| Abstract: | Circular dichroism and absorption spectra are measured on mixed solutions of acridine orange and poly(S-carboxymethyl-L -cysteine) at different pH and P/D mixing ratios. The observed circular dichroism spectra are classified into several types, mainly based on the number and sign of circular dichroic bands in the visible region. Three of them are associated with the absorption spectra characteristic of dimeric dye or higher aggregates of dye. Type I is observed with solutions, of which the pH is acid and P/D is higher than 4, and it has an unsymmetrical pair of positive and negative dichroic bands at 470 and 430 nm. This type is induced on the dye bound to the polymer in the β-conformation. Types II and III are considered to be characteristic of randomly coiled polymers. Type II is exhibited by solutions of P/D higher than 1 at pH 5–7 and has two dichroic bands around the same wavelengths as Type I but with opposite signs and an additional positive band at 560 nm. Type III, shown by solutions of P/D 2–0.6 at pH 6–10.5, has three dichroic bands around the same wavelengths as Type II but with signs opposite to it. The other two types of circular dichroism, induced for the solutions of P/D less than 1 at slightly acid pH, are associated with the absorption spectra of monomeric dye and are observed with disordered or randomly coiled polymer. They have a pair of dichroic bands at 540 and 425 nm, and the signs of these bands are opposite to each other in these two types. |
