Raman Spectroscopic Study of Aggregation Process of Antibiotic Amphotericin B Induced by H+, Na+, and K+ Ions

The normal and the preresonance Raman effects (NR and PRR) of spectroscopy have been used to monitor and explain the aggregation processes of amphotericin B (AmB) in aqueous solution at different pH values and containing the K+ and Na+ ions. The resonance-enhanced and normal vibrational Raman spectra were recorded with a semiconductor laser (ex 785 nm) and an argon laser (ex 514.5 nm) for investigation of interactions between AmB chromophores. The essential difference between the samples stimulated by resonance-enhanced and by near-infrared was in the C=C stretching mode region of polyene chain. The processes connected with the aggregation of AmB led to changes in the chromophore, which were only visible as a remarkable broadening of the band centered at 1558 cm(-1). The understanding of possible physical mechanisms responsible for the molecular aggregation of the drug is important from the pharmaceutical applicability standpoint.