Linear and circular dichroism studies of DNA-monoaminoacridine complexes

Abstract

The circular dichroism spectra of the DNA complexes with 1-, 2-, 3-, 4- and 9-aminoacridine and with four monoaminobenzacridines have been measured over a range of DNA-phosphate to dye ratios and, in the case of the 9-aminobenzo[a]acridine complex, over the pH range 3.3–10 and at high and low ionic strength. The linear dichroism spectra of streaming solutions of the DNA-dye complexes have been obtained with light propagated parallel and perpendicular to the flow-direction. The relations between the fraction of dye bound and the free dye concentration have been determined by spectrophotometric and by polarographic methods. The degree of binding at physiological pH is found to correlate with the relative antibacterial and mutagenic activities of the monoaminoacridines. The spectroscopic results support a modified intercalation model for the DNA-acridine complex in which the bound acridine molecule is sandwiched between two adjacent bases attached to a common sugar phosphate chain, and they indicate that a reduction of pH produces an unwinding of the two strands of the DNA helix additional to that due to the intercalation of bound dye.