Interaction of poly- ,L-glutamic acid with acridine orange

Interaction of poly-α,L -glutamic acid (PGLA) with acridine orange (AO) was studied with circular dichroism and absorption spectra measurements. The following results were observed: (1) the addition of a comparable amount of AO with the glutamyl residue to the PLGA solution at pH of 4.5 reduced the fraction of helix of the polymer; (2) when AO was added to the PGLA solution, the pH range of the helix-coil transition of the polymer shifted toward higher pH regions; and (3) when the mixture of the same amount of AO and the glutamyl residue was brought to the neutral and alkaline pH region, some induced circular dichroism bands were observed. In this case, it was assumed that PLGA in the system takes a helical form due to the neutralization of the anionized side chains by the cationic species of AO. We concluded that AO molecules bound to the carboxylate groups of the side chains of PLGA arrange to from a righthanded super-helix which surrounds the core of the righthanded α-helix of PLGA.