Raman spectra of nystatin. Influence of impurities

The Raman spectra of the polyene antibiotic nystatin have been investigated between 1500 and 1650 cm-1. Only one band is observed in the resonance Raman spectra obtained with a 3045 A excitation radiation. Two major bands are observed in the preresonance spectra of pure nystatin obtained with a 4545 A excitation. A supplementary band at 1557 cm-1 observed in the preresonance spectra of samples of commercial origin is ascribed to the presence of heptaene impurities, the Raman spectra of which are preferentially enhanced by resonance, owing to the closer proximity of their absorption to the excitation radiation.