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Electroreflectance spectroscopy in the visible and near-UV has been employed to study the influence of adsorbed pyridine on the surface reconstruction and the optical properties of Au(100). The pyridine-induced structural transition of the Au(100) electrode from a reconstructed (5 × 20) to an unreconstructed (1 × 1) surface has been monitored optically for various pyridine concentrations. It has been found that this surface structural transition coincides with a phase transition in the pyridine adlayer, which corresponds to a reorientation of the molecule from a flat π-bonded to a vertical N-bonded surface coordination. Pyridine adsorbs flat lying on the reconstructed surface, which is stable at negative surface charges, while on the unreconstructed, more open surface at positive charges the pyridine molecules assume a vertical, N-bonded position. Optical transitions involving surface states which display a strong dependence on the electrode potential (charge density) due to a Stark shift, were studied in the absence and presence of pyridine. Adsorption of pyridine causes a broadening and a gradual decrease of the surface state spectral features which suggests that the surface states undergo an adsorbate-induced level broadening, but are not quenched completely.

The role of the steric factors in the electrode reactions occurring on the interface covered by aliphatic alcohols and acids has been investigated, taking as an example the Cd 2+ /Cd(Hg) system. It has been shown that this process takes place inside the inner layer and the activated complex is created by the replacement of r ≠ water molecules from the surface. From studies carried out at surfactant concentrations corresponding to the plateau of the adsorption isotherm the steric factors r ≠ / r i have been determined ( r i is the number of solvent molecules replaced from the surface by one molecule of adsorbed surfactant). By comparison with investigations performed at lower coverages the magnitude of r ≠ and r i has been estimated. The influence of different factors on the experimental value of these parameters has been discussed.

The energetics of adsorption of tert-amyl alcohol (t-AA) onto a gold (100) single crystal electrode surface have been characterized quantitatively using chronocoulometry. The adsorption parameters were obtained from measurements of the charge density at the electrode surface. The precision of these measurements shows a marked improvement over previous results. Film and surface pressures, relative Gibbs surface excesses, Gibbs energies of adsorption, effective dipole moments and electrosorption valencies were determined as functions of the electrode potential and the surface charge density. The maximum surface excess obtained for this system is equal to 4.4 × 10 −10 mol cm −2 and the Gibbs energy is equal to − 17.4 kJ mol −1 at the potential of maximum adsorption (approximately 0.15 V(SCE)). These values are very close to those obtained for the adsorption of t-AA on the mercury electrode. Similarities and differences between the adsorption of t-AA at gold and mercury electrodes are discussed in detail.

Chronocoulometry recorded during the first 100 ms of double layer charging has been used to study the physical adsorption of neutral organic molecules on solid electrodes. The adsorption of cyclohexanol on gold is used to illustrate the method. The film pressure and the Gibbs surface excess for this system are determined as functions of potential from charge densities obtained by the analysis of the potentiostatic transients. Charge densities determined by chronocoulometry are compared with results obtained from the integration of differential capacities, which were independently measured at 25 Hz. Film pressures determined from these differential capacity measurements are shown to be unrealistically low and inconsistent with changes in bulk cyclohexanol concentration. In contrast, chronocoulometry gives consistent results and allows the determination of results that are comparable to those obtained on mercury.

The kinetics of homogeneous and heterogeneous electron exchange V 3+ /V 2+ was investigated in 1 M HClO 4 , water + t -butanol, mixed solvent solutions ( x t -but . varied from 0 to 0.65). Non-monotonic heterogeneous and monotonic homogeneous variations of the rate constants were observed. The solvent effect on the work of bringing the reactants from infinite separation to the reaction site was estimated with the Gouy-Chapman and Debye-Huckel approximations respectively. The homogeneous kinetics data were next used to calculate the reorganization energy in the heterogeneous reaction, λ het . Finally the influence of the solvent composition on the rate of the electrode reaction was separated into surface and bulk effects.

Etudes par chronocoulometrie de la physisorption de l'alcool tert-amylique sur la face (110) d'un monocristal d'or. La quantite de tensioactif adsorbe est determinee a partir de la densite de charge de l'electrode

The kinetics of deposition of Cu 2+ ion on the mercury electrode covered by monolayers of normal aliphatic alcohols containing from four to eight carbon atoms in the molecule were investigated. The relations between the film pressure or the bulk surfactant concentration and the rate of the electrode reaction were examined. The cross-sectional area of Cu 2+ ion transported through the monolayers was determined, and the magnitude of the lateral interactions between Cu 2+ ion and neighbouring water and alcohol molecules respectively, at the surfactant-free and surfactant-covered electrode surface, was estimated.

Chronocoulometry has been used in order to characterize quantitatively the energetics of pyridine adsorption onto a gold (100) single crystal electrode surface. Over the potential region investigated (−0.8 to+0.6 V), three orientations of the pyridine molecules on the gold surface have been observed. The pyridine orientation is influenced strongly by the electrode potential. At a positively charged surface, the pyridine assumes a vertical orientation with the nitrogen atom facing the gold surface. A limiting surface concentration corresponding to 6 × 10−10 mol cm−2 was determined for the vertical orientation. At a negatively charged surface and at low surface concentrations (Γ Γ > 1 × 10−10 mol cm−2) and for potentials close to zero charge, a third orientation, presumably intermediate between the flat and the vertical orientations, was observed. Reorientation from the intermediate to the vertical orientation takes the form of a phase transition. The potential of the phase transition coincides approximately with the potential of zero charge. The Gibbs energies of adsorption, electrosorption valencies, potentials and charges of the maximum adsorption were determined for the flat and the vertical orientation of pyridine. Adsorption of pyridine on the Au (100) surface is compared with the adsorption at polycrystalline Au and mercury electrodes.

The kinetics of Ni2+ deposition at the mercury electrode, from non-complexing electrolytes in mixed water methanol solvents has been investigated. The rate of this reaction, in the whole composition range, at large overpotentials is controlled by a limiting “chemical” process. The rate constants of the limiting process when plotted as a function of the solvent composition display a relationship similar to those observed for the large organic, bidendate ligands substitution reactions, believed to the controlled by the Ni(II)-solvent bond rupture. Hence, the limiting “chemical” process in Ni2+ discharge can be identified as the slow solvent dissociation step. These results confirm the mechanism of Ni2+ dischrage already proposed by Gierst and Dandoy on the basis of investigations performed in aqueous solutions.

Summary The discussion of the present state of understanding of the inhibition of electrode reactions by adsorbed organic compounds has been presented. It has been shown that the different models of the mechanism of inhibition may be reduced to the concept of competitive adsorption of activated complex, solvent and inhibitor molecules with different adsorption isotherms taken to describe adsorption of activated complex. On the basis of a statistical analysis of the literature data it has been shown that the inhibition may be well described by three different model equations originated from Flory-Huggins, Frumkin or Blomgren-Bockris adsorption isotherms for activated complex. Because of marked experimental errors both for the determination of the rate constant of the electrode process and the surface coverages of the electrode by the inhibitor, as well as a result of the impossibility or the proper correction of the rate constants for double layer effect it has been proved that the choice of the model of inhibition is not an ambiguous procedure if the measurements are carried out in the range of surface coverages 0

The adsorption of 3-methyl-isoquinoline at the mercury-water interface involves a number of rate-determining factors (local depletion uncompensated by mass transfer, influence of the diffuse-layer potential, slow kinetics) which has limited the present study to the most concentrated solutions. In that range, the major traits of the behaviour of 3-MeisoQ and isoQ are comparable at least qualitatively (rearrangement and desorption transitions, condensed layers, existence of a quasi-solid two-dimensional structure of invariant properties at negative potentials). Differences result from the steric hindrance of the methyl group on all adsorption modes, except that which involves the perpendicular-high orientation (with nitrogen and the methyl group facing the solution side of the interface). It appears that, as is the case for aliphatic alcohols or acids among others, meaningful comparison must be based on relative concentrations normalized with respect to the saturation value. The dependence of the rearrangement transition potential on surfactant concentration and ionic strength indicates that the inner potential difference is the most suitable independent variable.

The adsorption of 1,6-hexanediol at the Hg—aqueous solution interface was investigated. The differential capacity, interfacial tension and the zero charge potential were measured. Analysis of the results were carried out both at constant charge and at constant potential. Good congruence with respect to the potential and noncongruence with respect to the charge was found. It was shown that the hexanediol molecules orientate flat against the surface and the adsorption could be described equally well by the Frumkin or Flory—Huggins isotherms. Adsorption parameters for the hexanediol were compared with the literature data on adsorption of ethanediol and 1,4-butanediol. It was concluded that adsorption of diols does not affect the thickness of the inner layer. Thus, this adsorption is well described by the model of two parallel capacitors.

The adsoption of hydrogen and the kinetics of the hydrogen evolution reaction (HER) on the vitreous Pt 77 Si 23 alloy have been investigated. Five differently treated samples of the alloy have been studied and their electrocatalytic activities have been compared with those of pure polycrystalline Pt

The mechanism of Cd2+ discharge and cadmium amalgam dissolution in the absence and presence of organic neutral surfactants is compared. The generality of the stepwise mechanism of this reaction occurring on Hg electrode both covered and non-covered by the surfactants is shown. The reliability of the existence of Cd+ as an intermediate in the electrode reaction is discussed.

Summary The electrode kinetics of electroreduction of vanadium(III), cadmium(II), plumbite ion, Mn(NH3)x2+ and nitrobenzene free radical as well as oxidation of the manganese amalgam has been studied at mercury electrodes in a mixture of water with propanol, isopropanol and tert-butanol. With the exception of manganese(II) electroreduction the standard rate constants for other systems at first largely decrease with the increase of the organic component concentration and later slowly increase when the content of alcohol in the mixture increases. These changes of the rate constants were qualitatively explained. The influence of the couble-layer structure on the electrode kinetics in such systems was also studied. The measured formal potentials were compared with those calculated on the basis of the modified Born equation and the differences were explained in terms of selective hydration of ions and liquid junction potential.

With the use of the thermodynamics of the surface phase the distinction between inhibitive properties of the equilibrium and non-equilibrium surfactant adsorption on energetically uniform and non-uniform surface is shown. It was pointed out that these properties additionally depend on the position of the reactant inside or outside the adsorbed layer. The respective equations are derived. On the basis of thermodynamic arguments the critical reassessment of the present understanding of the inhibition phenomena is performed. The possibility of the appearance of a limiting rate at higher coverages of the electrode by surfactant is discussed.

Coadsorption of perchlorate ions and 3-methyl-isoquinoline molecules at the mercury—aqueous solution interface results in the formation of a condensed film. The process of ClO − 4 incorporation (or removal) is very slow. Characteristic relaxation times (about 10 −2 s) are several orders of magnitude larger than values typical of ion adsorption at a mercury—solution interface which is free from organic surfactant. The relationships between the rate of the process, the electrode potential and the amount of adsorbed ClO − 4 ions are determined and discussed. The results indicate that the rate of the overall process is controlled by a slow adsorption (or desorption) step whose kinetics are consonant with an isotherm of the Temkin type.

Chronocoulometry has been employed in order to investigate quantitatively the adsorption of pyridine from aqueous solution onto a polycrystalline gold electrode. It was found that at a negatively charged surface, pyridine adsorbs in the flat orientation, reaching a limiting surface concentration of 3 × 10 −10 mol cm −2 . Under the influence of the electric field pyridine reorients so that on the positively-charged surface the pyridine molecules assume the vertical orientation, presumably with the nitrogen facing the gold surface. A limiting surface concentration of 7 × 10 −10 mol cm −2 is reached in the vertical orientation. The standard Gibbs energy of adsorption was found to reach fairly large values (−38 kJ mol −1 ). The electrosorption valency was also determined and found to be −0.6 indicating that a partial charge transfer is involved in the pyridine adsorption.

A general discussion of lead UPD on gold faces is given. The electrosorption valency is determined by a simple experimental method. The effect of reconstruction of the substrate is discussed for the (100) gold face. Understanding of the cyclic voltammograms is achieved thanks to the comparison with the results obtained in UHV. Observation of the UPD region gives the energy spectrum of the faces.

The inhibitory effect of three homologous dialkyl-phenyl-phosphine oxides (C 6 H 5 (R) 2 ) PO; R=C 2 H 5 , C 3 H 7 , C 4 H 9 ) and trialkyl-phosphine oxides (R 1 (R 2 ) 2 PO, R 1 =C 5 H 11 , C 6 H 13 ; R 2 =CH 3 , C 2 H 5 ) on the Cu 2+ discharge reaction, at a fully covered dropping mercury electrode has been investigated by the polarographic technique. The rate of this electrode reaction has been correlated with the film pressure π. In contrast to what was observed at the electrode covered by the film of aliphatic alcohols [18], no linear relationship between π and the logarithm of the reaction rate has been found. In fact, at low film pressures the rate depends on π, but at higher π it attains, or tends to attain, a limiting value independent of π. To explain the differences in the mechanism of Cu 2+ discharge at the electrode surface covered by the films of aliphatic alcohols and phosphine oxides, a reaction channel in which the activated complex is created by a surface reaction between adsorbed reactant and surfactant has been considered. The equation describing the rate of a reaction following this channel has been derived. It has been shown that an equation described previously by Guidelli and Foresti [14] can be considered as a particular case of this relation.

The kinetics of homogeneous and electrochemical electron exchange between V 3+ and V 2+ was investigated in water + dimethylformaldehyde (DMF) mixed solvents (the mole fraction of DMF varied from 0 to 0.58). A good correlation between the rates of homogeneous and electrochemical reactions, as predicted by the Marcus theory, was found. Non-monotonic variations of the electron exchange rate constants as a function of the solvent composition were observed. For the homogeneous reaction the work of bringing the reactants from infinite separation to the reaction site was evaluated. The outer shell reorganization energy was calculated from the continuum model. The composition of the inner solvation shell was determined from spectrophotometric experiments. Results indicate that variations of the reaction rate with the solvent composition cannot be explained if the continuum model for the solvent is used. It is suggested that changes in hydrogen bonding in the outer solvation shell contribute to the activation energy of electron exchange.

The kinetics of reduction of Co(NH3)3+6, CrO2-4, S2O2-8 and O2 at a Hg electrode coated with monolayers of quinoline, iso-quinoline and 3-methyl-iso-quinoline have been investigated. The mechanism of electron transfer at the film-covered electrode depends on the structure of the superficial film. At a liquid-like film, the reacting ions are discharged both from inside and outside the film. Within the potential range where sold-like films are observed, it has been found that: (1) the rate of ETR reactions is slowed down by 6–7 orders of magnitude; (2) the decelerating effect of the film is distributed equally between changes in the probability of the electron transition and the energy of activation of ETR; (3) the logarithm of the reaction rate decreases linearly with the film thickness; (4) Tafel plots are linear and their slopes are slightly smaller than those observed for the bare electrode surface; and (5) the electronic transitions are probably elastic in character although distinction between elastic and resonance tunnelling is difficult for thin films.

The adsorption of pyridine at an Ag (110) single crystal electrode has been studied. In the range of potentials explored, adsorption, maximum coverage of the surface and the beginning of desorption are observed. At potentials close to the potential of zero charge the pyridine molecules assume a tilted orientation with the nitrogen atom facing the metal. The adsorption isotherms have been determined for the first time for a silver face.

Summary The effect of specific solvation of electrode and depolarizer by different constituents of mixed water-alcohol solvents on electrode kinetics was investigated for the case of the Mn 2+ /Mn/Hg system. By adding the complexing agent NH 3 , the cathodic process was shifted to the potential region where alcohols are desorbed from the electrode surface. Then the ions of depolarizer and the electrode surface are specifically solvated by water. The opposite condition of preferential solvation of the electrode surface by alcohol, and manganese ions by water, was realized during anodic dissolution of Mn(Hg) x . Little change in the cathodic rate constants and about 1 to 1.5 order of magnitude decrease in the speed of the anodic reaction by transfer from water to 8.1% alcohol demonstrated the importance of respective specific solvation as the main factor influencing charge transfer rate constant in mixed solvents. From potentiometric experiments stability constants for Mn(NH 3 ) x 2+ complexes were determined and average coordination numbers and complexes distribution as a function of ligand concentration presented. The detailed mechanism of the Mn 2+ discharge in presence of NH 3 was discussed.

Electrochemistry and polarization modulation Fourier transform infrared reflection absorption spectroscopy (PM-FTIRRAS) was employed to investigate fusion of small unilamellar vesicles of 1,2dioyl-sn-glycero-3-phosphatidyl choline (DOPC) onto the Au(111) electrode. Electrochemical studies demonstrated that the DOPC vesicles fuse and spread onto the gold electrode surface at small charge densities -8 microC cm(-2)sigmaM0 microC cm(-2)(if the static electric field is2 x 10(8) V/m) to form a bilayer. At sigmaM-8 microC cm(-2), the film is detached from the electrode surface; however, the film remains in close proximity to the surface. The PM-FTIRRAS experiments demonstrated that the field-driven transformation of the film involves changes in hydration, orientation, and conformation in the polar headgroup region and that changes in the packing and tilt of the acyl chains are consequences of the headgroup rearrangements.

Charge density measurements and polarization modulation infrared reflection absorption spectroscopy were employed to investigate the spreading of small unilamellar vesicles of a dimyristoylphosphatidylcholine (DMPC)/cholesterol (7:3 molar ratio) mixture onto an Au (111) electrode surface. The electrochemical experiments demonstrated that vesicles fuse and spread onto the Au (111) electrode surface, forming a bilayer, at rational potentials −0.4 V

Amyloid β, Aβ(1-42), is a component of senile plaques present in the brain of Alzheimer's disease patients and one of the main suspects responsible for pathological consequences of the disease. Herein, we directly visualize the Aβ activity toward a brain-like model membrane and demonstrate that this activity strongly depends on the Aβ oligomer size. PeakForce quantitative nanomechanical mapping mode of atomic force microscopy imaging revealed that the interaction of large-size (LS) Aβ oligomers, corresponding to high-molecular-weight Aβ oligomers, with the brain total lipid extract (BTLE) membrane resulted in accelerated Aβ fibrillogenesis on the membrane surface. Importantly, the fibrillogenesis did not affect integrity of the membrane. In contrast, small-size (SS) Aβ oligomers, corresponding to low-molecular-weight Aβ oligomers, created pores and then disintegrated the BTLE membrane. Both forms of the Aβ oligomers changed nanomechanical properties of the membrane by decreasing its Young's modulus by ∼45%. Our results demonstrated that both forms of Aβ oligomers induce the neurotoxic effect on the brain cells but their action toward the membrane differs significantly.

Disruption of the neuronal membrane by toxic amyloid β oligomers is hypothesized to be the major event associated with Alzheimer's disease's neurotoxicity. Misfolding of amyloid β is followed by aggregation via different pathways in which structurally different amyloid β oligomers can be formed. The respective toxic actions of these structurally diverse oligomers can vary significantly. Linking a particular toxic action to a structurally unique kind of amyloid β oligomers and resolving their toxicity-determining feature remains challenging because of their transient stability and heterogeneity. Moreover, the lipids that make up the membrane affect amyloid β oligomers' behavior, thus adding to the problem's complexity. The present review compares and analyzes the latest results to improve understanding of amyloid β oligomers' interaction with lipid bilayers.

This document is the Accepted Manuscript version of a Published Work that appeared in final form in Langmuir, copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see https://doi.org/10.1021/acs.langmuir.5b04052 A phospholipid bilayer composed of 1,2-dimyristoyl-d54-sn-glycero-3-phosphocholine (d54-DMPC) was deposited onto the Au(111) electrode modified with a self-assembled monolayer of 1-thio-β-d-glucose (β-Tg) via the Langmuir–Blodgett and Langmuir–Schaefer (LB-LS) techniques. Polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS) measurements were used to characterize structural and orientational changes in this model biological membrane on a hydrophilic surface modified gold electrode. The results of the spectroscopic measurements showed that the tilt angle of acyl chains obtained for deuterated DMPC bilayers supported on the β-Tg-modified gold is significantly lower than that reported previously for DMPC bilayers deposited directly on Au(111) electrodes. Moreover, tilt angles of ∼18° were obtained for d54-DMPC bilayers on β-Tg self-assembled monolayers (SAMs) at positive potentials, which are similar to the values calculated for h-DMPC deposited on bare gold in the desorbed state and to those observed for a stack of hydrated DMPC bilayers. This data confirms that the β-thioglucose SAM promotes the formation of a water cushion that separates the phospholipid bilayer from the metal surface. As a result, the DMPC polar heads are not in direct contact with the electrode and can adopt a zigzag configuration, which strengthens the chain–chain interactions and allows for an overall decrease in the tilt of the acyl chains. These novel supported model membranes may be especially useful in studies pertaining to the incorporation of peptides and proteins into phospholipid bilayers. Sinergia project no. CRSII2_154451/⁠1 financed by the Swiss National Science Foundation and Discovery grant from the Natural Sciences and Engineering Research Council of Canada

Cellulose, a biopolymer consisting of long chains of β (1→4) linked glucose sugars, is used as structural material by plants, bacteria, and some animals, and is the most abundant polymer on earth. Degradation of cellulose to glucose, a sugar easily fermented to ethanol, occurs by the enzymatic hydrolysis of cellulose by cellulase enzymes. The enzymes have a complex structure including carbohydrate binding modules responsible for binding the enzyme to the cellulose and catalytic domains responsible for the biodegradation of cellulose. Atomic force microscopy (AFM) was used to study native cellulose films prepared from a bacterial cellulose source, Acetobacter xylinum, using a novel application of the Langmuir-Blodgett technique. These films allowed high resolution AFM images of single fibers and their microfibril structure to be obtained. Further in situ AFM imaging studies of single cellulose fibers were performed in solution using cellulolytic enzymes. By using genetically modified enzymes with either active or inactive catalytic domains, the catalytic and binding properties of the enzyme-cellulose system can be independently investigated. Studying the modular enzyme action separately will provide insight into the mechanism of cellulose binding and contribute to our understanding of the biodegradation process.