The binding of amsacrine [4'-(9-acridinylamino)methanesulfon-<i>m</i>-anisidide] to calf thymus DNA was studied by UV-visible and resonance Raman spectroscopy. A shift of the UV-visible absorption band of amsacrine at 434 to 442 nm together with a decrease in the intensity of this band is observed upon amsacrine-DNA binding. The resonance Raman spectrum of DNA-bound amsacrine shows a general slight decrease in intensity relative to the spectrum of the free species. The significant decrease in intensity of the bands at 1165, 1265, and 1380 cm<sup>-1</sup> upon binding to DNA is attributed to the formation of a single amsacrine-DNA species. The assignment of these bands (1165, 1265, and 1380 cm<sup>-1</sup>), which was based upon a previous normal coordinate analysis (NCA) and molecular neglect of diatomic overlap (MNDO) calculation, and the observed lack of shift in the band positions upon binding are consistent with intercalation being the major binding mode of amsacrine, as inferred previously by other techniques.

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