Spectroscopic and electrochemical studies of the interaction between oleuropein, the major bio-phenol in olives, and salmon sperm DNA

• Interaction of oleuropein with double-stranded DNA was investigated.
• UV–vis absorption, fluorescence spectroscopy and voltammetry were applied.
• Thermal denaturation and competitive fluorescence techniques were also used.
• Binding constant of 1.4 × 104 M−1 was obtained for the interaction.

Interaction of oleuropein, the major bio-phenol in olive leaf and fruit, with salmon sperm double-stranded DNA was investigated by employing electronic absorption titrations, fluorescence quenching spectroscopy, competitive fluorescence spectroscopy, thermal denaturation and voltammetric studies. Titration of oleuropein with the DNA caused a hypochromism accompanied with a red shift indicating an intercalative mode of interaction. Binding constant of 1.4 × 104 M−1 was obtained for this interaction. From the curves of fluorescence titration of oleuropein with the DNA, binding constant and binding sites were calculated to be 8.61 × 103 M−1 and 1.05, respectively. Competitive studies with ethidium bromide (a well-known DNA intercalator) showed that the bio-phenol could take the place of ethidium bromide in the DNA intercalation sites. The interaction of oleuropein with DNA was also studied electrochemically. In the presence of the DNA, the anodic and cathodic peak currents of oleuropein decreased accompanied with increases in peak-to-peak potential separation and formal potential, indicating the intercalation of oleuropein into the DNA double helix. Moreover, melting temperature of the DNA was found to increase in the presence of oleuropein, indicating the stabilization of the DNA double helix due to an intercalative interaction.

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