Singlet oxygen (1Δg) production by pterin derivatives in aqueous solutions

Six compounds of the pterin family (pterin, 6-carboxypterin, 6-formylpterin, folic acid, biopterin and neopterin) have been investigated for their efficiencies of singlet oxygen (O-2((1)Delta(g))) production and quenching in aqueous solutions. The quantum yields of O-1(2) production (Phi(Delta)) have been determined by measurements of the O-1(2) luminescence in the near-infrared (1270 nm) upon continuous excitation of the sensitizer. Under our experimental conditions, all studied compounds (except folic acid) are relatively efficient O-1(2) sensitizers with Phi(Delta) values of up to 0.47. Results show that the nature of the substituent at position 6 on the pterin moiety, as well as the pH, affect considerably the capacity of pterins to produce O-1(2). All compounds investigated are efficient O-1(2) quenchers: the rate constant of O-1(2) total quenching (k(t)) by folic acid (3.0(+/- 0.3) x 10(7) M-1 s(-1)) is one order of magnitude larger than those for the other pterin derivatives investigated (1.4(+/- 0.1) x 10(6) M-1 s(-1 )to 2.9(+/- 0.3) x 10(6) M-1 s(-1)).