A fluorescence lifetime study of virginiamycin S using multifrequency phase fluorometry

Abstract

Using multifrequency phase fluorometry, fluorescence lifetimes have been assigned to the different protolytic forms of the antibiotic virginiamycin S. These lifetimes are 0.476 +/- 0.005 ns for the uncharged form, 1.28 +/- 0.2 and 7.4 +/- 0.2 ns for the zwitterionic form, 1.19 +/- 0.01 ns for the negatively charged form, and 1.9 +/- 0.1 ns for the double negatively charged form. The assignments are based on lifetime measurements as a function of pH, volume percent ethanol, and excitation wavelength. Excited-state proton transfer is taken into account. It is complete at pH values lower than 1, and no fluorescence of the fully protonated charged form is observed. At pH 8, an excited-state pK* increase is calculated, but proton association is too slow to cause excited-state proton transfer. The addition of divalent cations, at pH 9.4, increases the lifetime of the negatively charged form to a value dependent upon the specific nature of the cation (7.58 +/- 0.06 ns for Mg2+, 6.54 +/- 0.02 ns for Ca2+, and 3.74 +/- 0.05 ns for Ba2+). Monovalent cations do not influence the lifetimes, indicating that their binding to the macrocycle does not influence the fluorescent moiety. The model compound 3-hydroxypicolinamide shows an analogous behavior, but the retrieved lifetime can differ significantly.

Interaction between virginiamycin S and ribosomes is partly provided by a salt bridge with a magnesium ion

“…The addition of Mg2+ to VS, at pH higher than 9, whereby the negatively charged form predominates, results in an increase of the fluorescence lifetimes [cf. the preceding paper (Clays et al, 1991)]. This effect can be attributed to a reduced nonradiative decay rate, caused by Mg2+ complexation.…”

“…"Fluorescence lifetimes were determined by phase fluorometry as described by Clays et al (1991) in KP buffer, pH 7.4. b Fluorescence lifetimes were determined by phase fluorometry as described by Clays et al (1991) [4-(dicyanomethylene)-2-methyl-6-[/>-(dimethylamino)styryl]-47/-pyran]. After frequency doubling, excitation was produced at 330 nm.…”

“…All available statistical parameters were used to identify the exponentials involved in fluorescence decay. Details of phase measurements and analysis of the experimental data are described in the preceding paper (Clays et al, 1991).…”

“…To learn more about the VS protolytic form coordinating to alkaline earth cations, the influence of pH, solvent polarity, and cation concentration on the fluorescence decay of VS has been analyzed by multifrequency phase fluorometry. In the preceding paper (Clays et al, 1991), different fluorescence lifetimes associated with the different protolytic forms of VS were reported: addition of alkaline earth cations resulted in the lengthening of the fluorescence lifetimes. This phenomenon was attributed to a reduction of the nonradiative decay rate due to a reduction of the number of degrees of freedom for nonradiative relaxation.…”

Luminescent and gas sensor properties of the ZrO2:Hhpa:Eu3+ Hybrid Compound

“…Hybrid materials formed with Eu 3+ and one organic ligand are used to fabricate red luminophors for the obtention of white light emitter diodes (LEDs), since the emission of the white light can be obtained by the incorporation of blue, green, and red luminophors. The organic ligands act as antenna, which increase the luminescent intensity due to the presence of chromophores groups [1,[25][26][27][28][29].…”