PHOSPHORESCENCE QUENCHING OF POLY rA IN GLUCOSE-SODIUM ACETATE SOLUTION AT 77 K*

Abstract. The phosphorescence of poly rA at 77 K in an aqueous medium containing glucose is half-quenched by bound ethidium bromide at a fractional concentration, r_1/2, of 0.005, and by bound proflavine at r_1/2= 0.002: r_1/2= 0.024 for Co²⁺ and r_1/2= 0.039 for Mn²⁺. The decay of the dye-quenched poly rA phosphorescence is markedly nonexponential and decays more rapidly with increasing dye concentration, while the decay of the metal-ion quenched poly rA phosphorescence parallels that of the unquenched poly rA, independent of metal-ion concentration. Förster overlap integrals and critical distances for transfer of both poly rA singlet and triplet excitation to dye singlet states are calculated, and used to explain a consistent interpretation of the experimental results in terms of one-step direct excitation transfer from base to dye or metal ion in a highly folded polymer conformation.