Study of the interaction between nucleic acid and oxytetracycline–Eu3+ and its analytical application

In Tris–HCl buffer (pH=8.50), nucleic acid can enhance the fluorescence intensity of oxytetracycline (OTc)–Eu3+ complex and the enhancement of DNA is far larger than that of RNA. The electrostatic binding of the phosphate group of nucleic acids with Eu3+ in OTc–Eu3+ complex could decrease the nonradiative energy loss through O–H vibration of H2O molecule in Eu3+ complex. Therefore, the fluorescence of the system would be enhanced by nucleic acids. The enhancement of DNA comes from the groove binding and the electrostatic binding. It is the hydrophobic microenvironment of DNA groove that makes the fluorescence intensity of OTc–Eu–DNA system far stronger than that of OTc–Eu–RNA system. The above conclusion of the interaction mechanism between OTc–Eu3+ complex and nucleic acids can explain the effect of the factors such as salt concentration, KH2PO4, solvent polarity, etc., on the fluorescence intensity of the system.