Kerr constant dispersion. III. The interaction of acridine orange with DNA

The Kerr constant of the complex formed between acridine orange and DNA has been measured throughout the region of dye absorption in the visible spectrum (5500 to 4200 A) at ratios of the number of nucleotide units per dye molecule ranging from 2:1 to 36:1. Complete experimental results are given for ratios of 2:1 and 18:1. A single negative dispersion centered near the dye absorption maximum (5000 A) is found for the latter case; at low ratios two dispersions are found, a negative one at 5000 A and a positive one at 4600 A, indicating a high degree of dye-dye interaction. The intercalated structure is compatible with the results at high ratios; binding to a surface site (phosphate) is necessary to account for the dye-dye interactions present at low ratios.