Singlet Oxygen Quenching by Deoxygadusol and Related Mycosporine-Like Amino Acids from Phytoplankton Prorocentrum micans

Deoxygadusol (DG) and structurally related mycosporine-like amino acids, i.e. mycosporine glycine (MG) and mycosporine taurine (MT), were isolated from phytoplankton Prorocentrum micans and studied for the reactivity toward singlet oxygen. These water-soluble compounds with a cyclohexenone chromophore were all shown to be highly effective in quenching singlet oxygen (O2), with the efficiencies being significantly larger compared with histidine, a well-known O2 quencher. The O2 reaction rate constant (kQ) of DG was determined to be 5.4 × 10 Ms by a steady state method based on competitive inhibition of rubrene oxidation. The feasibility of this method was confirmed by estimating the kQ values for MG and two other quenchers, furfuryl alcohol and 1,4-diazabicyclo [2,2,2]octane, and comparing with those values determined by the time-resolved O2 decay method in the previous work.