ON COMPLEX FORMATION OF ACRIDINE DYES WITH DNA .7. DEPENDENCE OF BINDING ON DYE STRUCTURE

The binding constants for the complex formation of more than twenty ring nitrogen‐and amino‐substituted acridine derivatives with calf thymas DNA were measured by a fluorescence method. DNA quenches the fluorescence of the aminoacridine dyes so long as both amino hydrogens are not substituted. These dyes show an enhancement of their fluorescence intensity in the presence of DNA. Typical representatives of both are proflavine and acridine orange derivatives, respectively. A discussion of steric and electronic influences of various substituents attached to the ring nitrogen and amino groups on the binding led to the concept of different conformations for intercalated acridines without amino groups and the aminoacridines. The electrostatic binding site of the former seems to be the positively charged ring nitrogen, while the binding sites in the aminoacridines are so located that the amino groups are directed towards the negatively charged DNA phosphates. Copyright © 1969 John Wiley & Sons, Inc.