pH‐Dependent Absorption Spectrum of Oxyluciferin Analogues in the Presence of Adenosine Monophosphate

Abstract The photophysical properties of oxyluciferin, the light emitter responsible for firefly bioluminescence, are pH‐dependent. One of the potential proton acceptor/donor is adenosine monophosphate (AMP). We have studied three oxyluciferin synthetic analogues with or without AMP, in water, in the pH=5 to 11 range, using both experimental steady‐state absorption spectroscopy or the recently developed computational protocol that uses constant pH molecular dynamics and then hybrid QM/MM calculations (CpHMD‐then‐QM/MM). The latter features a systematic investigation of all the protonation microstates using molecular dynamics simulations coupled to thousands hybrid QM/MM vertical excitation energies. Our results demonstrate that AMP does not significantly modify the visible light absorption of the analogues, whatever the pH value. We also show that CpHMD‐then‐QM/MM is capable to qualitatively reproduce the pH‐dependent absorption spectrum of the analogues, despite the employed low QM level of theory.