Photophysical investigations of the interactions of phospholipids and a pyrene-substituted poly(acrylic acid) in dilute solutions

Abstract

Fluorescence spectra of a pyrene-substituted poly(acry1ic acid) (1) were measured in the presence of dipalmitoylphosphatidylglycerol (DPPG) at pH values of 4 and 7 to investigate the interactions between 1 and phospholipids. These photophysical investigations showed that at pH 4 mixed micelles of 1 and phospholipids were formed with the incorporation of 1 in the hydrophobic core of the mixed micelle. The measurements of fluorescence decay and quenching of fluorescence by nitromethane in solutions of 1 and DPPG also supported this model for the interactions of 1 and phospholipids. These results were in agreement with a calorimetric investigation of the interactions between phospholipids and poly(acry1ic acid) derivatives (Tirrell, D. A.; Takigawa, D. Y.; Seki, K. Ann. N.Y. Acad. Sci. 1985, 446, 237). The effects of head group and temperature on the interactions of 1 and phospholipids were also investigated. Investigations of the interactions of phospholipids and synthetic polymers could be expected to play important roles in the pursuit of scientific knowledge of the structures and functions of biological macromolecules and mem- branes. These investigations are also of importance for the synthesis of novel functional polymers for reactions in organized media and to mimic the functions of biological molecules. Tirrell and co-workers1,2 have investigated the interactions of a variety of synthetic polymers and phos- pholipids in aqueous solutions. Photophysical techniques have been extensively used in the investigations of the structure and functions of synthetic and biological mac- romolecule~.~ Photophysical properties of the pyrene chromophore covalently bound to poly(acry1ic acid) (PAA) have been used by Turro and Arora4 to investigate the inter- and intrapolymer interactions in dilute aqueous solutions of PAA and complementary polymers. Intra- chain interactions of pyrene groups in pyrene-substituted PAA (1) investigated by measurements of fluorescence spectra, fluorescence lifetimes, and quenching of fluores- cence were found to be useful probes for inter- and in-