D. Moebius

Photosensitive supramolecular systems based on amphiphilic crown ethers

Abstract An amphiphilic crown-ether styryl dye was synthesized and its properties at the interfaces were investigated. This dye, which in monolayers interacts with some cations and shows reversible changes of the light reflection after photoactivation near the absorption maximum, is an excellent component of functional organized systems.

Optical Characterization of Asphaltenes at the Air−Water Interface

Asphaltenes extracted from Arabian light crude oil have been investigated at the air-water interface of a Langmuir trough by in situ optical techniques. Brewster angle microscopy (BAM) and reflection spectroscopy have been used to extract new information about the microscopic organization of the asphaltene films in terms of association phenomena and chromophore orientation, respectively. The use of different spreading concentrations in the range 0.1-15 mg mL-1 reveals significant changes in the behavior at the interface with more condensed isotherms above 2 mg mL-1. This break point is related to the nanoaggregate-to-cluster association threshold in organic solution widely accepted in the recent asphaltene literature. BAM images support this observation with very different morphologies for the two spreading concentrations employed, 0.1 and 4 mg mL-1, respectively. The study of intensity changes in the corresponding normalized reflection spectra also confirms the transition in the asphaltene interfacial behavior between these two spreading concentrations. Finally, this technique helps with understanding the changes observed in the asphaltene films during a set of compression-decompression cycles.

Enhanced binding of porphyrin by a laterally organized monolayer

Abstract The effect of lateral organization of a mixed monolayer of dioctadecyl-dimethyl-ammonium bromide (DOMA) and methyl stearate (SME) at the air-water interface by interaction with a water-soluble porphyrin (PO) on binding of PO has been investigated with the aim of achieving molecular recognition. The organized monolayers were formed by co-spreading of the lipids DOMA and SME with PO. This technique should be more efficient in generating a laterally organized monolayer than reorganization of the lipid monolayer by molecules adsorbed from the aqueous subphase. By measuring surface pressure-area and surface potential-area isotherms as well as reflection spectra, an optimal molar ratio of PO:DOMA:SME was determined. The monolayers were transferred to hydrophobic glass plates by vertical dipping, and the PO was removed from the immersed plate by changing the pH. Readsorption of PO from dilute aqueous solution showed stronger binding by the organized monolayer as compared with a lipid monolayer of the same average composition.

Ionic selectivity of valinomycin in the dipalmitoylphosphatidylcholine monolayers

Abstract The surface pressure-molecular area and surface potential-molecular area isotherms for mixed monolayers of valinomycin and dipalmitoylphosphatidylcholine (DPPC) at various aqueous salt subphases were measured. Two additional states of valinomycin-DPPC monolayers were observed in the presence of K+ as compared with Na+ in the aqueous subphase. The strongest interactions between valinomycin and the zwitterionic phospholipid DPPC in monolayers occur during the complexation of valinomycin with K+ from aqueous subphase.