Ion selectivity of a poly(3-pentylmethoxythiophene) LB-layer modified carbon-fiber microelectrode as a consequence of the second order filtering in voltcoulometry

Ion selective properties of poly(3-pentylmethoxythiophene) Langmuir-Blodgett film modified carbon-fiber microelectrode are described. The study of the electrode behavior indicates that important features occur if two electrochemical methods, one of them being kinetics sensitive, are used. While in case of the typical steady-state voltammetry the electrode remains sensitive to both the cations and anions, the kinetics-sensitive properties of voltcoulometry based on the second-order filtering scheme disable the observation of anions. As a model system a mixture of copper and dopamine ions is used.     

Production of interferon-β by fibroblast cells on membranes prepared by extracellular matrix proteins

The fibroblast cells from normal human skin were cultured on Langmuir-Blodgett (LB) and cast membranes prepared using extracellular matrix proteins (e.g., collagen, fibronectin, laminin and vitronectin). The cell density of the fibroblast cells cultured on the cast membranes was found to be higher than that on the cast membranes made of fibronectin, vitronectin and collagen-blended membranes. This indicates that not only the primary structure of proteins but the preparation methods of the membranes, i.e., casting and LB methods, are a strong factor affecting cell growth. The concentration and production of interferon-β per unit cell were found to be higher on the LB membranes than on the cast membranes made of the same proteins except in the case of collagen. However, the cell density on the cast membranes was higher than that on the LB membranes. These results appear to result from the suppressed growth of NB1-RGB cells on the LB membranes leading to the enhanced production of interferon-β on the LB membranes. The highest production of interferon-β per unit cell was observed for the NB1-RGB cells on the collagen-blended membranes with fibronectin and vitronectin. The collagen-blended membranes appear to offer a more natural and appropriate environment for NB1-RGB cells to produce interferon-β. This revised version was published online in September 2006 with corrections to the Cover Date.     

Compositional domain immiscibility in whole myelin monolayers at the air-water interface and Langmuir-Blodgett films

Monomolecular layers of whole myelin membrane can be formed at the air-water interface from vesicles or from solvent solution of myelin. The films appear microheterogeneous as seen by epifluorescence and Brewster angle microscopy. The pattern consists mainly of two coexisting liquid phases over the whole compression isotherm. The liquid nature of the phases is apparent from the fluorescent probe behavior, domain mobility, deformability and boundary relaxation due to the line tension of the surface domains. The monolayers were transferred to alkylated glass and fluorescently labeled against myelin components. The immunolabeling of two major proteins of myelin (myelin basic protein, proteolipid-DM20) and of 2′,3′-cyclic nucleotide 3′-phosphodiesterase shows colocalization with probes partitioning preferentially in liquid-expanded lipid domains also containing ganglioside G_M1. A different phase showing an enrichment in cholesterol, galactocerebroside and phosphatidylserine markers is also found. The distribution of components is qualitatively independent of the lateral surface pressure and is generally constituted by one phase enriched in charged components in an expanded state coexisting with another phase enriched in non-charged constituents of lower compressibility. The domain immiscibility provides a physical basis for the microheterogeneity found in this membrane model system.     

铜／封口膜／酰化紫膜LB膜／氧化铟锡型菌紫质光电池的光电特性

ＲＨ５７％的ＡＰＭＬＢＦ构制的Ｃｕ／Ｐａｒａｆｉｌｍ／ＡＰＭＬＢＦ／ＩＴＯ型ＢＲ光电池具有的光电响应能力随ＡＰＭＬＢＦ暗适应程度增加而增大,光适应后趋于稳定。光电响应信号的大小随被光照的截面减小而变小;不同引线输出的信号极性与质子泵运相一致。结果认为这种光电池可用于进一步构制光电池组以模拟视网膜的某些功能。     

A scanning force- and fluorescence light microscopy study of the structure and function of a model pulmonary surfactant

The structure of an artificial pulmonary surfactant was studied by scanning force- and fluorescence light microscopy (SFM, and FLM, respectively). The surfactant – a mixture of dipalmitoylphosphatidylcholine (DPPC), dipalmitoylphosphatidylglycerol (DPPG) and recombinant surfactant-associated protein C (SP-C) – was prepared at the air-water interface of a Langmuir film balance and imaged by FLM under various states of compression. In order to visualize their topography by SFM, the films were transferred onto a solid mica support by the Langmuir-Blodgett (LB) technique. We found that a region of high film compressibility of the spread monolayer close to its equilibrium surface pressure (π=50 mN/m) was due to the exclusion of layered protrusions with each layer 5.5 to 6.5 nm thick. They remained associated with the monolayer and readily reinserted upon expansion of the film. Comparison with the FLM showed that the protrusions contained the protein in high concentration. The more the film was compressed, the larger was the number of layers on top of each other. The protrusions arose from regions of the monolayer with a distinct microstructure that may have been responsible for their formation. The molecular architecture of the microstructure remains to be elucidated, although some of it can be inferred from spectroscopic data in combination with the SFM topographical images. We illustrate our current understanding of the film structure with a molecular model. Received: 20 September 1996 / Accepted: 22 May 1997     

Interaction of nonsteroidal anti-inflammatory drugs with membranes: In vitro assessment and relevance for their biological actions

Nonsteroidal anti-inflammatory drugs (NSAIDs) are among the most commonly used drugs in the world due to their anti-inflammatory, analgesic and antipyretic properties. Nevertheless, the consumption of these drugs is still associated with the occurrence of a wide spectrum of adverse effects. Regarding the major role of membranes in cellular events, the hypothesis that the biological actions of NSAIDs may be related to their effect at the membrane level has triggered the in vitro assessment of NSAIDs-membrane interactions. The use of membrane mimetic models, cell cultures, a wide range of experimental techniques and molecular dynamics simulations has been providing significant information about drugs partition and location within membranes and also about their effect on diverse membrane properties. These studies have indeed been providing evidences that the effect of NSAIDs at membrane level may be an additional mechanism of action and toxicity of NSAIDs. In fact, the pharmacokinetic properties of NSAIDs are closely related to the ability of these drugs to interact and overcome biological membranes. Moreover, the therapeutic actions of NSAIDs may also result from the indirect inhibition of cyclooxygenase due to the disturbing effect of NSAIDs on membrane properties. Furthermore, increasing evidences suggest that the disordering effects of these drugs on membranes may be in the basis of the NSAIDs-induced toxicity in diverse organ systems. Overall, the study of NSAIDs-membrane interactions has proved to be not only important for the better understanding of their pharmacological actions, but also for the rational development of new approaches to overcome NSAIDs adverse effects.     

Field-Effect Transistor based on conducting Langmuir-Blodgett films of EDTTTF derivatives

A Field-Effect Transistor in which the channel is made of Langmuir-Blodgett layers of EDTTTF derivatives is described and studied. The device behaves as a P-channel MOSFET working in the depletion mode. A deep modulation of the film conduction properties and non-linear contact resistance effects have been observed.     

Lipid-Induced Organization of a Primary Amphipathic Peptide: A Coupled AFM-Monolayer Study

To better understand the nature of the mechanism involved in the membrane uptake of a vector peptide, the interactions between dioleoylphosphatidylcholine and a primary amphipathic peptide containing a signal peptide associated with a nuclear localization sequence have been studied by isotherms analysis of mixed monolayers spread at the air-water interface. The peptide and the lipid interact through strong hydrophobic interactions with expansion of the mean molecular area that resulted from a lipid-induced modification of the organization of the peptide at the interface. In addition, a phase separation occurs for peptide molar fraction ranging from about 0.08 to 0.4 Atomic force microscopy observations made on transferred monolayers confirm the existence of phase separation and further reveal that mixed lipid-peptide particles are formed, the size and shape of which depend on the peptide molar fraction. At low peptide contents, round-shaped particles are observed and an increase of the peptide amount, simultaneously to the lipidic phase separation, induces morphological changes from bowls to filamentous particles. Fourier transform infrared spectra (FTIR) obtained on transferred monolayers indicate that the peptide adopts a β-like structure for high peptide molar fractions. Such an approach involving complementary methods allows us to conclude that the lipid and the peptide have a nonideal miscibility and form mixed particles which phase separate. Received: 31 July 1998/Revised: 4 November 1998     

Enhanced activity of horseradish peroxidase in Langmuir-Blodgett films of phospholipids

The immobilization of enzymes in nanostructured films has potential applications, e.g. in biosensing, for which the activity may not only be preserved, but also enhanced if optimized conditions are identified. Optimization is not straightforward because several requirements must be fulfilled, including a suitable matrix and film-forming technique. In this study, we show that horseradish peroxidase (HRP) has its activity enhanced when immobilized in Langmuir-Blodgett (LB) films, in conjunction with dipalmitoylphosphatidylglycerol (DPPG). Incorporation of HRP into a DPPG monolayer at the air-water interface was demonstrated with compression isotherms, and Polarization-Modulation Infrared Reflection Absorption Spectroscopy (PM-IRRAS). From the PM-IRRAS data, we inferred that HRP was not denatured when adsorbed on a pre-formed, low pressure DPPG monolayer. A change in orientation was induced by the phospholipid matrix, with the amide CO and NH groups from HRP being oriented perpendicular to the surface, parallel to the DPPG acyl chains, i.e. the α-helix was inserted into the monolayer. The mixed DPPG-HRP monolayer could be transferred onto solid supports, to which HRP activity was ca. 23% higher than in solution. The control of molecular architecture and choice of a suitable phospholipid matrix allowed HRP-containing LB films to be used in sensing peroxide.