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The structural complexity of the cell envelope of Gram-negative bacteria limits the fabrication of realistic models of bacterial cell membranes. A vertical Langmuir-Blodgett withdrawing was used to deposit a 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoethanolamine (POPE) monolayer on the Au(111) surface. The second leaflet composed of di[3-deoxy-D-manno-octulosonyl]-lipid A (KLA) was deposited using Langmuir-Schaefer transfer. The use of an electrode material as a support for the POPE-KLA bilayer allowed electrochemical control of the membrane's stability, compactness, and structure. Capacitance-potential curves showed a typical pattern for the supported lipid bilayers electrochemical characteristic. The minimum membrane capacitance was ∼4 μF cm

Knowledge of the structure of the electrical double layer in ionic liquids (IL) is crucial for their applications in electrochemical technologies. We report the synthesis and applicability of an imidazolium-based amphiphilic ionic liquid with a perdeuterated alkyl chain for studies of electric potential-dependent rearrangements, and changes in the microenvironment in a monolayer on a Au(111) surface. Electrochemical measurements show two states of the organization of ions on the electrode surface. In situ IR spectroscopy shows that the alkyl chains in imidazolium cations change their orientation depending on the adsorption state. The methylene-d2 stretching modes in the perdeuterated IL display a reversible, potential-dependent appearance of a new band. The presence of this mode also depends on the anion in the IL. Supported by quantum chemical calculations, this new mode is assigned to a second νas (CD2 ) band in alkyl-chain fragments embedded in a polar environment of the anions/solvent present in the vicinity of the imidazolium cation and electrode. It is a measure of the potential-dependent segregation between polar and nonpolar environments in the layers of an IL closest to the electrode.

The cell membrane of Gram-negative bacteria interacting with an antimicrobial peptide presents a complex supramolecular assembly. Fabrication of models of bacterial cell membranes remains a large experimental challenge. Langmuir–Blodgett and Langmuir–Schaefer (LS–LB) transfer makes possible the deposition of multicomponent asymmetric lipid bilayers onto a gold surface. Two lipids: 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoethanolamine (POPE) and di[3-deoxy-D-manno-octulosonyl]-lipid A (KLA) were used to deposit a model of the outer membrane of Gram-negative bacteria on the Au(111) substrate. The use of gold as the solid substrate enables control of the membrane potential. Molecular scale changes in the model membrane exposed to physiological electric fields and interacting with melittin antimicrobial peptide are discussed in this paper. The interaction of the outer membrane with melittin leads to an increase in the membrane capacitance and permeability to ions and water. The stability of the outer membrane with bound melittin decreases at positive membrane potentials. In situ polarization modulation infrared reflection absorption spectroscopy is used to investigate membrane potential-dependent changes in the structure of the outer membrane interacting with melittin. The hydration of the ester carbonyl groups is not affected by the interaction with melittin. However, the orientation and hydrogen bond network with the carboxylate groups in KLA changes drastically after POPE–KLA bilayer interacts with melittin. We propose that the positively charged groups in the amino acids present at the C-terminus of the peptide interact directly with the polar head group of KLA. Simultaneously, the packing order in hydrocarbon chains in the membrane with bound melittin increases. A hydrophobic match between the chains in the lipids and the peptide, which spans the membrane, seems to be responsible for the ordering of the hydrocarbon chains region of the bilayer. The N-terminus enters into the hydrophobic region of the membrane and forms a channel to the hydrophilic head groups in POPE.

A self-assembled monolayer (SAM) on gold was prepared from a diaminoterephthalate (DAT) derivative as functional molecule and 1-decanthiol as a backfiller. The DAT derivative is N-protected by a te...

With nanoparticle-based inks, thin-film solar cells can be printed directly from solution, which promises cost reduction compared to conventional manufacturing methods. For synthesis of nanoparticl...

Piptoporus betulinus is a fungus known for its medicinal properties. It possesses antimicrobial, anti-inflammatory, and anti-cancer activity. In this study, several tests were performed to evaluate the cytotoxic effect of the ethanolic extract of Piptoporus betulinus on two melanoma human cell lines, WM115 primary and A375 metastatic cell lines, as well as Hs27 human skin fibroblasts. The extract proved to affect cancer cells in a dose-dependent manner, and at the same time showed a low cytotoxicity towards the normal cells. The total phenolic content (TPC) was determined spectrophotometrically by the Folin-Ciocalteu method (F-C), and the potential antioxidant activity was measured by ferric-reducing antioxidant power (FRAP) assay. One of the active compounds in the extract is betulin. It was isolated and then its cytotoxic activity was compared to the results obtained from the Piptoporus betulinus extract. To further understand the mechanism of action of the extract’s anticancer activity, tests on model cell membranes were conducted. A model membrane of a melanoma cell was designed and consisted of 1,2-dimyristoyl-sn-glycero-3-phosphocholine, disialoganglioside-GD1a and cholesterol: DMPC:GD1a:chol (5:2:3 mole ratio). Changes in a Langmuir monolayer were observed and described based on Π-Amol isotherm and compressibility modulus changes. LB lipid bilayers were deposited on a hydrophilic gold substrate and analyzed by IR and X-ray photoelectron spectroscopy. Our study provides new data on the effect of Piptoporus betulinus extract on melanoma cells and its impact on the model of melanoma plasma membranes.

Forisomes are giant self-assembling mechanoproteins that undergo reversible structural changes in response to Ca

The cell membrane of Gram-negative bacteria interacting with an antimicrobial peptide presents a complex supramolecular assembly. Fabrication of models of bacterial cell membranes remains a large experimental challenge. Langmuir-Blodgett and Langmuir-Schaefer (LS-LB) transfer makes possible the deposition of multicomponent asymmetric lipid bilayers onto a gold surface. Two lipids: 1-palmitoyl-2-oleoyl

The structure of cations and anions in ionic liquids is precisely selected to tune their properties for applications in catalysis, electrochemistry, or development of sensors. Substitution of a hyd...

Compatible solutes accumulate in the cytoplasm of halophilic microorganisms, enabling their survival in a high-salinity environment. Ectoine is such a compatible solute. It is a zwitterionic molecule that strongly interacts with surrounding water molecules and changes the dynamics of the local hydration shell. Ectoine interacts with biomolecules such as lipids, proteins, and DNA. The molecular interaction between ectoine and biomolecules, in particular the interaction between ectoine and DNA, is far from being understood. In this paper, we describe molecular aspects of the interaction between ectoine and double-stranded DNA (dsDNA). Two 20 base pairs-long dsDNA fragments were immobilized on a gold surface via a thiol-tether. The interaction between the dsDNA monolayers with diluted and concentrated ectoine solutions was examined by means of X-ray photoelectron and polarization modulation infrared reflection absorption spectroscopies (PM IRRAS). Experimental results indicate that the ability of ectoine to bind water reduces the strength of hydrogen bonds formed to the ribose-phosphate backbone in the dsDNA. In diluted (0.1 M) ectoine solution, DNA interacts predominantly with water molecules. The sugar-phosphate backbone is involved in the formation of strong hydrogen bonds to water, which, over time, leads to a reorientation of the planes of nucleic acid bases. This reorientation destabilizes the strength of hydrogen bonds between the bases and leads to a partial dehybridization of the dsDNA. In concentrated ectoine solution (2.5 M), almost all water molecules interact with ectoine. Under this condition, ectoine is able to interact directly with DNA. Density functional theory (DFT) calculations demonstrate that the direct interaction involves the nitrogen atoms in ectoine and phosphate groups in the DNA molecule. The results of the quantum-chemical calculations show that rearrangements in the ribose-phosphate backbone, caused by a direct interaction with ectoine, facilitates contacts between the O atom in the phosphate group and H atoms in a nucleic acid base. In the PM IRRA spectra, an increase in the number of IR absorption modes in the base pair frequency region proves that the hydrogen bonds between bases become weaker. Thus, a sequence of reorientations caused by interaction with ectoine leads to a breakdown of hydrogen bonds between bases in the double helix.

Adsorption of ions or neutral molecules on electrode surfaces leads to changes in the macroscopic properties of surfaces such as the surface energy, contact angle, surface charge density or surface potential. Potential-driven adsorption-desorption process of ions or neutral molecules on electrode surfaces belongs to an important research topic in electrochemistry. The process of adsorption of ions and molecules on the electrode surface may be understood at the molecular level when structure analyzing techniques, such as PM IRRAS, are applied to the electrochemical interface. Since the first application of PM IRRAS to the electrochemical interface the picture of potential-dependent changes in the structure, composition, and orientation of ions and amphiphilic molecules present on metallic electrode surfaces is available in the literature. Numerous studies are dedicated to investigate potential-dependent structural changes in biomimetic systems such as lipid bilayers, their interaction with proteins as well as self-assembled protein or DNA films.

Polarization modulation infrared reflection-absorption spectroscopy (PM IRRAS) is an advanced structure analyzing technique. The propagation of the electromagnetic radiation in a medium and its reflection and refraction describe the reflectivity of the incoming beam from a phase boundary and transmissivity into a second medium, respectively. When the incoming IR radiation encounters a metal surface, the IR beam is almost fully reflected from its surface. The reflectivity of the IR light depends in the state of polarization of the incoming radiation. This property gives the theoretical background of IRRAS. When the incoming IR radiation is double modulated: at the Fourier transform IR spectrometer and at a photoelastic modulator, the measured signal provides a differential spectrum which is proportional to the absorbance of the species absorbing the IR light on the mirror surface. In this chapter the theory of the propagation of electromagnetic radiation in a condensed medium and theoretical backgrounds of IRRAS, PM IRRAS and in situ electrochemical PM IRRAS are described.

Determination of potential-dependent changes in the composition and structure of redox-active molecules involved in electrochemical reactions is one of the most important research objects in electrochemistry. Reduction and oxidation reactions take place on the electrode surface indicating that a redox-active substrate, at least during the redox reaction, is in direct contact with the electrode surface. In this chapter the applicability of PM IRRAS for studies of changes in the composition, structure and orientation of redox-active species in sub-monolayer, monolayer, multilayer films deposited on the metallic electrode surface is described. Use of non-metallic electrodes, such as glassy carbon electrodes, is of large practical importance in modern electrochemistry. Indeed, PM IRRAS with electrochemical control was successfully applied to study structural changes in complex redox reactions in thick polymer and composite material films on the glassy carbon electrode.

Light weight metals such as magnesium and aluminum have excellent engineering properties which makes them attractive for industrial applications. Poor corrosion resistance is the major drawback for their wide applications. Corrosion of metal surfaces is a common but complex phenomenon, which depends on the sample environment. Despite intensive studies the molecular aspects of magnesium corrosion are not fully understood yet. Infrared spectroscopy is an excellent analytical technique to study the chemical composition and structure of molecules. Reflection based infrared spectroscopy techniques are applicable to investigate the structure of molecules adsorbed on surfaces. In this paper we demonstrate that magnesium with its passive layer is suitable for infrared reflection absorption spectroscopy experiments. On the pure magnesium surface the IR light is strongly reflected and the highest enhancement of the normal component of the p-polarized light (probing the species present on the surface) is obtained at grazing angles of incidence. Growth of the passive layer leads to a gradual shift of the optimal angle of incidence to lower values (60° vs. surface normal). Polarization modulation infrared reflection absorption spectroscopy is used to study changes in the composition and structure occurring during magnesium corrosion in air and in aqueous solutions. In air and in aqueous NaCl solution Mg(OH)2 and magnesium carbonate minerals coordinating water and hydroxide ions are formed on the surface. IR spectra provide clear evidence that the coordination of the Mg2+ to carbonate ions changes in time from mono- to bi- and polydentate. In the presence of orthophosphate ions in the electrolyte solution, the Mg(OH)2 layer disappears from the surface while magnesium phosphate salts crystalize on the metal surface.

Metal hexacyanometallates represent coordination network compounds with a large variety of structurally similar substances. It is well established that they can undergo multiple redox transitions accompanied by cation insertion/ejection. However, the exact assignment of structural changes has remained complicated partially due to the structural variability resulting from different preparation methods and the lack of in situ tools to follow the redox transition and structural changes simultaneously. In this communication we prepared cobalt hexacyanoferrate (CoHCF) and copper hexacyanoferrate (CuHCF) by electrochemical deposition and, additionally, CuHCF by layer-by-layer deposition. These hexacyanoferrate films have a suitable thickness for their spectroelectrochemical characterization by means of polarization modulation infrared reflection-absorption spectroscopy with electrochemical control. Potential-dependent structural changes were followed in both HCF films using the cyanide stretching mode ν(C N) whose detailed position reveals coordination and symmetry around the cyanide bridging ligand. CoHCF undergoes two redox reactions. The spectral analysis of the ν(C N) mode provides clear evidence that oxidation of N-coordinated Co (II) to Co (III) takes place in the first redox process, at E 1 °′ = 0.530 V. The second redox process at E 2 °′ = 0.685 V is assigned to a partial oxidation of the C-coordinated Fe (II) /Fe (III) . In CuHCF films, one redox process involves predominantly Fe (II) /Fe (III) centers. However, in the electrochemically deposited film a small fraction of the Cu (II) centers is oxidized to Cu (III) . The species containing Cu (III) ions are unstable and undergo electron transfer reactions leading to the oxidation of the Fe (II) to Fe (III) . In addition, CuHCF shows ‘annealing’ in which some cyanide groups change the coordination to C-coordinated Cu ions and N-coordinated Fe ions.

In this paper we analyze the changes in molecular orientation triggered by electrochemical reduction of an iron-containing surfactant in Langmuir-Blodgett films deposited onto gold electrodes. The metallosurfactant [Feiii(LN2O3)] (1) is an established molecular rectifier capable of unidirectional electron transfer between two electrodes. A gradual decrease in the activity is observed in sequential current vs. potential curves upon repeated cycles. Here we evaluate the redox response associated with the reduction of the Feiii/Feii couple in a single monolayer, as well as in a 5-layer LB film of 1. We use polarization modulation infrared reflection absorption spectroscopy (PM IRRAS) to follow structural and orientation changes associated with such applied potential scans. We observe that the reduction of the Fe center becomes increasingly irreversible because an Fe-Ophenolate bond is cleaved. This transformation is accompanied by an almost vertical change in the orientation of metallosurfactant molecules in LB films.

Adsorbed protein films consist of essential building blocks of many biotechnological and biomedical devices. The electrostatic potential may significantly modulate the protein behaviour on surfaces, affecting their structure and biological activity. In this study, lysozyme was used to investigate the effects of applied electric potentials on adsorption and the protein structure. The pH and the surface charge determine the amount and secondary structure of adsorbed lysozyme on a gold surface. In-situ measurements using polarization modulation infrared reflection absorption spectroscopy indicated that the concentration of both the adsorbed anions and the lysozyme led to conformational changes in the protein film, which was demonstrated by a greater amount of aggregated β-sheets in films fabricated at net positive charges of the Au electrode (Eads > Epzc). The changes in secondary structure involved two parallel processes. One comprised changes in the hydration/hydrogen-bond network at helices, leading to diverse helical structures: α-, 310- and/or π -helices. In the second process β-turns, β-sheets, and random coils displayed an ability to form aggregated β-sheet structures. The study illuminates the understanding of electrical potential-dependent changes involved in the protein misfolding process.

Planar asymmetric lipid bilayers composed of phosphatidylethanolamine and phosphatidylglycerol lipids are transferred onto a gold electrode surface. Lipids containing two saturated, one monounsaturated and two monounsaturated hydrocarbon chains compose the model membranes. Results of electrochemically controlled polarization modulation infrared reflection absorption spectroscopy and quartz crystal microbalance with energy dissipation studies reveal two different types of electric potential-dependent structural rearrangements in the bilayers. They are correlated with the geometry of the lipid molecule. Packing parameter correlates the cross-section area of the hydrophobic and hydrophilic parts of amphiphilic molecules. In bilayers composed of lipids with the packing parameter1, the hydrocarbon chains are tilted with respect to the bilayer plane and the polar head groups are well hydrated. At a threshold potential an abrupt flow of water through the bilayer is connected with membrane dehydration and upward orientation of the chains. In bilayers composed of lipids with packing parameter ≥1, electric potentials have negligible effect on the membrane structure. A simple rule correlating the packing parameter with molecular scale changes occurring at electrified membranes has a large diagnostic implication for biomimetic studies and our understanding of molecular processes occurring in biological cell membranes.

Droplet-based bio-printing (DBB) techniques have been extensively accepted due to their simplicity, flexibility and cost performance. However, the applicability of inkjet printing for bioprinting techniques still faces challenges, such as a narrow range of available bio-ink materials, cell damage due to the pressure strike and high shear rate during the printing process. Here, a new droplet-based printing technique, pneumatic conveying printing (PCP), is described. This new technique is successfully adopted for cell-printing purposes. The cells present in the bio-ink are not exposed to any significant pressure and therefore the PCP technique is gentle to the cells. Furthermore, PCP allows the usage of inks with viscosities higher than 1000 mPa s, enabling the usage of bio-inks with high cell concentrations (several tens of millions per millilitre). As a proof of concept, two different cell types were printed with this novel technique. To achieve a printing resolution of 400 to 600 μm, cells were encapsulated into a hydrogel containing calcium alginate. Deposition of the bio-ink drop containing sodium alginate on a surface pre-treated in CaCl

In this paper we analyze the changes in molecular orientation triggered by electrochemical reduction of an iron-containing surfactant in Langmuir-Blodgett films deposited onto gold electrodes. The metallosurfactant [Feiii(LN2O3)] (1) is an established molecular rectifier capable of unidirectional electron transfer between two electrodes. A gradual decrease in the activity is observed in sequential current vs. potential curves upon repeated cycles. Here we evaluate the redox response associated with the reduction of the Feiii/Feii couple in a single monolayer, as well as in a 5-layer LB film of 1. We use polarization modulation infrared reflection absorption spectroscopy (PM IRRAS) to follow structural and orientation changes associated with such applied potential scans. We observe that the reduction of the Fe center becomes increasingly irreversible because an Fe-Ophenolate bond is cleaved. This transformation is accompanied by an almost vertical change in the orientation of metallosurfactant molecules in LB films.

An ideal bioanalytical method would allow carrying out sensitive, selective, reproducible, fast, and in situ chemical measurements of the composition, structure and function of complex biological systems. Physical chemistry possesses advanced structure analyzing techniques which are suitable to solve, at a sub-molecular level, the structure of biomolecules. However, the prerequisite of the presence of the electrolyte solution limits the number of applicable structure analyzing techniques. Infrared spectroscopy is one of the most powerful analytical techniques used to identify the structure of biomolecules, monitor structural changes under various experimental environments and physical states. In addition, infrared reflection absorption spectroscopy (IRRAS) has been successfully applied to study supramolecular films at the solid|liquid interface. Assemblies of biomolecules belong to a particularly demanding because they bring specific for the maintenance of their functions experimental requirements which have to be taken into account planning in situ spectroelectrochemical experiments. In this paper potnential of in situ IRRAS under electrochemical control for studies of structural changes in assemblies of biomolecules such as lipid bilayers and protein films is described. Studies of different classes of biomolecules bring certain experimetnal conditions concerning the electrolyte composition, pH value, temperature or chemical nature of the solid support, which have to be fulfilled. Obviously, these conditons may significantly restrict the applicability of the in situ PM IRRAS. The selection of the solid substrate with required optical and electrical properties, the optical window and the electrolyte composition have to be adapted to the needs of biomolecules. Adjustement of experimetnal conditions as well as possibilites of the enlargement of the in situ PM IRRAS for studies of biomimetic assemblies is reviewed in this paper. Furthermore, experimetnal resutls reporting potenial driven changes in models of cell membranes and protein films are reviewed. Pioneering studies aiminig at the determination of structural changes in lipid membranes exposed to physiological electric fields and interacting simultaneously with protiens are described.

Titanium oxide–titanium carbide (TiOxCy) hybrid materials have tunable electronic properties ranging from semiconductive to semimetallic. They can therefore be employed in solar energy conversion applications and as potential substitute for carbon based electrocatalyst supports for use in fuel cells. Understanding of the optical properties of semimetallic TiOxCy is of great importance. In this paper we report on the optical properties of compact TiOxCy in the mid-IR spectral region. TiOxCy reflects the IR light similarly to metals and is therefore suitable as a new substrate for molecular adsorption studies with infrared reflection absorption spectroscopy. For the first time polarization modulation infrared reflection absorption spectroscopy (PM IRRAS) is applied to study quantitatively at the submolecular level the structure and orientation of fatty acid molecules in monolayers adsorbed on the TiOxCy surface. The analysis of the IR band intensities provides information on the structure, packing, and orie...

The morphology and structure of collagen type I adsorbed on gold electrodes were studied as a function of electrode potential and temperature by means of capacitance measurements, polarization modulation infrared reflection–absorption spectroscopy and scanning force microscopy at temperatures of 37 °C, 43 °C and 50 °C. The selected temperatures corresponded to the normal body temperature, temperature of denaturation of collagen molecules and denaturation of collagen fibrils, respectively. Independently of the solution temperature, collagen was adsorbed on gold electrodes in the potential range − 0.7 V E E

Unique electronic and ligand recognition properties of the DNA double helix provide basis for DNA applications in biomolecular electronic and biosensor devices. However, the relation between the structure of DNA at electrified interfaces and its electronic properties is still not well understood. Here, potential-driven changes in the submolecular structure of DNA double helices composed of either adenine-thymine (dAdT)25 or cytosine-guanine (dGdC)20 base pairs tethered to the gold electrodes are for the first time analyzed by in situ polarization modulation infrared reflection absorption spectroscopy (PM IRRAS) performed under the electrochemical control. It is shown that the conformation of the DNA duplexes tethered to gold electrodes via the C6 alkanethiol linker strongly depends on the nucleic acid sequence composition. The tilt of purine and pyrimidine rings of the complementary base pairs (dAdT and dGdC) depends on the potential applied to the electrode. By contrast, neither the conformation nor orie...

Monolayers of a new hybrid compound having two linearly coupled subunits with different functionalities were prepared on the silicon oxide and silicate-like surfaces using trichlorosilane as an anchoring group. The two subunits of the hybrid compound are a perfluorinated alkyl chain and an oligoethylene glycol chain. The synthesis of the new precursor compound, O -methyl hexaethylene glycol-icosafluorododecandiol-trichlorosilane is reported starting from commercially available triethylene glycol and perfluorododecan-1,12-diol as building blocks. The final and intermediate products were characterized by nuclear magnetic resonance ( 1 H NMR, 13 C NMR, 19 F NMR and 29 Si NMR), infrared spectroscopy (IR) and high resolution mass spectrometry with chemical ionization [HRMS (CI)]. The new compound was self-assembled on borosilicate glass, surface-oxidized silicon and silicon oxide surfaces. Properties of the self-assembled films as a function of the adsorption time were studied using contact angle measurements, X-ray photoelectron spectroscopy, polarization modulation infrared reflection absorption spectroscopy and scanning force microscopy. The adsorption of the hybrid silane on an atomically flat silica surface lead to the formation of poorly defined multilayer films. By contrast, the adsorption of the silane onto a less-ordered substrate resulted in the formation of a well-packed monolayer.

International audience; The influence of the potential applied to the polycrystalline gold electrode on the adsorption state and structure of collagen molecules were studied by means of electrochemistry, in situ ellipsometry and in situ polarization modulation infrared reflection-absorption spectroscopy. At the macroscopic level, potential and the corresponding charge accumulated on the gold electrode determine the adsorption process of the collagen film on the Au electrode surface. The protein film is stable on the electrode surface at potentials close to the potential of zero charge. The protein film sustains a large negative potential drop (Delta phi(M vertical bar S) >= -0.5 V) whereas it is unstable at a small positive potential drop (Delta phi(M vertical bar S) approximate to 0.1 V) across the film. Positive net charge accumulated on the Au surface causes electrostatic repulsions of collagen molecules bearing a positive net charge. Loosening of water and destabilization of the protein film reflect repulsions between the Au electrode and the collagen molecules. In contrast, at charge densities between -8 < sigma(M) < -20 mu C cm(-2) electrostatic attractions between the electrode surface and the protein molecule appear. A stable, well hydrated collagen film is formed on the Au surface. Higher negative charges accumulated on the electrode surface lead to swelling on the protein film by water and lead to the desorption of the protein film from the Au surface. In situ spectroelectrochemical studies show that at the molecular level neither the secondary structure nor the orientation of collagen molecules are affected by electrical potentials. Independently of the applied potential and electric fields acting on the film the collagen molecule maintains its native structure. Collagen molecules adsorbed on the Au surface form a heterogeneous film with well-defined structure and unusual stability at the molecular level.

Unsymmetric three component lipid bilayers containing 1,2-dimyristoyl- sn -glycero-3-phosphatidylcholine (DMPC), cholesterol and a ganglioside were prepared using the Langmuir–Blodgett–Langmuir–Schaefer (LB–LS) technique on the surface of a polycrystalline gold electrode. The lipid layer contains the ganglioside only in the outer layer, mimicking a natural cell membrane. Gangliosides are glycolipids containing at least one sialic acid residue and are proposed to be a binding partner for siglec proteins. Interaction between Siglec-4, the myelin-associated glycoprotein (MAG) and two gangliosides in lipid bilayers was investigated. MAG protein binds only to the sialic acid residue located at the terminal position in the oligosaccharide head group of a lipid molecule. In this study two gangliosides, the GD 1a having one terminal sialic acid residue and the GM 1 not possessing a terminal sialic acid residue in the polar head group were used. Under physiological conditions a lipid membrane is constantly exposed to high electric fields. Three component lipid bilayers transferred by the LB–LS method are characterized by capacitance minimum equal to 2.3 and 5.0 μF cm −2 in the film containing the GM 1 and GD 1a , respectively. The lipid bilayer desorbs form the electrode surface at E 1a in the presence of the protein hinders structural changes taking place in the lipid film exposed to changing electric fields. At the molecular level the binding of the protein to the GD 1a introduces structural changes not only in the glycolipid molecule, but in the whole membrane. In the polar head group of the GD 1a amide groups in sialic acid residues lose some water of hydration upon interaction with the protein. The hydrocarbon chains of the GD 1a exhibit ordering with respect to the surface normal. Reorientations in the ganglioside molecule may lead to changes in the phosphatidylcholine, main lipid component of the bilayer. In the DMPC molecule the dehydration of the ester group with simultaneous change in tilt of the acyl chains were observed.

During the last years, surface-bound coordination network compounds (CNCs) have found application for sensing purposes (electrical, optical, and magnetic read-out), charge storage, electrochromic and optoelectronic layers, transparent coatings, bipolar switches, thermoelectric materials, catalytic, photocatalytic and light harvesting applications [1]. However, most of these applications require electrically conductive coordination network compounds (CCNCs). This requirement severely limits the choice of CNCs for the above-mentioned applications. Hexacyanometallates are coordinative networks with high electrical and ion conductivity that possess interesting redox properties and tuneable electrochemical redox transitions associated with clear colour changes [2]. We developed and characterized CCNCs such as copper hexacyanoferrate as thin crystalline films and characterized their optical, magnetic, electrical and dielectric properties. Thin films of these compounds were fabricated on gold and silicon oxide coated by self-assembled, cyanide-terminated monolayers using alternating immersion in their precursor solutions. Atomic force microscopy (AFM) confirms the formation of copper hexacyanoferrate with cubic structure on the gold surface (Fig. 1). Fig. 1: AFM image of copper hexacyanoferrate film on a cyanide-terminated self-assembled monolayer on gold surface via layer-by-layer method. X-ray diffraction (XRD) analysis confirmed the crystalline nature of the films. The thin films can be switched by exploiting the redox chemistry of the metal centres. The modulation of the electrical transport properties provides great potential benefits for numerous future applications in microelectronic device technologies. Structural and electronic changes of the films were probed by X-ray photoelectron spectroscopy (XPS) and polarization modulation infrared reflection absorption spectroscopy (PM IRRAS) before and after electrochemical oxidation and reduction [3]. Results demonstrate the possibility for electrochemical switching of the material properties for each compound but also indicates the complications in those transitions originating in the existence of different structures and defects in which (mobile) alkali metal cations may or may not reside in the pores and provide charge compensation. Acknowledgement(s) Financial supports from DFG priority programme (SPP1928, Wi1617/24) is gratefully acknowledged. References: [1] J. Liu, W. Zhou, J. Liu, I. Howard, G. Kilibarda, S. Schlabach, D. Coupry, M. Addicoat, S. Yoneda and Y. Tsutsui, Angew. Chem. Int. Ed., 7441, 54 (2015). [2] J. J. Alexander and H. B. Gray, J. Am. Chem. Soc., 4260, 90 (1968). [3] P. Hosseini, G. Wittstock and I. Brand, J. Electroanal. Chem., 199, 812 (2017). Figure 1

The polarization modulation infrared reflection-absorption spectra of collagen adsorbed on a titania surface and quantum chemical calculations are used to describe components of the amide I mode to the protein structure at a sub-molecular level. In this study, imino acid rich and poor fragments, representing the entire collagen molecule, are taken into account. The amide I mode of the collagen triple helix is composed of three absorption bands which involve: (i) (∼1690cm(-1)) the CO stretching modes at unhydrated groups, (ii) (1655-1673cm(-1)) the CO stretching at carbonyl groups at imino acids and glycine forming intramolecular hydrogen bonds with H atoms at both NH2 and, unusual for proteins, CH2 groups at glycine at a neighbouring chain and (iii) (∼1640cm(-1)) the CO stretching at carbonyl groups forming hydrogen bonds between two, often charged, amino acids as well as hydrogen bonds to water along the entire helix. The IR spectrum of films prepared from diluted solutions (c

International audience; Polarization-modulation infrared reflection-absorption spectroscopy, surface pressure measurements and thermodynamic analysis were used to study enzymatic hydrolysis of lipid monolayers at the air/water interface. The Ca2+-requiring pork pancreatic phospholipase A2 was used as a catalyst. The substrates were pure 1,2-dilauroyl-sn-glycero-3-phosphocholine or mixed 1,2-dilauroyl-sn-glycero-3-phosphocholine - monosialotetrahexosylganglioside Langmuir films. The physicochemical properties of the monolayers were established with the aim of a correlation with enzyme activity. The infrared spectra were acquired upon the advancement of the catalysis; the latter was studied at a controlled surface pressure and area of the film. Changes of the intensity and frequency of different infrared signals characteristic for the two lipids were correlated with modification of the properties of the monolayer due to hydrolysis. The amide I signal characteristic for peptides permitted detecting the enzyme adsorbed at the interface. The thermodynamic and infrared results indicate that monosialotetrahexosylganglioside increases H-bonding of the lipid polar heads in the films. This effect, which may be responsible for the low activity of phospholipase A2 in the mixed films, could be used for developing enzyme-resistant lipid systems.

A biological membrane is a complex and fragile supramolecular assembly. Substitution of a cell membrane by a simpler model is desirable due to the development of biosensors, implants, and drugs. The biological membrane is constantly exposed to high electric fields, which influence the molecular scale order in the membrane. The deposition of a model lipid bilayer on the electrode surface provides the possibility of applying physiological electric fields to the membrane. A molecular level characterization of lipid bilayers adsorbed on an electrode surface is possible only when spectroscopic or microscopic techniques are in situ combined to an electrochemical experiment. In this chapter, various methods of preparation and characterization of supported planar lipid bilayers are described. The influence of electrical potential on the compactness, stability, and structure of symmetric and asymmetric lipid bilayers is described.

Control of the cell adhesion and growth on chemically patterned surfaces is important in an increasing number of applications in biotechnology and medicine, for example implants, in-vitro cellular assays, and biochips. This review covers patterning techniques for organic thin films suitable for site-directed guidance of cell adhesion to surfaces. Available surface patterning techniques are critically evaluated, with special emphasis on surface chemistry that can be switched in time and space during cultivation of cells. Examples from the authors' laboratory include the use of cell-repellent self-assembled monolayers (SAM) terminated by oligoethylene glycol (OEG) units and the lifting of the cell repellent properties by use of electrogenerated Br2/HOBr which can be performed with positionable microelectrodes. Structural changes of the SAM were analyzed by polarization-modulated infrared reflection absorption spectroscopy (PM IRRAS). Use of a soft array system of individually addressable microelectrodes enables formation of flexible and complex patterns in a short time and has the potential for further acceleration of probe-induced local manipulation of cell adhesion.

The sections in this article are Introduction Titanium in Contact with a Biomaterial Lipid Bilayers at the Titania Surface Formation of Lipid Bilayers on the Titania Surface Spreading of Vesicles on a TiO2 Surface: Comparison to a SiO2 Surface Interactions: Lipid Molecule–Titania Surface Structure and Conformation of Lipid Molecules in the Bilayer on the Titania Surface Structure of Phosphatidylcholine on the Titania Surface Characteristics of Extracellular Matrix Proteins on the Titania Surface Collagen Adsorption on Titania Surfaces Morphology of Collagen Adsorbed on an Oxidized Titanium Surface Adsorption of Collagen on a Hydroxylated Titania Surface Morphology and Structure of Collagen Adsorbed on a Calcified Titania Surface Conclusions Structure of Collagen on the Titania Surface: Theoretical Predictions Fibronectin Adsorption on the Titania Surface Morphology of Fibronectin Adsorbed on the Titania Surface Fibronectin–Titania Interactions Structure of Fibronectin Adsorbed onto the Titania Surface Atomic-Scale Picture of Fibronectin Adsorbed on the Titania Surface: Theoretical Predictions Conclusions Conclusions Acknowledgments Keywords: titania; lipid bilayer; collagen; fibronectin; implant material; surface-characterizing techniques

A lipid bilayer deposited on an electrode surface can serve as a benchmark system to investigate lipid-protein interactions in the presence of physiological electric fields. Recoverin and myelin-associated glycoprotein (MAG) are used to study the impact of strong and weak protein-lipid interactions on the structure of model lipid bilayers, respectively. The structural changes in lipid bilayers are followed using electrochemical polarization modulation infrared reflection-absorption spectroscopy (PM IRRAS). Recoverin contains a myristoyl group that anchors in the hydrophobic part of a cell membrane. Insertion of the protein into the 1,2-dimyristoyl-sn-glycero-3-phosphatidylcholine (DMPC)-cholesterol lipid bilayer leads to an increase in the capacitance of the lipid film adsorbed on a gold electrode surface. The stability and kinetics of the electric-field-driven adsorption-desorption process are not affected by the interaction with protein. Upon interaction with recoverin, the hydrophobic hydrocarbon chains become less ordered. The polar head groups are separated from each other, which allows for recoverin association in the membrane. MAG is known to interact with glycolipids present on the surface of a cell membrane. Upon probing the interaction of the DMPC-cholesterol-glycolipid bilayer with MAG a slight decrease in the capacity of the adsorbed lipid film is observed. The stability of the lipid bilayer increases towards negative potentials. At the molecular scale this interaction results in minor changes in the structure of the lipid bilayer. MAG causes small ordering in the hydrocarbon chains region and an increase in the hydration of the polar head groups. Combining an electrochemical approach with a structure-sensitive technique, such as PM IRRAS, is a powerful tool to follow small but significant changes in the structure of a supramolecular assembly.

A self-assembled monolayer (SAM) on gold was formed with specifically perdeuterated hexaethylene glycol-terminated alkanethiol HS(CD(2))(12)(O-CH(2)-CH(2))(6)OCH(3) (D-OEG). The structure of the d-alkane and the oligoethylene glycol (OEG) parts of the molecule in a SAM was studied by means of polarization modulation infrared reflection absorption spectroscopy. The D-OEG monolayers are highly ordered and exist in a crystalline phase. The d-alkane chain adopts an all-trans conformation. Both, the d-alkane chain and long axis of the OEG part make an angle of 26.0 degrees +/- 1.5 degrees with respect to the surface normal, a value characteristic for the tilt of solid n-alkane thiols in the SAMs on Au. The positions of nu(as)(COC) and CH(2) wagging and rocking modes indicate a helical arrangement of the OEG chains. The D-OEG SAMs were exposed to 25 muM Br(2) in two ways: (i) by immersion into the Br(2) solution and (ii) in the galvanic cell Au|D-OEG SAM|25 muM Br(2) + 0.1 M Na(2)SO(4)|| 50 muM KBr + 0.1 M Na(2)SO(4)|Au. In the galvanic cell, the oxidant (Br(2)) is scavenged by a heterogeneous electron transfer reaction, slowing the reaction of D-OEG with Br(2). The slow progress of the reaction with Br(2) allowed us to draw conclusions about molecular rearrangements taking place during this reaction. The reaction with Br(2) starts on boundaries and/or defects present in the SAM. First, at the defect place, the alpha-C atom of the OEG chain reacts with Br(2) and the OEG part of the molecule is removed from the monolayer. In consequence an increase in disorder in the OEG part of the SAM is observed. The same mechanism of the reaction with Br(2) is applied for the d-dodecane alkanethiol part of the molecule. This reaction is slow, thus the order and the tilt of the hydrocarbon chain changes only a little during the reaction time.