RESUMO
Mechanism and influence factors of resonance light scattering (RLS) spectra of 4-(2-pyridylazo)-resorcinol (PAR) aqueous solution were studied. In weak acidic solutions, strong RLS of PAR can be observed. The spectral feature of RLS is related to the absorption spectra of PAR. Acidity of the solutions influenced the acid-base equilibrium of PAR and its existing state, thereby influenced the RLS intensity. At pH 3.1 to pH 6.2, PAR exists as neutral molecule, which may assemble into molecular aggregates by hydrophobic force giving a light scattering enhancement. By a light polarization experiment, the RLS of PAR was demonstrated to be complete polarized light. The relationship between RLS intensity and PAR concentration was examined to be linear at a given set of experimental conditions.
Assuntos
Luz , Resorcinóis/química , Espalhamento de Radiação , Algoritmos , Compostos Cromogênicos/química , Fluorescência , Concentração de Íons de Hidrogênio , Cinética , Modelos Químicos , Espectrometria de Fluorescência/métodosRESUMO
Resonance light scattering (RLS), absorption and fluorescence spectra of aurintricarboxylic acid (ATA) were studied. In solutions with pH 3.7 to pH 11.0, the RLS signal was very weak, but increased sharply with a decrease in pH when pH < 3.7 and reached a maximum at pH 2.7. This enhancement effect of RLS occurred because the negative charged species of ATA were transformed into neutral molecules when pH decreased, and the neutral molecules assembled into supermolecular aggregates. Two peaks at 260 nm and 340 nm, respectively, and a valley at 300 nm, appeared in the RLS spectrum, whereas an absorption peak appeared at 300 nm in the absorption spectrum. This spectral feature reveals that the RLS spectrum was related to the absorption spectrum of ATA. The change in RLS intensity with the wavelength was not accordant with Rayleigh scattering law. The fluorescence excitation and emission spectra of ATA do not overlap, so resonance fluorescence was not involved in the RLS spectrum. Under a given set of experimental conditions, the RLS intensity increased with the increase in ATA concentration, which, however, was not a strictly linear relationship.
