Intercalator-DNA interactions revealed by NIR surface-enhanced Raman spectroscopy |
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Authors: | Sne?ana Miljani?,Adriana Dijano&scaron i?Igor Mato&scaron evi?,Ivo Piantanida |
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Affiliation: | a Laboratory of Analytical Chemistry, Department of Chemistry, Faculty of Science, University of Zagreb, Horvatovac 102a, HR-10000 Zagreb, Croatia b Laboratory for Study of Interactions of Biomacromolecules, Division of Chemistry and Biochemistry, Ru?er Boškovi? Institute, P.O.B. 1016, HR-10000 Zagreb, Croatia |
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Abstract: | Using 1064 nm excited surface-enhanced Raman spectroscopy (SERS) a well known intercalator, ethidium bromide (EB), and a structurally related compound, 4-methyl-2,7-diamino-5,10-diphenyl-4,9-diazapyrenium hydrogensulfate (ADAP), have been studied. Concentration dependent SERS spectra of both aromatic species (1 × 10−7-5 × 10−5 M) indicated existence of dimeric associates at high concentration and an equilibrium shift towards monomers with a concentration decrease. Interactions of the intercalating molecules with DNA have been studied for various intercalator/DNA (base pair) molar ratios ranging from 10/1 to 1/10. In colloidal samples containing an intercalator in excess relative to DNA binding sites (from 10/1 to 2/1) enhancement of the Raman scattering gradually weakened, indicating a decrease in a number of free molecules adsorbed on the metal surface due to binding with DNA. At the drug/DNA ratios of 1/2 and 1/5 weaker but observable SERS bands indicated insertion of the drug molecules between the base pairs (intercalation strongly diminished interaction of the drug molecules with metal surface) as well as non-intercalative binding of the drug molecules able to stay in closer contact with a metal surface. A total intercalation of EB and ADAP molecules (intercalator/DNA of 1/7 and 1/10) resulted in almost complete loss of the SERS signal. Intensity of the SERS spectra of the intercalator/DNA complexes relative to the SERS intensity of the free intercalating molecules diminished to a lesser degree for ADAP/DNA than for EB/DNA. The obtained difference was attributed to a larger aromatic surface of the ADAP molecules which, although intercalated, could be positioned near the enhancing nanoparticles, unlike the smaller EB molecules which were deeply inserted within the DNA helix. |
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Keywords: | Surface-enhanced Raman spectroscopy Intercalator Dimer Ethidium bromide DNA Interactions |
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