBX surface films are of lower stability due to their greater water solubility.

Altitude of atmospheric tracer transport towards Antarctica inpresent and glacial climate

The preferential altitude of transport of continental tracers towards Antarctica under present and Last Glacial Maximum (21 kyr BP) conditions is analysed using an atmospheric general circulation model with idealized tracers which are emitted at the surface of Australia and South America. It is shown that the difference between the preferential transport altitude of Australian and South American tracers is similar in glacial and interglacial climates. Australian tracers arriving in Antarctica are consistently transported at higher altitudes than tracers emitted in South America. The frequency of low-level transport is stronger at the LGM than at present, reflecting a more vigorous atmospheric circulation at the LGM as a consequence of increased baroclinicity. While the spatial patterns of the total tracer concentrations at the Antarctic surface differ for Australian and South American tracers, with the regions of maximum surface concentration being located to the south-east of the respective tracer sources, the spatial distribution of the part advected via upper atmospheric levels is very similar for the Australian and South American tracers, with a maximum over Queen Maud Land. The simulated changes in transport characteristics cannot explain observed glacial to interglacial variations of dust size spectra which have been interpreted as indicators of the relative intensity of upper and lower level atmospheric dust transport to Antarctica.

Contribution of atmospheric processes affecting the dynamics of air pollution in South-Western Europe during a typical summertime photochemical episode

Abstract. The southern Mediterranean region frequently experiences critical levels of photochemical pollutants during summertime. In order to account for the contribution of different atmospheric processes during this type of episodes, the WRF-ARW/HERMES/CMAQ modelling system was applied with high resolution (1 km2, 33 sigma vertical layers, 1 h) to assess the different dynamics in a coastal environment and an inland-continental zone: the North-Eastern and Central Iberian Peninsula (NEIP and CIP, respectively). The former is characterized by a very complex terrain, while the latter behaves as a flat area, which clearly affects the pattern of local flows. A representative type of photochemical pollution episode (occurring over 78% of summer days) which occurred during 17–18 June, 2004 is selected as the study period. The CMAQ Integrated Process Rate provides the hourly contributions of atmospheric processes to net O3, NOx and NMVOCs concentrations. The O3 photochemical formation occurs mainly in downwind areas from the main NOx emission sources during midday. At surface level it accounts for 50 to 75 μg m−3 h−1. The urban areas and main roads, as main sources of NOx emissions, act as O3 sinks, quenching up to −200 μg m−3 per hour during the traffic circulation peaks. The O3 concentration gradient generated, larger during daytime, increases the contribution of diffusion processes to ground-level O3 (up to 200 μg m−3 h−1 fluxes, mainly from upper vertical layers). The maximum positive contributions of gas-phase chemistry to O3 occur in the coastal domain at high levels (around 500 to 1500 m a.g.l.), while in the continental domain they take place in the whole atmospheric column under the PBL. The transport of ozone precursors by advective flows determines the location of the maximum O3 surface concentrations. The O3 chemical formation involves the oxidation of less NMVOCs in the NEIP than in the CIP domains, due to differences in chemical sensitivity between these areas. The dry deposition is an important sink in the lowest layer of the model, together with vertical diffusion flows. Finally, the contributions from cloud processes, wet deposition and heterogeneous chemistry are negligible during the whole episode, characterized by a high solar radiation and neither precipitation nor cloudiness. This process analysis provides new quantitative information about the origin of the peaks of O3 and its precursors, aiding the design of abatement strategies in South-Western Europe.

On the understanding of positive and negative ionization processes during ToF-SIMS depth profiling by co-sputtering with cesium and xenon

In this paper, ionization processes of secondary ions during ToF-SIMS dual beam depth profiling were studied by co-sputtering with 500 eV cesium and xenon ions and analyzing with 25 keV Ga + ions. The Cs/Xe technique consists in diluting the cesium sputtering/etching beam with xenon ions to control the cesium surface concentration during ToF-SIMS dual beam depth profiling. Several depth profiles of a H-terminated silicon wafer were performed with varying Cs beam concentration and the steady state Si, Xe and Cs surface concentrations were measured in situ by Auger electron spectroscopy. It was found that the implanted Cs surface concentration increases with the Cs fraction in the beam from 0% for the pure Xe beam to a maximum Cs surface concentration for the pure Cs beam. Secondly, the variation of the silicon work function, due to the Cs implantation, was measured in situ and during depth profiling as the shift of the secondary ion kinetic energy distributions. Finally, the positive and negative elemental ion yields generated by the Ga analysis beam were recorded and modeled with respect to varying Cs/Xe mixture. We found that the Si − and the Cs − yields increase exponentially with the decrease of the silicon’s work function while that of Cs + and Si + decrease exponentially, as expected by the electron tunneling model.

Partition and Water/Oil Adsorption of Some Surfactants

Adsorption isotherms have been determined at the water/oil interface for five biphasic systems involving surfactants (non-ionic and ionic) present in both phases at partition equilibrium. The systems studied were polyoxyethylene(23)lauryl ether (Brij35) in water/hexane and four ionic surfactants, hexadecyltrimethylammonium bromide (CTAB), and a series of three tetraalkylammonium dodecylsulfate (TEADS, TPADS, and TBADS) in water/CH 2Cl 2. Interfacial tension measurements performed at the water/air and water/oil interfaces provided all the necessary information for the determination of the adsorption parameters by taking partition into account. These measurements also allowed the comparison of the adsorption properties at both interfaces which showed an increase of the adsorption equilibrium constant and a decrease of the maximum surface concentration at the water/oil interface compared to water/air. The values of the critical aggregation concentration showed, in all cases, that only the surfactant dissolved in the aqueous phase contribute to the decrease of the water/oil interfacial tension. In the case of the four ionic surfactants, the critical aggregation concentration obtained in biphasic conditions were lowered because of the formation of mixed surfactant-CH 2Cl 2 aggregates.

Electrochemical Quartz Crystal Microbalance Study of Azurin Adsorption onto an Alkanethiol Self-Assembled Monolayer on Gold

A quartz crystal microbalance coupled with electrochemistry was used to examine the adsorption of azurin on a gold electrode modified with a self-assembled monolayer of octanethiol. Azurin adsorbed irreversibly to form a densely packed monolayer. The rate of azurin adsorption was related to the bulk concentration of azurin in solution within the concentration range studied. At a high azurin concentration (2.75 muM), adsorption was rapid with a stable adsorption maximum attained in 2-3 min. At a lower azurin solution concentration (0.35 muM), the time to reach a stable adsorption maximum was approximately 30 min. Interestingly, the maximum surface concentration attained for all solution concentrations studied by the QCM method was 25 +/- 1 pmol cm-2, close to that predicted for monolayer coverage. The dissipation was monitored during adsorption, and only small changes were detected, implying a rigid adsorption model, as needed when using the Sauerbrey equation. Cyclic voltammetric data were consistent with a one-electron, surface-confined CuII/CuI azurin process with fast electron-transfer kinetics. The electroactive surface concentration calculated using voltammetry was 7 +/- 1 pmol cm-2. The differences between the QCM and voltammetrically determined surface coverage values reflect, predominantly, the different measurement methods but imply that all surface-confined azurin is not electrochemically active on the time scale of cyclic voltammetry.

Hydrogen dissociation on oxide covered MgH 2 by catalytically active vacancies

MgH 2 is an important ingredient in modern reactive hydride composites to be used as hydrogen storage materials. The surface composition and chemical state of ball-milled MgH 2 is studied during hydrogen desorption by means of X-ray photoelectron spectroscopy. Simultaneously, the desorption rate of hydrogen is monitored, which is compared to dissociative properties of the surface investigated by hydrogen–deuterium exchange experiments. It is found that MgH 2 is also oxide covered during desorption demonstrating that MgO is able to recombine atomic hydrogen. The corresponding catalytic sites are associated with low coordinated surface vacancies on the oxide. The maximum surface concentration of these vacancies is very small, which is countered by a very high turnover frequency due to a small activation energy for dissociation of hydrogen of 0.1 eV on the single vacancy. The study provides insight into the catalytic role played by the oxide additives in MgH 2, which are superior catalysts for hydrogen sorption even when compared to 3d-metals.

Surfactant effects on thermocapillary interactions of deformable drops

A three-dimensional boundary-integral algorithm is used to study thermocapillary interactions of two deformable drops in the presence of bulk-insoluble, non-ionic surfactant. The primary effect of deformation is to slow down the rate of film drainage between drops in close approach and prevent coalescence in the absence of van der Waals forces. Both linear and non-linear models are used to describe the relationship between interfacial tension and surfactant surface concentration. In the linear model, non-monotonic behavior of the minimum separation between the drops as a function of the surface Peclet number Pe s is observed for equal drop and external medium viscosities and thermal conductivities. For bubbles with zero drop-to-medium viscosity and thermal conductivity ratios, however, the minimum separation increases with Pe s . There is a nearly linear relationship between the minimum drop separation and elasticity E. In the simplest non-linear equation of state, the product of the temperature and the surfactant concentration is retained by allowing non-zero values of the dimensionless gas constant Λ. For Λ = O ( 0.05 ) , it is possible for the smaller drop to move faster than the larger drop. In the Langmuir adsorption framework, the tendency of the smaller drop to catch up to the larger one decreases as the ratio of the equilibrium to maximum surfactant surface concentration increases. Finally, in the Frumkin model, a minimum in the drop separation occurs as a function of the interaction parameter λ F for trajectories with all other parameters held constant.

Purification, Surface Tensions, and Miscibility Gaps of Alkyldimethyl and Alkyldiethylphosphine Oxides

AbstractAlkyldimethyl (CnDMPO) with chain lengths of n = 8 (octyl), 10 (decyl), 12 (dodecyl), and 14 (tetradecyl) as well as alkyldiethyl (CnDEPO) phosphine oxides with chain lengths of n = 10, 12, and 14 were synthesized and purified to study how the adsorption properties and the location of the miscibility gap of these surfactants depend on the size of the head group and on the length of the alkyl chain. After surfactant purification, the surface tension isotherms were determined from which the cmc, the minimum surface tension σcmc, the maximum surface concentration Γmax, and the minimum surface area Amin were obtained. As expected, for one homologous series, a decrease in the cmc and an increase in Γmax was observed with increasing alkyl chain length. For two surfactants of the same alkyl chain length, the cmc values of the CnDEPO surfactants are approximately two times lower than those of the CnDMPO surfactants. However, the Γmax values of CnDEPO are lower than those of CnDMPO as two ethyl chains are sterically more demanding than two methyl chains. In addition to the adsorption properties, the location of the miscibility gap as a function of the alkyl chain length and the head group size was studied. Its location depends on the total number of carbon atoms and not primarily on the length of the main alkyl chain. This observation reflects the decreasing water solubility which can be tuned by increasing the length of either the main alkyl chain or of the shorter head group chains.

Adsorption of Alkylimidazolium and Alkylpyridinium Ionic Liquids onto Natural Soils

The mechanism of ionic liquid sorption onto selected natural soils differing in their organic content, cation exchange capacity, and particle size distribution was investigated in detail. Isotherms were employed to describe sorption. In most cases,the maximum achievable surface concentrations were well above CEC values. This observation may indicate that initially sorbed solutes modify the sorbent, a process favoring further sorption. The experimental data suggest that if a multilayer process occurs, such a mechanism will be applicable to all ionic liquids; but saturation of the second layer occurred only with the longest alkyl chain compound. The shorter alkyl chain cations did not reach saturation in the concentration range investigated here. The influence of the varying pH and ionic strength of an aquifer on sorption strength was also determined.

Electrochemically and catalytically active layer-by-layer films of myoglobin with zirconia formed by vapor-surface sol–gel deposition

Abstract A myoglobin (Mb) film was successfully assembled layer-by-layer with zirconia formed by vapor-surface sol–gel deposition on solid surfaces. The method involved vaporization of zirconium butoxide (Zr(OBu) 4 ) into thin layers of water, forming ZrO 2 sol–gel layers after hydrolysis of Zr(OBu) 4 . Mb was assembled by adsorption alternated with the ZrO 2 layers. The {ZrO 2 /Mb} n layer-by-layer films at pyrolytic graphite electrodes demonstrated a pair of well-defined and nearly reversible CV peaks at about −0.34 V vs SCE, characteristic of Mb Fe(III)/Fe(II) redox couple, and used to catalyze reduction of oxygen and hydrogen peroxide. FTIR spectroscopy and comparison studies with {ZrO 2 /catalase} n films suggest that Mb in the zirconia sol–gel films essentially retains its native structure. Compared with Mb layer-by-layer films assembled with ZrO 2 nanoparticles, {ZrO 2 /Mb} n films showed larger numbers of electroactive bilayers and higher maximum surface concentration of electroactive Mb, which may be related to the unique structure of ZrO 2 sol–gel with higher porosity.

Enzyme-encapsulated silica monolayers for rapid functionalization of a gold surface

We report a simple and rapid method for the deposition of amorphous silica onto a gold surface. The method is based on the ability of lysozyme to mediate the formation of silica nanoparticles. A monolayer of lysozyme is deposited via non-specific binding to gold. The lysozyme then mediates the self-assembled formation of a silica monolayer. The silica formation described herein occurs on a surface plasmon resonance (SPR) gold surface and is characterized by SPR spectroscopy. The silica layer significantly increases the surface area compared to the gold substrate and is directly compatible with a detection system. The maximum surface concentration of lysozyme was found to be a monolayer of 2.6 ng/mm 2 which allowed the deposition of a silica layer of a further 2 ng/mm 2. For additional surface functionalization, the silica was also demonstrated to be a suitable matrix for immobilization of biomolecules. The encapsulation of organophosphate hydrolase (OPH) was demonstrated as a model system. The silica forms at ambient conditions in a reaction that allows the encapsulation of enzymes directly during silica formation. OPH was successfully encapsulated within the silica particles and a detection limit for the substrate, paraoxon, using the surface-encapsulated enzyme was found to be 20 μM.

Comparative Permeation Study of Different Types of Myoglobin Layer‐by‐Layer Films and the Effect of Film Permeability on Their Electrochemistry and Electrocatalysis

AbstractThree different types of myoglobin (Mb) layer‐by‐layer films were assembled respectively with TiO2 sol‐gel by vapor‐surface deposition, TiO2 nanoparticles, and poly(styrenesulfonate), designated as {SG‐TiO2/Mb}n, {NP‐TiO2/Mb}n, and {PSS/Mb}n. The permeability of the films was studied and compared by rotating disk voltammetry (RDV) and electrochemical impedance spectroscopy (EIS) with different electroactive probes, showing a general permeability sequence of {SG‐TiO2/Mb}n&gt;{NP‐TiO2/Mb}n&gt;{PSS/Mb}n. The electrochemical and electrocatalytic activity of Mb in these films were also investigated and compared by cyclic voltammetry (CV), RDV, and amperometry, indicating that among the three Mb films, {SG‐TiO2/Mb}n films demonstrated the highest maximum surface concentration of electroactive Mb and the best electrocatalytic performances toward reduction of H2O2. All these advantages could be attributed to the unique architecture and porous structure of {SG‐TiO2/Mb}n films, which could greatly facilitate the mass transport of small counterions and catalytic substrates within the films. The various influencing factors on the permeability, electrochemistry, and electrocatalysis of the Mb films were also investigated in detail.

Comparative bioelectrochemical study of two types of myoglobin layer-by-layer films with alumina: Vapor-surface sol–gel deposited Al2O3 films versus Al2O3 nanoparticle films

Two types of layer-by-layer films of myoglobin (Mb) and Al2O3 were assembled on different surfaces and compared in Mb electrochemistry and bioelectrocatalysis. One type, designated as {SG-Al2O3/Mb}n, was assembled by alternate deposition of Al2O3 by vapor-surface sol–gel method from liquid aluminum butoxide and Mb by adsorption from its solution. Another type, designated as {NP-Al2O3/Mb}n, was constructed by alternate adsorption of Al2O3 nanoparticles and Mb from their dispersion or solution in the conventional layer-by-layer way. Quartz crystal microbalance (QCM), UV–vis spectroscopy, and cyclic voltammetry (CV) were used to monitor the growth of the two types of {Al2O3/Mb}n films. UV–vis and IR spectroscopy demonstrated that Mb in both types of {Al2O3/Mb}n films retained its near native structure. While both Mb films assembled on pyrolytic graphite (PG) electrodes exhibited a pair of well-defined, nearly reversible CV reduction–oxidation peaks for Mb heme Fe(III)/Fe(II) redox couple and good electrocatalytic reactivity toward reduction of oxygen and hydrogen peroxide, the {SG-Al2O3/Mb}n films demonstrated distinct advantages over the {NP-Al2O3/Mb}n films in larger maximum surface concentration of electroactive Mb and better biocatalytic performances. This may be mainly attributed to the higher porosity of {SG-Al2O3/Mb}n films than that of {NP-Al2O3/Mb}n films, which may be beneficial to counterion transport in the charge-hopping mechanism and the diffusion of catalytic substrates through the films.

Fabrication of Electroactive Layer-by-Layer Films of Myoglobin with Gold Nanoparticles of Different Sizes

Alternate adsorption of oppositely charged myoglobin (Mb) and gold nanoparticles with different sizes were used to assemble {Au/Mb}n layer-by-layer films on solid surfaces by electrostatic interaction between them. The direct electrochemistry of Mb was realized in {Au/Mb}n films at pyrolytic graphite (PG) electrodes, showing a pair of well-defined, nearly reversible cyclic voltammetry (CV) peaks for the Mb heme FeIII/FeII redox couple. Quartz crystal microbalance (QCM), electrochemical impedance spectroscopy (EIS), and CV were used to monitor or confirm the growth of the films. Compared with other Mb layer-by-layer films with nonconductive nanoparticles or polyions, {Au/Mb}n films showed much improved properties, such as smaller electron-transfer resistance (Rct) measured by EIS with Fe(CN)3-/4- redox probe, higher maximum surface concentration of electroactive Mb (Gamma*max), and better electrocatalytic activity toward reduction of O2 and H2O2, mainly because of the good conductivity of Au nanoparticles. Because of the high biocompatibility of Au nanoparticles, adsorbed Mb in the films retained its near native structure and biocatalytic activity. The size effect of Au nanoparticles on the electrochemical and electrocatalytic activity of Mb in {Au/Mb}n films was investigated, demonstrating that the {Au/Mb}n films assembled with smaller-sized Au nanoparticles have smaller Rct, higher Gamma*max, and better biocatalytic reactivity than those with larger size.

A simple modeling approach to study the regional impact of a Mediterranean forest isoprene emission on anthropogenic plumes

Abstract. Research during the past decades has outlined the importance of biogenic isoprene emission in tropospheric chemistry and regional ozone photo-oxidant pollution. The first part of this article focuses on the development and validation of a simple biogenic emission scheme designed for regional studies. Experimental data sets relative to Boreal, Tropical, Temperate and Mediterranean ecosystems are used to estimate the robustness of the scheme at the canopy scale, and over contrasted climatic and ecological conditions. A good agreement is generally found when comparing field measurements and simulated emission fluxes, encouraging us to consider the model suitable for regional application. Limitations of the scheme are nevertheless outlined as well as further on-going improvements. In the second part of the article, the emission scheme is used on line in the broader context of a meso-scale atmospheric chemistry model. Dynamically idealized simulations are carried out to study the chemical interactions of pollutant plumes with realistic isoprene emissions coming from a Mediterranean oak forest. Two types of anthropogenic sources, respectively representative of the Marseille (urban) and Martigues (industrial) French Mediterranean sites, and both characterized by different VOC/NOx are considered. For the Marseille scenario, the impact of biogenic emission on ozone production is larger when the forest is situated in a sub-urban configuration (i.e. downwind distance TOWN-FOREST &lt;30km, considering an advection velocity of 4.2 m.s-1). In this case the enhancement of ozone production due to isoprene can reach +37% in term of maximum surface concentrations and +11% in term of total ozone production. The impact of biogenic emission decreases quite rapidly when the TOWN-FOREST distance increases. For the Martigues scenario, the biogenic impact on the plume is significant up to TOWN-FOREST distance of 90km where the ozone maximum surface concentration enhancement can still reach +30%. For both cases, the importance of the VOC/NOx ratio in the anthropogenic plume and its evolution when interacting with the forest emission are outlined. In complement to real case studies, this idealized approach can be particularly useful for process and sensitivity studies and constitutes a valuable tool to build regional ozone control strategies.