Aggregation behavior of hydrophobically modified dextran in aqueous solution: a fluorescence probe study

摘要

Dextrans (M_W = 11.000 and M_W = 40.000) have been modified with 4-hexyl benzoyl chloride and their aggregation behavior was studied in aqueous solution employing the fluorescent probes pyrene and 1,8 anilinonaphtalene sulfonic acid sodium salt (1,8 ANS). The photophysical studies showed that above a critical concentration the derivatives tend to form aggregates having different properties, which depend on both the degree of substitution (alpha) and the molecualr weight of the sample. The paraemter alpha has a marked effect of the critical aggregation concentrations (CAC) and aggregate properties. hydrophobic microenvironments can be detected for substituted dextrands having alpha values varying from 0.01 to 0.19. CAC values decreased by two orders and magnitude when the molecualr weight increased from 11 to 40 kDa, leading to formation of more apolar aggregates and diminishing by about 30% the polarity of the microenvironments. Preaggregation was evidneced by pyrene excimer emission and intermolecular interactions were responsible by the formation of aggregates leading to solution behaviour similar to that of common surfactants.