The intercalation of 6-chloro-substituted-9-[[3-(dimethylamino)propyl]amino]acridines with DNA

A series of 6-chloro-2-substituted-9-[[3-(dimethylamino)propyl]amino]acridines has been prepared. The binding affinities and the unwinding angles for the acridine derivatives, relative to ethidium, were determined from viscometric titrations with ccs-DNA. The binding affinities were the same, within experimental error, ca. 2.0 X 10(-5). Similarly, with the exception of 11, the unwinding angles were close to 17 degrees. For 11 the unwinding angle (12 degrees) was smaller than the other derivatives. The general insensitivity of the apparent binding constants to substituent effects is attributable to a masking effect of the formal charge on the ring. The smaller unwinding angle for 11 is believed to arise from its relative dissymmetry, resulting in a "wedge" effect upon intercalation.