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The role of the anion on the ionophore properties of valinomycin was studied in a model floating bilayer lipid membrane (fBLM) using supporting electrolytes containing K+ with four different counter anion species (ClO4-, H2PO4-, Cl-, and F-). The electrochemical impedance spectra indicate that the membrane resistance of the bilayer decreases with the decrease of Gibbs free energy of anion solvation. The IR spectra demonstrate that valinomycin does not readily bind to K+ in the KH2PO4, KCl, and KF electrolyte solutions, but in the presence of KClO4, valinomycin readily binds to K+, forming a valinomycin-K+ complex. The results in the present paper reveal the role of the counter anion on the transport of cations by valinomycin across the lipid bilayer. The valinomycin-cation complex creates an ion pair with the anion, and this ion pair can enter the hydrophobic region of the bilayer transporting the cation across the membrane. Anions with low solvation energies facilitate the formation of the ion pair improving the ion conductivity of valinomycin-incorporated bilayers. This paper sheds new light on the transport mechanism of valinomycin ionophores and provides new information about the bioactivity of this molecule.

The inhibition effect of amiloride on alamethicin ion channels was studied in a model zwitterionic floating bilayer lipid membrane (fBLM). The EIS studies indicated that amiloride prevents the transport of ions through the alamethicin channels leading to an overall increase in membrane resistance. The PM-IRRAS data demonstrated that amiloride has no influence on the secondary structure of alamethicin but restricts the insertion of the peptides into the bilayer and blocks ion transport through preformed alamethicin channels. The effect of amiloride on ion channel formation in the floating bilayer formed by a zwitterionic lipid was compared to those of previous studies involving negatively charged fBLMs and tethered zwitterionic lipid bilayers. The findings from these studies show that the effects of amiloride on ion channel formation strongly depend on the mobility and charge of the membrane lipids.

The electrochemical impedance spectroscopy (EIS) and polarization-modulation infrared reflection absorption spectroscopy (PM-IRRAS) techniques were employed to study the ionophore properties of valinomycin in a model floating bilayer lipid membrane (fBLM) in perchlorate supporting electrolytes with potassium and sodium cations. Valinomycin decreases the membrane resistance of the fBLM in KClO4 solution by about 180 times, while it has a negligible effect on the membrane resistivity in NaClO4 solution. The IR spectra indicate that valinomycin forms a complex with K+, but not with Na+. The valinomycin-K+ complex adopts a small tilt angle with respect to the electrode surface normal and is well interdigitated between the acyl chains of the bilayer. The EIS and PM-IRRAS results indicate that valinomycin forms complexes with K+ and transports K+ across the lipid bilayer. This transport is potential independent and hence has a passive character.

The knowledge of the structure and properties of water adsorbed on metal surfaces is relevant for understanding electrocatalytic reactions. A monolayer of Pd deposited at a gold electrode surface i...

Neurodegeneration in Alzheimer's disease is associated with disruption of the neuronal cell membrane by the amyloid β (Aβ) peptide. However, the disruption mechanism and the resulting changes in membrane properties remain to be elucidated. To address this issue, herein the interaction of amyloid β monomers (AβMs) and amyloid β oligomers (AβOs) with a floating bilayer lipid membrane (fBLM) was studied using electrochemical and IR spectroscopy techniques. IR measurements showed that both Aβ forms interacted similarly with the hydrophobic membrane core (lipid acyl chains), causing conformational and orientational changes of the lipid acyl chains, thus decreasing acyl chain mobility and altering the lipid packing unit cell. In the presence of AβOs, these changes were more significant than those in the presence of AβMs. However, respective interactions of AβMs and AβOs with the membrane hydrophilic exterior (lipid heads) were quite different. AβMs dehydrated lipid heads without affecting their orientation while AβOs changed the orientation of lipid heads keeping their hydration level intact. Electrochemical measurements showed that only AβOs porated the fBLM, thus significantly changing the fBLM electrical properties. The present results provide new molecular-level insight into the mechanism of membrane destruction by AβOs and changes in the membrane properties.

Cu-based nanomaterials have been widely considered to be promising electrocatalysts for the direct conversion of CO2 to high-value hydrocarbons. However, poor selectivity and slow kinetics have hindered the use of Cu-based catalysts for large-scale industrial applications. In this work, we report on a tunable Cu-based synthesis strategy using a dynamic hydrogen bubble template (DHBT) coupled with a sputtered Ag thin film for the electrochemical reduction of CO2 to ethanol. Remarkably, the introduction of Ag into the base of the three-dimensional (3D) Cu nanostructure induced changes in the CO2 reduction reaction (CO2RR) pathway, which resulted in the generation of ethanol with high Faradaic Efficiency (FE). This observation was further investigated through Tafel and electrochemical impedance spectroscopic analyses. The rational design of the electrocatalyst was shown to promote the spillover of formed CO intermediates from the Ag sites to the 3D porous Cu nanostructure for further reduction to C2 products. Finally, challenges toward the development of multi-metallic electrocatalysts for the direct catalysis of CO2 to hydrocarbons were elucidated, and future perspectives were highlighted.

Protein misfolding diseases, like Alzheimer's, Parkinson's, and Huntington's disease, are associated with misfolded protein aggregation. Alzheimer's disease is related to a progressive neuronal death induced by small amyloid β oligomers. Here, we describe the procedure to prepare and identify different types of small toxic amyloid β oligomers by atomic force microscopy (AFM).

Protein misfolding diseases, like Alzheimer's, Parkinson's, and Huntington's disease, are associated with misfolded protein aggregation. Alzheimer's disease is related to a progressive neuronal death induced by small amyloid β oligomers. Here, we describe the procedure to prepare and identify different types of small toxic amyloid β oligomers by atomic force microscopy (AFM).

Natural Sciences and Engineering Research Council of Canada (NSERC)

The structure of water in the submembrane region of the bilayer of DPhPC floating (fBLM) on a monolayer of 1-thio-β-d-glucose (β-Tg)-modified gold nanoparticle film was studied by the surface-enhanced infrared absorption spectroscopy (SEIRAS). SEIRAS employs surface enhancement of the mean square electric field of the photon, which is acting on a few molecular layers above the film of gold nanoparticles. Therefore, it is uniquely suited to probe water molecules in the submembrane region and provides unique information concerning the structure of the hydrogen bond network of water surrounding the lipid bilayer. The IR spectra indicated that water with a strong hydrogen network is separating the membrane from the gold surface. This water is more ordered than the water in the bulk. When alamethicin, a peptide forming ion channels, is inserted into the membrane, the network is only slightly loosened. The addition of amiloride, an ion channel blocker, results in a significant decrease in the amount of water in the submembrane region. The remaining water has a significantly distorted hydrogen bond network. This study provides unique information about the effect of the ion channel on water transport across the bilayer. The electrode potential has a relatively small effect on water structure in the submembrane region. However, the IR studies demonstrated that water is less ordered at positive transmembrane potentials. The present results provide significant insight into the nature of hydration of a floating lipid bilayer on the gold electrode surface.

Valinomycin, a cyclic peptide, was incorporated into a biomimetic lipid membrane tethered to the surface of a gold (111) electrode. Electrochemical impedance spectroscopy was used to study the ionophore properties of the peptide, and polarization modulation infrared reflection absorption spectroscopy was employed to determine the conformation and orientation of valinomycin in the membrane. The combination of these two techniques provided unique information about the ionophore mechanism where valinomycin transports ions across the membrane by creating a complex with potassium ions and forming an ion pair with a counter anion. The ion pair resides within the hydrophobic fragment of the membrane and adopts a small angle of ∼22° with respect to the surface normal. This novel study provides new insights explaining the valinomycin ion transport mechanism in model biological membranes.

Monolayers of 1,2-dipalmitoyl-sn-glycero-3-cytidine were incubated with guanine in a 0.1 M NaF electrolyte at the surface of a Langmuir trough and transferred to gold (111) electrodes using the Lan...

The effects of amiloride on the structure and conductivity of alamethicin ion pore formation within negatively charged, gold-supported, 1,2-dimyristoyl- sn-glycero-3-phosphocholine/Egg-PG membranes were investigated with the help of electrochemical impedance spectroscopy (EIS), photon polarization modulation-infrared reflection spectroscopy (PM-IRRAS), and atomic force microscopy (AFM). The EIS results indicate that ion conductivity across negatively charged phospholipid bilayers containing alamethicin decreases by an order of magnitude when amiloride is introduced to the system. Despite the reduction in ion conductivity, the PM-IRRAS data shows that amiloride does not inhibit ion channel formation by alamethicin peptides. High-resolution AFM images revealed that amiloride enlarges and distorts the shape of alamethicin ion pores when introduced to the system, indicating that it is inserting itself into the mouth of the alamethicin pores. This effect is driven by electrostatic interactions between positively charged amiloride molecules and the negative charge on the membrane.

Chronocoulometry was applied to determine charge in a monolayer of nucleolipid (1,2-dipalmitoyl-sn‑glycero-3-(cytidine diphosphate)) deposited at a gold electrode surface. The immersion method was used to measure the potential of zero charge of the interface (Epzci), which is a sum of charge on the monolayer of the nucleolipid and charge on the gold surface. Photon polarization infrared reflection absorption spectroscopy (PM-IRRAS) was used to determine formation of the Watson-Crick complex between terminal cytidine moiety of the nucleolipid and guanine (its complementary base) added to the solution. The combination of electrochemical and spectroscopic studies allowed one to demonstrate that the Watson-Crick complex is formed when the interface is positively charged. The potential applied to the electrode affects not only the complex formation but also orientation of the cytosine moiety. The complex is formed when the cytosine moiety is oriented assuming a small angle with respect to the electrode surface. Ministerio de Ciencia e Innovación CTQ2014-57515-C2-1-R, RED2018-102412-T Junta de Andalucía FQM202 Natural Sciences and Engineering Research Council of Canada (NSERC) RG-03958

Alzheimer's disease (AD) is characterized by progressive neurodegeneration associated with amyloid β (Aβ) peptide aggregation. The aggregation of Aβ monomers (AβMs) leads to the formation of Aβ oligomers (AβOs), the neurotoxic Aβ form, capable of permeating the cell membrane. Here, we investigated the effect of a fluorene-based active drug candidate, named K162, on both Aβ aggregation and AβO toxicity toward the bilayer lipid membrane (BLM). Electrochemical impedance spectroscopy (EIS), atomic force microscopy (AFM), and molecular dynamics (MD) were employed to show that K162 inhibits AβOs-induced BLM permeation, thus preserving BLM integrity. In the presence of K162, only shallow defects on the BLM surface were formed. Apparently, K162 modifies Aβ aggregation by bypassing the formation of toxic AβOs, and only nontoxic AβMs, dimers (AβDs), and fibrils (AβFs) are produced. Unlike other Aβ toxicity inhibitors, K162 preserves neurologically beneficial AβMs. This unique K162 inhibition mechanism provides an alternative AD therapeutic strategy that could be explored in the future.

Summary Planar solid-supported lipid bilayers have been developed as simplified biological membranes to model the physical properties of cell membrane processes. Lipid bilayer membranes supported at conductive metal substrates provide a unique opportunity to investigate the effect of the static electric field on the membrane structure and function. The insights gained from this research can be used to develop novel biosensors and biomedical devices. This review summarizes the recent developments in metal-supported biomimetic membrane systems. It provides an overview of the various models, such as metal-supported monolayers and bilayers, hybrid bilayers, tethered bilayers, and floating bilayers, used to study membrane processes at electrode surfaces, such as metal-supported monolayers and bilayers, hybrid, tethered, and floating bilayers. The paper discusses the recent advancements in these biomimetic models and describes the fundamental knowledge about membrane processes that has been extracted from these different platforms. The potential for the design and improvement of biomedical devices using metal-supported bilayers is also discussed. Metal-supported bilayers allow for the application of a plethora of spectroscopic and surface imaging techniques to obtain information about the voltage-dependent properties of biomolecules at the molecular level. The underlying methodology of these analytical techniques and the structural, chemical and kinetic information extracted are reviewed.

Electrochemical impedance spectroscopy (EIS), atomic force microscopy (AFM), and photon polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS) were employed to investigate the formation of alamethicin pores in negatively charged bilayers composed of a mixture of 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) and egg-PG floating at gold (111) electrode surfaces modified by self-assembled monolayers of 1-thio-β-d-glucose (β-Tg). The EIS data showed that the presence of alamethicin decreases the membrane resistivity by about 1 order of magnitude. PM-IRRAS measurements provided information about the tilt angles of peptide helical axis with respect to the bilayer normal. The small tilt angles obtained for the peptide helical axis prove that the alamethicin molecules were inserted into the DMPC/egg-PG membranes. The tilt angles decreased when negative potentials were applied, which correlates with the observed decrease in membrane resistivity, indicating that ion pore formation is assisted by the transmembrane potential. Molecular resolution AFM images provided visual evidence that alamethicin molecules aggregate forming hexagonal porous 2D lattices with periodicities of 2.0 ± 0.2 nm. The pore formation by alamethicin in the negatively charged membrane was compared with the interaction of this peptide with a bilayer formed by zwitterionic lipids. The comparison of these results showed that alamethicin preferentially forms ion translocating pores in negatively charged phospholipid membranes. Natural Sciences and Engineering Research Council of Canada (NSERC)

Alamethicin was reconstituted into 1,2-di-O-phytanyl-sn-glycero-3-phosphocholine (DPhPC) bilayer supported at the gold (111) electrode surface using a combination of Langmuir-Blodgett/Langmuir-Schaefer deposition techniques. Chronocoulometry was employed to describe the behavior of the bilayer as a function of the electrode potential. Electrochemical impedance spectroscopy (EIS) was used to determine the membrane resistivity and capacitance. The photon polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS) measurements provided complementary information about the conformation and orientation of the alamethicin and DPhPC molecules in the adsorbed bilayer. The electrochemistry results demonstrated that the bilayer is stable at the electrode surface at potentials between 0.0 V and − 0.5 V vs Epzc. At more negative potentials, a progressive electro-dewetting of the membrane from the electrode surface takes place. The membrane is detached from the electrode surface when (E-Epzc) is more negative than − 1.1 V. The PM-IRRAS results illustrate that alamethicin peptides assume a surface state where their helices assume a large angle with respect to the surface normal at potentials close to Epzc. When negative potentials are applied, the alamethicin molecules are inserted into the membrane. Peptide insertion is complete at (E-Epzc) ~ − 0.5 V. The membrane resistivity determined from the ESI data indicates that alamethicin molecules adopt an open channel state when the helices are inserted into the membrane and a closed channel state (non-conductive) at E close to Epzc where they assume a flat orientation on the surface. The IR spectra collected during the negative and positive potential scans demonstrated that the open and closed ion channel states are potential controlled and reversible. In contrast to the significant changes in alamethicin orientation, the tilt angle of the acyl chains of DPhPC molecules show little to no change with the electrode potential. The data presented in this paper provides insight on the voltage-gating behavior of the alamethicin ion channels incorporated into phospholipid bilayers.

Development of a reproducible two-dimensional array of gold nanoparticles (AuNPs) through a guided assembly approach and sequentially using an electrochemical cleaning procedure to remove all cappi...

Alamethicin was reconstituted into DPhPC/DPTL tethered bilayer lipid membranes (tBLMs) to gain a better understanding of ion pore formation. The properties of the ion-conductive alamethicin pores were investigated by electrochemical impedance spectroscopy (EIS) and polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS) as a function of the peptide concentration within the membrane. At low peptide concentrations (≤ 5%), the alamethicin-incorporated tBLM displays the highest membrane resistance since the alamethicin molecules adopt a surface state where the tilt angles of the helices are large with respect to the surface normal. At alamethicin concentrations ranging from 10 to 20 mol%, the tilt angles of the helices decrease to lower values signifying that the alamethicin molecules are inserting into the tBLM. Consequently, the membrane resistivity is also lowered indicating that the peptides are forming ion conductive channels. The results show an excellent correlation between molecular information concerning the orientation and conformation of alamethicin molecules obtained from the PM-IRRAS measurements and electrochemical properties of the membranes measured by EIS. These findings reveal that the alamethicin concentration within the film is directly related to the ion conductance across membrane.

In situ ATR-SEIRAS experiments were carried out to describe water structure at the surface of multilayers of Pd modified nanopatterned gold film electrodes in contact with aqueous 0.1 M HClO4 solution. The results show that the surface water becomes more ordered when the thickness of the Pd film increases. The “ice-like water” band becomes stronger and for the electrode with 5 ML Pd@Au, the ratio of “ice-like water” to “liquid-like water” becomes larger than that in bulk water. Concomitantly, the population of “monomers” or small water clusters diminishes. All surface water bands increase when hydrogen adsorption takes place. The bending band corresponding to “monomers” or “multimers” water is observed chiefly at the potentials of hydrogen adsorption.

A mixed monolayer of 1,2-dipalmitoyl-sn-glycero-3-(cytidine diphosphate) nucleolipid (DG-CDP) and 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) was transferred from the air–water interface onto an gold (1 1 1) electrode surface using the Langmuir-Schaeffer (horizontal touch) technique. Compression isotherms were recorded for the monolayer spread at the air–water interface. These measurements demonstrated that the mixture composition 7:3 of DG-CDP:DPPC displayed reduced repulsive interactions between polar heads and ideal packing of acyl chains. Chronocoulometric experiments were performed to demonstrate stability of this film at the gold–solution interface. Photon polarization modulation infrared reflection absorption spectroscopy showed that the tilt angle of the acyl chains is slightly higher, and the chains are less twisted in the mixed than in the pure nucleolipid monolayer. In the mixed film, the tilt of the cytosine moiety (the sensing element of the monolayer) assumes a large angle with respect to the surface normal, even when the monolayer becomes detached from the gold surface. The mixed monolayer has improved properties for future applications for detection of guanine, its complementary base. Ministerio de Ciencia e Innovación CTQ2014-57515-C2-1-R, RED2018-102412-T Junta de Andalucía FQM202 Natural Sciences and Engineering Research Council of Canada (NSERC) RG-03958

A laboratory-grown nickel sample was used to investigate the galvanostatic dissolution under industrial electroplating conditions. The sample contained multiple layers corresponding to changes in the Ni(CO)4 decomposition temperature ranging from 200 to 280 °C. Cyclic voltammetry curves were used to determine the active dissolution, passive and transpassive potentials regions of the sample. Chronopotentiometric curves recorded during galvanostatic dissolution displayed oscillations indicating that the dissolution mechanism involved the breakdown of the passive layer and repassivation of the surface. Scanning electron microscopy (SEM) and white light interference microscopy (WLIM) were used to observe changes in morphology and roughness of the surface. The SEM images revealed the formation of pits with lacy covers at the surface during initial stages of the dissolution. At increased dissolution times, a transition from the lacy covered pits to open pits was observed. The images showed that preferential dissolution occurs on Ni layers grown at higher Ni(CO)4 decomposition temperatures. At longer dissolution times, the preferential dissolution also takes place at the boundaries between nickel laminae, which corresponds to the decomposition of Ni(CO)4 at different temperatures. Vale Canada and the Natural Sciences and Engineering Research Council (NSERC) of Canada.

The charge number per adsorbed molecule and surface concentration of 2,3-di- O -phytanyl- sn -glycero-1-octaethyleneglycol-D,L-α-lipoic acid ester (DPOL) at a Au(111) electrode surface was investigated by chronocoulometry using two different film deposition methods. First, a known amount of the thiolipid was transferred from the air-water interface of a Langmuir trough onto the gold electrode surface via a Langmuir-Blodgett (LB) deposition. The charge density measurements for this monolayer system were used to determine the charge number per adsorbed DPOL molecule (electrosorption valency). The observed electrosorption valency values of the adsorbed DPOL film were much lower than the expected number of transferred electrons for a simple reductive desorption process. In the second deposition method, charge densities were measured for the electrode covered by a self-assembled DPOL monolayer. The electrosorption valency values determined from the LB DPOL film were used to calculate the packing density of the DPOL molecules within the self-assembled monolayer. The surface concentration of the molecules within the thiol monolayer with octaethylene glycol chains gave similar results to a related thiolipid with tetraethylene glycol chains (DPTL). This new finding indicates that both of these molecules (DPTL and DPOL) assume a brush conformation in densely packed self-assembled monolayers.

Valinomycin, a cyclic peptide, was incorporated into a biomimetic lipid membrane tethered to the surface of a gold (111) electrode. Electrochemical impedance spectroscopy was used to study the ionophore properties of the peptide, and polarization modulation infrared reflection absorption spectroscopy was employed to determine the conformation and orientation of valinomycin in the membrane. The combination of these two techniques provided unique information about the ionophore mechanism where valinomycin transports ions across the membrane by creating a complex with potassium ions and forming an ion pair with a counter anion. The ion pair resides within the hydrophobic fragment of the membrane and adopts a small angle of ∼22° with respect to the surface normal. This novel study provides new insights explaining the valinomycin ion transport mechanism in model biological membranes.

Monolayers of 1,2-dipalmitoyl

Colicin E1 is a channel-forming bacteriocin produced by certain Escherichia coli cells in an effort to reduce competition from other bacterial strains. The colicin E1 channel domain was incorporated into a 1,2-diphytanoyl- sn-glycero-3-phosphocholine floating bilayer situated on a 1-thio-?-d-glucose-modified gold (111) surface. The electrochemical properties of the colicin E1 channel in the floating bilayer were measured by electrochemical impedance spectroscopy; the configuration and orientation of colicin E1 in the bilayer were determined by polarization-modulation-infrared-reflection absorption spectroscopy. The EIS and IR results indicate that colicin E1 adopts a closed-channel state at the positive transmembrane potential, leading to high membrane resistance and a large tilt angle of ?-helices. When the transmembrane potential becomes negative, colicin E1 begins to insert into the lipid bilayer, corresponding to low membrane resistance and a low tilt angle of ?-helices. The insertion of colicin E1 into the lipid bilayer is driven by the negative transmembrane potential, and the ion-channel open and closed states are potential reversible. The data in this report provide new insights into the voltage-gated mechanism of colicin E1 ion channels in phospholipid bilayers and illustrate that the floating bilayer lipid membrane at the metal electrode surface is a robust platform to study membrane-active proteins and peptides in a quasi-natural environment.

Two 4-thio pseudo-glycolipids, a disulfide and a thiol, were synthesized as candidates to build tethered bilayer lipid membranes (tBLMs) on gold (111) surface. Monolayers of the disulfide and thiol were built on gold surfaces using the self-assembly and Langmuir-Blodgett (LB) transfer methods. Monolayers were prepared in several solvents and at various temperatures; their quality was assessed by differential capacitance. Best monolayers were achieved when the disulfide was self-assembled in ethanol. The quality of such monolayers was further improved by allowing the assembly to proceed under stirring of the solution at increased temperatures. The charge number per adsorbed molecule and surface concentration of disulfide on gold (111) surface were determined by chronocoulometry. A DPhPC/disulfide tBLM was then built by vesicle fusion of 1,2-diphytanyl-sn-glycero-3-phosphocholine (DPhPC) on top of the disulfide monolayer. The minimum capacitance of the gold electrode with tBLM (1.3 mF cm 2) was close to the value of a real cell membrane and the AFM force spectroscopy measurements showed that the DPhPC/disulfide tBLM had a thickness of 6.2 ± 0.6 nm consistent with the thickness expected for a bilayer. Finally, the potential of the tBLM to study transmembrane proteins was assessed by investigating the reconstitution of gramicidin A into the membrane by polarization modulation infrared absorption spectroscopy (PM-IRRAS). These results demonstrate that the disulfide is a good candidate to construct tBLMs on gold surface and to study transmembrane proteins. Natural Sciences and Engineering Research Council of Canada 2020-12-12

The effect of the electrode potential on the orientation and conformation of the 1,2-dipalmitoyl- sn-glycero-3-cytidine monolayer deposited on a gold (111) electrode surface was described. The potential of zero free charge ( Epzc) for the monolayer-covered electrode was determined to be -0.2 V vs SCE. The differential capacitance and charge density data indicated that the monolayer is stable at the electrode surface when ( E - Epzc) > 0.0 V. At negative rational potentials, a progressive detachment (electrodewetting) of the monolayer occurs. The monolayer is fully detached from the electrode surface at ( E - Epzc) 0.0 V, the plane of the cytosine moiety assumes a small angle of ∼20° with respect to the surface. At negative potentials, the tilt angle of the cytosine fragment increases and rotates. With the help of DFT calculations, these changes were explained by the repulsion of the positive pole of the cytosine permanent dipole moment by the positively charged gold surface and its attraction to the metal surface at negative electrode potentials. This work provides unique information for the future development of sensors based on the molecular recognition of nucleoside targets.

An applied approach for in situ characterization of oxide ore samples exposed to a thiosulfate-based leaching solution with shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS) is discussed. Differences in passive layer growth during thiosulfate leaching were observed in the SHINERS spectra between the untreated and pressure oxidation (POX)-treated oxide ore samples received from Barrick Gold Corporation. The SHINERS spectra revealed that the passive layer at the untreated oxide ore–electrolyte interface contains metal sulfides and significant quantities of polysulfide chains (Sn/Sn2−) of variable lengths after longer exposure to the leaching solution. However, the passive layer observed with the POX-treated sample was found to be predominantly metal sulfides with only a small quantity of polysulfide chains. From these results, it was concluded that the POX pretreatment process may successfully destroy or inactivate minerals found in the ore that are responsible for catalysing thiosulfate decomposition into polysulfides which results in low gold extraction efficiencies. Copyright © 2016 John Wiley & Sons, Ltd.

Characterization of copper and ammonia interactions with the passive layer that impedes gold dissolution with thiosulfate based electrolytes at extended time frames was performed with electrochemistry and shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS). Generalized two-dimensional correlation spectroscopy (2DCOS) was also employed to assist interpretation of the collected SHINERS spectra. Growth of the complex passive layer mixture on a polycrystalline gold electrode immersed in a 0.10 M Na2S2O3 electrolyte was found to initially proceed through formation of sulfides adsorbed to the gold electrode surface (SERS band at ca. 326 and 309 cm−1) followed by rapid transformation to cyclo-S8 (474, 218, and 152 cm−1) and polysulfides/polythionates (459 cm−1). After stable formation of the passive film, the addition of Cu2+ resulted in the partial removal of the passive layer. The removal of the components of the passive layer proceeded according to the following sequence; polysulfides were fastest, cyclo-S8 next, followed by S ( ads ) 2 − . The end product was observed to be a combination of copper and gold sulfides. In an independent study, the addition of ammonia displayed a similar ability to remove the passive layer constituents, albeit at much slower rates. From these observations it can be concluded that copper and ammonia play a vital function in preventing passive layer formation, allowing increased mass transport of thiosulfate and the oxidant across the electrode-electrolyte interface, thereby allowing a higher gold extraction efficiency.

We describe a method for the fabrication of gold nanorod arrays and their characterization. The initial requirements were for a robust substrate with strong surface enhancement of Raman scattering with minimal surface contamination. The rods with length up to 20 μm were electrochemically deposited in alumina templates bonded to gold-coated silicon wafers. After the removal of the template, surface-bound cyanide from the deposition process was removed by mild electropolishing. Reflectance and cathodoluminescence measurements revealed transverse dipole and quadrupole plasmon modes. Surface enhancement of 106 was determined by taking Raman spectra of self-assembled monolayers of 4-aminothiophenol. The enhancement factor (EF) was found to be independent of nanorod aspect ratio because only the length of the nanorods was varied while their diameter was kept constant, and because of the large length of nanorods only the transverse plasmons were excited.

Reduction of oxygen catalyzed by laccase was studied by surface-enhanced infrared absorption spectroscopy (SEIRAS) combined with electrochemical techniques. Laccase molecules were adsorbed on modified carbon nanotubes (CNTs). SEIRAS provided spectra of Amide I band of adsorbed laccase. Fourier self-deconvolution (FSD) and two-dimensional correlation spectroscopy (2D COS) techniques were employed to reveal the sub-band structure of the Amide I band. The analysis demonstrated that laccase adsorbed on CNTs remains its native state both in the oxidized and reduced states. The detailed analysis showed that change of the oxidation state leads to a small change of the secondary structure of the protein. This change is comparable to the change observed for similar blue-copper oxidases in solution during redox titration. The results of this study demonstrated that CNT's immobilized laccase is an excellent catalyst of oxygen reduction. This study illustrates power of quantitative analysis of IR data to provide information about three-dimensional structure of surface immobilized proteins.

A hybrid bilayer lipid membrane (hBLM), constructed with a 1-hexadecanethiol self-assembled interior leaflet and a 1,2-dipalmitoyl-sn-glycero-3-cytidine nucleolipid exterior leaflet, was deposited at the surface of a gold (111) electrode. This system was used to investigate the molecular recognition reaction between the cytosine moieties of the lipid head group with guanine molecules in the bulk electrolyte solution. Electrochemical measurements and photon polarization modulation infrared reflection absorption spectroscopy (PMIRRAS) were employed to characterize the system and determine the extent of the molecular recognition reaction. The capacitance of the hBLM-covered gold electrode was very low (~1 μF cm−2), therefore the charge density at the gold surface was small. Changing the electrode potential had a minimal effect on the complexation between the cytosine moieties and guanine molecules due to small changes in the static electric field across the membrane. This behavior favored the formation of the guanine–cytosine complex.

The insertion and ion-conducting channel properties of alamethicin reconstituted into a 1,2-di- O-phytanyl- sn-glycero-3-phosphocholine bilayer floating on the surface of a gold (111) electrode modified with a 1-thio-β-d-glucose (β-Tg) self-assembled monolayer were investigated using a combination of electrochemical impedance spectroscopy (EIS) and polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS). The hydrophilic β-Tg monolayer separated the bilayer from the gold substrate and created a water-rich spacer region, which better represents natural cell membranes. The EIS measurements acquired information about the membrane resistivity (a measure of membrane porosity), and the PM-IRRAS experiments provided insight into the conformation and orientation of the membrane constituents as a function of the transmembrane potential. The results showed that the presence of alamethicin had a small effect on the conformation and orientation of phospholipid molecules within the bilayer for all studied potentials. In contrast, the alamethicin peptides assumed a surface state, where the helical axes adopted a large tilt angle with respect to the surface normal, at small transmembrane potentials, and inserted into the bilayer at sufficiently negative transmembrane potentials forming pores, which behaved as barrel-stave ion channels for ionic transport across the membrane. The results indicated that insertion of alamethincin peptides into the bilayer was driven by the dipole-field interactions and that the transitions between the inserted and surface states were electrochemically reversible. Additionally, the EIS measurements performed on phospholipid bilayers without alamethicin also showed that the application of negative transmembrane potentials introduces defects into the bilayer. The membrane resistances measured in both the absence and presence of alamethicin show similar dependencies on the electrode potential, suggesting that the insertion of the peptide may also be assisted by the electroporation of the membrane. The findings in this study provide new insights into the mechanism of alamethicin insertion into phospholipid bilayers.

Unilamellar DMPC/DMPG vesicles in the absence and presence of alamethicin were fused onto the surface of a gold electrode modified with a 1-thio-β-d-glucose self-assembled monolayer. The resulting floating bilayer lipid membranes (fBLMs) were investigated using atomic force microscopy (AFM) and electrochemical impedance spectroscopy (EIS). A corrugated film structure was observed for the pure DMPC/DMPG fBLMs due to surface stress between the tightly packed lipids. These corrugations are removed by the addition of alamethicin suggesting the lipid-peptide interactions alleviate the overall surface stress creating a more uniform bilayer. Both DMPC/DMPG films in the absence and presence of alamethicin had thickness of 5.5 ± 0.9 nm demonstrating that alamethicin has a minimal effect on the overall bilayer thickness. However, a significant decrease in membrane resistivity was observed when alamethicin was inserted into the fBLM indicating that the peptides are forming ion conducting pores. A direct visualization of the alamethicin pores was obtained by molecular resolution AFM images revealing that the pores are not randomly dispersed throughout the bilayer, but instead form hexagonal aggregates. The diameter of an individual pore within the aggregates is equal to 2.3 ± 0.3 nm, which is consistent with the size of a hexameric pore predicted by molecular dynamics simulations. Additionally, the image revealed a broad size distribution of alamethicin aggregates, which explains the origin of multiple conductivity states observed for the incorporation of alamethicin into free standing bilayer lipid membranes. Natural Sciences and Engineering Research Council of Canada

The dissolution mechanism of nickel grown by the carbonyl process was investigated using laboratory Ni samples. These samples were purposely engineered to form an alternating lamellar structure of Ni layers grown under two limiting conditions. Three layers deposited from low nickel carbonyl gas concentrations (5%) at a decomposition temperature of 280 °C (LC/HT) were deposited between four layers formed from high nickel carbonyl gas concentrations (40%) at a decomposition temperature of 200 °C (HC/LT). These lamellar structures were used to simulate the two extremes found within an industrial decomposition chamber for nickel pellets grown using the Mond process. Cyclic voltammetry and fluctuations in the electrode potential were recorded during the 120 min constant current dissolution experiment. Complementary scanning electron microscopy (SEM) and white light interference microscopy (WLIM) measurements were used to monitor the changes in surface morphology, texture and roughness as a function of the dissolution time. The electrochemical measurements showed that the dissolution of the sample proceeded in the transpassive regime at overvoltages above 300 mV. Large oscillations were observed in the chronopotentiogram, which suggests that the passive layer breaks down and then regrows on the surface of the nickel samples. SEM and WLIM images revealed that pits with lacy coverings were formed during the initial stages of nickel dissolution. With increasing dissolution time, the LC/HT regions dissolved at a significantly faster rate than the HC/LT regions and the lacy covers were more readily removed causing the transition to an open pit dissolution mechanism. The formation of trenches at boundaries between the lamina was observed at longer dissolution times. The average depth and width of the trenches also increased as a function of dissolution time. The results from the laboratory-grown lamellar nickel samples in this study clearly show preferential dissolution at boundaries between the lamina and that the dissolution of the LC/HT regions proceeds faster than the dissolution of the HC/LT regions. Natural Sciences and Engineering Research Council (NSERC) of Canada and Vale Canada

Preparation of a nanoparticle modified gold substrate designed for characterization of hydrophilic self-assembled monolayers (SAMs) of 1-thio-β-D-glucose (TG) with electrochemical surface-enhanced Raman spectroscopy (EC-SERS) is presented. Citrate stabilized gold nanoparticles were deposited on a polycrystalline gold electrode and subjected to an electrochemical desorption procedure to completely remove all traces of adsorbed citrate. Complete desorption of citrate was confirmed by recording cyclic voltammetry curves and SERS spectra. The citrate-free nanoparticle modified gold electrode was then incubated in a 1 mg mL(-1) aqueous solution of TG for 16 h prior to being characterized by EC-SERS. The SERS spectra confirmed that at potentials more negative than -0.10 V vs SCE thioglucose forms a monolayer in which the majority of the molecules preserve their lactol ring structure and only a small fraction of molecules appear to be oxidized. At potentials more positive than -0.10 V, the oxidation of TG molecules becomes prominent, and at potentials more positive than 0.20 V vs SCE, the monolayer of TG consists chiefly of oxidized product. The SERS spectra collected in the double layer region suggest the SAM of TG is well hydrated and hence can be used for hydrophilic modifications of a gold surface.

Surface-enhanced infrared reflection-absorption spectroscopy (SEIRAS) was used to investigate the structure of water that is incorporated within a film of sodium dodecyl sulfate (SDS) adsorbed at a thin gold nanoparticle film deposited onto a silicon substrate. Previous studies on a Au(111) electrode surface showed that SDS molecules form long-range ordered hemicylindrical hemimicelles (phase I) for potentials -0.2 ≤ E ≤ 0.45 V vs Ag/AgCl and a disordered bilayer (phase II) for potentials E ≥ 0.5 V vs Ag/AgCl. The SEIRA spectra demonstrated that the hemimicellar film is water-rich and contains both a network of hydrogen-bonded water and a disturbed network of hydrogen bonds consisting of monomeric and dimeric water in the hydrophobic region of the film. No network water was observed in phase II of the film. However, SEIRAS data showed that sulfate groups in the disordered bilayer are hydrated. The SEIRAS spectra of the film of SDS were compared to the previously measured spectra obtained using subtractively normalized interfacial Fourier transform IR spectroscopy (SNIFTIRS). The complementarity of the spectroscopic information obtained by these two techniques was demonstrated.

The anodic dissolution of two laboratory-made Ni samples obtained using the carbonyl method was investigated to understand the origin of residue formation in the anode basket in an electroplating tank. The first sample was obtained with 3 ppm addition of carbonyl sulfide to introduce a small amount of sulfur (CN-S sample). The second was obtained without sulfur impurities (CN sample). Linear sweep voltammetry and chronopotentiometry were applied to characterize the dissolution of these samples. The dissolution of the CN-S sample took place in the active region at low overpotentials. This behavior is determined by the presence of sulfur impurities that break down the passive layer and facilitate Ni dissolution. The CN sample without sulfur was dissolved at high overpotentials. The overpotential-time plots displayed regular large amplitude oscillations in which the overvoltage periodically moved between the transpassive and passive regimes. The anodic dissolution of this sample was controlled by two competing processes: breakdown and formation of the passive layer. Scanning electron microscopy and white light interference microscopy were applied to monitor the morphological changes of the two samples as a function of the dissolution time. The results of these studies showed that the CN-S sample dissolved uniformly across the surface. However, the roughness and the aspect ratio of the protruding features on the surface increased with time. This sample produced a fine residue due to detachment of small protruding crystallites. In contrast, the dissolution of the CN sample involved pit formation and took place predominantly from the bulk of the pits. The dissolution of this sample left a porous skeleton of more passivated Ni. The residue in this case consisted of large, porous chunks of the skeleton.

Electrochemical methods are combined with shell-isolated nanoparticle-enhanced Raman spectroscopy (EC-SHINERS) for a comprehensive study of pyridine adsorption on Au(111), Au(100) and Au(110) single crystal electrode surfaces. The effects of crystallographic orientation, pyridine concentration, and applied potential are elucidated, and the formation of a second pyridine adlayer on Au(111) is observed spectroscopically for the first time. Electrochemical and SHINERS results correlate extremely well throughout this study, and we demonstrate the potential of EC-SHINERS for thorough characterization of processes occurring on single crystal surfaces. Our method is expected to open up many new possibilities in surface science, electrochemistry and catalysis. Analytical figures of merit are discussed.

A gold nanorod (AuNR) array electrode was employed to record SERS spectra as a function of immersion time in electrolyte solutions of tetrathionate, trithionate, the [Au(S 2 O 3 ) 2 ] 3− complex, sulfide and thiosulfate. The generalized two-dimensional correlation spectroscopy was employed to deconvolute broad bands in the SERS spectra. The results show that the polythionates, tetrathionate and trithionate, sulfide, and the [Au(S 2 O 3 ) 2 ] 3− complex decompose to form cyclo-S 8 , polymeric and monoatomic sulfur at the gold surface. The relative amount of these different forms of sulfur in the film formed at the surface depends on the nature of the electrolyte species. The decomposition of tetrathionate leads predominantly to the formation of cyclo-S 8 . Comparable amounts of all three forms of sulfur are formed in the solution of the [Au(S 2 O 3 ) 2 ] 3− complex. Monoatomic sulfur is formed predominantly at the gold surface in solutions of trithionate and thiosulfate. In contrast to the previous suggestions, the results of this study demonstrate that polythionates are not present in the passive layer during gold leaching from thiosulfate solutions at a prolonged leaching times.

Electrochemical scanning tunneling microscopy (EC-STM) was employed to study the aggregation of trichogin OMe (TCG), an antimicrobial peptide, incorporated into a lipid monolayer. High-resolution EC-STM images show that trichogin molecules aggregate to form channels in the lipid monolayer. Two types of aggregates were observed in the images. The first consisted of a bundle of six TCG molecules surrounding a central pore. The structure and dimensions of this channel are similar to aggregates that in bilayers are described by the barrel-stave model. The EC-STM images also reveal that channels aggregate further to form a hexagonal lattice of a two dimensional (2D) nanocrystal. The model of 2D lattice was built from trimers of TCG molecules that alternatingly are oriented with either hydrophilic or hydrophobic faces to each other. In this way each TCG molecule is oriented partially with its hydrophilic face towards the hexameric pore allowing the formation of the column of water inside this pore.

Polarized attenuated total reflection infrared (ATR-IR) spectroscopy, fluorescence microscopy, and fluorescence spectroscopy were used to characterize a lipid coating composed of 70 mol % 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) and 30 mol % cholesterol, supported on a spherical hydrogel scaffold. The fluorescence microscopy images show an association between the lipid coating and the hydrogel scaffold. Fluorescence permeability measurements revealed that the phospholipid coating acts as a permeability barrier, exhibiting characteristics of a lamellar bilayer coating structure. Variable evanescent wave penetration depth ATR-IR spectroscopy studies validated the determination of quantitative molecular orientation information for a lipid coating supported on a spherical scaffold. These polarized ATR-IR studies measured an average DMPC acyl chain tilt angle of ∼21-25°, with respect to the surface normal.

To date, detailed studies of the thickness of coatings using surface plasmon resonance have been limited to samples that are very uniform in thickness, and this technique has not been applied quantitatively to samples that are inherently rough or undergo instabilities with time. Our manuscript describes a significant improvement to surface plasmon resonance imaging (SPRi) that allows this sensitive technique to be used for quantitative tracking of the thickness and roughness of surface coatings that are rough on the scale of tens of nanometers. We tested this approach by studying samples with an idealized, one-dimensional roughness: patterned channels in a thin polymer film. We find that a novel analysis of the SPRi data collected with the plane of incidence parallel to the patterned channels allows the determination of the thickness profile of the channels in the polymer film, which is in agreement with that measured using atomic force microscopy. We have further validated our approach by performing SPRi measurements perpendicular to the patterned channels, for which the measured SPR curve agrees well with the single SPR curve calculated using the average thickness determined from the thickness profile as determined using AFM. We applied this analysis technique to track the average thickness and RMS roughness of cellulose microfibrils upon exposure to cellulolytic enzymes, providing quantitative determinations of the times of action of the enzymes that are of direct interest to the cellulosic ethanol industry.

Surface-enhanced infrared absorption spectroscopy (SEIRAS) was employed to study structure of water in a phospholipid bilayer deposited at a gold electrode surface. The technique employs attenuated total reflection (ATR) and an enhancement of the electric field of the IR photon that decays steeply with distance from the metal surface. These conditions allow one to subtract the background from the bulk water and to determine spectra of water in the bilayer or in a confined space between the metal surface and the bilayer. The IR data demonstrated that three types of water are present in the supported bilayer. At potentials close to zero charge the polar heads of the phospholipid molecules retain hydration water. At intermediate charge densities water penetrating deeply into the bilayer and multimers of water molecules were detected in the bilayer. At charge densities more negative than −20 μC/cm2 the bilayer is lifted from the metal surface and liquid like water appears in the space separating the bilayer from the metal.

The effect of amiloride, an acid-sensing ion channel (ASIC) blocker, on the formation of alamethicin ion channels in tethered zwitterionic phospholipid bilayers was investigated using electrochemical impedance spectroscopy (EIS) and polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS). EIS measurements show a decrease in conductivity indicating that ion transported across the alamethicin-rich phospholipid membrane is inhibited by the presence of amiloride. The PM-IRRAS spectra indicate that amiloride has no effect on the secondary structure of the alamethicin peptide. The IR data suggests that amiloride does not block ion translocation through the alamethicin ion pore but prevents the insertion of alamethicin peptides into the biomembrane suppressing the formation of ion channels. The mechanism responsible for amiloride inhibition is explained in terms of the electrostatic interactions between the molecule and membrane surface. Amiloride is positively charged at physiological pH levels invoking a repulsive force on the positive pole of the alamethicin molecular dipole. These repulsive interactions prevent the insertion of the alamethicin peptides into the hydrophobic core of the lipid bilayer. The present paper offers a molecular view of the interactions that occur between amiloride, an ion channel inhibitor, with the lipids and ion channel forming peptides in model tBLMs.