Species Responsible for the Fluorescence of 1: N6‐Ethenoadenosine

Abstract

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. 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. 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. Copyright © 1974, Wiley Blackwell. All rights reserved