DETECTION OF INTRAMOLECULAR ASSOCIATIONS IN HYDROPHOBICALLY-MODIFIED PECTIN DERIVATIVES USING FLUORESCENT-PROBES

Hydrophobically modified pectin derivatives were prepared by immobiliz ation of long alkyl chains (C-12-C-18) at various substitution ratios, using two different synthetic pathways, one affording covalent fixati on and the other one leading to a mere ionic association. These deriva tives display an associative tendency in semidilute as well as in dilu te aqueous solutions. This phenomenon, which stems from both intra- an d intermolecular interactions between hydrophobic groups, results in t he formation of hydrophobic microdomains. The latter can be characteri zed, especially in the dilute regime, thanks to fluorescence spectrosc opy. Fluorescent molecular rotors, as well as pyrene, a classical fluo rescence probe of widespread use, witness the variations of the medium polarity. In addition, they can also provide further information, par ticularly about the local cohesion of the microenvironment of the prob e, without performing any complementary experiment, for example, the a ddition of quenchers together with the fluorescent probe in the polyme r solutions. CAC values derived from polarity changes (CAC(polarity)), using the molecular rotor as well as pyrene as the fluorescence probe s, are significantly different from those determined from the cohesion of the microenvironment (CAC(cohesion)), accessible only with the mol ecular rotor. This latter type of fluorophore may therefore enable us to determine more accurately the actual critical aggregation concentra tion.