A fully hydrated Nafion membrane is generally treated as a three-component system comprising the tetrafluoroethylene-like main chain, the fluorinated side chain ending with a sulfonic acid group, and absorbed water. We applied the contrast variation small-angle neutron scattering technique to decompose scattering intensity profiles to partial scattering functions (PSFs) of each component in Nafion quantitatively. In the large scale (>30 nm), structural heterogeneities were observed in the main-and side-chain domains but not in water domains. In the middle scale (5−30 nm), a bicontinuous-like structure of crystalline and amorphous phases with a mean separation distance of 11 nm was observed, as a result of the main-chain semicrystalline templating effect. In the small scale (<5 nm), another bicontinuouslike structure exists in the amorphous phase with a mean separation distance of about 4 nm, indicating a well-connected water network responsible for the good membrane conductivity. Cross-term analysis of PSFs for two components suggested the location of each component that the main-chain domains tends to phase-separate from either the side-chain or water domains, but the sidechain and water domains are closely attached through sulfonic acid groups.

The solid-substrate-dependent structure and dynamics of molecules in a supported lipid bilayer (SLB) were directly investigated via atomic force microscopy (AFM) and single particle tracking (SPT) measurements. The appearance of either vertical or horizontal heterogeneities in the SLB was found to be strongly dependent on the underlying substrates. SLB has been widely used as a biointerface with incorporated proteins and other biological materials. Both silica and mica are popular substrates for SLB. Using single-molecule dynamics, the fluidity of the upper and lower membrane leaflets was found to depend on the substrate, undergoing coupling and decoupling on the SiO/Si and mica substrates, respectively. The anisotropic diffusion caused by the locally destabilized structure of the SLB at atomic steps appeared on the AlO(0001) substrate because of the strong van der Waals interaction between the SLB and the substrate. Our finding that the well-defined surfaces of mica and sapphire result in asymmetry and anisotropy in the plasma membrane is useful for the design of new plasma-membrane-mimetic systems. The application of well-defined supporting substrates for SLBs should have similar effects as cell membrane scaffolds, which regulate the dynamic structure of the membrane.

We examined an emission of light from a single metallic nanoparticle based on surface plasmon (SP) resonance for determination of three-dimensional orientation of nanoparticles as well as their optical properties. The defocused image of individual Au nanorods (Au NRs) is recorded by changing the focus distance under total internal reflection microscopy (TIRM) observations. Numerical and statistical analysis revealed that the observed light distribution patterns of Au NRs defocused images were classified into two groups. One is explained by considering that a single dipole dominates its light emission property. The other is explained by assuming the presence of multidipoles. This result leads us to a consideration that the emission of light coupled with the transverse and the longitudinal SP modes was observed reflecting the optical characteristics of NRs. Additionally, unique multiple ring patterns were also observed by placing Au NRs at the vicinity of nanoscopic structure, reflecting the distance between NRs and the wall of the structure in the scale less than a few tens of nanometers. The inclusive SP measurement for both the transverse and longitudinal axes of these anisotropic metal NRs using a defocused imaging system brings us reliable optical and conformational information.

The lipid bilayer environment around membrane proteins strongly affects their structure and functions. Here, we aimed to study the fusion of proteoliposomes (PLs) derived from cultured cells with an artificial lipid bilayer membrane and the distribution of the PL components after the fusion. PLs, which were extracted as a crude membrane fraction from Chinese hamster ovary (CHO) cells, formed isolated domains in a supported lipid bilayer (SLB), comprising phosphatidylcholine (PC), phosphatidylethanolamine (PE), and cholesterol (Chol), after the fusion. Observation with a fluorescence microscope and an atomic force microscope showed that the membrane fusion occurred selectively at microdomains in the PC + PE + Chol-SLB, and that almost all the components of the PL were retained in the domain. PLs derived from human embryonic kidney 293 (HEK) cells also formed isolated domains in the PC + PE + Chol-SLB, but their fusion kinetics was different from that of the CHO-PLs. We attempted to explain the mechanism of the PL-SLB fusion and the difference between CHO- and HEK-PLs, based on a kinetic model. The domains that contained the whole cell membrane components provided environments similar to that of natural cell membranes, and were thus effective for studying membrane proteins using artificial lipid bilayer membranes.