Spectroscopic studies on the interaction of three partially hydrogenated acridine dyes with calf thymus DNA and their...

The interaction of three partially hydrogenated acridine dyes (acridine I, acridine II and acridine III) with calf thymus DNA was studied using spectrophotometric and spectrofluorometric methods. This paper presents the evidence for the formation of complexes between acridine I, II and III with calf thymus DNA. From the results of this studies various binding parameters were evaluated. The binding constant for acridine I and acridine III ranged from 2.1 to 4.4 x 10(5) M-1 for the P/D ratio from 4.29 to 0.56 while for acridine II this constant increased from 0.78 to 2.26 x 10(5) M-1 for the P/D ratio 12 to 2.38 and decreased to 1.47 at P/D ratio 1.34. The Scatchard analysis indicated a cooperative binding of acridine II to calf thymus DNA as compared to acridine I and III. A red shift in the visible absorption bands for dye DNA complexes (for acridine I = 8, acridine II = 7, and acridine III = 9 nm) suggested an electronically coupled interaction mode for the dyes. It is concluded that acridine II interacted stronger with calf thymus DNA than acridine I or III. The results are interpreted in terms of their crystal structures and also with the already reported DNA binder structures.