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Surface-enhanced Raman study of the intaractions between the intercalator ADAP and DNA

Intercalators are fused-ring aromatic molecules with positive charges on an attached side chain and/or the ring system itself. Intercalation of a planar system between DNA base pairs can induce structural alternations in such way that cell proliferation is blocked. Therefore, intercalators are used as antitumor drugs. 4-Methyl-2, 7-diamino-5, 10-diphenyl-4, 9-diazapyrenium hydrogensulfate (ADAP) is a molecule that belongs to the 4, 9-diazapyrenium compounds. It is developed as a potential antitumor drug with higher stability constants of polynucleotide complexes in comparison to other related compounds from the same structural group.Since ADAP molecules are dark blue colored and fluoresce very intensively, Raman spectra could not be observed. Surface-enhanced Raman scattering (SERS) was therefore used to obtain and analyze vibrational spectra of the compound. SERS spectra of colloidal solutions containing ADAP and DNA in a ratio from 10/1 to 1/10 revealed decrease in the Raman scattering from the ADAP molecules attached on the silver nanoparticles. Intensity of the characteristic ADAP SERS bands diminishes with increasing the DNA concentration down to the ADAP/DNA ratio of 1/5, when no more bands were obtained in the spectra. A loss of the surface enhanced Raman signal implies placement of the ADAP molecules away from the enhancing surface, supporting the theory of intercalation of ADAP molecules between the DNA base pairs.

surface-enhanced Raman scattering; intercalator; DNA

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