Interaction of antimalarial drug quinacrine with nucleic acids of variablesequence studied by spectroscopic methods

The interaction of antimalarial drug quinacrine (QA) with polynucleotides i s studied by UV-visible absorption, fluorescence and surface-enhanced Raman spectroscopy (SERS). The polynucleotides employed for such a study were ca lf thymus DNA, poly(A).poly(T), poly(A).poly(U), poly(C).poly(G) and poly(d G-dC).poly(dG-dC). Absorption and fluorescence spectra of QA complexes indi cate that an interaction with the biomolecule is taking place, although dif ferent interaction mechanisms are probable depending on the sequence. The S ERS spectra also reflect spectral changes which depend on the polymer seque nce and that can be correlated to those observed by fluorescence, with the advantage of the detailed structural information provided by this vibration al technique. QA interacts with polynucleotides through its diprotonated fo rm and by ring stacking. The strength of such interaction is extremely sequ ence dependent, thus suggesting different interaction mechanisms in each ca se. The SERS technique allows the simultaneous study of those polynucleotid e moieties that are directly involved in the interaction thanks to the shor t-range character of the SERS spectroscopy. The interaction of QA with the above nucleic acids lead to a different change in the chain stability and f lexibility which is further related to the different denaturation tendency of the polymer in the presence of the metal surface.