QUENCHING OF THE FLUORESCENCE OF NAPHTHALENE DERIVATIVES BY NUCLEIC-ACID COMPONENTS

Interactions of two fluorescent pesticides: N-methyl 1-naphthylcarbama te (carbaryl) and N,N-diethyl-2-(1-naphthoxy)propionamide (naproamide) , as well as 1-methoxynaphthalene, with nucleic acids components were investigated in aqueous solution (phosphate buffer, pH 6.5) and in DMS O by UV absorption, steady-state and time-resolved fluorescence spectr oscopy. As follows from the Stern-Volmer plots constructed on the basi s of the intensity and lifetime measurements, nucleosides and nucleoti des quench fluorescence of the naphthalene derivatives. Quenching was mainly a dynamic process. Bimolecular quenching rate constants k(q), d etermined from lifetime measurements, were in the range of (1.3-6.0) x 10(9) M-1 s(-1) in aqueous solution and approximately one order of ma gnitude lower in DMSO k(q) (less than or equal to 0.02-0.9) x 10(9) M- 1 s(-1). The mechanism of the dynamic fluorescence quenching in both s olvents was discussed in terms of an excited state electron transfer. The ground state complexation of the naphthalene derivatives and nucle ic acid components, responsible for a static quenching, was characteri zed by rather low values of association constants (K-s < 17 M-1) in aq ueous solution and the process was negligible in DMSO (K-s < 4 M-1). T he fluorescence study indicated a weak affinity of N,N-diethyl-2-(1-na phthoxy)propionamide pesticide to calf thymus DNA.