Direct Visualization of the Dynamic Hydrolysis Process of an l-DPPC Monolayer Catalyzed by Phospholipase D at the Air/Water Interface

Helicity Manipulation of a Double-Paddled Binaphthyl in a Two-Dimensional Matrix Field at the Air-Water Interface

Molecular behavior and functionality are affected by their prevailing immediate environment. Molecular machines function according to conformational variations and have been studied largely in solution states. In order to access more highly complex functional molecular machines, it is necessary to analyze and control them in various environments. We have designed and synthesized a bisbinaphthyldurene (BBD) molecule that has two binaphthyl groups connected through a central durene moiety, allowing for the formation of several conformers. In density functional theory (DFT) calculations, BBD has five major conformers, denoted anti-1/anti-2/syn-1/syn-2/flat. It has been demonstrated that BBD exhibits different conformations in solution (anti-1 and syn-1) than on a gold surface (syn dimer and flat). In this work, the ratio of BBD conformations has been controlled in mixed monolayers with several different lipids at an air-water interface in order to compare conformational activity under different conditions. The conformations of BBD in transferred films obtained by using Langmuir-Blodgett techniques were estimated from circular dichroism spectra and DFT calculations. It has been found that the conformation of BBD in the mixed monolayer depends on its aggregated state, which has been controlled here by the mechanical properties and miscibility. In mixed monolayers with "hard" lipids having less miscibility with BBD as well as in cast film, BBD is self-aggregated and mostly forms stable anti-1 and syn-1 conformations, while unstable anti-2 and syn-2 conformers dominated in the more dispersed states involving "soft" lipids, which show good miscibility with BBD. Conformational changes in BBD are due to the formation of different aggregated states in each mixed monolayer according to the miscibility. Overall, BBD molecular conformations (and the resulting spectra) could be tuned by controlling the environment whether in solution, on a solid substrate, or in an admixture with lipids at the air-water interface.

Structural-Size Control of Domain from Nano to Micro: Logical Balancing between Attractive and Repulsive Interactions in Two Dimensions

Molecules aggregate to form a structure through various interactions involving dispersion force, electrostatic force, and so on. In two-dimensional systems, a surface energetic effect is further important for the molecular aggregation structure. We show that the domain size and its morphology in the mixed monomolecular film composed of hydrocarbon and fluorocarbon skeletons with different surface free energies extremely change depending on pH and NaCl concentration in the subphase. Such morphological changes can be interpreted by the balance of dipole density and line tension, which help in the development of an understanding of phase separation phenomena and provide a novel technique for structural control in two dimensions.

Applications of Brewster angle microscopy from biological materials to biological systems

Brewster angle microscopy (BAM) is a powerful technique that allows for real-time visualization of Langmuir monolayers. The lateral organization of these films can be investigated, including phase separation and the formation of domains, which may be of different sizes and shapes depending on the properties of the monolayer. Different molecules or small changes within a molecule such as the molecule's length or presence of a double bond can alter the monolayer's lateral organization that is usually undetected using surface pressure-area isotherms. The effect of such changes can be clearly observed using BAM in real-time, under full hydration, which is an experimental advantage in many cases. While previous BAM reviews focused more on selected compounds or compared the impact of structural variations on the lateral domain formation, this review provided a broader overview of BAM application using biological materials and systems including the visualization of amphiphilic molecules, proteins, drugs, extracts, DNA, and nanoparticles at the air-water interface.

Effect of phospholipase A2 hydrolysis products on calcium oxalate precipitation at lipid interfaces

Urinary stones are commonly composed of an inorganic component, calcium oxalate, or calcium phosphate and an organic matrix of lipids, carbohydrates, and proteinaceous matter. Of interest is the role that the organic matrix elements may play as catalysts for the heterogeneous nucleation of the calcium salts, and a number of studies have examined the role of lipids in calcium oxalate monohydrate (COM) formation. In this study, products of lipid hydrolysis from phospholipase A(2) (PLA(2)) are examined for their effect on COM formation using Langmuir monolayers as model lipid membrane assemblies. The enzyme PLA(2) hydrolyzes DPPC monolayers in the presence of a supersaturated calcium oxalate subphase, inducing the rapid and plentiful nucleation of calcium oxalate at the lipid interface. To investigate the cause of increased crystal formation in the presence of the enzyme, Langmuir monolayers modeling the hydrolysis products were investigated. Calcium oxalate crystal growth at a ternary monolayer of dipalmitoylphosphatidylcholine (DPPC), palmitic acid (PA), and a 22-carbon chain lysophospholipid (22:0 Lyso PC) dramatically increases relative to monolayers of just DPPC. Binary monolayers of DPPC with either PA or the 22:0 Lyso PC and single-component monolayers of PA were also studied. It is demonstrated that the fatty acid generated during lipid hydrolysis causes a significant increase in the extent of heterogeneous nucleation of calcium oxalate from supersaturated solutions. The results imply a possible link between increased phospholipase activity, which is associated with hyperoxaluria, and calcium oxalate precipitation.

Dynamic adsorption and characterization of phospholipid and mixed phospholipid/protein layers at liquid/liquid interfaces

Drop profile analysis tensiometry is applied to study the adsorption dynamics of phospholipids, proteins and phospholipid/protein mixtures at liquid/liquid interfaces. Measurements of the dynamic interfacial tension of phospholipid layers give information on the adsorption mechanism and the structure of the adsorption layer. The equilibrium and dynamic adsorption of pure protein solutions, i.e. human serum album (HSA), beta-lactoglobulin (beta-LG), beta-casein (beta-CA), can be explained well by the thermodynamic model of Frumkin and the diffusion-controlled adsorption theory. The adsorption behavior from mixed phospholipid/protein solutions was also investigated in terms of dynamic interfacial tensions. Interestingly, a "skin-like" folded film of pure protein or phospholipid/protein complex layers can be observed at curved surfaces at the water/oil interfaces. The addition of phospholipids accelerates the formation of the folded structure at the drop surface through co-adsorption of proteins.

Hydrolysis characterization of phospholipid monolayers catalyzed by different phospholipases at the air-water interface

Combination of some newly developed microscopic and spectroscopic techniques with conventional Langmuir monolayer method can provide more quantitative information with the molecular orientation and reorganization process of spread amphiphilic molecules at the air/water interface. These techniques are extended to investigate the hydrolysis process of spreading lipid monolayer catalyzed by different enzymes, phospholipases A2, C and D, respectively. Synchrotron X-ray diffraction and infrared reflection absorption spectroscopy are able directly to give the structural information of the assembled monolayer, interfacial activity of amphiphiles and their components at the interface. Microscopic technique such as Brewster angle microscopy (BAM), fluorescence microscopy (FM) can be used to trace the morphological changes dynamically as the spreading lipid monolayer is hydrolyzed at the air/water interface. We summary here some latest progress in this filed and give a brief review over the hydrolysis features of phospholipid monolayer catalyzed by different enzymes. It is attempted to establish a model of membrane hydrolysis process in order to better understand the mechanism of membrane metabolism and signal transduction in a living system.

Molecular assembly of biomimetic microcapsules

Our recent work on the fabrication of microcapsules comprised of human serum albumin (HSA) and -α-dimyristoylphosphatitic acid (DMPA) by means of stepwise adsorption of HSA and DMPA on fluid droplet surfaces or charged colloids and subsequent dissolution of the cores is reviewed. The lipid self-assembles as a bilayer on the protein surface and the completed microcapsule serves as a biomimetic membrane model. The DMPA/HSA microcapsules have good biocompatibility and the potential for the insertion of recognition units in the lipid bilayers. The structure and properties of the lipid/protein microcapsules are described and their potential for applications in sustained drug release are introduced.

Example of an organic reaction in a Langmuir film: Reduction of an amphiphilic ketone by NaBH4

Langmuir monolayers of an amphiphilic ketone 1 have been studied on pure water and on aqueous subphases containing sodium borohydride. Changes in the compression isotherm and in the monolayer morphology were observed when the concentration of NaBH4 or the delay between spreading and compression was increased. These modifications were specific to NaBH4 and suggested that a chemical reaction is taking place along the monolayer. Modifications in the IR spectrum of the corresponding Langmuir-Blodgett film confirmed the reduction of the ketone group of 1 when spread on aqueous subphases of sodium borohydride. Analysis of the compression isotherms demonstrated that this reaction occurred for all surface pressures and therefore indicated that the ketone group of 1 is accessible to the borohydride whatever the compression state of the monolayer.