Thermoresponsive-fluorescent isopropylacrylamide-vinylpyridine-pyrenemethylacrylamide terpolymer and its complexation behaviour with DNA

Temperature and pH-responsive, fluorescent random terpolymer of N-isopropylacrylamide (NIPA), 4-vinylpyridine (4VP) and N-pyrenemethylacrylamide (PyMeA) was synthesized. Temperature and pH-dependent fluorescence behaviour of poly(NIPA-4VP-PyMeA) terpolymer was investigated by fluorescence spectroscopy. The protonation of terpolymer (i.e. high cationic charge) in the acidic pH region provided significantly higher values for the ratio of the first to third vibronic band intensities (I1/I3) with respect to that found for pyrene in an aqueous medium (i.e. 1.87). I1/I3 ratio significantly decreased with increasing pH depending upon the decreasing polarity of microenvironment due to the deprotonation of terpolymer. As a new potential carrier for DNA-delivery, the interaction of fluorescent poly(NIPA-4VP-PyMeA) terpolymer with DNA was investigated. The addition of DNA into the fluorescent terpolymer solution resulted in the formation of stable, colloidal terpolymer-DNA complex due to the bridge formation between phosphate groups of DNA and protonated 4VP units of the fluorescent terpolymer. The hydrodynamic diameter of DNA-poly(NIPA-4VP-PyMeA) terpolymer complex increased with increasing DNA concentration. The formation of colloidal complex particles lower than 1 μm at the pHs close to the physiological pH value showed that poly(NIPA-VP-PyMeA) terpolymer could be utilized as a new fluorescent non-viral vector for DNA delivery.