Spectroscopic properties of complexes of acridine orange with glycosaminoglycans. II. Aggregated complexes—evidence for long‐range order

Aggregated complexes of acridine orange with dermatan and chondroitin sulfates have been studied in aqueous solution by absorption and circular dichroism spectroscopy. Aggregation was found to be favored at high‐dye and glycosaminoglycan concentrations, and in solutions where anionic sites of the glycosaminoglycan are effectively complexed with dye. The aggregates can be removed from solution by centrifugation at 27,000 × g for 1 hr or by filtration through a membrane containing pores of 0.1 μm diameter. The aggregated complexes exhibit large‐magnitude‐ellipticity circular dichroism bands. In addition, the circular dichroism spectrum observed for a solution containing aggregated acridine orange/chondroitin 4‐sulfate complexes is nearly a mirror image of that obtained for aggregated acridine orange/dermatan sulfate complexes. Cooperative alterations (sharp transitions) in the circular dichroism ellipticities of the aggregates occur at elevated temperatures, and result in spectroscopically distinct aggregates upon cooling. The circular dichroism properties and temperature effects are attributed to a supramolecular ordering of acridine orange/glycosaminoglycan complexes within the aggregates, which can be reorganized to a more stable form at high temperatures. Mixed aggregates, containing two different glycosaminoglycans, can be formed. The circular dichroism properties of the mixed aggregates also indicate the existence of long‐range order in the arrangement of the complexes. Mixed aggregates containing dermatan sulfate and either chondroitin 4‐sulfate or chondroitin 6‐sulfate resemble pure dermatan sulfate aggregates in circular dichroism characteristics.