Nanodomain formation in lipid membranes probed by time-resolved fluorescence

Thermo-driven self-assembly of a PEG-containing amphiphile in a bilayer membrane

Self-assembly of lipid molecules in a plasma membrane, namely lipid raft formation, is involved in various dynamic functions of cells. Inspired by the raft formation observed in the cells, here we studied thermally induced self-assembly of a synthetic amphiphile, bola-AkDPA, in a bilayer membrane. The synthetic amphiphile consists of a hydrophobic unit including fluorescent aromatic and aliphatic components and hydrophilic tetraethylene glycol chains attached at both ends of the hydrophobic unit. In a polar solvent, bola-AkDPA formed aggregates to show excimer emission. In a lipid bilayer membrane, bola-AkDPA showed intensified excimer emission upon increase of its concentration or elevation of the temperature; bola-type amphiphiles containing oligoethylene glycol chains likely tend to form self-assemblies in a bilayer membrane triggered by thermal stimuli.

A synthetic multi-block amphiphile containing oligoethylene glycol chains formed a self-assembly in a bilayer membrane triggered by thermal stimuli.

New insights in the study of pyrene excimer fluorescence to characterize macromolecules and their supramolecular assemblies in solution

This report highlights some of the recent developments that have been made in the quantitative analysis of fluorescence decays acquired with pyrene-labeled macromolecules. With these new analytical tools, macromolecules of different composition and architecture can now be labeled in a variety of ways with the pyrene chromophore, and the kinetics of pyrene excimer formation can be described to retrieve quantitative information about the internal dynamics of the macromolecules studied. In particular, this review presents the procedure that was followed to develop these new analytical tools and how the process of pyrene excimer formation with vinyl polymers, poly(L-glutamic acid), dendrimers, associative polymers, surfactants, and lipids labeled with pyrene has been successfully characterized thanks to these analysis programs.

Characterization of the behavior of a pyrene substituted gemini surfactant in water by fluorescence

Time-resolved fluorescence was applied to characterize the behavior in solution of a gemini surfactant substituted with pyrene (Py-3-12). Upon association in water, excimer formation by Py-3-12 can be probed by acquiring pyrene monomer and excimer fluorescence decays which can be fitted globally according to the model free (MF) analysis to yield quantitative information about the internal dynamics of the Py-3-12 surfactant micelles as well as a complete description of the distribution of the different pyrene species in solution either incorporated inside the micelles or free in solution. A proof of procedure for the MF analysis was established by noting that the concentrations of free surfactant in solution, [Py-3-12](free), was found to equal the critical micelle concentration (CMC) for surfactant concentrations larger than the CMC. (I(E)/I(M))(SPC), the ratio of pyrene monomer to excimer fluorescence intensities, was calculated from parameters retrieved from the MF analysis of the fluorescence decays and was found to be independent of sample geometry. This work demonstrates how time-resolved fluorescence can be used to study the properties of pyrene-labeled macromolecules under conditions where large absorptions and inner filter effects usually distort the steady-state fluorescence signals. It was found that the pyrene excimer is formed mostly by diffusion within the Py-3-12 micelles, which suggests that the pyrene microenvironment is fluid, an important feature for future studies on the interactions of Py-3-12 with DNA.

Fluorescence studies of a series of monodisperse telechelic α,ω-dipyrenyl poly(N-isopropylacrylamide)s in ethanol and in water

Steady-state and time-resolved fluorescence measurements were performed on solutions in ethanol and in water (23 °C) of a series of poly(N-isopropylacrylamide)s labeled with a pyrenyl group at each chain end (Py2-PNIPAM) and ranging in molecular weight (Mn) from 5 900 to 44 500 g·mol−1. Water and ethanol are of similar solvent quality towards the PNIPAM chain. The pyrene labels, in contrast, are soluble in ethanol but not in water. The efficiency of excimer formation for Py2-PNIPAM samples in ethanol decreased with increasing chain length, a trend typical of pyrene end-labeled polymers in good solvents. The ratio IE/IM, where IE is the Py excimer emission intensity and IM is the Py monomer emission intensity, scaled as Mn−1.4, where Mn is the number-average molecular weight of the sample. The kinetics of excimer formation were more complex for aqueous Py2-PNIPAM solutions, as a consequence of pyrene–pyrene association prior to excitation. The excimer time-dependent profiles exhibited significantly faster rise times, compared with the situation in ethanol, and they could not be fitted with the traditional Birks scheme. The results are discussed in the context of the solution properties of telechelic amphiphilic PNIPAMs and are compared with data gathered previously in studies of dipyrenyl end-labeled poly(ethylene oxides), the only other polymers soluble in water and organic solvents subjected to similar studies in the past.