The circular polarization of fluorescence of the ionophore lasalocid A (X-537A) and some of its metal complexes

The conformation of the ionophore lasalocid A (X-537A) and its complexes with metal ions was probed by the circular polarization of their luminescence (CPL). The CPL of each complex in methanol was found to be different than when in n-hexane. Furthermore, the different metal ion complexes investigated had a different CPL spectrum in each solvent. These findings indicate wide variability in the conformation of the complexes depending on the metal ion and the solvent. From the spectral behaviour of the CPL it was concluded that at least some of the complexes exist in more than one form in solution. A comparison between the CPL and CD spectra indicates a change in the conformation of the ionophore in the vicinity of the salicylate chromophore upon electronic excitation.