Fluorescence study of some structural and compositional effects on the aggregation of hydrophobized hyaluronan

The aggregation behavior of four samples of hydrophobically modified hyaluronan was examined in water and in 0.15 M NaCl. The samples differed in the length of their hydrocarbon modifying chains, degree of substitution, or hyaluronan molecular weight. The critical aggregation concentration was determined by fluorescence spec-troscopy using pyrene as a probe. Aggregation was observed even with hyaluronan modified by a short alkyl chain (C6). The critical aggregation concentration decreased with increasing alkyl chain length and with increasing hyaluronan molecular weight at a comparable degree of substitution. Aggregation was detected over a rather broad concentration interval, indicating a progressive formation of aggregates. Two populations of ag-gregates were detected for the oleyl substitution. The addition of NaCl had only minor effect on the critical aggregation concentration.