Effect of electrolytes, nucleotides and DNA on the fluorescence of flavopereirine natural alkaloid

Abstract

The absorption and fluorescence characteristics of flavopereirine, a pharmaceutically important natural alkaloid, were studied to reveal how the complex formation and the change of the microenvironment affect the deactivation kinetics from the singlet-excited state. The fluorescence lifetime was not influenced by the ionic strength, but a significant deuterium effect was observed showing that hydrogen bonding in the singlet-excited state promoted energy dissipation. Nucleotides caused both static and dynamic quenching. The rate constant of the latter process increased when the nucleobase was capable of donating electron to the excited flavopereirine. The spectrophotometric measurements provided evidence for non-cooperative binding to double-stranded DNA with an equilibrium constant of 4.6 × 10⁵ M⁻¹. Time-resolved fluorescence signals showed that three kinds of complexes are formed with distinct fluorescence lifetimes. Flavopereirine binding to chondroitin sulfate was also found, which led to different fluorescence characteristics at pH 2 and 6.