Bisimidazoacridones: Effect of molecular environment on conformation and photophysical properties

Bisimidazoacridones (BIA) are highly selective antineoplastic and antiviral agents. Ultraviolet-visible spectroscopy and steady-state and time-resolve d fluorescence spectroscopy studies were carried out to probe the behavior of BLA in aqueoms and nonaqueous (organic solvents, colloid micelles) solut ions. Three ranges of fluorescence lifetimes were revealed: similar to 0.2- 0.5 ns (presumably reflecting the chromophore-chromophore interaction), sim ilar to 1-5 ns (interpreted as linker-perturbed chromophore decay) and simi lar to 6-12 ns (nonperturbed chromophore decay). The pre-exponential and st eady-state contributions of these components to the decay signal as well as the data on steady-state fluorescence intensities, wavelength maxima and b andwidths showed that the BIA conformations in solution were sensitive to t he environment and influenced strongly by their propensity to minimize hydr ophobic interactions. In water, the molecules tend to adopt condensed confo rmations that bring the two imidazoacridone moieties into close proximity ( resulting in intramolecular fluorescence energy transfer), while in nonaque ous systems the conformations become more relaxed, The transfer from a pola r to more lipophilic environment of macromolecules is suggested to he the m ain driving force for binding of BW to biomacromolecules, such as nucleic a cids.