INVOLVEMENT OF NUCLEIC BASES IN THE QUENCHING OF THE FLUORESCENCE OF ACRIDINE BY METHYLVIOLOGEN

Hybrid molecules 5a-5c having a 9-acridinyl moiety connected to a viol ogen moiety through alkyl chains of three, six and nine carbons, respe ctively, were synthesized. The acridine and viologen rings of 5a were stacked in an aqueous solution. The other compounds, 5b and 5c, exist in a conformation separating the acridine and viologen units. Using ab sorption changes of the acridine chromophore of 5a-5c in the presence of calf thymus DNA, binding constants were determined to be 10(5)-10(6 ) M-1 even at high salt concentrations (0.1-0.3 M). The binding affini ty and the number of the associated counter-ions with the DNA complex of 5a were smaller than those of 5b and 5c. This is in agreement with the molecular model consideration in which the methylene chain of 5a w as too short to allow interaction of the viologen with the phosphate a nions of DNA. Electrochemical study of the viologen units of 5a-5c in the presence of DNA also supported the binding behavior obtained by th e spectrophotometric method. Fluorometric study revealed that the quen ching of the fluorescence of the acridine by the viologen is enhanced on the DNA matrix.