The orientation of the transition dipole moments of a polyene antibiotic Amphotericin B under UV–VIS studies

• The Amphotericin B’s transition dipole moment direction for absorption is assigned.
• The angles between absorption and emission transition dipole moments are specified.
• The anisotropy data revealed antiparallel dimeric structure of Amphotericin B.

Amphotericin B (AmB) belongs to naturally occurring fluorescent antibiotics, commonly used in the treatment of life-threatening fungal infections. Open question regarding mechanism of action of this molecule calls for its orientation and organization studies in biomembranes. Here, we present studies on linear dichroism and fluorescence polarization of AmB embedded in isotropic and oriented poly(vinyl) alcohol films to characterize their transition dipole moments to low energy excited electronic transitions S1 (2Ag−) and S2 (1Bu+). The dichroic ratio and fluorescence anisotropy data were analyzed for stretched PVA films doped AmB. The results show that the transition moment for absorption makes an angle φ = 27° ± 2° with the molecular axis of AmB defined by the film stretching direction. The angles between the absorption and emission transition moments have been found for both the low excited electronic states, S2 (β = 4° ± 5°) and S1 (β = 6° ± 5°). The fluorescence anisotropy analysis from the S2 state reveals additional component assigned to antiparallel AmB dimeric structure.

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