The complex between 9-(n-decanyl)acridone and bovine serum albumin. Part 2. What do fluorescence probes probe?

Factor analysis indicates that the fluorescence spectrum of 9-(n-decanyl)acridone (NDA), when bound to Bovine Serum Albumin (BSA), can be described quite adequately as the sum of two spectra, attributed to a "free" and a "bound" species. Kinetic evidence indicates that upon electronic excitation the system undergoes a net increase in free NDA, relative to the equilibrium distribution in the ground state, which would be consistent with Lewis acid sites on BSA being responsible for the binding. The system does not attain a position of equilibrium during the duration of the excited singlet state. This permits the determination of excited state rate constants for binding and unbinding of NDA on BSA, as well as the decay constants for the two forms of the probe.