title: Solution conformation of a nitrobenzoxadiazole derivative of the polyene antibiotic nystatin: a FRET study.
abstract: Nystatin is a polyene antibiotic frequently applied in the treatment of topical fungal infections. In this work, a 7-nitrobenz-2-oxa-1,3-diazole (NBD) hexanoyl amide derivative of nystatin was synthesized and its detailed photophysical characterization is presented. The average conformation of the labelled antibiotic in tetrahydrofuran, ethanol and methanol was determined by intramolecular (tetraene to NBD) fluorescence resonance energy transfer measurements. At variance with the literature [Can. J. Chem. 63 (1985) 77-85], it was concluded that there is no need to invoke a solvent-dependent conformational equilibrium between extended and closed conformers of the antibiotic, because the mean tetraene-to-NBD separating distance was found to remain constant (approximately 18 A) in all the solvents studied. In addition, the large solvent dependence of the fluorescence anisotropy observed for the non-derivatized nystatin, was rationalized on the basis of the prolate ellipsoidal geometry of the molecule. It was concluded that the rod shaped and amphipathic antibiotic remains monomeric in different solvents within the concentration range studied (2-20 microM).
authors.affiliation: Centro de Química-Física Molecular, Complexo I, Instituto Superior Técnico, Av. Rovisco Pais, P-1049-001 Lisbon, Portugal.
authors.forename: Liana
authors.initials: L
authors.lastname: Silva
authors.forename: Ana
authors.initials: A
authors.lastname: Coutinho
authors.forename: Alexander
authors.initials: A
authors.lastname: Fedorov
authors.forename: Manuel
authors.initials: M
authors.lastname: Prieto
mesh_terms: D005454:Fluorescence Polarization / Q000379:methods; D031541:Fluorescence Resonance Energy Transfer / Q000379:methods; D008968:Molecular Conformation; D009761:Nystatin / Q000031:analogs & derivatives* / Q000032:analysis* / Q000737:chemistry*; D011090:Polyenes / Q000032:analysis / Q000737:chemistry; D012996:Solutions
chemical_list: D011090:Polyenes; D012996:Solutions; D009761:Nystatin; C048450:NBD-nystatin