Search

International audience; It has been recently demonstrated that molecular and molecular cluster guest species can intercalate within lamellar stacks of purple membrane (PM), and be subsequently dried to produce functional bioinorganic nanocomposite films. However, the mechanism for the intercalation process remains to be fully understood. Here we employ surface X-ray scattering to study the intercalation of aminopropyl silicic acid (APS) or aminopropyl-functionalised magnesium phyllosilicate (AMP) molecular clusters into PM films. The composite films are prepared under aqueous conditions by guest infiltration into preformed PM films, or by co-assembly from an aqueous dispersion of PM sheets and guest molecules/clusters. Our results show that addition of an aqueous solution of guest molecules to a dried preformed PM film results in loss of the lamellar phase, and that subsequent air-drying induces re-stacking of the lipid/protein membrane sheets along with retention of a 2-3 nm hydration layer within the inter-lamellar spaces. We propose that this hydration layer is necessary for the intercalation of APS molecules or AMP oligomers into the PM film, and their subsequent condensation and retention as nano-thin inorganic lamellae within the composite mesostructure after drying. Our results indicate that the intercalated nanocomposites prepared from preformed PM films have a higher degree of ordering than those produced by co-assembly more...

To investigate effects of redox-active functional groups on the coordination chemistry and electronic properties of N-heterocyclic carbenes (NHCs), we prepared a series of complexes comprising 1,3-diferrocenylimidazolylidene and -benzimidazolylidene (1 and 2, respectively), 1-ferrocenyl-3-methyl- and 1,3-diphenyl-5-ferrocenylbenzimidazolylidene (3 and 4, respectively), N,N′-diisobutyldiaminocarbene[3]ferrocenophane (FcDAC), and 1,3-dimesitylnaphthoquinoimidazolylidene (NqMes) ligands and coordinated [Ir(COD)Cl] (COD = 1,5-cyclooctadiene), [Ir(CO)2Cl], and [M(CO)5] (M = Cr, Mo, W) units. The coordination chemistry of the aforementioned NHCs was investigated by X-ray crystallography, and their electronic properties were studied by NMR and IR spectroscopy, as well as electrochemistry. No significant variation in νCO was observed among metal carbonyl complexes supported by 2−4 and FcDAC, indicating that the number (one vs two) of redox-active groups, the location (N atom vs backbone) of the redox-active group... more...

Despite extensive studies with many experimental techniques, the morphology and structure of the self-assembled aggregates of quaternary alkyl ammonium bromides (CnTABs; where n denotes the number of hydrocarbons in the surfactant tail) at the solid-liquid interface remains controversial, with results from atomic force microscopy (AFM) imaging pointing to a variety of surface aggregates such as cylinders and surface micelles, whilst surface force measurements and neutron reflectivity (NR) measurements reporting bilayer structures. Using a home-built liquid cell that employs the "bending mica" method, we have performed unprecedented synchrotron X-ray reflectometry (XRR) measurements to study the adsorption behaviour of a C nTAB series (n = 10, 12, 14, 16 and 18) at the mica-water interface at different surfactant concentrations. We find that our XRR data cannot be described by surface aggregates such as cylindrical and spherical structures reported by AFM studies. In addition we have observed that the bilayer thickness, surface coverage and the tilt angle all depend on the surfactant concentration and surfactant hydrocarbon chain length n, and that the bilayer thickness reaches a maximum value at approximately the critical micellisation concentration (∼1 cmc) for all the CnTABs investigated. We propose that CnTABs form disordered bilayer structures on mica at concentrations below cmc, whilst at ∼1 cmc they form more densely packed bilayers with the tails possibly tilted at an angle θt ranging from ∼40 to 60° with respect to the surface normal in order to satisfy the packing constraints due to the mica lattice charge, i.e. so that the cross-section area of the tilted chain would match that of the area of the lattice charge (As ≅ 46.8 Å2). As the surfactant concentration further increases, we find that the bilayer thickness decreases, and we ascribe this to the desorption of surfactant molecules, which recovers certain disorder and fluidity in the chain and thus leads to interdigitated bilayers again. In light of our XRR results, previously unattainable at the mica-water interface, we suggest that the surface aggregates observed by AFM could be induced by the interaction between the scanning probe and the surfactant layer, thus representing transient surface aggregation morphologies; whereas the CnTAB bilayers we observe with XRR are intrinsic structures under quiescent conditions. The suggestion of such quiescent bilayers will have fundamental implications to processes such as lubrication, self-assembly under confinement, detergency and wetting, where the morphology and structure of surfactant layers at the solid-liquid interface is an important consideration. © 2013 The Royal Society of Chemistry. more...

Conducting polymers have shown great potential for application in electronic devices. A major challenge in such applications is to control the supramolecular structures these materials form to optimise the functionality. In this work we probe the structure of oligo(aniline) thin films (of sub-μm thickness) drop cast on a silicon substrate using synchrotron surface diffraction. Self-assembly was induced through doping with an acid surfactant, bis(ethyl hexyl) phosphate (BEHP), resulting in the formation of well-ordered lamellae with the d-spacing ranging from 2.15 nm to 2.35 nm. The exact structural characteristics depended both on the oligomer chain length and film thickness, as well as the doping ratio. Complementary UV/Vis spectroscopy measurements confirm that such thin films retain their bulk electronic properties. Our results point to a simple and effective ionic self-assembly approach to prepare thin films with well-defined structures by tailoring parameters such as the oligomer molecular architecture, the nanofilm composition and the interfacial roughness. more...

The self-assembly behaviour, structure, and consequently the electronic properties of electroactive organic molecules can differ significantly from those of the bulk material when confined to thin films. Here we have examined the self-organised in-plane and out-of-plane structures of aniline oligomers in thin films using surface-sensitive grazing-incidence X-ray scattering (GIXS). Thin films of the aniline tetramer (TANI) and octamer (OANI) were prepared both in their native emeraldine base (EB) oxidation state and in the doped emeraldine salt (ES) state (combined with the acid surfactant bis(ethyl hexyl)phosphate (BEHP)), using a simple drop-casting and solvent annealing process. It was found that the presence of the acid surfactant induced self-organisation into highly ordered structures. The details of these structures, such as the morphology, orientation relative to the underlying substrate and the degree of orientation were found to depend on the molecular architecture of the oligomer. The BEHP-doped TANI system formed a highly oriented hexagonal unit cell (lattice parameters: a = b = 2.53 nm, c = 2.91 nm, γ = 120°), whereas the BEHP-doped OANI complex adopted a randomly oriented lamellar structure (d-spacing = 2.25 nm). Such detailed structural information reveals that the self-assembly behaviour and the packing of oligomer–BEHP complexes, when confined to thin films, are indeed different to that of the bulk phase materials. Furthermore, the molecular architecture of the oligomers directly influenced the structural changes of the doped films in response to in situ thermal treatment. These results demonstrate that through a simple processing route the morphology of electroactive oligomer films can be tailored by molecular design. These findings are important to future applications where thin film structure is a crucial consideration for device function and performance. more...

Lamellar structures self-assembled from purple membranes (PM) of Halobacterium salinarum are promising building units for bio-electronic devices, due to proton pumping ability of the PM. The functionality and durability of such devices are hinged on the structural integrity of PM lamellae. Using X-ray diffraction, we examined the structure of PM multilayers on silicon when challenged with two types of nanoparticles (NPs): carboxymethyl-dextran coated magnetite (2.4 nm core size) and citrate-stabilised gold (5 nm core size). We tried to infiltrate the PM multilayers with the NPs using two alternative routes: facile penetration (FP) and co-assembly (CS) by solution mixing. We found that under all conditions the NPs did not disrupt the overall lamellar structure of the PM films or enter the inter-lamellar space, although the presence of NPs affected the self-assembly process of the PM films. This caused an increase in the disorder in the film structure, as assessed by the decreasing number of layers in the multilayer stack as the NP concentration increased. Despite this, UV-Vis spectroscopic measurements showed that the conformation of the retinal residue within the protein was intact so the proton pumping functionality of PM multilayers would be retained in all samples with added NPs. Our results show that the effects of NPs on the PM structure and functionality are subtle and complex, and we will discuss the structural integrity of lipid-protein composite PM films against NP infiltration in terms of their high bending modulus as compared with that of fluid lipid bilayers. more...