H. Ringsdorf

COUPLING OF PROTON TRANSLOCATION THROUGH ATPASE INCORPORATED INTO SUPPORTED LIPID BILAYERS TO AN ELECTROCHEMICAL PROCESS

Abstract H+-ATPase is incorporated into solid-supported lipid bilayers separated from the gold support by a peptide spacer. The translocation of protons across the lipid film to the inner side is coupled to the discharge of protons at the gold surface. The overall process is investigated by square wave voltammetry (SWV) and double potential-pulse chronoamperometry (CA). As a result, the formation of a proton gradient is monitored by SWV whereas currents measured by CA monitor the stationary state when the enzyme activity is directly coupled to the charge transfer at the electrode. These currents markedly depend on the number of ATPases present in the bilayer.

Polymerization of hydrocarbon and fluorocarbon amphiphiles in Langmuir-Blodgett multilayers

Abstract Langmuir-Blodgett multilayers of polymerizable carboxylic acids with hydrocarbon or fluorocarbon chains were prepared. The multilayers were polymerized by UV light and the reactions were studied by UV/visible spectroscopy. The polyreactions strongly influence the multilayer structures which were investigated by X-ray small-angle scattering and scanning electron microscopy. The spreading behaviour of the monomers, the preparation of multilayers, their reactivities in multilayers and structural effects caused by the polyreactions are discussed with regard to the hydrophilic head groups, the polymerizable groups and the hydrophobic chains.

Orientation, recognition, and photoreaction of nucleolipids in model membranes

Amphiphiles with nucleobases and nucleosides as headgroups have been synthesized. Their surface behavior was investigated in monolayers at the air/water interface. The double chain nucleolipids form stable monolayers with nearly identical surface pressure-area diagrams, whereas the spreading behavior of the mono chain amphiphiles is dominated by the various nucleobase-headgroups. When measuring the interactions between nucleolipid monolayers and nucleobases (monomeric and polymeric ones), specific base-base effects could be observed: the complementary nucleobases solubilized in the subphase expand the monolayer more than the non-complementary ones. Photodimerization reactions of thymine-amphiphiles were investigated in mono- and multilayers as well as in spin-coated films.

Oriented ultrathin membranes from monomeric and polymeric amphiphiles: Monolayers, liposomes and multilayers☆

Abstract Oriented polymeric membranes were originally prepared by polymerization or polycondensation of preoriented monomers. The introduction of hydrophilic spacer groups into the polymeric amphiphiles allowed the formation of highly ordered systems (monolayers, liposomes and multilayers) from prepolymerized amphiphiles. Because of the partial decoupling of the different mobilities and orientational tendencies of the polymer chain and the amphiphilic side groups, these polymers are able to self-organize. In monolayer experiments the high degree of order of these membranes can be demonstrated by their surface pressure vs. area diagrams. Polymeric liposomes can be prepared by ultrasonication of prepolymerized lipids. In addition, the combination of the order and mobility of these polymeric amphiphiles with hydrophilic spacer groups allowed the formation of Langmuir-Blodgett multilayers with a high layer correlation. Thus disturbances in highly oriented layers, normally taking place during the polymerization reaction (e.g. contractions) of oriented monomeric layers, can be avoided.

Surface plasmon studies of specific recognition reactions at self-assembled monolayers on gold

Abstract Specific recognition reactions of proteins at functionalized interfaces were observed with plasmon surface polariton (PSP) spectroscopy. This optical method offers a vertical resolution of about 0.2 nm in aqueous media. Different types of receptor surfaces were prepared, either by self-assembly of biotinylated alkane thiols or by specific adsorption of streptavidin monolayers. The corresponding substrates were streptavidin and a biotinylated monoclonal antibody. Their binding properties are inversely related to the packing density of the receptors. A good accessibility is only given in the case of a “diluted” presentation of the receptors at the interface. Both binding site and diffusion limited adsorption have been observed.

Microstructure and lateral diffusion in monolayers of polymerizable amphiphiles

Lipid analogue amphiphilic molecules containing polymerizable units were investigated in monolayers at the air/water interface by using film balance measurements, fluorescence microscopy, and photobleaching techniques. The polymerizable groups (diene-, diyne-, and methacrylate units) were introduced into the hydrophobic alkyl chains or into the polar head of the amphiphilic molecules.In the case of the diene- and diyne-containing compounds the polymerizable units are incorporated into the hydrophobic alkyl chains, enabling them to form a two-dimensional network. Due to the free chain flexibility of the monomers the lateral mobility was comparable to that of saturated lipid analogues and decreases upon polymerization proportionally to the dose of UV irradiation. In addition, fluid/solid phase transitions of compounds with polymerizable groups in the hydrophobic part tend to vanish during the formation of the polymers. However, the direct observation of the growth of polymeric crystalline domains can be followed by using diacetylene lipid analogues.In the case of the methacrylate derivatives the polymerizable unit was coupled to the polar part via a flexible spacer. For these systems the characteristics of the monomeric phase transition are retained after polymerization. However, it shows a significant, strong decrease of the in-plane mobility already in the fluid-expanded phase of the polymer. The quantitative measurements of the lateral diffusion in the monolayers can be correlated with fluorescence microscopic images of their structure.

Covalently attached polymer mono- and multilayers on silanized glass substrates

Abstract Applying grazing incidence FTIR and ellipsometry, the reaction of poly [(1-methyl-vinyl isocyanate)-alt-(maleic anhydride)](IAP) with amino-silanized glass and silicon oxide surfaces has been investigated. A reactive surface containing isocyanate and anhydride groups was formed after the adsorption of the polymer. The layer could be further functionalized using 2-aminoethanol. Multilayers could be built up by adsorbing a second layer of IAP onto an already reacted first layer of IAP.

Light-induced modifications of Langmuir-Blodgett multilayer assemblies containing amphotropic azocopolymers

Abstract Photochromic multilayers of amphotropic copolymers with rod-like azobenzene moieties as side groups which exhibit thermotropic liquid crystalline behaviour in bulk were prepared by the Langmuir-Blodgett (LB) technique. They were characterized by UV-Vis spectroscopy as well as energy-dispersive small angle X-ray scattering. States of different structures have been realized on irradiation with UV or visible light or annealing within the temperature range of the mesophase. For untreated LB multilayers, a layer spacing d 0 (45 ± 1) A and an in-plane optical anisotropy in the direction of vertical dipping were detected. On annealing of the LB film a new layered structure with spacing d 1 = (52 ± 1) A , d 2 = (55 ± 2) A and d 3 ≈ (62 ± 1) A has been obtained, having no optical in-plane anisotropy. Some of these layer spacings corresponding to those of the liquid crystalline bulk phase. The irradiation of the film with non-polarized light of 365 nm gives rise to a loss of the layered structure as well as the optical anisotropy. A polarized illumination of the film at 63 °C destroys the d2 structure and favours d1. On leaving the film at this temperature in the dark the d2 arrangement appears again. Futhermore, an in-plane anisotropy has been induced or modified using linearly polarized light.

Polymerization of eicosenoic acid and octadecyl fumarate in Langmuir-Blodgett multilayers

Abstract Langmuir-Blodgett multilayers of 2-eicosenoic acid and octadecyl fumarate were irradiated by ultra-violet (u.v.) light. The reaction was monitored by u.v. spectroscopy, and the photoproducts were isolated and identified to be polymers. The multilayers of both amphiphiles undergo substantial structural changes during polymerization, as observed by u.v. spectroscopy, small-angle X-ray scattering and scanning electron microscopy. The kinetics of the changes were investigated. The long-term stability and the thermal behaviour of monomeric and polymeric multilayers were studied as well. Partially polymerized samples underwent phase separation on storage. The melting of the multilayer structure was found to be partially reversible. Models for the different processes observed and their correlation are discussed.

Polymeric amphiphiles with hydrophilic main chain spacers: studies in monolayers and Langmuir-Blodgett multilayers

A methacrylic lipid was polymerized to form an amphiphilic homopolymer and random copolymers with various levels of acrylic acid comonomers. The behavior of these polymeric lipids was investigated in monolayers at the air-water interface and in Langmuir-Blodgett multilayers on polymer foil supports. The acrylic acid acts as a hydrophilic spacer along the polymer backbone, and improves the ability of the polymer to self-organize into highly ordered monolayers and ultimately LB multilayers. It is shown that the quality and stability of the multilayers increase substantially with the increase in comonomer content.