Analysis of myoglobin adsorption to Cu(II)-IDA and Ni(II)-IDA functionalized Langmuir monolayers by grazing incidence neutron and X-ray techniques

The adsorption of myoglobin to Langmuir monolayers of a metal-chelating lipid in crystalline phase was studied using neutron and X-ray reflectivity (NR and XR) and grazing incidence X-ray diffraction (GIXD). In this system, adsorption is due to the interaction between chelated divalent copper or nickel ions and the histidine moieties at the outer surface of the protein. The binding interaction of histidine with the Ni-IDA complex is known to be much weaker than that with Cu-IDA. Adsorption was examined under conditions of constant surface area with an initial pressure of 40 mN/m. After approximately 12 h little further change in reflectivity was detected, although the surface pressure continued to slowly increase. For chelated Cu2+ ions, the adsorbed layer structure in the final state was examined for bulk myoglobin concentrations of 0.10 and 10 microM. For the case of 10 microM, the final layer thickness was approximately 43 A. This corresponds well to the two thicker dimensions of myoglobin in the native state (44 A x 44 A x 25 A) and so is consistent with an end-on orientation for this disk-shaped protein at high packing density. However, the final average volume fraction of amino acid segments in the layer was 0.55, which is substantially greater than the value of 0.44 calculated for a completed monolayer from the crystal structure. This suggests an alternative interpretation based on denaturation. GIXD was used to follow the effect of protein binding on the crystalline packing of the lipids and to check for crystallinity within the layer of adsorbed myoglobin. Despite the strong adsorption of myoglobin, very little change was observed in the structure of the DSIDA film. There was no direct evidence in the XR or GIXD for peptide insertion into the lipid tail region. Also, no evidence for in-plane crystallinity within the adsorbed layer of myoglobin was observed. For 0.1 microM bulk myoglobin concentration, the average segment volume fraction was only 0.13 and the layer thickness was < or = 25 A. Adsorption of myoglobin to DSIDA-loaded with Ni2+ was examined at bulk concentrations of 10 and 50 microM. At 10 microM myoglobin, the adsorbed amount was comparable to that obtained for adsorption to Cu2+-loaded DSIDA monolayers at 0.1 M. But interestingly, the adsorbed layer thickness was 38 A, substantially greater than that obtained at low coverage with Cu-IDA. This indicates that either there are different preferred orientations for isolated myoglobin molecules adsorbed to Cu-IDA and Ni-IDA monolayer films or else myoglobin denatures to a different extent in the two cases. Either interpretation can be explained by the very different binding energies for individual interactions in the two cases. At 50 microM myoglobin, the thickness and segement volume fraction in the adsorbed layer for Ni-IDA were comparable to the values obtained with Cu-IDA at 10 microM myoglobin.     

Synthesis of novel amphiphilic azobenzenes and X-ray scattering studies of their Langmuir monolayers

We report a simple synthetic route to novel symmetrical alkylated and acylated amphiphilic 4,4'-diaminoazobenzene dyes, with their optical axis perpendicular to the amphiphilic direction of the molecule. Three different substitution patterns are reported, two of which are highly amphiphilic. At the air-water interface, the amphiphilic azobenzenes form noncrystalline but stable Langmuir films that display an unusual reversible monolayer collapse close to 35 mN/m. The structures and phase transitions were studied by X-ray reflectivity (XR) and grazing-incidence X-ray diffraction, both utilizing synchrotron radiation. Compression beyond the collapse point does not change the XR data, showing that the film is unchanged at the molecular level, even at areas less than half of that of the collapse. This leads to the conclusion that few macroscopic collapse sites are responsible for reversibly removing large amounts of material from the interface.     

Elasticity of crystalline beta-sheet monolayers

Designed amphiphilic beta-sheet peptides with the sequence Pro-Glu-(Phe-Glu)(n)-Pro (n = 2-7) were previously shown by grazing incidence X-ray diffraction (GIXD), to form ordered two-dimensional (2-D) monolayer structures at interfaces induced by the proline residues at peptide termini. The GIXD diffraction pattern was modeled with two coexisting lattice arrangements, suggesting structural flexibility exhibited in the multiple ways by which beta-strands and their amino acid side chains pack into ordered 2-D structures. Here, we find by in-situ GIXD measurements that the ordered beta-sheet assemblies may undergo a quasi-reversible compression and expansion cycle at the air-water interface. The diffraction measurements indicate that on compression the repeat distance that corresponds to the long axes of the peptide strands may decrease by up to 37% in length. Upon expansion the compressed beta-sheet assemblies revert elastically to their original conformation. The interstrand repeat distance along the peptide hydrogen bonds apparently does not change along the film compression and expansion. Based on the GIXD data, at surface pressures higher than approximately 3 mN/m, beyond the peptide limiting area per molecule, the compressibility is 7.4 +/- 0.6 m/N. The out-of-plane Bragg rod diffraction patterns imply that in the compressed state the beta-strands buckle up in reaction to the increase in surface pressure. At low surface pressure, the 2-D compressibility of the crystalline beta-sheet was estimated at approximately 32 m/N attributed to interdomain rearrangements.     

Nanohole structure prepared by a polystyrene-block-poly(methyl methacrylate)/poly(methyl methacrylate) mixture film

Cylindrical nanoporous structures were prepared by using a mixture film of polystyrene-block-poly(methyl methacrylate) copolymer (PS-b-PMMA) and PMMA homopolymer (hPMMA), and they were analyzed by transmission electron microtomography (TEMT), X-ray reflectivity (XR), and grazing incidence small-angle X-ray scattering. For this purpose, the mixture film was spin-coated onto a silicon wafer modified by a neutral brush for PS and PMMA blocks, which generates PMMA cylindrical microdomains oriented normal to the substrate. Two methods were employed to prepare nanoporous structures: (1) all of the PMMA phase (PMMA block and PMMA homopolymer) in the film was removed by UV irradiation, followed by rinsing with a selective solvent (acetic acid) to PMMA and (2) only PMMA homopolymer was removed by selective solvent etching without UV irradiation. We found via TEMT and XR that the nanoporous structure in the film prepared by UV irradiation exhibited almost perfect cylindrical shape throughout the entire film thickness. However, when the film was rinsed with a selective solvent, nanoporous structures were not straight cylinders but had a funnel shape in which the diameter of nanopores located near the top of the film was larger than that located near the bottom of the film.     

Morphology of poly(lactide)-block-poly(dimethylsiloxane)-block-polylactide high-χ triblock copolymer film studied by grazing incidence small-angle X-ray scattering

The morphologies of poly(lactide)-block-poly(dimethylsiloxane)-block-polylactide (PLA-b-PDMS-b-PLA) triblock copolymer films were studied using a combination of grazing-incidence small-angle X-ray scattering, X-ray reflectivity and scanning electron microscopy. This block copolymer is characterized by a high Flory–Huggins interaction parameter which leads to the self-assembly of periodic high-resolution nanodomains. In this article, we performed a detailed analysis of GISAXS patterns, in the frame of the Distorted Wave Born Approximation, in order to determine the morphology of blocks and their spatial arrangement. For a low volume fraction of PLA (17%), a three-dimensional hexagonal lattice of PLA spherical blocks is revealed, while, for a PLA fraction twice larger, in-plane (parallel) PLA lying cylinders adopt a two-dimensional centered rectangular lattice. Moreover, the in-depth electron density profile of the polymer film for the cylindrical morphology was extracted from the XRR data, revealing the presence of interfacial layers at the top surface and at the interface with the Si substrate.     

Study of alkyl organic monolayers with different molecular chain lengths directly attached to silicon

Alkyl organic monolayers with different alkyl molecular chain lengths directly attached to silicon were prepared at 160 degrees C from 1-decene (C10), 1-dodecene (C12), 1-tetradecene (C14), 1-hexadecene (C16), and 1-octadecene (C18). These monolayers were characterized on the basis of water contact angle measurement, ellipsometry, X-ray reflectivity (XR), X-ray photoelectron spectroscopy (XPS), and grazing incidence X-ray diffraction (GIXD) to elucidate the effect of the molecular chain length on the molecular arrangement and packing density of the monolayers. Water contact angle and XPS measurements showed that C12, C14, and C16 monolayers have a comparably higher quality, while the quality of C10 and C18 monolayers is worse. GIXD revealed that the alkyl monolayers directly attached to the Si were all amorphously structured regardless of their alkyl chain length. The amorphous structure of the alkyl monolayers could be attributed to the rigid Si-C bonding, low quality of hydrogen-terminated silicon substrate, and/or low mobility of physisorbed molecules.     

Formation of large PEE domains in PEE212-PEO112 diblock copolymer monolayers: shift of the PEO-desorption transition

PEE212-PEO112 diblock copolymer monolayers are studied at the air/water interface. At large molecular areas, with X-ray reflectivity, PEE domains are observed, which are partly immersed into the water. The domain thickness increases on compression (28 to 40 A). With off-specular X-ray reflectivity, an average domain radius of 750 A is found, but there are also smaller domains. Due to these space constraints, most PEO blocks form a brush beneath the PEE domains. Only a few PEO blocks form a corona surrounding the domains and adsorb flatly onto the air/water interface. The PEO desorption transition is observed at the typical pressure of 9 mN/m, when the flatly adsorbed PEO is compressed at a domain fraction of 95%. It occurs at 6 A2/EO monomer, about half the value found for lipopolymers or diblock copolymers with NPEE approximately NPEO or NPEE < NPEO. Apparently, the thickness of the PEE domains is determined by the forces from the two interfaces, not by the PEO block, for which flat adsorption beneath the domain would be more favorable instead of formation of a PEO brush.     

Penetration and interactions of the antimicrobial peptide, microcin J25, into uncharged phospholipid monolayers

Microcin J25 forms stable monolayers at the air-water interface showing a collapse at a surface pressure of 5 mN/m, 220 mV of surface potential, and 6 fV per squared centimeter of surface potential per unit of molecular surface density. The adsorption of microcin J25 from the subphase at clean interfaces leads to a rise of 10 mN/m in surface pressure and a surface potential of 220 mV. From these data microcin appears to be a poor surfactant per se. Nevertheless, the interaction with the lipid monolayer further increase the stability of the peptide at the interface depending on the mode in which the monolayer is formed. Spreading with egg PC leads to nonideal mixing up to 7 mN/m, with hyperpolarization and expansion of components at the interface, with a small excess free energy of mixing caused by favorable contributions to entropy due to molecular area expansion compensating for the unfavorable enthalpy changes arising from repulsive dipolar interactions. Above 7 mN/m microcin is squeezed out, leaving a film of pure phospholipid. Nevertheless, the presence of lipid at 10 and 20 mN/m stabilize further microcin at the interface and adsorption from the subphase proceeds up to 30 mN/m, equivalent to surface pressure in bilayers.     

Two-dimensional self-assembly of linear poly(ethylene oxide)-b-poly(epsilon-caprolactone) copolymers at the air-water interface

The interfacial properties of amphiphilic linear diblock copolymers based on poly(ethylene oxide) and poly(epsilon-caprolactone) (PEO-b-PCL) were studied at the air-water (A/W) interface by surface pressure measurements (isotherms and hysteresis experiments). The resulting Langmuir monolayers were transferred onto mica substrates and the Langmuir-Blodgett (LB) film morphologies were investigated by atomic force microscopy (AFM). All block copolymers had the same PEO segment (Mn = 2670 g/mol) and different PCL chain lengths (Mn = 1270; 2110; 3110 and 4010 g/mol). Isothermal characterization of the block copolymer samples indicated the presence of three distinct phase transitions around 6.5, 10.5, and 13.5 mN/m. The phase transitions at 6.5 and 13.5 mN/m correspond to the dissolution of the PEO segments in the water subphase and crystallization of the PCL blocks above the interface similarly as for the corresponding homopolymers, respectively. The phase transition at 10.5 mN/m was not observed for the homopolymers alone or for their blends and arises from a brush formation of the PEO segments anchored underneath the adsorbed hydrophobic PCL segments. AFM analysis confirmed the presence of PCL crystals in the LB films with unusual hairlike/needlelike architectures significantly different from those obtained for PCL homopolymers.     

POSS基杂化含氟丙烯酸酯共聚物涂膜的表面相分离与疏水性研究

采用自由基溶液聚合法成功合成了多面体低聚倍半硅氧烷(POSS)基杂化含氟丙烯酸酯共聚物,并采用核磁共振仪(NMR)和凝胶渗透色谱仪(GPC)表征了共聚物,其中POSS和含氟单体分步加入到反应中.首先将共聚物溶解到三氟三氯乙烷(F113)和乙酸乙酯的混合溶剂中配制成溶液,然后通过直接在玻璃片上滴落共聚物溶液制备了共聚物涂膜.采用扫描电子显微镜(SEM)、X-射线光电子能谱(XPS)、原子力显微镜(AFM)和接触角测量仪考察了F113和乙酸乙酯的配比对共聚物涂膜表面形貌、表面元素组成、表面粗糙度以及表面疏水性的影响.实验数据表明POSS在表面能够聚集成纳米颗粒并能极大增强涂膜表面粗糙度和疏水性.共聚物表面同时存在POSS聚集与有机相微相分离两类相分离行为,并形成了复合粗糙结构.虽然POSS和含氟段竞争迁移到表面,但是随着混合溶剂中F113的增多,涂膜表面含氟量越来越多,同时POSS在表面的聚集体越来越少,表面平均粗糙度越来越小,最终涂膜的疏水性越来越强,这说明F113有助于提升氟的趋表迁移能力,使涂膜表面含氟链段占据较多的表面空间,从而抑制了POSS在表面聚集分布.当使用纯F113作为溶剂时,共聚物涂膜的表面氟含量为45.25%,平均粗糙度为93.4 nm,此时静态水接触角最大为135.0?,表现出优异的疏水性.     

Hygrothermal degradation of (3-glycidoxypropyl)trimethoxysilane films studied by neutron and X-ray reflectivity and attenuated total reflection infrared spectroscopy

Thin films of organosilanes have great technological importance in the areas of adhesion promotion, durability, and corrosion resistance. However, it is well-known that water can degrade organosilane films, particularly at elevated temperatures. In this work, X-ray and neutron reflectivity (XR and NR) were combined with attenuated total reflection infrared (ATR-IR) spectroscopy to study the chemical and structural changes within thin films of (3-glycidoxypropyl)trimethoxysilane (GPS) after exposure for various periods of time to air saturated with either D2O or H2O at 80 degrees C. For NR and XR, ultrathin (approximately 100 A) films were prepared by spin-coating. Both D2O and H2O provide neutron scattering contrast with GPS. Variations in the neutron scattering length density (SLD) profiles (a function of mass density and atomic composition) with conditioning time were measured after drying the samples out and also swelled with H2O or D2O vapor at room temperature. For samples that were dried out prior to measurement, little or no change was observed for H2O conditioning up to 3.5 days, but large changes were observed after 30 days of conditioning. The range of conditioning time for this structural change was narrowed to between 4 and 10 days with XR. The SLD profiles indicated that the top portion of the GPS film was transformed into a thick low-density layer after conditioning, but the bottom portion showed little structural change. A previous NR study of as-prepared GPS films involving swelling with deuterated nitrobenzene showed that the central portion of the film has much lower cross-link density than the region nearest the substrate. The present data show that the central portion also swells to a much greater extent with water and hydrolyzes more rapidly. The chemical degradation mechanism was identified by IR as hydrolysis of siloxane bonds. For ATR-IR, GPS films were prepared by dip-coating, which resulted in a greater and more variable thickness than for the spin-coated samples. The IR spectra revealed an increase in vicinal silanol generation over the first 3 days of conditioning followed by geminal silanol generation. Thus, the structural change detected by NR and XR roughly coincided with the onset of geminal silanol generation. Finally, little change in the reflectivity data was observed for films conditioned with D2O at 80 degrees C for 1 month. This indicates that hydrolysis of Si-O-Si is much slower with D2O than with H2O.     

DNA condensation and interaction with zwitterionic phospholipids mediated by divalent cations

Artificial viruses are considered to be a promising tool in gene therapy. To find lipid-DNA complexes with high transfection efficiency but without toxicity is a fundamental aim. Although cationic lipids are frequently toxic for cells, neutral lipids are completely nontoxic. Zwitterionic lipids do not interact with DNA directly; however, the interaction can be mediated by divalent cations. Langmuir monolayers represent a well-defined model system to study the DNA-lipid complexes at the air/water interface (quasi-2D systems). In this work, isotherms, infrared reflection absorption spectroscopy (IRRAS), X-ray reflectivity (XR), grazing incidence X-ray diffraction (GIXD), and Brewster angle microscopy (BAM) measurements are used to study the interaction of calf thymus DNA with DMPE (1,2-dimyristoyl-phosphatidylethanolamine) monolayers mediated by Ca2+ or Mg2+ ions. DNA adsorption is observed only in the presence of divalent cations. At low lateral pressure, the DNA partially penetrates into the lipid monolayer but is squeezed out at high pressure. The adsorption layer has a thickness of 18-19 A. Additionally, GIXD provides information about a one-dimensional ordering of adsorbed DNA. The periodic distance between DNA strands depends on the type of the divalent cation.     

Interfacial behaviors of PMMA-PEO block copolymers at the air/water interface

Amphiphilic block copolymers are attracting con-siderable attention because they exhibit unique self- assembly properties in selective organic solvents[1―4]. Semicrystalline poly(ethylene oxide) (PEO), having many interesting physicochemical properties s…     

In situ characterization of functional purple membrane monolayers at the air-water interface

The purple membrane (PM) of Halobacterium salinarum contains a single type of protein, bacterio-rhodopsin (bR), which is a member of the seven alpha-helices transmembrane protein family. This protein is a photoactive proton pump, translocating one proton from the cytoplasmic to the extracellular side of the PM per photon absorbed. bR is found in trimers in PM, where they are assembled in a two-dimensional hexagonal lattice. We show herein that stable and functional films can be built in monolayers at the air-water interface by spreading aqueous suspensions of purified and native PM patches. In situ spectroscopic measurements at the air-water interface indicate that bR remains photoactive in this environment. Physical parameters of these PM films, such as protein molecular area, irreversible in-plane aggregation, z-axis orientation, film thickness, and surface roughness, were determined from surface pressure and surface potential-area isotherms, fluorescence spectroscopy, and X-ray reflectivity at the air-water interface. We find that PM do form organized monolayers of membranes, with an optimal packing density at a surface pressure of approximately 20 mN/m, although no preferential vectorial alignment, with respect to the plane normal to the membrane, can be detected from fluorescence quenching experiments.     

Effect of water contact on the density distributions of thin supported polymer films investigated by an X-ray reflectivity method

The diffusion processes of water molecules into polymer films (PMMA/PS homopolymers and random copolymers) in contact with liquid water were investigated using gravimetric methods and X-ray reflectivity (XRR) analysis. Methods of water contact and XRR measurement were designed for studying the systems in the nonequilibrium state of diffusion. Gravimetric measurements confirmed the Fickian diffusion behavior of films in contact with water. Vertical density distributions in PMMA and methylmethacrylate-rich copolymer films demonstrate the existence of a water-rich layer at the interface. However, with further absorption of water into the film, the overall density increased throughout the film. The results suggest that the diffusion of water into the polymer film occurs to recover density uniformity with a high concentration of water molecules at the surface. Some XRR data for the PS- and styrene-rich copolymer films could not be fit and converted to a vertical density distribution because of their huge diffusion coefficients. However, the reflectivity curves for these films and the vertical density distribution after sufficient water contact suggested that the surfaces of these films were commonly diffused after water contact. Atomic force microscopy (AFM) analysis demonstrated that the surface roughness of these films actually increased with water content.     

Water surface covering of fluorinated amphiphilic triblock copolymers: surface pressure-area and X-ray reflectivity investigations

Monolayers of ABA amphiphilic triblock block copolymers are studied using surface pressure-area and X-ray reflectivity (XR) measurements. The triblock copolymers are composed of long poly(ethylene oxide) (PEO) middle blocks with poly((perfluorohexyl)ethyl methacrylate) (PFMA) end blocks. The surface pressure-area isotherms of water-insoluble species show two pseudoplateaus. The plateau at low surface pressure is consistent with the pseudoplateau observed for PEO copolymers in the literature. The plateau in the brush region can be assigned to the horizontal to vertical rearrangement of whole PFMA chains at the air-water interface, which was followed by XR measurements. For water-soluble species with a very low amount of PFMA no (significant) second pseudoplateau and no enrichment of PFMA at the air-water interface were observed.     

Computer simulation studies of Newton black films

We study via molecular dynamics simulations thin films (Newton black films, NBF) consisting of water coated with sodium dodecyl sulfate (SDS) surfactants. We analyze in detail the film properties (distribution of particles, pair correlation functions, roughness of the film, tilt angle of the hydrocarbon chain, electron density profiles, and mobility of water molecules) as a function of water content in the film core (i.e., film thickness, H). Our simulations indicate that water is part of the bilayer structure as solvation water. We estimate that around 2.25 water molecules per surfactant are part of this solvation structure. The structural analysis of the NBF shows that the headgroups exhibit a high degree of in-plane ordering. We find evidence for the existence of cavities in the monolayer, where only water is present. The basic structure of the monolayer is conserved down to water contents of the order of 4 water molecules per surfactant (H approximately equal to 11 A). The computed monolayer roughness for the present model is 2.5 A, in good agreement with the experimental data. We find that the roughness is very sensitive to the details of the interatomic potentials. Water mobility calculations emphasize the sluggish dynamics of very thin NBF. Diffusion coefficients of water in the lateral direction strongly decrease with film thickness. We find that the typical mean squared displacement of water in the direction normal to the bilayer is between 9 and 80 A2. Overall, our results indicate that the equilibrium SDS Newton black films studied in the X-ray experiments contain from 2 to 4 water molecules per surfactant.     

Amorphous iron-(hydr) oxide networks at liquid/vapor interfaces: In situ X-ray scattering and spectroscopy studies

Surface sensitive X-ray reflectivity (XR), fluorescence (XF), and grazing incidence X-ray diffraction (GIXD) experiments were conducted to determine the accumulation of ferric iron Fe (III) or ferrous iron Fe (II) under dihexadecyl phosphate (DHDP) or arachidic acid (AA) Langmuir monolayers at liquid/vapor interfaces. Analysis of the X-ray reflectivity and fluorescence data of monolayers on the aqueous subphases containing FeCl(3) indicates remarkably high levels of surface-bound Fe (III) in number of Fe(3+) ions per molecule (DHDP or AA) that exceed the amount necessary to neutralize a hypothetically completely deprotonated monolayer (DHDP or AA). These results suggest that nano-scale iron (hydr) oxide complexes (oxides, hydroxides or oxyhydroxides) bind to the headgroups and effectively overcompensate the maximum possible charges at the interface. The lack of evidence of in-plane ordering in GIXD measurements and strong effects on the surface-pressure versus molecular area isotherms indicate that an amorphous network of iron (hydr) oxide complexes contiguous to the headgroups is formed. Similar experiments with FeCl(2) generally resulted with the oxidation of Fe (II)-Fe (III) which consequently leads to ferric Fe (III) complexes binding albeit with less iron at the interface. Controlling the oxidation of Fe (II) changes the nature and amount of binding significantly. The implications to biomineralization of iron (hydr) oxides are briefly discussed.     

8-羟基喹啉镧两亲性配合物LB膜的双层电致发光器件

以具有不同层数的两亲配合物二[2-(N-十六烷基氨基甲酰基)-8-羟基喹啉]合镧[La(HQ)₂Cl]的LB膜为发光层,PBD为电子传输层,制备了双层结构的电致发光(EL)器件:ITO/LB膜/PBD/Al.器件产生黄绿色注入式发光.LB膜的层数和沉积压对器件的性能具有重要影响.在16V激发电压下,5,11和21层LB膜双层EL器件的电流密度分别为48,29和16.4mA/cm²,启亮电压阀值为7.5,8.5和9.5V.器件的亮度随电流密度和驱动电压的增加而增加.在相同偏压下,21层LB膜EL器件的亮度大于5和11层LB膜的器件.在25mN/m沉积的LB膜制备的EL器件具有较高的亮度(1219cd/m₂)和击穿电压.     

Structure and phase behavior of archaeal lipid monolayers

We report X-ray reflectivity (XRR) and grazing incidence X-ray diffraction (GIXD) measurements of archaeal bipolar tetraether lipid monolayers at the air-water interface. Specifically, Langmuir films made of the polar lipid fraction E (PLFE) isolated from the thermoacidophilic archaeon Sulfolobus acidocaldarius grown at three different temperatures, i.e., 68, 76, and 81 °C, were examined. The dependence of the structure and packing properties of PLFE monolayers on surface pressure were analyzed in a temperature range between 10 and 50 °C at different pH values. Additionally, the interaction of PLFE monolayers (using lipids derived from cells grown at 76 °C) with the ion channel peptide gramicidin was investigated as a function of surface pressure. A total monolayer thickness of approximately 30 ? was found for all monolayers, hinting at a U-shaped conformation of the molecules with both head groups in contact with the interface. The monolayer thickness increased with rising film pressure and decreased with increasing temperature. At 10 and 20 °C, large, highly crystalline domains were observed by GIXD, whereas at higher temperatures no distinct crystallinity could be observed. For lipids derived from cells grown at higher temperatures, a slightly more rigid structure in the lipid dibiphytanyl chains was observed. A change in the pH of the subphase had an influence only on the structure of the lipid head groups. The addition of gramicidin to an PLFE monolayer led to a more disordered state as observed by XRR. In GIXD measurements, no major changes in lateral organization could be observed, except for a decrease of the size of crystalline domains, indicating that gramicidin resides mainly in the disordered areas of the monolayer and causes local membrane perturbation, only.