STRUCTURAL DETERMINATION AND INTERIOR POLARITY OF SELF-AGGREGATES PREPARED FROM DEOXYCHOLIC ACID-MODIFIED CHITOSAN IN WATER

Hydrophobically modified chitosan derivatives containing 0.6-5.1 deoxy cholic acid groups per 100 anhydroglucose units of chitosan were synth esized by an EDC-mediated coupling reaction. Self-aggregates of the ch itosan derivatives in aqueous media were formed by sonication with a P robe-type sonifier. The mean diameter of self-aggregates determined by dynamic light scattering decreased slightly with an increasing degree of substitution (DS) by hydrophobic groups. Photophysical and photoch emical characteristics of self-aggregates were examined by fluorescenc e probe techniques. Measurement of the binding equilibrium constant (K -v), for pyrene and lifetime (tau) for 1,6-diphenyl-1,3,5-hexatriene ( BPH) showed that the interior of self-aggregates became nonpolar as th e DS was increased, Microviscosity of the interior of self-aggregates determined by measuring an anisotropy value for DPH was not significan tly affected by the DS of hydrophobic groups. The aggregation number o f deoxycholic acid groups per one hydrophobic microdomain !(n(DCA)) wa s estimated by the steady-state fluorescence quenching method with 1-d odecylpyridinium chloride and was almost independent-of the DS. From t he re suits of the fluorescence quenching experiment, it was conjectur ed that there may be multiple (rather than one) hydrophobic microdomai ns in a self-aggregate.