Temperature-induced chirality reversal of induced circular dichroism of premicellar aggregates of acridine orange derivatives and dodecanoyl-L-threonine in aqueous solution

Circular dichroism (CD) and absorption spectra were measured for acridine orange derivatives: 3,6-bis(dimethylamino) acridine (AO), 3,6-bis(dimethylamino)-10-methylacridinium bromide (C(1)AO), and 3,6-bis(dimethylamino)-10-dodecylacridinium bromide (C(12)AO) in aqueous dodecanoyl-L-threonine (C(12)Thr) solutions at 30, 40, 50, and 60 degrees C and pH 8-9. CD spectra were not induced for AO and C(1)AO in C(12)Thr aqueous solutions. Induced circular dichroism (ICD) based on the exciton interaction was found for premicellar aggregates of C(12)AO with C(12)Thr, but the micellar aggregates failed to induce CD for solubilized C(12)AO at a higher concentration than C(12)Thr critical micelle concentration. The maximum ICD intensity was observed for 1:1.2 aggregates of C(12)AO and C(12)Thr. The ICD spectrum indicated positive chirality at 30 degrees C, but negative chirality at 50 degrees C. The chirality transition occurred at 40 similar to 45 degrees C. The slow change in both the absorption and ICD spectra is ascribed partly to the rearrangement of dye alignment and partly to the growth of the aggregate; the system reaches final phase separation after a few days.