The Solution Conformation and Some Spectroscopic Properties of 1,N⁶‐Ethenoadenosine Monophosphate, a Fluorescent Analogue of AMP

The conformation of ethenoadenosine monophosphate in aqueous solution at pH 2.0 has been shown to be very similar to that of AMP through use of the lanthanide‐shift proton‐magnetic‐resonance technique. The p K a , for protonation of the 9‐position of etheno‐AMP is 4.3 at 298 K, but at all pH values in the range 1.0–9.6, fluorescence is emitted from the protonated form of the heterocyclic ring system. This conclusion is based on the pH, temperature and KI dependence of the emission spectrum. When dissolved in ethanol the quantum yield of etheno‐AMP fluorescence falls to about 40% of its value in water. There are unlikely to be large changes in the energies of the emissions of ethenoadenosine derivatives when bound to biological structures, but their quantum yields may well be reduced, especially if binding affects the ease with which the rings can be protonated.