Fourier Transform Infrared Reflection Absorption Spectroscopy Research Articles

Lithography on GaP(1 0 0) surfaces

Two types of lithographic methods were used to modify GaP(1 0 0) surfaces with commercially available alkanethiol molecules: microcontact printing (μCP) and “dip-pen” nanolithography (DPN). The patterned surfaces were characterized by atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared reflection absorption spectroscopy (FT-IRRAS). The characterization was done in order to understand the quality of each type of pattern, its chemical composition, and the organization of the molecules on the surface. Differences between the two lithographic methods used to do lithography on the GaP(1 0 0) in this study were dependent on the chosen molecular “ink”.

Potassium ion sensing using a self-assembled calix[4]crown monolayer by surface plasmon resonance

Abstract The precise detection of K + ion is crucial because K + ion plays a leading role in membrane transport. Current K + ion detection methods suffered low resolution and detection limit. Calix[4]crown-5 derivatives are well known as K + ionophores. We described here a K + ion-sensing system using a self-assembled monolayer of calix[4]crown-5 derivative (calix[4]crown) modified gold chip based on surface plasmon resonance (SPR). The calix[4]crown sensing layer was characterized by atomic-force microscopy (AFM), SPR, Fourier transform infrared reflection absorption spectroscopy (FTIR-RAS) and cyclic voltammetry (CV). It was found calix[4]crown was assembled as a monolayer on Au surface. The SPR angle was found to be modulated by various concentrations of K + ion due to the interaction between the calix[4]crown and K + ion. This calix[4]crown monolayer showed a more sensitive and selective binding toward potassium ion over other alkali and alkaline earth metal ions. From the simple SPR spectroscopic analysis, we were able to monitor K + ion concentration with a wide range of 1.0 × 10 −12 to 1.0 × 10 −2 M in an aqueous solution with a pH 6–8. These experimental results showed a useful method for the design of simple and precise potassium ion biosensors.

Synthesis and Characterization of a Thiol-Tethered Tripyridyl Porphyrin on Au(111)

Porphyrins are actively studied for use in molecular and organic electronic components of devices because of their diverse tunable optical and electronic properties. In this study, mixed self-assembled monolayers (SAMs) of dodecanethiol and a tripyridyl porphyrin attached to a thiol tether via a perfluorinated phenyl ring (TPy3PF4−SC5SH) were prepared on Au(111) substrates. The synthetic strategy allows for rapid formation of derivatives with different tethers. The surface structural and electronic properties of mixed monolayer SAMs of the porphyrin inserted into the dodecanethiol matrix were investigated using scanning tunneling microscopy (STM), atomic force microscopy (AFM), Fourier transform infrared reflection−absorption spectroscopy (FT-IRAS), and X-ray photoelectron spectroscopy (XPS). Density functional theory (DFT) calculations were also employed to evaluate the analytical vibrational frequencies of the TPy3PF4−SC5SH molecule as well as its electronic structure. For the mixed monolayers, the morphology of the porphyrin molecules was probed by STM where it was found that the molecules assembled into domains of ∼2 and 6 nm. AFM shows that the molecules protrude above the n-dodecanethiol layer by ∼0.9 nm, while by STM, apparent heights of only ∼0.5 nm were observed, suggesting limited tunneling efficiency. Stochastic switching of the porphyrin molecules was also observed during STM measurements in the mixed monolayer and is likely associated with conformational changes within the monolayer since these molecules tended to insert near defects within the SAM.

Reflection–Absorption Fourier Transform Infrared Spectroscopic Study of Transferred Films of Poly(dimethylsiloxane) Using the Langmuir–Blodgett Technique

Reflection–absorption Fourier transform infrared spectroscopy (RA-FTIR) has been utilized to investigate the tertiary structures of a series of poly(dimethylsiloxane) (PDMS) films transferred to silver substrates using the Langmuir–Blodgett technique. A surface pressure−area isotherm of PDMS of molecular weight of 2400 Da with low polydispersity (PDI of 1.09) was measured on a water subphase at 20 °C. Films were transferred onto silver substrates at various surface pressures associated with regions on the isotherm where structural changes are indicated. The infrared data from the films indicated the structural changes identified by analysis of the isotherm could be related to polymeric backbone orientational adjustments. This was evidenced by relative intensity changes of the asymmetric and symmetric Si−O−Si stretches located at 1050 and 1110 cm−1, respectively. Infrared data from the films also showed increases in absorption consistent with varying film thickness. Ratios of the peak intensity of 1265 cm−1 for the various films were compared with theoretical and experimentally observed film thicknesses reported by Fox, Taylor, and Zisman.(1) There was a positive correlation between the peak intensity ratios and structural thickness ratios reported by these authors which supports the proposed structures of caterpillar, zigzag, and helical coil. Furthermore, we report new infrared data supporting the model of structural change in the isotherm proposed by Lenk and Koberstein(2) based on the formation of helical coils with varying number of monomeric units per turn which form based on the surface pressure.

Investigation of the role of oxygen in NO reduction by C 2H 4 on the surface of stepped Pt(3 3 2)

The influence of pre-dosed oxygen on NO–C 2H 4 interactions on the surface of stepped Pt(3 3 2) has been investigated using Fourier transform infrared reflection–absorption spectroscopy (FTIR-RAS) and thermal desorption spectroscopy (TDS). The presence of oxygen significantly suppresses the adsorption of NO on the steps of Pt(3 3 2), leading to a very specific adsorption state for NO molecules when oxygen–NO co-adlayers are annealed to 350 K (assigned as atop NO on step edges). An oxygen-exchange reaction also takes place between these two kinds of adsorbed molecules, but there appears to be no other chemical reaction, which can result in the formation of higher-valence NOx. C 2H 4 molecules which are post-dosed at 250 K to adlayers consisting of 18O and NO do not have strong interactions with either the NO or the 18O atoms. In particular, interactions which may result in the formation of new surface species that are intermediates for N 2 production appear to be absent. However, C 2H 4 is oxidized to C 18O 2 by 18O atoms at higher annealing temperature. This reaction scavenges surface 18O atoms quickly, and the adsorption of NO molecules on step sites is therefore quickly restored. As a consequence, NO dissociation on steps proceeds very effectively, giving rise to N 2 desorption which closely resembles that following only NO exposure on a clean Pt(3 3 2), both in peak intensity and desorption temperature. It is concluded that the presence of 18O 2 in the selective catalytic reduction (SCR) of NO with C 2H 4 on the surface of Pt(3 3 2) does not play a role of activating reactants.

The Influence of Chemical Pre-treatment and Magnesium Surface Enrichment on Bonding of Succinic Acid Molecules to Aluminium Alloy

In the present study a combined Fourier Transform Infrared Reflection–Absorption Spectroscopy (FT-IR–RAS) and Auger electron spectroscopy (AES) analysis was performed to investigate the bonding of organic coatings to oxides formed on Al–Mg based alloys. The interfacial bonding of a model molecule, succinic acid, mimicking the functional groups used in practical coatings was studied in detail on various differently pre-treated aluminium alloy (AA5182, 4.8 wt% magnesium) surfaces. Besides these differently pre-treated alloy surfaces, also pure magnesium and aluminium were studied for reference. The surface and near-surface composition of the alloys was studied by Auger electron spectroscopy, ion-milling away the surface oxides to obtain a depth profile. The results show that after heat treatment, the oxides are as much enriched in magnesium as aluminium although the bulk concentration of magnesium is only 4.8 wt%. FT-IR–RAS shows that bonding of the succinic acid molecules takes place in a range of configurations, varying between bridging bidentates and unidentates. The relative portion of unidentates increases with the magnesium surface concentration. This is attributed to the difference in bond lengths of Mg–O and Al–O, forcing the carboxylic acid groups to stretch or to attach to only one oxide group (unidentate) instead of two (bidentate). Also the mixed OH/CO3 surface after Mg enrichment at the surface has less room for bonding with two groups, thus affecting the bonding configuration in a similar way.

Interactions among 18O2, C2H4, and NO on the surface of stepped Pt(332)

The influence of co-adsorbed 18O2 (18O) on NO/C2H4 reactions on the surface of stepped Pt(332) has been investigated using Fourier transform infrared reflection–absorption spectroscopy (FTIR-RAS) and thermal desorption spectroscopy (TDS). The presence of 18O2 (18O) results in changes in C2H4 dissociation behavior, with formation of ethylidyne taking place at surface temperature much higher than that in the absence of 18O2 (18O). Pre-annealing 18O2/C2H4 co-adlayers to 250 and 300 K does not lead to significantly different IR spectra, but a variety of spectra are observed when the 250 K and 300 K 18O/C2H4 co-adlayers are further exposed to 0.8 L NO at 90 K, depending on the 18O2 pre-exposure. NO adsorption in bridge sites, both on steps and on terraces is more significantly suppressed for the co-adlayers in which 18O2/C2H4 is pre-annealed to 250 K. This site-blocking effect is enhanced with increasing 18O2 exposure. However, no new surface species, which are intermediates for N2 production, are detected. Thermal desorption spectra indicate that various species are produced, but only N2 and H2 desorption have intensities that can be reliably analyzed (that is to be able to quantitatively elucidate how the yields of these two species vary with change in the ratios of NO to C2H4 and 18O2). Desorption of both N2 and H2 is more strongly dependent on 18O2 exposure than on the temperature to which 18O2/C2H4 adlayers are pre-annealed. The presence of 18O2, irrespective of the dosing sequence, suppresses N2 desorption, but this effect is much weaker when 18O2 is post-dosed. For the case with 18O2 pre-dosed, irrespective of the annealing temperature (250 K or 300 K), N2 desorption is greatly suppressed at an 18O2 exposure of 0.2 L, but thereafter remains almost unchanged with increasing 18O2 exposure from 0.4 to 1.6 L. This feature of N2 desorption is explained by the restoration of the adsorption of NO onto steps and the subsequent NO dissociation on these sites. In contrast, H2 desorption decreases continuously and disappears at 0.8 L 18O2 and higher. It is concluded that the presence of 18O2 in the reaction of NO with C2H4 on the surface of Pt(332) does not play any role of activating the surface reactants.Key words: NO, platinum, C2H4, deNOx, hydrocarbon, selective catalytic reduction.

Adsorption and electro-oxidation of N-alkyl and N,N’-dialkyl thioureas on gold electrodes in acid solutions. A combined FTIRRAS and voltammetry study

The adsorption and electro-oxidation of N-alkyl and N,N’-dialkyl thioureas on polycrystalline gold in aqueous acid solutions is studied by Fourier-transformed infrared reflection absorption spectroscopy (FTIRRAS) and voltammetry. The potential ranges for different electrochemical processes, including electrodissolution of gold and electro-oxidation of thioureas, are determined by cyclic voltammetry. The gradual depletion of thioureas and the progressive formation of products from adsorbed and soluble species in the thin solution layer in contact with the electrode are followed through changes in band intensity of infrared (IR) spectra. Adsorbates of thioureas are formed at 0.05 V and remain on the surface up to E = 1.2 V, a potential at which their electro-oxidation takes place. Irrespective of the type of thiourea, the first electro-oxidation process from soluble thioureas starts at ca. 0.45 V with the formation of their respective disulphide. This process is preceded by the electrodissolution of gold via the formation of gold–thiourea soluble complex species. From ca. 1.2 V upwards the second electro-oxidation process results in the formation of carbon dioxide, sulphate ions and C≡N-containing species. The latter are produced only from N-alkyl thioureas, in which the presence of free amine groups makes the formation of a C≡N bond possible, as a previous stage to the production of carbon dioxide and sulphate ions as final products. From the correlation between voltammetric and spectroscopic data a general reaction pathway for the adsorption of thioureas and their electro-oxidation on gold is advanced.

Building a novel vitronectin assay by immobilization of integrin on calixarene monolayer

Membrane proteins possess significant hydrophobic domains and are likely to deplete their native activity immobilized on the solid surface relative to those occurring in a membrane environment. To investigate an efficient immobilization method, calix[4]crown-ether monolayer as an artificial protein linker system was constructed on the gold surface and characterized by Fourier transform infrared reflection absorption spectroscopy (FTIR-RAS), atomic force microscopy (AFM) and cyclic voltammetry (CV). Integrin α vβ 3 was functionally immobilized onto the monolayer and the integrin–vitronectin interaction was investigated by surface plasmon resonance (SPR). It was found that calix[4]crown-ether was assembled as a monolayer on the gold surface. Orientation and accessibility of integrin α vβ 3 was assessed by sensitive binding of its natural ligand, vitronectin at pg mL −1 level. Moreover, surface coverage of integrin layer and thickness calculated through SPR curve simulation verified that integrin layer was a monolayer in activated form. In combination with the SPR method, this calix[4]crown monolayer provided a reliable and simple experimental platform for the investigation of isolated membrane proteins under experimental conditions resembling those of their native properties.

Ultrastructural Studies on the Collagen of the Marine Sponge Chondrosia reniformis Nardo

The ultrastructure of isolated fibrils of Chondrosia reniformis sponge collagen was investigated by collecting characteristic data, such as fibril thickness, width, D-band periodicity, and height modulation, using atomic force microscopy (AFM) and transmission electron microscopy (TEM). Therefore an adapted pre-processing of the insoluble collagen into homogeneous suspensions using neutral buffer solutions was essential, and several purification steps have been developed. Fourier transform infrared reflection-absorption spectroscopy (FT-IRAS) of the purified sponge collagen showed remarkable analogy of peak positions and intensities with the spectra of fibrillar calf skin type I collagen, despite the diverse phylogenetic and evolutionary origin. The sponge collagen's morphology is compared with that of other fibrillar collagens, and the typical banding of the separated single fibrils is discussed by comparison of topographical data obtained using AFM and corresponding TEM investigations using common staining methods. As the TEM images of the negatively stained fibrils showed alternating dark and light bands, AFM revealed a characteristic periodicity of protrusions (overlap zones) followed by two equal interband regions (gap zones). AFM and TEM results were correlated and multiperiodicity in Chondrosia collagen's banding is demonstrated. The periodic dark bands observed in TEM images correspond directly to the periodic protrusions seen by AFM. As a result, we provide an improved, updated model of the collagen's structure and organization.

Deposition of functional cellulose films on titanium alloy surfaces

Titanium alloy (TiAl6V4) surfaces were treated with ultraviolet (UV) radiation to remove organic “contamination” molecules which remained on the surfaces after conventional cleaning processes. The UV-technique simultaneously revealed reactive surface hydroxyl groups at the metal surface which were monitored by the reaction with perfluorooctanoylchloride and application of Fourier-Transform infrared reflection-absorption spectroscopy and contact angle measurements, respectively. Two different cellulose polymers each made soluble in methanol by functionalized hydroxylalkyl-spacer groups and their mixtures were deposited on UV-treated TiAl6V4 surfaces. Atomic force microscopy measurements could reveal polymer films which covered the metal surfaces completely without defects. Differences were indicated in the surface structure, especially between the pure cellulose phosphate films and cinnamate containing cellulose films.

The role of co-adsorbed O 2 on the catalytic reduction of NO with 13C 2H 5OH on the surface of Pt(3 3 2)

The influence of pre-dosed O 2 on the catalytic reduction of NO with 13C 2H 5OH on the surface of stepped Pt(3 3 2) was investigated using Fourier transform infra red reflection–absorption spectroscopy (FTIR-RAS) and thermal desorption spectroscopy (TDS). We show that the oxidation of 13C 2H 5OH with O 2 is a very effective reaction, occurring at 150 K and giving rise to acetate. The presence of NO does not lead to any evident oxidation of 13C 2H 5OH irrespective of the annealing temperature. For the case of O 2 + 13C 2H 5OH + NO co-adlayers, oxidation of 13C 2H 5OH also takes place at 150 K. However, no new surface species that are supposed to be an intermediate for the production of N 2 are detected. The influence of O 2 on the production and desorption of N 2 is intimately related to both O 2 and 13C 2H 5OH coverage. The presence of pre-dosed O 2 does not greatly promote N 2 desorption. In fact, N 2 desorption is suppressed quantitatively with increasing O 2 coverage, after which unreacted, or left-over O atoms appear and remain on steps. It is concluded that the presence of pre-dosed O 2 does not play a role of activating reactants in the catalytic reduction of NO with 13C 2H 5OH on the surface of Pt(3 3 2).

Formation and Characterization of Self-Assembled Phenylboronic Acid Derivative Monolayers toward Developing Monosaccaride Sensing-Interface

We designed and synthesized phenylboronic acid as a molecular recognitionmodel system for saccharide detection. The phenylboronic acid derivatives that haveboronic acid moiety are well known to interact with saccharides in aqueous solution; thus,they can be applied to a functional interface of saccharide sensing through the formation ofself-assembled monolayer (SAM). In this study, self-assembled phenylboronic acidderivative monolayers were formed on Au surface and carefully characterized by atomicforce microscopy (AFM), Fourier transform infrared reflection absorption spectroscopy(FTIR-RAS), surface enhanced Raman spectroscopy (SERS), and surface electrochemicalmeasurements. The saccharide sensing application was investigated using surface plasmonresonance (SPR) spectroscopy. The phenylboronic acid monolayers showed goodsensitivity of monosaccharide sensing even at the low concentration range (1.0 × 10-12 M).The SPR angle shift derived from interaction between phenylboronic acid andmonosaccharide was increased with increasing the alkyl spacer length of synthesizedphenylboronic acid derivatives.

Elastomeric Nanoparticle Composites Covalently Bound to Al2O3/GaAs Surfaces

This article reports the modification of Al2O3/GaAs surfaces with multifunctional soft materials. Siloxane elastomers were covalently bound to dopamine-modified Al2O3/GaAs semiconductor surfaces using MPt (M = Fe, Ni) nanoparticles. The sizes of the monodisperse FePt and NiPt nanoparticles were less than 5 nm. The surfaces of the nanoparticles as well as the Al2O3/GaAs substrates were modified with allyl-functionalized dopamine that utilized a dihydroxy group as a strong ligand. The immobilization of the elastomers was performed via a hydrosilation reaction of the allyl-functionalized dopamines with the siloxane backbones. X-ray photoelectron spectroscopy (XPS) experiments confirmed the covalent bonding of the siloxane elastomers to the oxide layer on the semiconductor surface. Fourier transform-infrared reflection absorption spectroscopy (FT-IRRAS) measurements revealed that the allyl functional groups are bonded to the siloxane backbones. The FT-IRRAS data also showed that the density of the allyl groups on the surface was lower than that of the siloxane backbones. The mechanical properties of the surface-bound nanocomposites were tested using nanoindentation experiments. The nanoindentation data showed that the soft matrix composed of the elastomeric coating on the surfaces behaves differently from the inner, hard Al2O3/GaAs substrate.

Catalytic reduction of NO in the presence of benzene on a Pt(3 3 2) surface

The catalytic reduction of NO in the presence of benzene on the surface of Pt(3 3 2) has been studied using Fourier transform infra red reflection-absorption spectroscopy (FTIR-RAS) and thermal desorption spectroscopy (TDS). IR spectra show that while the presence of benzene molecules at low coverage (e.g., following an exposure of just 0.25 L) promotes NO–Pt interaction, the adsorption of NO on Pt(3 3 2) at higher benzene coverages is suppressed. It is also shown that there are no strong interactions between the adsorbed NO molecules and the benzene itself or benzene-derived hydrocarbons, which can lead to the formation of intermediate species that are essential for N 2 production. TDS results show that the adsorbed benzene molecules undergo dehydrogenation accompanied by hydrogen desorption starting at 300 K and achieving a maximum at 394 K. Subsequent dehydrogenation of the benzene-derived hydrocarbons then begins with hydrogen desorption starting at 500 K. N 2 desorption from NO adlayers on clean Pt(3 3 2) surface becomes significant at temperatures higher than 400 K, giving rise to a peak at 465 K. This peak corresponds to N 2 desorption from NO dissociation on step sites. The presence of benzene promotes N 2 desorption, depending on the benzene coverage. When the benzene exposure is 0.25 L, the N 2 desorption peak at 459 K is dramatically increased. Increasing benzene coverage also results in the intensification of N 2 desorption at ∼410 K. At benzene exposures of 2.4 L, N 2 desorption develops as a broad peak with a maximum at ∼439 K. It is concluded that the catalytic reduction of NO by platinum in the presence of benzene proceeds by NO decomposition and subsequent oxygen removal at temperatures lower than 500 K, and NO dissociation is a rate-limiting step. The contribution of benzene to N 2 desorption is mainly attributed to providing a source of H, which quickly reacts with NO-derived atomic O, leaving the surface with more vacant sites for further NO dissociation.

NO−C2H4 Reactions on the Surface of Stepped Pt(332)

NO−C2H4 interactions on the surface of stepped Pt(332) have been studied using Fourier transform infrared reflection−absorption spectroscopy (FTIR-RAS) and thermal desorption spectroscopy (TDS). IR data show that pre-dosed C2H4 molecules suppress the adsorption of NO on the surface of Pt(332) to an extent depending on both C2H4 coverage and the temperatures to which C2H4 pre-adlayers are annealed. At 90 K, the adsorption of NO on step sites is significantly suppressed by C2H4 following exposures greater than 0.32 L. This site-blocking effect persists and is even enhanced when annealing C2H4 pre-adlayers to 200 K, a temperature at which the adsorbed C2H4 molecules are not dissociated. As annealing temperatures are increased beyond 260 K, an ethylidyne species forms and is located on terraces. Consequently, the adsorption of NO on step sites is restored but to an extent smaller than that on a clean Pt(332) surface. The IR spectra also indicate that there are no detectable intermediates resulting from direct chemical reactions between NO and C2H4/C2H4-derived hydrocarbons, which can promote N2 production. The co-adsorption of C2H4- and C2H4-derived hydrocarbons does significantly promote N2 desorption, being dependent on the temperatures to which pre-dosed C2H4 adlayers are annealed. Annealing C2H4 adlayers to temperatures ≤300 K significantly enhances N2 desorption at temperatures below 400 K, giving rise to a peak at about 340−380 K. This low-temperature N2 desorption disappears completely after annealing the C2H4 adlayers to >350 K. N2 desorption at ∼460 K appears to be slightly enhanced. NO dissociation is the rate-limiting step in the reduction of NO by C2H4- and C2H4-derived hydrocarbons. The contribution of C2H4- and C2H4-derived hydrocarbons to N2 desorption is mainly attributed to 1) weakening of N−O bonds through an electron-donation effect; and 2) providing a source of reductants, i.e., H, CHx, C2Hx, and even C, which react with the atomic O from NO dissociation, leaving the surface with more vacant sites for further NO dissociation. The generation of CHx and C2Hx therefore plays a central role in the NO reduction mechanism.

Study of Electron Transfer in Ferrocene-Labeled Collagen-like Peptides

This study describes the electron transfer (ET) phenomenon through a series of (Pro-Hyp-Gly) repeat units containing collagen mimics. The peptides contain redox-active ferrocene (Fc) and thiol-functionalized cystein (Cys) at the N- and C-terminals, respectively. Peptide films were prepared on gold surfaces and characterized by X-ray photoelectron spectroscopy (XPS), ellipsometry, and Fourier transform-reflection absorption infrared spectroscopy (FT-RAIRS). Electrochemical investigations of the films showed a linear but weakly distance-dependent ET. The importance of H-bonding was realized, and the possibility of a conformationally gated ET mechanism has been discussed.

NO–methanol interaction on the surface of Pt(3 3 2)

The interaction between NO and CH 3OH on the surface of stepped Pt(3 3 2) was investigated using Fourier transform infra red reflection–absorption spectroscopy (FTIR-RAS) and thermal desorption spectroscopy (TDS). At 90 K, pre-dosed CH 3OH molecules preferentially adsorb on step sites, suppressing the adsorption of NO molecules on the same sites. However, due to a much stronger interaction with Pt, at 150 K and higher, the adsorption of NO molecules on step sites is restored, giving rise to peaks closely resembling those of NO molecules adsorbed on clean Pt(3 3 2) surface. Adsorbed CH 3OH is very reactive on this surface, and is readily oxidized to formate in the presence of O 2, even at 150 K. In contrast, reactions between CH 3OH and co-adsorbed NO are slight to non-existent. There are no new peaks in association with intermediates resulting from CH 3OH–NO interactions. It is concluded that the reduction of NO with CH 3OH on Pt(3 3 2) does not proceed through a mechanism of forming intermediates.

Infrared spectra and ferro‐electricity of ultra‐thin films of vinylidene fluoride and trifluoroethylene copolymer

AbstractThe structures of ultra‐thin films of vinylidene fluoride and trifluoroethylene copolymer were characterized using Fourier transform infrared reflection absorption spectroscopy (FTIR‐RAS), FTIR transmission spectroscopy (FTIR‐TRS), atomic force microscopy, and wide‐angle X‐ray diffraction. The ferro‐electricity was determined from polarization charge (a displacement (D)–electric field (E) hysteresis). FTIR‐RAS and FTIR‐TRS measurements showed that the molecular chains of polymers (crystal c‐axis) near the substrate tended to align parallel to the substrate. However, thermal annealing of the sample films at temperatures above 145 °C caused a marked change in molecular alignment of the polymer chains (crystal c‐axis) from parallel to normal to the substrate, and, further, caused a conformation change from trans to partially gauche forms. Copyright © 2007 Society of Chemical Industry

Molecular-scale structural and functional characterization of sparsely tethered bilayer lipid membranes

Surface-tethered biomimetic bilayer membranes (tethered bilayer lipid membranes (tBLMs)) were formed on gold surfaces from phospholipids and a synthetic 1-thiahexa(ethylene oxide) lipid, WC14. They were characterized using electrochemical impedance spectroscopy, neutron reflection (NR), and Fourier-transform infrared reflection-absorption spectroscopy (FT-IRRAS) to obtain functional and structural information. The authors found that electrically insulating membranes (conductance and capacitance as low as 1 microS cm(-2) and 0.6 microF cm(-2), respectively) with high surface coverage (>95% completion of the outer leaflet) can be formed from a range of lipids in a simple two-step process that consists of the formation of a self-assembled monolayer (SAM) and bilayer completion by "rapid solvent exchange." NR provided a molecularly resolved characterization of the interface architecture and, in particular, the constitution of the space between the tBLM and the solid support. In tBLMs based on SAMs of pure WC14, the hexa(ethylene oxide) tether region had low hydration even though FT-IRRAS showed that this region is structurally disordered. However, on mixed SAMs made from the coadsorption of WC14 with a short-chain "backfiller," beta-mercaptoethanol, the submembrane spaces between the tBLM and the substrates contained up to 60% exchangeable solvent by volume, as judged from NR and contrast variation of the solvent. Complete and stable "sparsely tethered" BLMs (stBLMs) can be readily prepared from SAMs chemisorbed from solutions with low WC14 proportions. Phospholipids with unsaturated or saturated, straight or branched chains all formed qualitatively similar stBLMs.