Fluorescence Studies of Pyrene Capture by Naphthalene-Labeled Diblock Copolymer Micelles in Aqueous Media

Abstract

Fluorescence techniques are used to characterize the diffusion of pyrene into several naphthalene-labeled diblock copolymer micelles as a function of pH. The capture of pyrene by the micelles is composed of a fast and a slow process, as shown by intensity and spectral changes in pyrene fluorescence observed when a solution containing pyrene is mixed with a solution containing labeled micelles. The most important pH effect was at low pH: The corona is collapsed. Sensitized pyrene fluorescence results are in accord with a model in which solubilization occurs within the micellar core. Equilibration time of the sensitized fluorescence suggests a pyrene diffusion constant on the order of 10 -16 cm 2 /s. Several anomalous photophysical features suggest that the micelle core may have a complex structure.POLYMERIC MICELLES have recently received considerable attention because of their potential usefulness in many areas as a matrix for controlled release and uptake of small molecules in aqueous and organic environments (1,2,4,5; for a review,

Fluorescence and Aggregation Behavior of Poly(amidoamine) Dendrimers Peripherally Modified with Aromatic Chromophores: the Effect of Dendritic Architectures

“…FRET is known to depend on the following three factors: 32 (1) the extent of spectral overlap of acceptor absorption and donor emission, (2) the quantum yields of the donor, and (3) the distance between the donor and acceptor. FRET is a long-range and through-space interaction, which is independent of the intervening medium between donor and acceptor, such as solvents, chemical bonds, and polymer backbones. − The distance dependence of FRET has been employed as a “spectroscopic ruler” for a variety of applications, such as distance measurement between donor and acceptor, 51a,b protein folding, 51c,d conformational changes, 51e,f macromolecular associations,51g membrane fusion, and lipid exchange 51h. The photophysical phenomenon of FRET between donor and acceptor covalently attached to a polymer has been termed “photo harvesting” by Webber 52 and the “antenna effect” by Guillet .…”

“…The photophysical phenomenon of FRET between donor and acceptor covalently attached to a polymer has been termed “photo harvesting” by Webber 52 and the “antenna effect” by Guillet . The naphthalene/pyrene energy transfer pair has been employed to study the compatibility, thermo-reversible phase transition, and steric hindrance of polymers by Morawetz,54a Winnik,54b and Webber 52b. In our previous work, we attempted to employ FRET to measure the bilayer thickness of vesicles made from amphiphilic copolymers.…”