Using the atomic force microscope (AFM), surface-forces measurements are made in water between chemically modified AFM probes and model membranes created by Langmuir-Blodgett (LB) deposition. A series of four different lipid monolayers with varying headgroups and monolayer properties were transferred onto monolayers on mica for analysis. Using a hydrophilic probe, the bilayers are elastically deformed at low load and punctured at a repeatable, material-dependent breakthrough force. Using hydrophobic probes, the bilayers are punctured on contact, at loads near zero, in all cases. This effect is also manifest when imaging mixed LB monolayers, which show a large topography contrast at-low load when using hydrophilic tips but none when using hydrophobic tips. These results provide evidence that the forces required to deform lipid bilayers are dramatically changed in the vicinity of nonpolar surfaces, which is central to the understanding of membrane fusion processes and the function of membrane-associated proteins.

Mixed distearoylphosphatidylethanol amine (DSPE) and dioleoylphosphatidylethanolamine (DOPE) monolayers and bilayers have been deposited on mica using the Langmuir-Blodgett (LB) technique, as a model system for biomembranes. Investigation with atomic force microscopy revealed phase-separation for both monolayers in air and bilayers in water in the form of microscopic DSPE domains embedded in a DOPE matrix. For the monolayers in air, the step height measured between the higher DSPE phase and the lower DOPE phase was larger than expected from the molecular lengths, and a significant contrast in adhesion and friction was observed despite identical lipid end groups. This unexpected behavior resulted primarily from a difference in the film mechanical properties, the DOPE phase being inelastically deformed by the probe. For the bilayers in water, similar trends were found in terms of height, adhesion, and friction, but an additional short-range repulsive hydration/steric force over the DSPE phase contributed to the observed differences.

Tetrakis(cumylphenoxy) phthalocyanine, H 2 Pc(Cp) 4 , and the family of related compounds containing transition metal ions in the center of the macrocyclic ring, MPc(Cp) 4 , will spread from organic solvents to give pressure vs. area isotherms typical of monolayers, but classical monomolecular films are not formed. Mixed films containing a classical component as a transfer promoter, such as stearamide, produce Langmuir-Blodgett (LB) multilayers of better quality than the MPc(Cp) 4 compounds alone. As a structural model, a simple mixed film containing stacked, ordered MPc(Cp) 4 molecules was originally postulated, but more recent observations by transmission electron microscopy and by IR reflectance-absorbance spectroscopy have revealed a more complex and less well-ordered morphology than previously suspected. In mixed films transferred by the LB technique, a two-dimensional colloidal dispersion of MPc(Cp) 4 aggregates is formed. Disk-like aggregates more than one monomolecular layer thick are observed in single-component films and are also seen dispersed in the second component of mixed films. Differential scanning calorimetry also suggests a significant degree of phase separation in the two-component LB films. Small melting point depressions relative to the melting points of single-component monolayers indicate that the melting points of two-component films containing MPc(Cp) 4 are determined by the transfer promoters.

Abstract : This invention relates general to phthalocyanine compounds, and more particularly to the preparation of aryloxy, arylthio, alkyloxy, and alkylthio phthalocyanine compounds and their subsequent incorporation into semiconducting thin films by the Langmuir-Blodgett technique. One object of the current invention is to modify phthalocyanine so that it can be used in film deposition techniques that operate with compounds soluble in organic solvents, one of which is the Langmuir-Blodgett film transfer technique. Another object of the invention is to produce orderly films from the chemically modified phthalocyanine that have electrical and other properties similar to, and better than, those of conventional phythalocyanines. Another object is to produce phthalocyanines suitable for Langmuir-Blodgett film transfer without the need for difficult carbon atom substitution on the phthalocyanilne ring. These and other objects are achieved by attaching aryloxy or arylthio or alkyloxy or alkylthio substitution at up to four points about the periphery of a phthalocyanine ring. The resulting compounds dissolve in organic solvents and are suitable for the making of Langmuir-Blodgett films.

: This paper describes studies in which metal-free and metal substituted phthalocyanine films were sublimed onto the surfaces of interdigital electrodes in order to measure the change in the conductivity when the coated electrodes were exposed to a series of test gases. Also reported are data on tetracumylphenoxy and tetraoctadecyl ether derivatives of the metal-free and metal substituted phthalocyanines which were synthesized specifically for use as coating materials to be applied one monolayer at a time by the Langmuir-Blodgett (LB) method. (Author)