Incorporation Of Gramicidin Research Articles

Alignment of lyotropic liquid crystals using magnetic nanoparticles improves ionic transport through built-in peptide ion channels

Hypothesis: We hypothesize that simultaneous incorporation of ion channel peptides (in this case, potassium channel as a model) and hydrophobic magnetite Fe3O4 nanoparticles (hFe3O4NPs) within lipidic hexagonal mesophases, and aligning them using an external magnetic field can significantly enhance ion transport through lipid membranes.Experiments: In this study, we successfully characterized the incorporation of gramicidin membrane ion channels and hFe3O4NPs in the lipidic hexagonal structure using SAXS and cryo-TEM methods. Additionally, we thoroughly investigated the conductive characteristics of freestanding films of lipidic hexagonal mesophases, both with and without gramicidin potassium channels, utilizing a range of electrochemical techniques, including impedance spectroscopy, normal pulse voltammetry, and chronoamperometry.Findings: Our research reveals a state-of-the-art breakthrough in enhancing ion transport in lyotropic liquid crystals as matrices for integral proteins and peptides. We demonstrate the remarkable efficacy of membranes composed of hexagonal lipid mesophases embedded with K+ transporting peptides. This enhancement is achieved through doping with hFe3O4NPs and exposure to a magnetic field. We investigate the intricate interplay between the conductive properties of the lipidic hexagonal structure, hFe3O4NPs, gramicidin incorporation, and the influence of Ca2+ on K+ channels. Furthermore, our study unveils a new direction in ion channel studies and biomimetic membrane investigations, presenting a versatile model for biomimetic membranes with unprecedented ion transport capabilities under an appropriately oriented magnetic field. These findings hold promise for advancing membrane technology and various biotechnological and biomedical applications of membrane proteins.

Nanodelivery of the Gramicidin Peptide for Enhancing Antimicrobial Activity

AbstractGramicidin S (GraS) is an amphiphilic peptide that has emerged as an effective alternative antibiotic. However, its applicability is restricted for clinical uses due to its effect on eukaryotic cells and low aqueous solubility. In this work, a novel water‐soluble peptide formulation with bactericidal activity is developed by the incorporation of Gramicidin S in the lipid bilayer of liposomes (L‐GraS). As a result, GraS included in the lipid vesicles is stabilized in aqueous medium and showed antimicrobial activity against Staphylococcus aureus. In addition, L‐GraS reveals enhanced biocompatibility with mammalian cells in comparison with the free peptide. Molecular dynamics simulations shed light on the collective behavior between GraS peptides and liposomes from a molecular approach. The molecular dynamic simulations are in agreement with experimental results and further confirm the effective incorporation of GraS in the liposomes, letting understand the best formulation procedure of the vesicles. Therefore, the L‐GraS nanosystem presented here is an interesting alternative to conventional antibiotics, with less restrictions and promising features to improve current therapies.Practical Applications: Incorporation of GraS in liposomes is an interesting approach to increase the solubility of the peptide, thus expanding its therapeutic horizon as a promising alternative to combat bacterial colonization especially in wound infections.

Effects of Channel Forming Peptides on Lipid Bilayer Dynamics and Leaflet Coupling

Altering the material properties of lipid bilayers has been shown to affect the biological activity of a number of channel-forming peptides and proteins. A prototypical example is gramicidin, in which the channel formation and lifetime directly depends on the lipid membrane in which it is embedded. However, less is known about how a membrane-spanning channel affects the lipid bilayer properties, particularly the elasticity. Here we use neutron spin echo spectroscopy (NSE) to measure both the collective bending and thickness fluctuation dynamics in dimyristoylphosphatidylcholine (DMPC) and dipalmitoylphosphatidylcholine (DPPC) bilayers containing gramicidin at low peptide/lipid ratios. At these low concentrations, gramicidin incorporation did not have a measurable effect on the average bilayer structure but significantly impacted the collective membrane dynamics. The bending modulus of DMPC membranes increased with increasing gramicidin concentration, while the trend in DPPC was non-monotonic and first decreased at low gramicidin concentrations before increasing at higher concentrations. In contrast, the thickness fluctuation amplitude increased with increasing gramicidin concentration in both the DMPC and DPPC lipid bilayers. Notably, combining the bending and thickness fluctuation results revealed that the seemingly disparate concentration trends in the DMPC and DPPC lipid bilayers were both consistent with an increase in coupling between the bilayer leaflets with increasing gramicidin concentration. Together these results demonstrate that channel formation can have considerable effects on the surrounding lipid membrane elasticity and highlight the interplay between lipids and peptides in determining the membrane dynamics.

Probing peptide and protein insertion in a biomimetic S-layer supported lipid membrane platform.

The most important aspect of synthetic lipid membrane architectures is their ability to study functional membrane-active peptides and membrane proteins in an environment close to nature. Here, we report on the generation and performance of a biomimetic platform, the S-layer supported lipid membrane (SsLM), to investigate the structural and electrical characteristics of the membrane-active peptide gramicidin and the transmembrane protein α-hemolysin in real-time using a quartz crystal microbalance with dissipation monitoring in combination with electrochemical impedance spectroscopy. A shift in membrane resistance is caused by the interaction of α-hemolysin and gramicidin with SsLMs, even if only an attachment onto, or functional channels through the lipid membrane, respectively, are formed. Moreover, the obtained results did not indicate the formation of functional α-hemolysin pores, but evidence for functional incorporation of gramicidin into this biomimetic architecture is provided.

Nanopore-Spanning Lipid Bilayers on Silicon Nitride Membranes That Seal and Selectively Transport Ions

We report the formation of POPC lipid bilayers that span 130 nm pores in a freestanding silicon nitride film supported on a silicon substrate. These solvent-free lipid membranes self-assemble on organosilane-treated Si3N4 via the fusion of 200 nm unilamellar vesicles. Membrane fluidity is verified by fluorescence recovery after photobleaching (FRAP), and membrane resistance in excess of 1 GΩ is demonstrated using electrical impedance spectroscopy (EIS). An array of 40,000 membranes maintained high impedance over 72 h, followed by rupture of most of the membranes by 82 h. Membrane incorporation of gramicidin, a model ion channel, resulted in increased membrane conductance. This membrane conductance was diminished when the gramicidin channels were blocked with CaCl2, indicating that the change in membrane conductance results from gramicidin-mediated ion transport. These very stable, biologically functional pore-spanning membranes open many possibilities for silicon-based ion-channel devices for applications such as biosensors and high-throughput drug screening.

The Effect of Incorporation of Gramicidin on the Translational Lipid Diffusion in Bicontinuous Cubic Monoolein/Water Mesophases

Abstract The influence of incorporating the polypeptide gramicidin on the lateral mobility of the monoacylglyceride monoolein (MO) in its bicontinuous cubic lipid mesophases is studied applying static field gradient NMR. The effects of gramicidin on the topology, structure and phase behaviour of the system are characterized by small-angle x-ray scattering (SAXS) experiments. On the structural level the experiments show significant shifts in the boundaries of the various mesophases. Measurements of the translational dynamics are restricted to cubic mesophases, where the diffusion coefficients of lipid and additive are determined both by geometrical obstruction and by lipid-protein interaction effects.

Protein-induced bilayer perturbations: Lipid ordering and hydrophobic coupling

The host lipid bilayer is increasingly being recognized as an important non-specific regulator of membrane protein function. Despite considerable progress the interplay between hydrophobic coupling and lipid ordering is still elusive. We use electron spin resonance (ESR) to study the interaction between the model protein gramicidin and lipid bilayers of varying thickness. The free energy of the interaction is up to −6 kJ/mol; thus not strongly favored over lipid–lipid interactions. Incorporation of gramicidin results in increased order parameters with increased protein concentration and hydrophobic mismatch. Our findings also show that at high protein:lipid ratios the lipids are motionally restricted but not completely immobilized. Both exchange on and off rate values for the lipid ↔ gramicidin interaction are lowest at optimal hydrophobic matching. Hydrophobic mismatch of few Å results in up to 10-fold increased exchange rates as compared to the ‘optimal’ match situation pointing to the regulatory role of hydrophobic coupling in lipid–protein interactions.

Potassium ion transport by gramicidin and valinomycin across a Ag(111)-supported tethered bilayer lipid membrane

A tethered bilayer lipid membrane (tBLM) was prepared by anchoring a thiolipid monolayer to a Ag(1 1 1) single crystal from a thiolipid solution in ethanol; a diphytanoylphosphatidylcholine monolayer was then self-assembled on top of the thiolipid monolayer from a lipid solution in hexane or ethanol. The thickness of the mixed thiolipid|lipid bilayer was estimated at 7.5 ± 0.5 nm by scratching holes in the tBLM with an AFM tip and determining their height profile and the frequency distribution of height. The effect of the incorporation of gramicidin A and valinomycin upon K + ion transport across the tBLM was investigated by electrochemical impedance spectroscopy. The position of the inflection point of the sigmoidal curve of the in-phase component of the electrode admittance against potential allowed the determination of an approximate scale of the absolute potential difference across the whole Ag(1 1 1)|(aqueous solution) interface, on the basis of a model of the electrified interface.

Robust hybrid thin films that incorporate lamellar phospholipid bilayer assemblies and transmembrane proteins

This study describes facile methods based on sol-gel processing for the formation of robust thin films that incorporate phospholipid bilayer membranes and transmembrane proteins as multilamellar assemblies in cross-linked silica matrices. Transmission electron microscopy and x-ray diffraction were used to examine the lamellar structure of the hybrid thin films containing1, 2-dioleyl-sn-glycero-3-phospoethanolamine (DOPE), an unsaturated lipid, and 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC), a saturated lipid. While the d spacing measured for DOPE containing films varied (from 35 to 48 A) depending on the amount of DOPE added to the coating solution (10-1 wt %), similar changes were not observed for the films containing saturated lipid, DMPC (d spacing approximately 43 A). Addition of purple membrane containing bacteriorhodopsin to the DOPE/silica coating solution led to the formation of multilamellar vesicle-like structures within the thin films. Mild sonication of these solutions containing the purple membrane prior to coating led to the formation thin films with planar multilamellar structures that exhibit uniform d spacing. The study further investigates the effects of incorporation of gramicidin and sonication on the structure of hybrid films and speculates on the eventual application of thin films prepared in this manner.

Incorporation of channel-forming peptides in a Hg-supported lipid bilayer

The channel-forming peptides gramicidin and alamethicin were incorporated in a mercury-supported lipid bilayer composed of a tethered thiolipid monolayer with a self-assembled dioleoylphosphatidylcholine monolayer on top of it. The thiolipid consists of a hexapeptide chain with a high tendency to form a 3 10-helical structure, which terminates at the N-terminus end with a sulfydryl group for anchoring to the metal while the C-terminus end is covalently linked to the polar head of dimyristolylphosphatidylethanolamine. The hexapeptide moiety has two triethyleneoxy side chains that impart a satisfactory hydrophilicity and are intended to keep the anchored thiolpeptide chains sufficiently apart, so as to accommodate water molecules and inorganic ions and to create a suitable environment for the incorporation of integral proteins. Changes in the conductance of this biomimetic membrane following the incorporation of gramicidin and alamethicin were detected by impedance spectroscopy. The surface dipole potential of the hexapeptide chain and the transmembrane potential of the lipid bilayer were estimated by using a simple electrostatic model of the mercury|solution interphase.

Effect of membrane potential depolarization on the organization of the actin cytoskeleton of eye epithelia. The role of adherens junctions

We have previously determined that the depolarization of the plasma membrane potential of confluent bovine corneal endothelial cells in culture, provokes a characteristic reorganization of the actin cytoskeleton. The purposes of the present work are to investigate whether similar responses are exhibited by other epithelia, irrespectively of their specific functions and embryonic origin, and to test the hypothesis that the cytoskeletal reorganization induced by membrane depolarization requires of a well-organized circumferential actin disposition in order to take place. For this, we have performed studies on three different cultured epithelia of the eye: bovine corneal endothelium, bovine retinal pigment epithelium and cellular lines of murine lens epithelium. For all of these cells, we explored the effects of plasma membrane depolarization, achieved via the incorporation of gramicidin D to the bathing media or by the replacement of extracellular sodium chloride by potassium gluconate, on the cadherin and actin distribution. The membrane potential changes were monitored by fluorescence microscopy using oxonol V; fluorescent probes were also used for F-actin and cadherin. Detergent extraction and Western blot analysis were employed to reveal the relative amount of cadherin attached to the cytoskeleton. The main findings of this study are that different confluent cultured epithelia exhibiting a well-defined circumferential pattern of actin distribution respond to plasma membrane depolarization by similar modifications in the actin cystoskeleton to those reported for bovine corneal endothelial cells. On the other hand, epithelia that do not exhibit such actin pattern in confluence, as well as non-confluent monolayers, do not display noticeable actin modifications in response to the depolarizing procedures. While in the former cells, cadherin is predominantly located at the lateral membrane domain, the cells that do not respond to membrane depolarization mainly display their cadherin in the intracellular compartment. We suggest that the typical peripheral disposition of actin, associated to well-established epithelial-type adherens junctions (i.e. zonula adherens), is a pre-requisite for the cytoskeletal organizational modifications exhibited by epithelial cells in response to the depolarization of the plasma membrane potential.

The Effects of Gramicidin on the Structure of Phospholipid Assemblies

Gramicidin is an antibiotic peptide that can be incorporated into the monolayers of cell membranes. Dimerization through hydrogen bonding between gramicidin monomers in opposing leaflets of the membrane results in the formation of an iontophoretic channel. Surrounding phospholipids influence the gating properties of this channel. Conversely, gramicidin incorporation has been shown to affect the structure of spontaneously formed lipid assemblies. Using small-angle x-ray diffraction and model systems composed of phospholipids and gramicidin, the effects produced by gramicidin on lipid layers were measured. These measurements explore how peptides are able to modulate the spontaneous curvature properties of phospholipid assemblies. The reverse hexagonal, HII, phase formed by dioleoylphosphatidylethanolamine (DOPE) monolayers decreased in lattice dimension with increasing incorporation of gramicidin. This indicated that gramicidin itself was adding negative curvature to the lipid layers. In this system, gramicidin was measured to have an apparent intrinsic radius of curvature, R0pgram, of −7.1Å. The addition of up to 4mol% gramicidin in DOPE did not result in the monolayers becoming stiffer, as measured by the monolayer bending moduli. Dioleoylphosphatidylcholine (DOPC) alone forms the lamellar (Lα) phase when hydrated, but undergoes a transition into the reverse hexagonal (HII) phase when mixed with gramicidin. The lattice dimension decreases systematically with increased gramicidin content. Again, this indicated that gramicidin was adding negative curvature to the lipid monolayers but the mixture behaved structurally much less consistently than DOPE/gramicidin. Only at 12mol% gramicidin in dioleoylphosphatidylcholine could an apparent radius of intrinsic curvature of gramicidin (R0pgram) be estimated as −7.4Å. This mixture formed monolayers that were very resistant to bending, with a measured bending modulus of 115kT.

Peroxyl radicals promoted changes in water permeability through gramicidin channels in DPPC and lecithin-PC vesicles

Gramicidin incorporation to DPPC or lecithin-PC large unilamellar vesicles (LUVs) leads to pore formation that, under hyper-osmotic conditions, produces a noticeable increase in the rate of trans-membrane water flow. This pore formation is more efficient in the more fluid lecithin-PC LUVs. Exposure of these vesicles to peroxyl radicals generated in the aerobic thermolysis of 2,2′-azo-bis(2-amidinopropane) (AAPH), changes the physical properties of the bilayer (as sensed employing fluorescent probes), modifies gramicidin molecules (as sensed by the decrease in Trp fluorescence) and notably reduces the transbilayer rate of water outflow. In order to evaluate if this reduced water-transport capacity is due to changes in the membrane due to lipid-peroxidation and/or direct damage to gramicidin channels, results obtained in the oxidable vesicles (lecithin-PC) were compared to those obtained in DPPC vesicles. The data obtained show that most of the water transport efficiency loss can be ascribed to a direct disruption of gramicidin channels by AAPH derived peroxyl radicals.

Nonspecific Depolarization of the Plasma Membrane Potential Induces Cytoskeletal Modifications of Bovine Corneal Endothelial Cells in Culture

Modifications in the cell membrane potential have been suggested to affect signaling mechanisms participating in diverse cellular processes, many of which involve structural cellular alterations. In order to contribute some evidence in this respect, we explored the effects of several depolarizing procedures on the structure and monolayer organization of bovine corneal endothelial cells in culture. Visually confluent cell monolayers were incubated with or without the depolarizing agent, either in a saline solution or in culture medium for up to 30 min. Membrane potential was monitored by fluorescence microscopy using oxonol V. Fluorescent probes were employed for F-actin, microtubules, and vinculin. Depolarization of the plasma membrane, achieved via the incorporation of gramicidin D into confluent endothelial cells or by modifications of the extracellular saline composition, provoked an increment of oxonol fluorescence and changes in cell morphology, consisting mainly of modifications in the cytoskeletal organization. In some areas, noticeable intercellular spaces appear. The cytoskeleton modifications mainly consist of a marked redistribution of F-actin and microtubules, with accompanying changes in vinculin localization. The results suggest that the depolarization of the plasma membrane potential may participate in mechanisms involved in cytoskeleton organization and monolayer continuity in corneal endothelial cells in culture.

Effect of gramicidin addition upon the physicochemical properties of dipalmitoyl phosphatidyl choline large unilamellar vesicles

In this work, we report the results bearing on the effect of gramicidin incorporation upon the dynamic and structural properties of dipalmitoyl phosphatidyl choline (DPPC) large unilamellar vesicle (LUVs). Results were obtained at different depths in the bilayer, both in the bulk of the bilayer and the vicinity of the added pentadecapeptide. This analysis was performed employing a series of extrinsic fluorescent probes (1,6-diphenyl-1,3,5-hexatriene (DPH), 1-(4-trimethylammonium phenyl)-6-phenyl-1,3,5-hexatriene (TMA-DPH), 6-dodecanoyl-2-dimethyl aminenaphthalene (Laurdan), pyrenedodecanoic acid, pyrene butyric acid, 1-hexadecanoyl-2-(1-pyrenedecanoyl)-sn-glycero-3-phosphocholine (Py–C 10–PC) and 1,2-bis-(1-pyrenedecanoyl)-sn-glycero-3-phosphocholine (bis-Py–C 10–PC)). Fluorescence measurements were carried out after direct excitation of the probe or after its excitation by resonant energy transfer (RET) from the intrinsic tryptophan groups of the polypeptide. The last procedure allows an evaluation of the lipidic annulus properties in the vicinity of the incorporated polypeptide. In the gel state, gramicidin incorporation increases the order near the vesicle interface, as sensed by TMA-DPH. This increase is observed, above the phase transition temperature, over all the bilayer. This effect is probably related to a decrease in the lateral diffusion of the lipids, as evidenced by the reduced formation of intermolecular excimers following Py–C 10–PC excitation. Gramicidin incorporation also increases the penetration and/or mobility of water molecules located near the bilayer interface. In the gel phase, these changes are more relevant in the central part of the bilayer. When the LUVs are in the liquid crystalline state, the effect is observed through all the bilayer. In this state, the polypeptide incorporation also increases the diffusion/concentration of oxygen, irrespective of the probe localization. Resonance energy transfer between Trp residues and Laurdan, Py–C 10–PC or bis-Py–C 10–PC dyes was employed to evaluate the properties of the lipidic annulus surrounding the polypeptide. In the gel phase, gramicidin incorporation produces an increase in the penetration and/or dynamics of water molecules, while in the liquid crystalline state it leads to a decrease of the acyl chain mobility in the deepest parts of the bilayer.

Deposition of highly resistive lipid bilayer on silicon–silicon dioxide electrode and incorporation of gramicidin studied by ac impedance spectroscopy

Highly resistive planar supported lipid membranes were deposited onto highly doped p-type silicon–silicon dioxide electrodes. Physical parameters of the substrates (e.g. dopant, doping ratio and oxide layer thickness) were optimized by a combined study using ellipsometry and ac impedance spectroscopy. Lipid bilayer was deposited by fusion of small unilamellar vesicles, and the self-assembling of the homogeneous bilayer could be monitored as a function of time. Impedance spectroscopy over a wide frequency range (from 20 kHz to 10 mHz) enables separating membrane resistance and capacitance from the background signals. Membrane resistance amounted to 1.0 MΩ cm 2, and the capacitance was around 0.7 μF cm −2. The resistance obtained here is comparable to that of the freestanding black lipid membrane. Although the area of the supported membrane (0.5 cm 2) is much larger than that of the black lipid membrane (∼0.002 cm 2), the electrical properties were stable for more than a week. Gramicidin D was inserted into the membrane from trifluoroethanol solution, and activity of the channels was checked in terms of membrane conductance and ion selectivity. Functional incorporation of ion channels into the supported membrane demonstrated here suggested that the gramicidin monomers could diffuse over the membranes to form transmembrane pores.

Supported planar bilayer formation by vesicle fusion: the interaction of phospholipid vesicles with surfaces and the effect of gramicidin on bilayer properties using atomic force microscopy

We have used magnetic alternating current mode atomic force microscopy (MAC–AFM) to investigate the formation of supported phospholipid bilayers (SPB) by the method of vesicle fusion. The systems studied were dioleoylphosphatidylcholine (DOPC) on mica and mica modified with 3-aminopropyl-triethoxy-silane (APTES), and DOPC vesicles with gramicidin incorporated on mica and APTES-modified mica. The AFM images reveal three stages of bilayer formation: localized disklike features that are single bilayer footprints of the vesicles, partial continuous coverage, and finally complete bilayer formation. The mechanism of supported phospholipid bilayers formation is the fusion of proximal vesicles, rather than surface disk migration. This mechanism does not appear to be affected by incorporation of gramicidin or by surface modification. Once formed, the bilayer develops circular defects one bilayer deep. These defects grow in size and number until a dynamic equilibrium is reached.

Effect of temperature, pressure and lipid acyl chain length on the structure and phase behaviour of phospholipid–gramicidin bilayers

We investigated the effect of incorporation of gramicidin D (GD) on the structure and phase behaviour of aqueous dispersions of fully hydrated neutral phospholipid bilayers of different chain lengths 1,2-dimyristoyl-sn-glycero-3-phosphatidylcholine (DMPC), 1,2-dipalmitoyl-sn-glycero-3-phosphatidylcholine (DPPC) and 1,2-distearoyl-sn-glycero-3-phosphatidylcholine (DSPC). A temperature range of 0–80°C and a pressure range of 0.001–10 kbar (1 bar=105 Pa) were covered. Pressure was applied so as to be able to tune the lipid chain lengths and conformation and to select specific gel phases. Infrared spectral parameters obtained by FT-IR spectroscopy, such as frequencies, intensities and bandwidths, were used to detect structural and dynamic changes upon incorporation of GD into the lipid bilayers. Analysis of the amide I band frequencies allowed us to determine the corresponding peptide structure adopted in the lipid environment. At a concentration of 5 mol% of GD in lipid bilayers, the structure of the temperature- and pressure-dependent lipid phases is significantly altered by the insertion of the polypeptide and broad gel–fluid co-existence regions are induced. Further, the lipid matrix has the ability to modulate the conformation of the inserted polypeptide. The balance between double-helical and helical dimer structures depends significantly on the phospholipid hydrocarbon chain length and phase state. The larger the hydrophobic mismatch, the higher is the population of the double-helical structures. By formation of broad gel–fluid co-existence regions, the system has a further means of avoiding large hydrophobic mismatch. In these regions, a molecular sorting mechanism seems to be very likely. No pressure-induced unfolding of the polypeptide is observed up to pressures of 10 kbar.

A robust gel-bilayer channel biosensor

We demonstrate a novel protective configuration for a gated channel biosensor. The bilayer membrane containing the channel proteins is formed by a simple self-assembly technique ensuring continuous coverage of the interface between two slabs of agarose gel by a biomimetic lamella in a fluid state. The gel protects both membrane surfaces from mechanical shock and contact with low-energy media while allowing diffusion of biomolecules up to 10 MDa in weight. The technique has been demonstrated using both dioleoyl-phosphatidylcholine (DOPC) and a phosphatidylcholine lipid cross-linked with a short polysiloxane chain (PSPC). The conductance per unit area of the channel-free membrane produced by this method was less than 25 S m−2 for DOPC and 2 S m−2 for PSPC, and the bilayer nature of the barrier in both cases has been demonstrated by measurement of the capacitance. The applicability to sensors has been confirmed using gramicidin-D, a 1·1 kDa unilamellar lipid bilayer pore former, and partially confirmed using valinomycin, a selective ion transporter. On incorporation of gramicidin the membrane conductance increased by over an order of magnitude. © 1998 John Wiley & Sons, Ltd.

A Fourier transform infrared study of the lamellar liquid crystalline phase of dimethyldodecyl amineoxide-water and dimethyldodecyl amineoxide-gramicidin-D-water systems

Abstract The overall conformational order of the alkyl tail of the lyotropic lamellar phase of the dimethyldodecyl amineoxide, (CH3)2ON+(CH2)11CH3 (DDAO)H2O system (75.7 wt.%) has been studied by using Fourier transform infrared spectroscopy. The spectral region 1000–1400 cm−1, covering the CH2 wagging modes and the methyl umbrella modes of DDAO, has been recorded in the temperature interval 3–60°C and at different mole fractions of gramicidin-D with respect to DDAO (Xg = 0.03, 0.05 and 0.1) for both DDAO-H2O and DDAO-D2O systems. It has been shown that the DDAO amphiphile molecules of the lamellar phase reorganise in a phase-like transition near 25–30°C. The DDAO-water system does not show any significant bands corresponding to a double gauche conformation at 1355 cm−1 nor to a gauche-transgauche (kinked) conformation at 1367 cm−1. These bands are probably present but hidden in the broad low-frequency side of the CH3 umbrella band at 1377 cm−1. Upon incorporation of gramicidin into the lamellar phase both head group and acyl chain spectra of the lipid change in such a way as to indicate a decreased “ordering” of the molecules, as judged by comparison with spectra of the same molecule in a micellar environment, and with increased fluidity of the acyl chains.