Fatty Acid Multilayers Research Articles

Vapor Sorption into Pure and Mixed Fatty Acid Multilayers

The sorption of polar and nonpolar vapors into Langmuir-Blodgett multilayers of pure arachidic acid (C 2 0 ) was compared to that in films formed of a 1:1 mixture of behenic acid (C 2 2 ) and stearic acid (C 1 8 ). The mass of vapor sorbed was quantified using a quartz crystal microbalance. Film swelling was determined using multiple beam interferometry as implemented in the surface forces apparatus. We find that the solubility of water in the pure and the mixed films is the same. Moreover, the absorption of water is ideal in the sense that the film swelling observed is consistent with the incorporation of water at its bulk molar volume. In contrast, the solubilities of pentane, decane, and pentanol were higher in the mixed fatty acid films than in the pure film. The additional free volume available in the mixed films (due to alkane chain mismatch) also results in nonideal absorption of these organic vapors. Vapor sorption kinetic data support the hypothesis that the transport rate is governed primarily by large pitlike defects spanning multiple layers within the film structure.

Characterisation of fatty acid multilayers using a TSM biosensor

Thickness shear mode (TSM) biosensors have many potential applications within the pharmaceutical sciences as a means of measuring mass changes in the nanogram range, film thickness, viscosity and shear moduli. This study addresses the possible use of the TSM sensor as a biosensor for measuring drug partition coefficients. In order to realise this potential, some fundamental understanding is required of the behaviour of lipid films on the sensor. The present study characterises the behaviour of fatty acid multilayers as a suitable model chemical system. Frequency shifts and impedance spectra are presented for multilayers of three fatty acid films coated on to the sensor using a Langmuir-Blodgett trough. The results indicate that the frequency shift is non-linear at lower numbers of fatty acid layers but the response is Sauerbrey-like at higher numbers of layers. Also at high numbers of layers, changes in the impedance spectra indicate viscoelastic behaviour in thicker membranes. An inverse relationship is observed between chain length and frequency shift, which is attributed to variations in the topography of the sensor surface. This work demonstrates the importance of fully characterising the physical behaviour of the lipid multilayers prior to using these systems for the measurement of drug partition coefficients.

Assembly of Supported Membranes Studied by Surface Plasmon Microscopy

A home-made surface plasmon microscopy (SPM) was used in cooperation with surface plasmon resonance spectroscopy (SPR) to analyze the assembly process of the organized fatty acid LB films. The planar fatty acid multilayers were deposited on a support by piling up different layers of stearic acid and/or palmitic acid monolayers in different regions, which were possible to be imaged by SPM in the same vision field. A good contrast was obtained between different thickness regions and the numerical values of thickness for different regions were calculated according to the resonance angles.

Numerical simulation of the infrared spectra of thin organic films

We present results of numerical simulations of the infrared spectra of thin films of behenic acid (b.a.) in different spectroscopic configurations. A model of independent oscillators was used to derive the optical constants of the material in the infrared region and, from these, the reflectance expressions corresponding to several experimental situations. In this manner, the theoretical attenuated total reflection spectra could be fitted to the experimental result through a steepest-descent routine, and the spectroscopic parameters so optmized were used in the numerical computation of the behavior of the optical constants and of the different spectra of interest. We present results for both Langmuir-Blodgett thin films and thicker evaporated samples of b.a. deposited on ZnSe crystals. In the former case, we also analyze the best suited experimental configuration for the thickness estimate of the films. We have shown that the preliminary use of numerical simulation techniques can simplify the investigation of the spectroscopic properties of thin organic films by allowing the operating limits and capabilities of each experiment to be estimated. Since fatty acid multilayers are the prototypal organized molecular structures, we expect that these techniques become specially important in the spectroscopic investigation of molecular order in thin organic films.

Influence of Lipidic Matrix and Structural Lipidic Reorganization on Choline Oxidase Activity Retained in LB Films

This work focuses on the influence of the nature of the lipidic matrix and of the hydrophobic or hydrophilic lipidic environment on choline oxidase activity retained in Langmuir−Blodgett (LB) films prepared with behenic acid or with mixed dipalmitoylphosphatidylcholine (DPPC) and dipalmitoylphosphatidic acid (DPPA). The enzyme activity was detected through an electrochemical sensor whose platinum electrode was coated with the protein−lipid LB films. It was shown that the hydrophilic environment provided by the phospholipidic LB films was directly responsible for an inactivation of choline oxidase likely due to a competition with the choline moiety of DPPC. The environment provided by the carboxylic groups of the fatty acid multilayers allowed retention of the higest activity. The absence of stability of choline oxidase activity in behenic acid LB films was explained by repulsive electrostatic interactions between the protein and the lipidic molecules, which appeared during the immersion of the LB films in the alkaline buffer required to detect the enzyme activity in optimal conditions. These unfavorable interactions, previously shown to be responsible for a lipidic structural reorganization of choline oxidase−behenic acid LB films, seem to be here responsible for a likely unfolding, yielding protein denaturation. Because it controls the electrostatic interactions between the protein and the lipidic molecules, which may be very unfavorable even in the optimal conditions of the enzyme activity, pH acts as a key parameter of the expression of the enzyme activity in the LB films.

Supramolecular architecture and molecular bioelectronics

Ordered monolay ers and multilayers of lipids, DNA, fatty acids and proteins, and processes of their interfacing with silicon, gold and other inorganic substrates, form the basis of a new emerging field, called molecular bioelectronics, at the crossing of molecular biology and submicron electronics. Numerous electronic and biotechnological applications result from the above supramolecular architectures, namely from the Langmuir-Blodgett (LB) films of proteins involved in molecular recognition, actuation and information processing, in catalytic activity and electron transfer, because of their unique structural and functional stability to long storage, experimental manipulation and temperatures up to 200 °C. Few key examples of molecular bioelectronics are here summarized.

Thermodesorption processes of langmuir layers of aliphatic acids and salts

Thermodesorption processes of mono-and multilayers of fatty acids and their salts with 14 to 24 carbon atoms were investigated by ellipsometry and IR spectroscopy. Cadmium, calcium, strontium, and barium salt layers, unlike the layers of pure acids, have a complex phase composition which includes not only separate acid and salt phases, but also intermediate acid-salt forms. The initial phase composition of multilayer systems determines their thermodesorption spectrum observed upon heating the samples. It was found that before the removal of molecules to the gaseous phase, phase transitions are possible in the films, similar to those observed in crystals and caused by the change of molecular conformations in the layer. Energy characteristics of thermodesorption processes are estimated for pure acid layers and for separate phases in salt layers. Possible qualitative models of the processes are discussed.

Surface morphology and stability of Langmuir-Blodgett mono- and multilayers of saturated fatty acids by scanning force microscopy

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTSurface morphology and stability of Langmuir-Blodgett mono- and multilayers of saturated fatty acids by scanning force microscopyA. Schaper, L. Wolthaus, D. Moebius, and T. M. JovinCite this: Langmuir 1993, 9, 8, 2178–2184Publication Date (Print):August 1, 1993Publication History Published online1 May 2002Published inissue 1 August 1993https://doi.org/10.1021/la00032a046RIGHTS & PERMISSIONSArticle Views196Altmetric-Citations57LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (4 MB) Get e-Alerts Get e-Alerts

Electrical Properties of Multilayer Films Containing a Carotene Derivative

Abstract The electrical properties of Langmuir-Blodgett films containing ethyl β-apo-8′-carotenoate are reported. The incorporation of this derivative of carotene into fatty acid multilayers was found to increase substantially the electrical conductivity measured perpendicular to the substrate plane. An increase in the in-plane conductivity could also be achieved by exposure of the multilayer assembly to iodine vapour.

An electrical investigation into multilayer assemblies of charge-transfer materials

Metal/Langmuir-Blodgett film/metal structures based on amphiphilic charge-transfer materials have been fabricated and the DC conductivity perpendicular to the plane of the film has been measured. Linear current-voltage behaviour was observed for small applied biases. In contrast, the high-field (>105 V cm-1) current against voltage characteristics exhibited a log (current) against voltage0.5 dependence, similar to that measured for fatty acid multilayers. No evidence for rectification has been found in structures containing both donor and acceptor materials. However, devices incorporating a tetracyanoquinodimethane derivative invariably possessed output voltages with no applied bias; a significant dispersion in the low-frequency capacitance was also noted for these structures.

Orientation and lateral mobility of cytochrome c on the surface of ultrathin lipid multilayer films

We have previously shown that cytochrome c can be electrostatically bound to an ultrathin multilayer film having a negatively charged hydrophilic surface; furthermore, x-ray diffraction and absorption spectroscopy techniques indicated that the cytochrome c was bound to the surface of these ultrathin multilayer films as a molecular monolayer. The ultrathin fatty acid multilayers were formed on alkylated glass, using the Langmuir-Blodgett method. In this study, optical linear dichroism was used to determine the average orientation of the heme group within cytochrome c relative to the multilayer surface plane. The cytochrome c was either electrostatically or covalently bound to the surface of an ultrathin multilayer film. Horse heart cytochrome c was electrostatically bound to the hydrophilic surface of fatty acid multilayer films having an odd number of monolayers. Ultrathin multilayer films having an even number of monolayers would not bind cytochrome c, as expected for such hydrophobic surfaces. Yeast cytochrome c was covalently bound to the surface of a multilayer film having an even number of fatty acid monolayers plus a surface monolayer of thioethyl stearate. After washing extensively with buffer, the multilayer films with either electrostatically or covalently bound cytochrome c were analyzed for bound protein by optical absorption spectroscopy; the orientation of the cytochrome c heme was then investigated via optical linear dichroism. Polarized optical absorption spectra were measured from 450 to 600 nm at angles of 0 degrees, 30 degrees, and 45 degrees between the incident light beam and the normal to the surface plane of the multilayer. The dichroic ratio for the heme alpha-band at 550 nm as a function of incidence angle indicated that the heme of the electrostatically-bound monolayer of cytochrome c lies, on average, nearly parallel to the surface plane of the ultrathin multilayer. Similar results were obtained for the covalently-bound yeast cytochrome c. Furthermore, fluorescence recovery after photobleaching (FRAP) was used to characterize the lateral mobility of the electrostatically bound cytochrome c over the monolayer plane. The optical linear dichroism and these initial FRAP studies have indicated that cytochrome c electrostatically bound to a lipid surface maintains a well-defined orientation relative to the membrane surface while exhibiting measurable, but highly restricted, lateral motion in the plane of the surface.

The location of cytochrome c on the surface of ultrathin lipid multilayer films using x-ray diffraction

X-ray diffraction and spectroscopic techniques were used to characterize ultrathin fatty acid multilayers having a bound surface layer of cytochrome c. Three to six monolayers of arachidic acid were deposited onto an alkylated glass surface, using the Langmuir-Blodgett method. These fatty acid multilayer films were stored either in a 1 mM NaHCO3 pH 7.5 solution or a buffered 10 microM cytochrome c solution, pH 7.5. After washing extensively with buffer, these multilayer films were assayed for bound cytochrome c by optical spectroscopy. It was found that the cytochrome c bound only to the odd-numbered monolayer films (which have hydrophilic surfaces). The theoretical number of cytochrome c molecules bound to the ultrathin multilayer films having three or five monolayers was calculated as N = 1.2 x 10(13)/cm2 (assuming a hexagonally close-packed monolayer of protein), which would produce an optical density of 0.002 at a wavelength of 550 nm; for a three or five monolayer ultrathin film that was incubated with cytochrome c, OD550 approximately equal to 0.002. The protein was released from the film when treated with greater than 100 mM KCl solution, as would be expected for an electrostatic interaction. Meridional x-ray diffraction data were collected from the arachidic acid films with and without a bound cytochrome c layer. A box refinement technique, previously shown to be effective in deriving the profile structures of nonperiodic ultrathin films, was used to determine the multilayer electron density profiles. The electron density profiles and their autocorrelation functions showed that bound cytochrome c resulted in an additional electron dense feature on the multilayer surface, consistent with a bound cytochrome c monolayer. The position of the bound protein relative to the multilayer surface was independent of the number of fatty acid monolayers in the multilayer. Future studies will use these methods to investigate the structures of membrane protein complexes bound directly to the surface of multilayer films.

The Electronic Absorption Spectra of Fatty Acid Mono-, Bi-, and Multilayers with Bivalent Metal Ions

Abstract The electronic absorption spectra of fatty acid multilayers with bivalent metal ions were studied in the vacuum ultraviolet (VUV) to ultraviolet (UV) energy region below 8 eV; they are due to transitions in the carboxylic acid and metal carboxylate moieties. Infrared (IR) absorptions due to the C–O stretching vibration in the carboxylate moiety are also studied. Stearic acid multilayers without metal ions are shown to form hydrogen-bonded dimers. The spectra of multilayers with metal ions show a marked dependence on the subphase pH which is different for different kinds of adsorbed metal ions. Their VUV spectra are conspicuously dependent on the kind of metal ions adsorbed. All the multilayers with alkaline earth metals, metals of the 2B group, transition metals, Cu, and Pb have at least two bands in the VUV region, 7.3–6.3 eV. The polarization spectra of the Ba stearate multilayer suggest that the two transitions may be the intramolecular π-π* and n-π* transitions in the carboxylate anion moiety. The multilayers with Cu and Pb have another band in the UV region. The spectra of the UV bands of the Pb and Cu stearate mono-, bi-, and multilayers were studied. In the Pb stearate layers, the positions of the UV bands in the bi- and multilayers are the same, but those in the monolayers are at considerably shorter wavelengths. The positions of the UV band in the Cu stearate mono-, bi-, and multilayers are successively red shifted. The polarization spectra of the UV bands of the mono- and bilayers showed that they are charge-transfer bands between the Pb or Cu ion and the coordinated carboxylate moiety.

The Vacuum Ultraviolet Absorption Spectra of Fatty Acid Multilayers

Abstract The electronic absorption spectra of fatty acid multilayers were measured in the vacuum ultraviolet region with an energy below 10 eV. From the chain length dependence of the spectra, the strong absorption (above 8 eV) was assigned to the σ-σ* transitions in the alkane chain moiety, and the weaker one (below 8 eV), to the transitions in the car boxy lie acid and metal car boxy late moieties. The polarized spectra of the Ba stearate multilayer showed that the band near 8.8 eV was polarized perpendicularly to the alkane chain. The spectra of the stearic acid multilayer without metal ions and the multilayer of the Zn stearate showed that their alkane chains were titled against the normal of the layer plane.

Critical reflection of neutrons. A new technique for investigating interfacial phenomena

The possibility of using neutron critical reflection for investigating interfacial phenomena is assessed. Calculations of the reflectivity of neutrons as a function of angle of incidence have been made for a variety of interfaces, using both an optical model and the Schrodinger equation. The information on the structure of the interfacial region that could be derived from reflectivity profiles is described for the following systems: fatty acid multilayers, black films, the liquid–vapour interface for a one-component system, the solution–vapour interface and the electrode–solution interface.Preliminary experiments have also been done to test the technique using thin films of deuterated stearic acid and copper on glass.

Monolayer assemblies with functional units of sensitizing and conducting molecular components: Photovoltage, dark conduction and photoconduction in systems with aluminium and barium electrodes

Vectorial charge separation was studied in assemblies in which a mixed monolayer of an indocarbocyanine dye with the chromophores in the layer plane, a chain-like π electron system oriented perpendicular to the layer plane, and a layer of acceptor molecules were sandwiched between metal electrodes. The cyanine dye was excited by light and the excited electron could move via the π electron system and the acceptor to the positively biased electrode. The logarithm of the photocurrent increases linearly with the bias voltage. If the conducting π electron system and the acceptor are absent, the photocurrent is about an order of magnitude smaller and its logarithm depends linearly on the square root of the bias voltage. In both cases the photocurrent is proportional to the light intensity and shows the same temperature dependence. The results are interpreted by assuming that the excited electron is transferred to some interlayer state by tunnelling (low temperature mode) or by thermal activation (high temperature mode). In the absence of the conducting element and the acceptor the electron moves to the positively biased electrode with a low probability. In their presence the electron is transferred to the interlayer states spaced one monolayer away from this electrode, and then tunnelling from there to the electrode is rate limiting. If these arrangements are sandwiched between metals of very different work functions (aluminium and barium) a photovoltage can be measured and is interpreted as being caused by a vectorial electron transfer through the molecular functional unit towards the metal with the smaller work function. The dark conductivity through fatty acid multilayers sandwiched between an aluminium and a barium electrode was measured and was interpreted. The hopping of electrons between interlayer states adjacent to the aluminium electrode is rate limiting.

Raman spectroscopy of fatty acid Blodgett-Langmuir multilayer assemblies

The Raman Spectra of Blodgett-Langmuir multilayer assemblies made from behenic acid, barium behenate and barium cis-13 erucate are reported. In particular, the peak height intensity ratio of the hydrocarbon chain methylene CH stretch Raman bands, I 2890 I 2850 , for each multilayer assembly is compared to that of phosphatidylcholine in powders and water dispersions as well as to samples of crystalline hydrocarbon chains. It is found that the fatty acid multilayers are more ordered than the phospholipid samples but less ordered than the crystalline samples. It is suggested that Blodgett-Langmuir multilayer assemblies of lipid might be a useful reference in quantitative studies of packing order in lipid phases.

Theoretical calculation of the dielectric constant of a bilayer membrane

The dielectric constant (epsilon) and refractive index (n) of a bilayer lipid membrane is determined from the known values of the polarizabilities of the carbon-carbon and carbon-hydrogen bonds. It is assumed that the hydrocarbon chains are hexagonally arranged in an all-trans conformation perpendicular to the plane of the membrane. The only variable in the calculation is the average separation between the chains and the theory relates epsilon to this separation. The calculation and results differ significantly from those presented in a 1968 publication by Ohki. It is shown that a thin membrane is not homogeneously polarized by the applied field. This effect is analysed and the dependence of epsilon on the membrane thickness is determined. The theoretical results are in good quantitative agreement with experimental measurements on bulk paraffins and on oriented multilayers of saturated fatty acids. The most important conclusion is that the dielectric constant for an applied field perpendicular to the membrane (which is the appropriate value for capacitance measurements) differs by only a few percent from the value for the macroscopic (bulk) liquid hydrocarbon. Thus the dielectric constant of a bilayer membrane can be approximated by the value for the appropriate bulk hydrocarbon.

X-ray diffraction from fatty-acid multilayers. Angular width of reflexions from systems with few unit cells

X-ray diffraction from fatty-acid multilayers. Angular width of reflexions from systems with few unit cells

X-ray diffraction from fatty-acid multilayers. Significance of intensity data in low-angle diffraction

X-ray diffraction from fatty-acid multilayers. Significance of intensity data in low-angle diffraction