PLoS ONE (Jan 2022)

Oxidation-reduction and photophysical properties of isomeric forms of Safranin.

  • Eskil M E Andersen,
  • Hsin Wang,
  • Joshua S H Khoo,
  • Jose F Cerda,
  • Ronald L Koder

DOI
https://doi.org/10.1371/journal.pone.0265105
Journal volume & issue
Vol. 17, no. 6
p. e0265105

Abstract

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Safranine O is widely used in the bioenergetics community as an indicator dye to determine membrane potentials and as an electron transfer mediator in potentiometric titrations. Here we show that two different commercial preparations of Safranine O contain less than sixty percent by weight of the title compound, with the rest primarily consisting of two closely related safranine isomers. All three major isomer components were isolated using reverse phase HPLC and their structures determined using mass spectrometry and two-dimensional NMR. These Safranines have two-electron midpoint potentials ranging from -272 to -315 mV vs. SHE. We have also investigated the absorption and fluorescence spectra of the compounds and found that they display distinct spectral and photophysical properties. While this mixture may aid in Safranine O's utility as a mediator compound, membrane potential measurements must take this range of dye potentials into account.