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

Abstract

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 (C1AO), and 3,6-bis(dimethylamino)-10-dodecylacridinium bromide (C12AO) in aqueous dodecanoyl-l-threonine (C12Thr) solutions at 30, 40, 50, and 60 °C and pH 8–9. CD spectra were not induced for AO and C1AO in C12Thr aqueous solutions. Induced circular dichroism (ICD) based on the exciton interaction was found for premicellar aggregates of C12AO with C12Thr, but the micellar aggregates failed to induce CD for solubilized C12AO at a higher concentration than C12Thr critical micelle concentration. The maximum ICD intensity was observed for 1:1.2 aggregates of C12AO and C12Thr. The ICD spectrum indicated positive chirality at 30 °C, but negative chirality at 50 °C. The chirality transition occurred at 40∼45 °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.