Solar Radiation Exposure of Dihydrobiopterin and Biopterin in Aqueous Solution

IPIÑA, ADRIANA; CASTAÑO, CAROLINA; DANTOLA, MARIA LAURA; THOMAS, ANDRÉS H.

Córdoba

Congreso; 16th International Congress on Photobiology; 2014

International Union of Photobiology

Dihydrobiopterin (H2Bip) and Biopterin (Bip) accumulate in the skin of patients suffering from vitiligo. H2Bip and Bip undergo photooxidation upon UV radiation and the latter acts as a photosensitizer of biomolecules [1-2]. In this work we analyse the photochemical reactions of these compounds exposed to sunlight in La Plata (34.90ºS, 57.92ºW) between Spring equinox and Summer solstice period, recording the spectral solar irradiance with a high-resolution spectrometer. The photochemical reactions were followed by HPLC and UV-Vis spectrophotometry. Under solar exposure H2Bip undergoes dimerization and oxidation to Bip, which, in turn, is photooxidized into 6-formylpterin (Fop). Additionally, UV excitation induces the oxidation of Fop to 6-carboxypterin, which is much more photostable than Bip and Fop and then it is accumulated in the solution. Rates of reactant consumption and quantum yields were determined under different meteorological conditions. We have demonstrated that solar radiation causes significant oxidation of the pterin derivatives investigated, even in cloudy days. The biological implications of our results are discussed. Figure. Absorption factor from H2Bip (gray curve), solar spectral photon irradiance measured at noon in a clear sky day (black curve) and the convolution of them (shaded area).  Acknowledgments The authors thank CONICET for the postdoctoral fellowship and IFIR-CONICET-UNR for letting us borrow the spectrometer.  [1] [1] M. Vignoni, F.M. Cabrerizo, C. Lorente, C. Claparols, E. Oliveros, A.H. Thomas, Org. Biomol. Chem., 2010, 8 (4), 800. [2] M. Vignoni, F.M. Cabrerizo, C. Lorente, A.H. Thomas, Photochem. Photobiol., 2009, 85(1), 365.