Analysis of the photophysical properties of zearalenone using density functional theory

The intrinsic photophysical properties of the resorcylic acid moiety of zearalenone offer a convenient label free method to determine zearalenone levels in contaminated agricultural products. Steady-state fluorescence and density functional methods were applied to investigate the role of structural chemistry on zearalenone detection. Geometry optimization calculations using the B3LYP density functional identified a tautomeric form of zearalenone. Excited state geometries for zearalenone and a tautomeric form were obtained by MNDO semi-empirical optimizations. Steady-state fluorescence studies suggest that fluorescence quenching at neutral pH is associated with water interactions. Time-dependent density functional and ground state calculations indicate that the anionic and dianionic forms of zearalenone possess lower band gaps, excitation energies, and the lowest unoccupied molecular orbitals are positioned over the non-fluorophoric portion of zearalenone. These results suggest that deprotonation of one or more of the phenolic hydroxyls diminishes the intensity of the fluorescence emission of zearalenone.