Bimolecular Layer Research Articles

Effect of Metal Ions on Monolayer Collapses

A Langmuir monolayer of stearic acid on pure water and in the presence of certain divalent metal ions such as Cd and Pb at pH approximately 6.5 of the subphase water collapses at constant area, while for other divalent ions such as Mg, Co, Zn, and Mn at the same subphase pH the monolayer collapses nearly at constant pressure. Films of stearic acid with Cd, Pb, Mn, and Co in the subphase (at pH approximately 6.5) have been transferred onto hydrophilic Si(001) using a horizontal deposition technique, just after and long after collapse. Electron density profiles obtained from X-ray reflectivity analysis show that a three-molecular-layer structure starts to form just after constant area collapse, where in the lowest molecular layer, in contact with the substrate, molecules are in asymmetric configuration, i.e., both hydrocarbon tails are on the same side of the metal-bearing headgroup that touches the substrate, while the molecules above the first layer are in symmetric conformation of the tails with respect to the headgroups. Further along collapse, when the surface pressure starts to rise again with a decrease in area, more layers with molecules in the symmetric configuration are added, but the coverage is poor. On the other hand, only bimolecular layers form after constant pressure collapse, with the lower and upper layers having molecules in asymmetric and symmetric configurations, respectively, and the upper molecular layer density increases with compression of the monolayer after collapse. A "Ries mechanism" for constant area collapse and a "folding and sliding mechanism" for constant pressure collapse have been proposed.

Preparation and characterization of new hybrid organic/inorganic systems derived from calcium ( α-aminoalkyl)-phosphonates and -phosphonocarboxylates

We have studied the phenomenon of calcium complexation by lab synthesized amphiphilic ( α-aminoalkyl)-phosphonocarboxylic or -phosphonic acids. The electrical conductivity of aqueous solutions of sodium salts of all these acids was measured versus the volume of a calcium salt solution added. It appeared that calcium complexes are formed in a Ca/P atomic ratio close to 1. Calcium phosphonocarboxylates and calcium phosphonates were also precipitated by mixing aqueous solutions of disodium salts of phosphorus amphiphiles and calcium nitrate solutions. Before chemical analysis, these complexes were calcined to remove the organic part. In the mineralized products, calcium and phosphate were assayed: the Ca/P atomic ratio was equal to 1. X-ray diffraction and IR spectroscopy showed that they are made entirely of β pyrophosphate (Ca 2P 2O 7), a result in agreement with previous chemical analysis. The chemical formula of the starting calcium complexes could be written as CaL⋅2H 2O (L = ligand). The SEM micrographs of these complexes show plate-like structures. XRD patterns are characteristic of layered structures. These facts suggest that calcium complexes are composed of alternating bimolecular layers of calcium alkylphosphonocarboxylates or calcium alkylphosphonates, the chains being tilted and partially interdigitated.

Dramatic enhancement of capillary wave fluctuations of a decorated water surface

We have demonstrated by x-ray diffuse scattering that a bimolecular layer of a preformed three-tailed amphiphile, ferric stearate, drastically enhances capillary wave fluctuations on water surface due to a reduction in surface tension to 1 mN/m . The bimolecular layer is composed of molecules in symmetric configuration, on top of molecules in asymmetric configuration with ferric ions in contact with water. Unlike the usual Langmuir monolayers, this layer of molecules does not rupture under compression, but becomes thicker. This behavior mimics folding of a membrane on a liquid surface and is closely related to the cohesive interaction brought by the ferric ions. The low effective tension of this artificial membrane depends on the available area and reduces as the microscopic excess area increases.

Micelle Formation and Surface Adsorption of Octaethylene Glycol Monoalkyl Ether (CnE8)

Abstract The surface tension was measured against the concentration of CnE8 (n = 14, 16, and 18) at temperatures of 298.2, 303.2, 308.2, 313.2, and 318.2 K, from which the critical micelle concentration (CMC) was determined. The CMC decreased with increasing carbon number at lower temperatures, where the decreasing rate became much smaller at higher temperatures. The CMC values were examined by pyrene fluorescence, and the I1/I3 ratio of the pyrene spectrum steeply decreased below the CMC, and finally reached a plateau at higher surfactant concentrations. The I1/I3 ratios indicate that the microenvironment of pyrene in the micellar region becomes more hydrophobic with increasing the alkyl chain of CnE8. The aggregation number by a static light-scattering method increased with increasing the alkyl chain at a definite temperature and with raising the temperature for all of the surfactants. The thermodynamic parameters (ΔG°, ΔH°, TΔS°) of the micelle formation were calculated from the temperature dependence of CMC and the aggregation number, and the micellization was found to be entropy-driven. The surface excess concentration (Γ) was also determined from the change in the surface tension with the concentration from which the molecular surface area (A) below the CMC was evaluated. The molecular surface areas suggest that longer monoalkyl ethers form a bi-molecular layer with the hydrophobic tail intruding inwards. The positive entropy change (Δs) for the surface adsorption decreased and stayed almost constant with increasing concentration for C14E8 and C16E8, while the change remained almost zero for C18E8 at whole concentrations below the CMC. These results suggest that the non-fully extended alkyl chain in the bulk could not well contribute to a positive entropy change upon adsorption, which results in a smaller decreasing rate in CMC with increasing carbon number of alkylchain for C16E8 and C18E8 compared with the decreasing rate for CnE8 with n less than 14.

Algicidal activity of rhamnolipid biosurfactants produced by Pseudomonas aeruginosa

The algicidal activity of the rhamnolipid biosurfactants (the mixture of Rha-Rha-C 10-C 10 and Rha-C 10-C 10) produced by Pseudomonas aeruginosa was investigated in the present paper. The results indicated that the biosurfactants had potential algicidal effects on the harmful algal bloom (HAB) species, Heterosigma akashiwo. The growth of H. akashiwo was strongly inhibited in medium containing rhamnolipids (0.4–3.0 mg L −1); moreover, the rhamnolipids showed strong lytic activity toward H. akashiwo at higher concentrations (≥4.0 mg L −1). In addition, the effects of the rhamnolipids on the growth of Gymnodinium sp. and Prorocentrum dentatum, another two kinds of HAB species, were also studied. Compared with the dramatic algicidal effect on H. akashiwo, the cells of P. dentatum were inhibited or lysed at higher concentrations (1.0–10.0 mg L −1), while the cells of Gymnodinium sp. were not suppressed with the same treatment, indicating the rhamnolipids had the potential for the selective control of HABs. Morphometric analysis at ultrastructural level by transmission electron micrographs indicated that the extent of ultrastructural damage of the alga was severe at high concentrations of rhamnolipids and during extended periods of contact. The first response occurred in the plasma membrane which partly disintegrated. The lack of membrane facilitated the rhamnolipid biosurfactants into the cells and allowed damage to other organelles, which resulted in the injury of chloroplast, vacuolization of mitochondria and deformation of the cristae, disruption of nuclear membrane and condensation of chromatin in nucleus, suggesting that the lytic activity of rhamnolipids was mainly due to their powerful surfactivity and their tendency to cohere on the surface of phospholipids bimolecular layer of the cells and further destroyed the layers, and then the structure of quasi-membrane configurations inside the cells was disintegrated, following by the irreversible damage to the ultrastructure and the loss of the function of organelles, consequently leading the cells to lyse.

Ammonium 4-methoxycinnamate.

In the title compound, NH(4)(+).C(10)H(9)O(3)(-), bimolecular layers of the anions are formed between layers of the cations. There are N-H.O hydrogen bonds between the ammonium ion and the carboxylate groups of the anions. In the crystal structure, the C=C moiety of the cinnamate ion makes an angle of 117.1 (2) degrees with that of the nearest neighbour, indicating that a pedal rotation is required before beta-type [2+2]-photodimerization can take place, which is the predominant mode of the photochemistry of this compound.

Osteoblast cell membrane hybrid bilayers for studying cell–cell interactions

Osteoblast-like cells were grown on a surface that presents cell membrane components to the cells in culture. The culture surface was a bimolecular layer formed by the interaction of osteoblast plasma membrane vesicles with an alkanethiol monolayer. The potential of these osteoblast-membrane hybrid bilayers for promoting osteoblast adhesion, growth and differentiation was examined. UMR-106 osteoblast-like cells cultured on these surfaces are normal in appearance, and in the presence of serum, proliferate as well or better than on control surfaces. The level of alkaline phosphatase production in the presence and absence of serum suggests that the osteoblast-like cells retain their differentiated phenotype, and appear to respond to the cell surface ligands presented by the osteoblast-membrane biomimetic surface. These observations suggest that biomimetic membrane films prepared from osteoblast cell membranes support osteoblast cell growth, allow the cells to maintain their differentiation state and may be suitable as a model system to probe cell-cell interactions.

Formation of Layered Silica−Alcohol Nanostructured Materials from Alkoxytrichlorosilanes

Novel layered silica−organic nanostructured materials were prepared by hydrolysis and condensation of alkoxytrichlorosilanes (n-CnH2n+1OSiCl3, n = 12, 14, 16, 18, and 20) as single precursors. The formation relies on the self-assembly of alkoxysilanetriols (n-CnH2n+1OSi(OH)3) generated by the preferential hydrolysis of Si−Cl groups in the precursors. The products exhibited the XRD patterns indicative of layered structures whose d spacings varied in the range of 3.95 to 6.13 nm depending on the alkyl chain lengths. The SEM images of the products showed well-defined platelike morphologies on micrometer length scales, reflecting the layered structures of the products. Further structural characterization by solid-state 29Si and 13C NMR and FTIR revealed that the layered structures consisted of bimolecular layers of long-chain alcohols and thin silica layers. Condensation of alkoxysilanetriols proceeded in the solid state to form silica networks, being accompanied by the cleavage of the alkoxy groups. The present results provide a new approach for the construction of silica-based nanostructured materials with well-regulated organic arrays and silica networks.

Highly ordered photoluminescent self-assembled films based on polyoxotungstoeuropate complex Na9[EuW10O36]Electronic supplementary information (ESI) available: IR, absorption and emission spectra, XRD pattern and SEM image of EuW10–C16TA film. See www.rsc.org/suppdata/jm/b2/b210965d/

A novel highly ordered layered superlattice multibilayer film is prepared by casting the chloroform solutions of ionic complex between a polyoxotungstoeuropate anion EuW10O369− (EuW10) and a hexadecyltrimethylammonium cation (C16TA) on hydrophilic substrates. A variety of techniques, including FT-IR and UV–vis spectroscopies, differential scanning calorimetry (DSC), X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) have been used to characterize the structure of the composite film. The lamellae consist of alternating layers of polyoxotungstoeuropate and bimolecular layers of surfactant, with the surfactant alkyl chains tilted 30.8° to the lamellar surface and noninterdigititated. The photoluminescent behavior of the film at room temperature has also been investigated by fluorescence spectroscopy to show the characteristic Eu3+ emission pattern of 5D0 → 7Fj. The fluorescence spectra and fluorescence lifetime of the composite film are quite different from those found for EuW10 solid powder and EuW10 dilute aqueous solution.

The first cell membranes.

Organic compounds are synthesized in the interstellar medium and can be delivered to planetary surfaces such as the early Earth, where they mix with endogenous species. Some of these compounds are amphiphilic, having polar and nonpolar groups on the same molecule. Amphiphilic compounds spontaneously self-assemble into more complex structures such as bimolecular layers, which in turn form closed membranous vesicles. The first forms of cellular life required self-assembled membranes that were likely to have been produced from amphiphilic compounds on the prebiotic Earth. Laboratory simulations show that such vesicles readily encapsulate functional macromolecules, including nucleic acids and polymerases. The goal of future investigations will be to fabricate artificial cells as models of the origin of life.

Formation and Structure of Titanium Alkyl Phosphates

Titanium alkyl phosphates (TiAP) synthesized by the reactions of Ti(SO 4) 2 with monohexyl, monooctyl, and monodecyl phosphates in aqueous media were characterized by various means. The XRD patterns of TiAP showed a strong diffraction peak and two weak ones below 2θ=15°. The TiAP particle prepared using octyl phosphate gave rise to the lattice patterns having uniform alternating spacings of ca. 0.7 and ca. 2.0 nm. When treated at 900°C, TiAP crystallized as TiP 2O 7. The chemical formula could be shown as (ROPO 3) 2Ti·0.44H 2O. These facts suggest that the TiAP is composed of a multilayer alternating bimolecular layer of alkyl phosphates and hydrated titanium phosphate phase. Alkyl groups in the layers were removed by outgassing above 300°C to give the materials having mesopores with a diameter of ca. 2 nm.

X-ray diffraction study of gadolinium stearate Langmuir-Blodgett films

The comparative structural studies of gadolinium stearate Langmuir-Blodgett films prepared with the use of two different subphases (aqueous solutions of gadolinium chloride and gadolinium acetate) have been performed by the methods of X-ray diffractometry. The films were applied onto single-crystal silicon substrates coated with a native-oxide layer either with the use of buffer molecular stearic-acid layers or without such layers. It was established that the films obtained with the use of gadolinium acetate and the preliminarily formed buffer layers are, in fact, single-phase Y-type films with highly ordered molecular structure, and the thickness of the bimolecular layer d = (51.3 ± 0.5) A.

Electrochemical Control of Vesicle Formation with a Double-Tailed Cationic Surfactant Bearing Ferrocenyl Moieties

We already reported spontaneous vesicle formation in aqueous solutions of bis(11-ferrocenyl(undecyl))dimethylammonium bromide (11-BFDMA), a newly synthesized ferrocene-modified double-chain-type cationic surfactant (Kakizawa, Y.; Sakai, H.; Nishiyama, K.; Abe, M. Langmuir 1996, 12, 921.). We have examined in this study electrochemical control of vesicle formation of 11-BFDMA using the redox reaction of ferrocenyl groups in their molecules. Static light scattering, conductivity, and cyclic voltammogram measurements on the solution revealed that vesicles made of the reduced form of 11-BFDMA disintegrate and change into smaller molecular aggregates including micelles through oxidation of ferrocenyl groups. Oxidation of ferrocenyl groups also caused a remarkable decrease in the solubilization equilibrium constant for benzene in 11-BFDMA solution and release into the bulk phase of benzene solubilized in bimolecular layers of 11-BFDMA vesicles. In addition, glucose entrapped in the inner aqueous phase of the ve...

Crystal Structures of Several Fluoro-Mesogens

Crystal structures of 4-propyloxyphenyl 4-(4-trifluoromethylbenzoyloxy)benzoate (I), p-phenylene 4-methoxy-benzoate 4-trifluoromethylbenzoate (II), ethyl 4-[2-(perfluorooctyl)ethoxy]benzoate (III), and 3-[2-(perfluorooctyl)ethoxy]nitrobenzene (IV) have been determined. All the crystals have smectic-like layer structures. In a layer, molecules are arranged in an antiparallel way in I and II, where CF3 groups are sorrounded by alkyl groups. In III and IV, head-to-head arrangements result in the segregation of perfluorochains and the other moieties in bimolecular layers.

Intercalation of n-alkylamines into layered materials: a method for the recognition of isomorphism in semicrystalline compounds

n-Alkylamines were intercalated into Ti2O3(H2AsO4)2·2H2O (TiOAs) and Zr2O3(HAsO4)·3H2O (ZrOAs) by exposing the solids to the amine vapour. The formulae of the intercalation compounds are Ti2O3(H2AsO4)2·1.7CnH2n + 1NH2·2H2O and Zr2O3(HAsO4)·0.6CnH2n+1NH2·2H2O (n = 3–6), respectively. The intercalated amines form bimolecular layers in the interlayer space of the polyvalent metal arsenates. The changes in the basal spacing of the intercalation compounds as a function of the length of the alkyl chain were used for evaluation of the free area associated with each active centre in the arsenate layers: 11.8 (TiOAs) and 10.8 A2 (ZrOAs). The comparison of these data with analogous data reported for n-alkylamine intercalation into other metal(IV) arsenates and metal(IV) phosphates resulted in the formulation of a procedure for the recognition of isomorphism in semicrystalline compounds.

Synthesis and characterization of thermotropic amphiphilic liquid crystals: semiperfluoroalkyl-β-D-glucopyranosides

As part of our study of the mesomorphic properties of glucopyranosides containing fluorinated chains, this paper focuses on an investigation of the liquid crystalline behaviour of nonaromatic compounds. The synthesis of eight single-tailed materials which contain a semiperfluoroalkyl chain linked to the polar glucose head group is described. Using polarized optical microscopy, DSC and X-ray diffraction all the materials were found to show only monomesomorphism, a smectic A phase with bimolecular layers. The thermal behaviour is discussed in comparison with the previously reported data on the series of parent compounds.

Myelin basic protein–lipid complex: an atomic force microscopy study

Myelin basic protein (MBP) efficiently bound Dilauroyl- lα-phosphatidic acid (DLPA) monolayers at the air water interface. Langmuir–Blodgett (LB) films were prepared from these monolayers and the hydrophilic surface of the upper layer was inspected by atomic force microscopy (AFM) in a water solution. The topography images of nominally four-layer films of DLPA in the absence of MBP revealed regions of different thickness corresponding to different numbers of lipid bimolecular layers. This morphology is characteristic of those lipid films which reorganise spontaneously when kept under an aqueous solution. The DLPA films containing MBP did not reorganise; their thicknesses were uniform and surfaces were usually covered by disordered clusters of protein molecules. Quasi-ordered arrays of smaller particles were observed in films with small amounts of bound protein. The surface charge densities of DLPA and DLPA-MPA films were investigated performing force-distance measurements by using tips modified with surface carboxyl groups. The curves obtained on pure lipid films showed repulsive forces well described in terms of double layer forces. Repulsive forces were not observed in the presence of a uniform MBP overlayer indicating that MBP neutralised most of the lipid charge.

Measurement and control of the crystal growth rate of tetragonal hen egg-white lysozyme imaged with an atomic force microscope

The step velocity of the tetragonal hen egg-white lysozyme (1 1 0) crystal plane toward the [0 0 1] direction could be controlled and measured accurately on a nanometer scale using a specially designed sealed sample vessel on an atomic force microscope. The effects of lysozyme and NaCl concentration on the step velocity were also examined. The step velocity was a non-linear function of supersaturation ( σ). The heights of steps and 2D islands corresponded to a bimolecular layer and the dominant growth unit was estimated as a tetramer. Crystal growth apparently stopped when the supersaturation was reduced to less than 0.69.

Electroluminescent device with biphenylpyrazine derivative Eu salt LB (Langmuir–Blodgett) film as a molecular-size emissive layer

Using the Eu salt Langmuir–Blodgett (LB) film of a biphenylpyrazine derivative (C4BPy), we fabricated a double-heterostructure device with molecular-size emissive layer, ITO/diamine hole-transporting layer/ Eu salt LB film of C4BPy (two monolayers)/oxadiazole electron-transporting layer/MgAg. When the DH device was driven at 170 K, only sharp red emission due to the Eu salt bimolecular layer was observed, and no emission due to the HTL and the ETL was observed. The result demonstrates that the C4BPy Eu salt bimolecular layer was successfully actuated as molecular-size emissive layer. The external quantum efficiency and maximum luminance of the device were 0.01% and 3 cd/m 2, respectively.

Modification of amorphous aluminum phosphate with alkyl phosphates

Synthetic amorphous aluminum phosphate (AlPO 4) particles were treated with monohexyl, monooctyl, and monodecyl phosphates in acetone, and the resulting materials were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared (FTIR) spectroscopy, thermogravimetric and differential thermal analyses (TG/DTA), and adsorption of N 2. XRD patterns of the modified samples showed a strong diffraction peak and two weak ones below 2θ = 15°. The d-values of these peaks linearly increased with elongating of alkyl groups of the phosphates. After the treatment, particle size increased without formation of new particles. These results reveal that a multilayer alternating bimolecular layer of alkyl phosphates and aluminum phosphate phase is formed on the surface of AlPO 4 particles by the modification with alkyl phosphates. The layered structure disappeared on outgassing above 300°C, accompanying the removal of alkyl groups, formation of mesopores, and variation of surface structure.