Increase In Surface Concentration Research Articles

Grafting of antibacterial polymers on stainless steel via surface‐initiated atom transfer radical polymerization for inhibiting biocorrosion by Desulfovibrio desulfuricans

To enhance the biocorrosion resistance of stainless steel (SS) and to impart its surface with bactericidal function for inhibiting bacterial adhesion and biofilm formation, well-defined functional polymer brushes were grafted via surface-initiated atom transfer radical polymerization (ATRP) from SS substrates. The trichlorosilane coupling agent, containing the alkyl halide ATRP initiator, was first immobilized on the hydroxylated SS (SS-OH) substrates for surface-initiated ATRP of (2-dimethylamino)ethyl methacrylate (DMAEMA). The tertiary amino groups of covalently immobilized DMAEMA polymer or P(DMAEMA), brushes on the SS substrates were quaternized with benzyl halide to produce the biocidal functionality. Alternatively, covalent coupling of viologen moieties to the tertiary amino groups of P(DMAEMA) brushes on the SS surface resulted in an increase in surface concentration of quaternary ammonium groups, accompanied by substantially enhanced antibacterial and anticorrosion capabilities against Desulfovibrio desulfuricans in anaerobic seawater, as revealed by antibacterial assay and electrochemical studies. With the inherent advantages of high corrosion resistance of SS, and the good antibacterial and anticorrosion capabilities of the viologen-quaternized P(DMAEMA) brushes, the functionalized SS is potentially useful in harsh seawater environments and for desalination plants.

Phage M13KO7 detection with biosensor based on imaging ellipsometry and AFM microscopic confirmation

A rapid detection and identification of pathogens is important for minimizing transfer and spread of disease. A label-free and multiplex biosensor based on imaging ellipsometry (BIE) had been developed for the detection of phage M13KO7. The surface of silicon wafer is modified with aldehyde, and proteins can be patterned homogeneously and simultaneously on the surface of silicon wafer in an array format by a microfluidic system. Avidin is immobilized on the surface for biotin-anti-M13 immobilization by means of interaction between avidin and biotin, which will serve as ligand against phage M13KO7. Phages M13KO7 are specifically captured by the ligand when phage M13KO7 solution passes over the surface, resulting in a significant increase of mass surface concentration of the anti-M13 binding phage M13KO7 layer, which could be detected by imaging ellipsometry with a sensitivity of 10 9 pfu/ml. Moreover, atomic force microscopy is also used to confirm the fact that phage M13KO7 has been directly captured by ligands on the surface. It indicates that BIE is competent for direct detection of phage M13KO7 and has potential in the field of virus detection.

Conformational Flexibility of the N-Terminal Domain of Apolipoprotein A-I Bound to Spherical Lipid Particles

Lipid binding of human apolipoprotein A-I (apoA-I) occurs initially through the C-terminal alpha-helices followed by conformational reorganization of the N-terminal helix bundle. This led us to hypothesize that apoA-I has multiple lipid-bound conformations, in which the N-terminal helix bundle adopts either open or closed conformations anchored by the C-terminal domain. To investigate such possible conformations of apoA-I at the surface of a spherical lipid particle, site-specific labeling of the N- and C-terminal helices in apoA-I by N-(1-pyrene)maleimide was employed after substitution of a Cys residue for Val-53 or Phe-229. Neither mutagenesis nor the pyrene labeling caused discernible changes in the lipid-free structure and lipid interaction of apoA-I. Taking advantage of a significant increase in fluorescence when a pyrene-labeled helix is in contact with the lipid surface, we monitored the behaviors of the N- and C-terminal helices upon binding of apoA-I to egg PC small unilamellar vesicles. Comparison of the binding isotherms for pyrene-labeled apoA-I as well as a C-terminal helical peptide suggests that an increase in surface concentration of apoA-I causes dissociation of the N-terminal helix from the surface leaving the C-terminal helix attached. Consistent with this, isothermal titration calorimetry measurements showed that the enthalpy of apoA-I binding to the lipid surface under near saturated conditions is much less exothermic than that for binding at a low surface concentration, indicating the N-terminal helix bundle is out of contact with lipid at high apoA-I surface concentrations. Interestingly, the presence of cholesterol significantly induces the open conformation of the helix bundle. These results provide insight into the multiple lipid-bound conformations that the N-terminal helix bundle of apoA-I can adopt on a lipid or lipoprotein particle, depending upon the availability of space on the surface and the surface composition.

Selective oxidation of carbon monoxide over CuO–CeO2 catalyst: Effect of hydrothermal treatment

Copper oxide–ceria (CuO–CeO2) catalyst for selective oxidation of carbon monoxide (CO) was prepared by co-precipitation and hydrothermal treatment methods and evaluated for catalytic activity in a reformate gas composition which simulated the produced gas from methanol steam reforming. By applying the condition of hydrothermal treatment, the catalytic activity of CuO–CeO2 catalyst was increased and the operating temperature window, in which the concentration of carbon monoxide was lower than 10ppm, was widened. From the thermogravimetric (TG) results of hydrothermally treated catalyst precursor, CuO–CeO2 catalyst did not show any improvement in physical properties such as Brunauer Emmett Teller (BET) surface area, pore volume and average pore diameter, but the chemical stability might be enhanced by hydrothermal treatment. By hydrothermal treatment, cuprous ion in the CuO–CeO2 catalyst migrated to the surface of catalyst resulting in increased surface concentration of copper and formation of cupric oxide on the surface of catalyst during calcination. While increasing the calcination temperature (i.e. above 800°C), the phase separation occurred with a part of copper and cupric oxide was formed on the surface of catalyst which was observed in X-ray diffraction (XRD) analysis.

Excitation Energy Transfer and Trapping in Dye‐Loaded Solid Particles

The photophysics of several systems composed of a single dye or pairs of dyes attached to solid particles has been studied in the dry solid state at high dye concentrations taking into account light scattering and inner filter effects. Interaction among dye molecules and singlet-singlet energy transfer are relevant in these conditions, as has been demonstrated for pairs of dyes with suitable spectral overlap. For single dyes, after correction for radiative energy transfer, fluorescence quenching is observed as the surface concentration increases. This effect is explained by two different trapping models. Irrespective of the nature of the traps, concentration quenching may be of static (trap absorption) and dynamic (energy transfer) nature. The unraveling of energy trapping mechanisms is a key to the development of efficient photoactive solid materials.

Co-decorated carbon nanotubes as a promoter of Co–Mo–K oxide catalyst for synthesis of higher alcohols from syngas

Abstract A metal cobalt-decorated multi-walled carbon nanotube (MWCNT)-promoted Co–Mo–K oxide-based catalyst was developed, with excellent performance for the selective formation of C 2–9 -alcohols from syngas. Under reaction condition of 5.0 MPa and 593 K, the space–time-yield of C 2–9 -alcohols reached 628 mg/(g h) over the Co 1 Mo 1 K 0.05 –12%(4.2% Co/MWCNT) catalyst. The addition of a minor amount of the Co-decorated MWCNTs into the Co 1 Mo 1 K 0.05 host catalyst caused little change in the apparent activation energy for the higher alcohol synthesis (HAS), but led to an increase of surface concentration of the two kinds of catalytically active species, CoO(OH)/Co 3 O 4 and Mo 4+ , both closely associated with the alcohol generation. Addition of 5% CO 2 in the feed gas at properly elevated reaction temperature (593 K) could further enhance the surface concentration of those active Mo and Co species. An excellent adsorption performance of the Co-decorated MWCNTs as promoter for H 2 would be conducive to generating a surface micro-environment with a high concentration of H-adspecies on the functioning catalyst, thus increasing the rate of surface hydrogenation reactions in the HAS. In addition, high concentration of H-adspecies on the catalyst would, through synergistic action with the CO 2 in the feed gas, greatly inhibit the water–gas-shift side-reaction. All these factors contribute to an increase in the yield of alcohols.

Fluoride effects on ectopic bone formation in young and old rats

This study evaluated the effect of fluoride on bone fluoride levels and on ectopic bone formation in young and old rats. Eighty male Wistar rats were assigned to four groups (n = 20/g), which differed according to the fluoride concentration in their drinking water (0, 5, 15 and 50 mg/l). When half of the rats were 90 days old, demineralized bone matrix (DBM) was implanted. The other rats received DBM implants when they were 365 days old. The animals were killed 28 days after. Fluoride in the femur surface, whole femur and plasma was analyzed with an electrode. The implants were analyzed histomorphometrically. Data were tested for statistically significant differences by ANOVA, Tukey's test, t-test and linear regression (p < 0.05). Increases in plasma, femur surface and whole femur fluoride concentrations were observed as water fluoride levels increased. There was also a trend for increase in plasma and femur fluoride concentrations as age increased. Significant positive correlations were found between plasma and femur surface, plasma and femur and femur surface and femur fluoride concentrations. The morphometric analyses indicated an increase in bone formation for younger rats that received 5 mg/l of fluoride in the drinking water. However, this was not statistically significant. The younger rats that received 50 mg/l of fluoride showed impairment in bone formation. Bone formation was not significantly affected among the older rats. The results suggest that lower doses of fluoride in the drinking water, which slightly increase plasma fluoride levels, may have an anabolic effect on bone formation in younger rats.

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.

Fluorescence Correlation Spectroscopy at the Oil−Water Interface: Hard Disk Diffusion Behavior in Dilute β-Lactoglobulin Layers Precedes Monolayer Formation

We have performed a thorough characterization of fluorescence correlations spectroscopy (FCS) applied to oil-water interfaces of viscous oil droplets in aqueous solution, including numerical wave-optical calculations of the detection geometry and regularized multicomponent analysis of sample data. It is shown how significant errors in the estimation of the surface concentration can be avoided when FCS is applied to an interface region. We present data on the adsorption dynamics of beta-lactoglobulin (BLG), a well-studied model system. It is found that electrostatic repulsion slows the adsorption process and reduces the initial saturation density far below the monolayer concentration. During the first stages of adsorption, the diffusion coefficients of adsorbed protein closely follow the 2D hard disk model of Lahtinen et al.1 in response to increased surface concentration, which suggests that protein-protein interactions are limited to long-range Coulombic interactions at this stage.

Adsorption of Octyl Cyanide at the Free Water Surface as Studied by Monte Carlo Simulation

Monte Carlo simulations of the adsorption layer of octyl cyanide have been performed on the canonical (N, V, T) ensemble at 300 K. The systems simulated cover the range of octyl cyanide surface densities from 0.27 to 7.83 mumol/m2. The surface density value at which the saturation of the adsorption layer occurs is estimated to be 1.7 mumol/m2. At low surface densities, the main driving force of the adsorption is found to be the formation of hydrogen bonds between the water and octyl cyanide molecules, whereas at higher surface concentrations, the dipole-dipole attraction between the neighboring adsorbed octyl cyanide molecules becomes more important. At low surface concentrations, the water-octyl cyanide hydrogen bonds prefer tilted alignments relative to the interface; however, in the case of the saturated adsorption layer, the number of such hydrogen bonds is maximized, leading to the preference of these bonds for the orientation perpendicular to the interface. Contrary to nonionic surfactants of multiple hydrogen bonding abilities (e.g., 1-octanol, C8E3), the increasing surface concentration of octyl cyanide was not found to lead to considerable competition of the molecules for positions of optimal arrangement. As a consequence, the energy and geometry of the water-octyl cyanide hydrogen bonds are found to be insensitive to the octyl cyanide surface concentration.

Counterion and Surface Density Dependence of the Adsorption Layer of Ionic Surfactants at the Vapor−Aqueous Solution Interface: A Computer Simulation Study

To test the validity of currently used adsorption theories and understand the origin of the lack of their ability of adequately describing existing surface tension measurement data, we have performed a series of molecular dynamics simulations of the adsorption layer of alkali decyl sulfate at the vapor/aqueous solution interface. The simulations have been performed with five different cations (i.e., Li+, Na+, K+, Rb+, and Cs+) at two different surface concentrations (i.e., 2 micromol/m2 and 4 micromol/m2). The obtained results clearly show that the thickness of the outer Helmholtz plate, a key quantity of the various adsorption theories, depends on two parameters, that is, the size of the cations and the surface density of the anionic surfactant. Namely, with increasing surface concentration, the electrostatic attraction between the two, oppositely charged, layers becomes stronger, leading to a considerable shrinking of the outer Helmholtz plate. Furthermore, this layer is found to be thicker in the presence of larger cations. The former effect could be important in understanding the anomalous shape of the adsorption isotherms of alkali alkyl sulfate surfactants, while the second effect seems to be essential in explaining the cation specificity of these isotherms.

How Polymer Surface Diffusion Depends on Surface Coverage

Measurements are presented of how surface diffusion of flexible polymers at the solid−liquid interface is controlled by surface coverage. Surface coverage is varied over the full range from dilute to saturated surface coverage. The method of measurement is fluorescence correlation spectroscopy (FCS), and the systems are poly(ethylene oxide) (PEG) and dextran adsorbed onto methyl-terminated self-assembled monolayers in buffered aqueous solution. A detailed study of PEG (Mw = 10 800 g mol-1) shows nonmonotonic behavior. The translational diffusion coefficient (D) at first increases with increasing surface concentration, presumably because the number of adsorption sites per molecule decreases as chains switch from pancake to loop−train−tail conformation. Excellent fits to behavior characteristic of a single diffusion process argue against aggregation or crystallization in the adsorbed state. In-situ ellipsometry measurements appear to rule out conformation changes to a hypothetical helical structure, as this would introduce birefringence to the adsorbed polymer layer causing deviations from the observed linear growth of apparent layer thickness with increasing surface coverage. For all three samples studied (PEG of Mw = 10 800 and 20 000 g mol-1 and also dextran with Mw = 10 000 g mol-1), D at surface coverages larger than the estimated surface overlap concentration slow by 1 order of magnitude, presumably reflecting crowding and entanglement with neighboring chains.

Interplay between Shear Stress and Adhesion on Neutrophil Locomotion

Leukocyte locomotion over the lumen of inflamed endothelial cells is a critical step, following firm adhesion, in the inflammatory response. Once firmly adherent, the cell will spread and will either undergo diapedesis through individual vascular endothelial cells or will migrate to tight junctions before extravasating to the site of injury or infection. Little is known about the mechanisms of neutrophil spreading or locomotion, or how motility is affected by the physical environment. We performed a systematic study to investigate the effect of the type of adhesive ligand and shear stress on neutrophil motility by employing a parallel-plate flow chamber with reconstituted protein surfaces of E-selectin, E-selectin/PECAM-1, and E-selectin/ICAM-1. We find that the level and type of adhesive ligand and the shear rate are intertwined in affecting several metrics of migration, such as the migration velocity, random motility, index of migration, and the percentage of cells moving in the direction of flow. On surfaces with high levels of PECAM-1, there is a near doubling in random motility at a shear rate of 180 s −1 compared to the motility in the absence of flow. On surfaces with ICAM-1, neutrophil random motility exhibits a weaker response to shear rate, decreasing slightly when shear rate is increased from static conditions to 180 s −1, and is only slightly higher at 1000 s −1 than in the absence of flow. The random motility increases with increasing surface concentrations of E-selectin and PECAM-1 under static and flow conditions. Our findings illustrate that the endothelium may regulate neutrophil migration in postcapillary venules through the presentation of various adhesion ligands at sites of inflammation.

A Novel PDMS Microfluidic Spotter for Fabrication of Protein Chips and Microarrays

A novel polydimethyl siloxane (PDMS) microfluidic spotter system has been developed for the patterning of surface microarrays that require individually addressing each spot area and high probe density. Microfluidic channels are used to address each spot region, and large spot arrays can be addressed in parallel. Fluorescence intensity measurement of dye-spotted samples compared to control and pipetted drops demonstrated a minimum of three-fold increase in dye surface density compared to pin-spotted dyes. Surface plasmon resonance (SPR) measurement of protein-spotted samples as compared to pin-spotted samples demonstrated an 86-fold increase in protein surface concentration. The spotting system has been applied successfully to protein microarrays for SPR applications, in both a 12-spot linear and 48-spot two-dimensional (2-D) array format. This novel spotter system can be applied to the production of high-throughput arrays in the fields of genomics, proteomics, immunoassays, and fluorescence or luminescence assays

Oxidation of CO over Ru containing perovskite type oxides

Perovskite type catalysts La0.7Sr0.3Cr1−xRuxO3 (0.025≤x≤0.100) were synthesized by annealing a mixture of metal oxides and carbonates gradually up to 1000°C in air, and characterized by XRPD, XPS, TPD, SEM-EDS and the van der Pauw method. The CO oxidation activity was investigated in a differential recycle reactor. According to the XRPD results, all samples achieved a perovskite structure, with a small presence of SrCrO4 phase. The XPS results revealed that the surface composition of all samples differed considerably from the stoichiometric value with an important segregation of strontium and mainly ruthenium with regard to chromium at the surface of the catalysts. The sharp decrease of resistivity with increasing surface concentration of ruthenium and the independence of the resistivity on temperature for the sample with x=0.100 imply the possible presence of SrRuO3, La–Ru–O and highly dispersed RuO2 (invisible by XRPD), known as good electric conductors, at the surface. The CO oxidation activity increases with increasing the degree of substitution (x). The surface concentrations of ruthenium are almost the same in the samples with x=0.075 and 0.100. Those samples showed the similar values of resistivity in whole investigated temperature range and very close CO oxidation activity, which indicates that the concentration of Ru4+ in the surface region and its stability are determining factors for the CO oxidation activity. The main results of this study are that ruthenium perovskites have a high thermal stability and CO oxidation activity.

Microanalysis of Glass Surfaces after Thermal Exposure

Heating of alkali-silicate glasses causes changes in the composition of the surface, caused by the migration of the alkali ions. X-ray microanalysis is a suitable and powerful tool for the investigation of the surface changes on the micron scale. The paper presents a study of the surface changes in the composition of alkali-silicate glasses, namely in 10% K2O · 90% SiO2, 15% K2O · 85% SiO2, and 5% Na2O · 10% K2O · 85% SiO2 (all in molar%). These glasses were annealed to various temperatures in argon atmosphere to prevent surface water corrosion. In addition, annealing time was varied from 6 to 24 hours. The different primary electron energies (7 keV, 10 keV, and 20 keV) were used to trace alkali depth profile. Results show the increased surface concentration of alkalis at higher temperatures for all glasses.

Cordierite as catalyst support for nanocrystalline CuO/Fe 2O 3 system

CuO, Fe 2O 3 and CuO–Fe 2O 3 samples supported on cordierite (commercial grade) were prepared by wet impregnation method using finely powdered support material, copper and/or iron nitrates. The extent of loading was varied between 5 and 20 wt.% CuO, Fe 2O 3 or CuO–Fe 2O 3. The physicochemical, surface and catalytic properties of the various solids calcined at 350–700 °C were investigated using XRD, EDX, nitrogen adsorption at 77 K and CO-oxidation by O 2 at 220–280 °C. The results obtained revealed that the employed cordierite preheated at 350–700 °C was well-crystallized magnesium aluminum silicate (Mg 2Al 4Si 5O 18). Loading of 20 wt.% CuO or Fe 2O 3 on the cordierite surface calcined at 350 °C led to a partial dissolution of the added oxides in the support lattice forming solid solutions. The other portions remained as separate nanocrystalline CuO or Fe 2O 3 phases. The dissolved portions of the transition metal oxide increased upon increasing the calcination temperature from 350 to 500 °C. Loading of 20 wt.% CuO–Fe 2O 3 on the cordierite surface followed by calcination at 350 °C resulted in a solid–solid interaction between some of CuO and Fe 2O 3 yielding iron cuprate Fe 2CuO 4, which decomposed at ≥500 °C yielding copper and iron oxides. The portion of Fe 2O 3 dissolved in the cordierite lattice at 500 °C is twice that of CuO. The S BET of cordierite increased several times by treating with small amounts of Fe 2O 3 or CuO. The increase was more pronounced by treating with Fe 2O 3. The catalytic activity of the cordierite increased progressively by increasing the amount of oxide(s) added. The mixed oxides system supported on cordierite and calcined at 350–700 °C showed catalytic activities much bigger than those measured for the individual supported systems. The synergistic effect manifested in case of solids calcined at 350 °C was attributed to the formation of surface iron cuprate. The significant increase in surface concentration of copper species on top surface layers of the solids treated with mixtures of copper and ferric oxides could be responsible for the synergistic effect for the mixed oxide catalysts calcined at 500 or 700 °C.

Understanding the Activation of Listeria monocytogenes Phosphatidylinositol‐Specific Phospholipase C

The phosphatidylinositol-specific phospholipase C (PI-PLC) from Listeria monocytogenes (a monomer in solution) shows unusual kinetic properties compared to other well-studied phospholipases: (i) increased specific activity with decreasing protein concentration, (ii) activation of the phosphotransferase step by salts, and (iii) activation of both the interfacial phosphotransferase and water-soluble phosphodiesterase steps by zwitterionic and neutral amphiphiles. A variety of biophysical studies (fluorescence, NMR, monolayer, vesicle binding) of enzyme/lipid complexes coupled with kinetics have allowed us to propose a model that accounts for these features. The enzyme binds tightly to anionic surfaces and much more weakly to a zwitterionic interface. The tight binding can be reduced by adding KCl at concentrations that activate the enzyme. In the crystal structure of the enzyme, many basic residues are clustered on the bottom side of TIM-barrel far away from the opening to the active site. These cause the enzyme to adopt a non-productive orientation on negatively charged membranes that leads to a reversible clustering of anionic lipids and vesicle aggregation. An increased surface concentration of zwitterionic / neutral amphiphiles along with the salt disperses the anionic substrate, shields charges on the protein, and enhances productive encounters of the protein with substrate molecules. This model has been tested by examining the behavior of enzyme with citraconylated lysines and mutants of neutral surface residues at the rim of the active site. The unusual kinetic behavior of this PI-PLC also appears to contribute to the escape of L. monocytogenes from primary vacuoles during infection. Supported by NIH GM 60418.

Effects of thermally-activated diffusion on 72 keV Ni ion implantation into Cu targets at elevated temperatures

This work experimentally and theoretically investigates the effects of thermally-activated diffusion on the depth profiles of nickel atoms in copper. Nickel ions of 72keV and 5×1015ions/cm2 were implanted into copper targets at elevated temperatures of 200, 400 and 500°C, respectively. The experimental nickel depth profiles were obtained by the secondary ion mass spectrometry (SIMS). The calculated profiles were obtained using a thermally-activated diffusion model in which both the radiation-enhanced diffusion (RED) and radiation-induced segregation (RIS) are considered. Furthermore, lattice dilation and preferential sputtering were taken into account by means of an appropriate coordinate transformation. The results indicated a strong temperature-dependence of nickel depth profiles. In addition, the nickel depth profiles tend to broaden and surface concentration increase with temperatures.

Electrochemical formation and electron transfer through self-assembled monolayers of 4-mercaptophenol on mercury

Formation and reductive desorption of self-assembled monolayers of 4-mercaptophenol on mercury have been studied by using cathodic stripping voltammetry. Voltammetric peak shapes and integrated areas are consistent with a sequential reorientation of adsorbed molecules from a flat to a perpendicular orientation as their surface concentration increases. The rate of Ru ( NH 3 ) 6 3 + reduction in the presence of full grown thiol monolayers has been determined by impedance measurements. The frequency dispersion of the electrode admittance was found to obey Randles’ behavior, though the parallel capacitance was observed to depend on the redox probe concentration when the monolayers became ionized at pH > 4. Non-ionized 4-mercaptophenol monolayers are more effective electron conductors than alkanethiol monolayers of the same thickness. After correcting for the diffuse layer potential drop, faster electron transfer rates are observed in the presence of ionized monolayers. This increase of reactivity correlates with results obtained from quantum chemical calculations performed on a model system, which predict an increase of donor–acceptor electronic coupling when the intervening molecular bridge becomes deprotonated.