Species Responsible for the Fluorescence of 1: N6-Ethenoadenosine

Abstract

1 Fluorescence lifetimes and emission spectra of 1: N6-ethenoadenosine 5′-monophosphate (ɛAMP) in aqueous solution over the pH range 1.5 to 12.0 indicate the presence of only one emitting fluorophore. 2 The loss at low pH of fluorescence emission at 415 nm from the neutral 1: N6-ethenoadenine fluorophore is due to the conversion of the fluorescent unprotonated form to the non-fluorescent protonated form by protonation at N-9. This conclusion is based on the pH dependence of the fluorescence lifetimes and quantum efficiences of ɛAMP over the range 1.5 to 12.0. 3 The observation of a fluorescence quantum efficiency of 86% that of ɛAMP in aqueous solution (pH 6.8) for 1:N6-etheno-9-propyladenine (ɛ-PrAde) in dry dioxane where it cannot acquire a proton in the excited state is direct evidence that the unprotonated form of the ɛ-adenine fluorophore is responsible for the fluorescence emission.