Competition for space between a protein and lipid monolayers.

Competitive adsorption is a general problem both in polymer and in biological systems. The equilibrium composition at a surface in contact either with polymer solutions or biological fluids depends on the competition between all the surface active material present in the medium. Such competition is particularly important in cell membranes where membrane proteins generated on ribosomes have to incorporate in the cell.

A new, simple approach to confer permanent antimicrobial properties to hydroxylated surfaces by surface functionalization.

A new, simple method to obtain ultrathin polycationic monolayers on hydroxylated surfaces is described which uses a bifunctional copolymer comprising a reactive part (trimethoxysilane) and positive charges (quaternary ammonium salts) to confer antimicrobial properties.

Electron transport through rectifying self-assembled monolayer diodes on silicon: Fermi-level pinning at the molecule-metal interface.

We report the synthesis and characterization of molecular rectifying diodes on silicon using sequential grafting of self-assembled monolayers of alkyl chains bearing a pi group at their outer end (Si/sigma-pi/metal junctions). We investigate the structure-performance relationships of these molecular devices, and we examine the extent to which the nature of the pi end group (change in the energy position of their molecular orbitals) drives the properties of these molecular diodes. Self-assembled monolayers of alkyl chains (different chain lengths from 6 to 15 methylene groups) functionalized by phenyl, anthracene, pyrene, ethylene dioxythiophene, ethylene dioxyphenyl, thiophene, terthiophene, and quaterthiophene were synthesized and characterized by contact angle measurements, ellipsometry, Fourier transform infrared spectroscopy, and atomic force microscopy.

Formation of a DNA layer on Langmuir-Blodgett films and its enzymatic digestion.

Here, we report a system we have developed where long double-stranded DNAs (dsDNAs) are immobilized on a monolayer of Zn-arachidate. We have applied the Langmuir-Blodgett technique to form the monolayer of Zn-arachidate where Zn(II) is bound to arachidic acid through charge neutralization. Because tetrahedral Zn(II) participates in DNA recognition through coordination, we have been able to layer DNA over the Zn-arachidate monolayer.

Evidence of a charge-density threshold for optimum efficiency of biocidal cationic surfaces.

The deposition of organic monolayers containing quaternary ammonium groups has been shown by many authors to confer biocidal properties on a large variety of solid surfaces. In a search for the controlling factors, the authors have grafted quaternized poly(vinylpyridine) chains on glass surfaces by two different methods and varied the charge density within the organic layer between 10(12) and 10(16) positive charges per cm2. The measurements show that this parameter has a large influence on the killing efficiency.

Transcription of T7 DNA immobilised on latex beads and Langmuir-Blodgett film.

The recognition of DNA is the first and most important condition for biological applications, including transcription and translation regulators and DNA sensors. For this purpose, we have developed few systems where we were able to immobilize long double-stranded DNA (dsDNA) successfully to the surfaces of different solid substrates. To achieve this, we have chosen polystyrene beads and standard Langmuir-Blodgett monolayer of Zn-arachidate.

Influence of multivalent counterions adsorption on Langmuir films.

It has been shown recently by neutron and X-ray reflectivity that nanometer-sized multivalent counterions (Keggin salts) can assemble as a dense monomolecular sublayer beneath a charged Langmuir monolayer of opposite sign. We have conducted experiments that examine the surface pressure isotherms of docosamine surfactant monolayers under such conditions and have shown that they undergo dramatic modifications when the Keggin salts are added. We model these experimental results by a close-packed sublayer of counterions on which charged surfactants can organize and form complexes.

Plasma surface modification of organic materials: comparison between polyethylene films and octadecyltrichlorosilane self-assembled monolayers.

Low-pressure low-frequency NH3 plasmas have been used for the surface modification of bulk polyethylene films and of octadecyltrichlorosilane (OTS) self-assembled monolayers deposited on oxidized silicon wafers. The incorporation of nitrogen-containing groups by the plasma treatment has been followed by contact angle measurements and by X-ray photoelectron spectroscopy. The surface degradation of the OTS monolayers due to plasma etching has been measured separately by optical ellipsometry with subnanometric accuracy.

Towards "designer" surfaces: functionalisation of self-assembled monolayer (SAM) on colloidal gold by alkene metathesis.

A variety of groups like a Fischer carbene complex, an N-hydroxysuccinimide or a ferrocene derivative have been grafted by ruthenium-catalyzed cross-metathesis reaction with terminal alkene groups on monolayer-protected gold clusters as a mild and convenient strategy to anchor functional molecules.

Shear viscosity of langmuir monolayers in the low-density limit.

We have measured the shear viscosity in the liquid phase of several Langmuir monolayers with an accuracy better than 30%. The method is based on the optical monitoring of the Brownian diffusion of submicron latex spheres floating at the air-water interface. The values are between 1 and 11x10(-10) N s m(-1), which is 10 to 100 times lower than previous data on similar systems.

Structures in colloidal physical chemistry.

The vast range of technological and industrial application of colloidal systems is largely a direct result of their diversity of structure on microscopic and mesoscopic scales. Recent progress in understanding these structures allows for greater control of the macroscopic properties, as well as providing new avenues of fundamental research in physics, chemistry and materials science.

Quantitative studies of evanescent wave intensity profiles using optical fluorescence.

The fluorescence of uniformly distributed chromophores in an organic solution has been used to probe the energy density profile of an optical evanescent wave, generated by total internal reflection at the solid-solution interface. The results obtained in the case of an aqueous fluorescein solution in contact with a highly polished silica surface are in good quantitative agreement with the expected exponential decay of the optical energy at the interface. It also justifies the use of the newly developed evanescent wave-induced fluorescence technique to study adsorption and depletion layers of polymer in solution close to solids walls.

Light-scattering studies of the monomer-dimer states of gramicidin A.

Measurements of the intensity and autocorrelation function of ligh quasielastically scattered by gramicidin A indicate that the molecules exist as dimers in methanol and dioxane and monomers in dimethyl sulfoxide when solute concentrations range from 18 to 50 mg/ml. This gives further evidence that gramicidin A can dimerize in low-polarity media such as the hydrocarbon part of the membrane bilayers.