Emission properties of dihydropterins in aqueous solutions

Pterins belong to a class of heterocyclic compounds present in a wide range of living systems and accumulate in the skin of patients affected by vitiligo, a depigmentation disorder. The study of the emission of 7,8-dihydropterins is difficult because these compounds are more or less unstable in the presence of O-2 and their solutions are contaminated with oxidized pterins which have much higher fluorescence quantum yields (Phi(F)). In this work, the emission properties of six compounds of the dihydropterin family (6-formyl-7,8-dihydropterin (H(2)Fop), sepiapterin (Sep), 7,8-dihydrobiopterin (H(2)Bip), 7,8-dihydroneopterin (H(2)Nep), 6-hydroxymethyl-7,8-dihydropterin (H(2)Hmp), and 6-methyl-7,8-dihydropterin (H(2)Mep)) have been studied in aqueous solution. The fluorescence characteristics (spectra, Phi(F), lifetimes (tau(F))) of the neutral form of these compounds have been investigated using the single-photon-counting technique. Phi(F) and tau(F) values obtained lie in the ranges 3-9 x 10(-3) and 0.18-0.34 ns, respectively. The results are compared to those previously reported for oxidized pterins.