Emission properties of dihydropterins in aqueous solutions

MARIANA P. SERRANO, MARIANA VIGNONI, M. LAURA DÁNTOLA, CAROLINA LORENTE AND ANDRÉS H. THOMAS

Mendoza

Congreso; 21st I-APS Conference; 2011

I-APS, INIFTA, UBA

Pterins, heterocyclic compounds derived from 2-aminopteridin-4-(3H)-one or pterin [1], arepresent in biological systems in multiple forms. They can exist in different oxidation states:oxidized (or aromatic) pterins and reduced pterins. Within the latter group, 7,8-dihydropterinsand 5,6,7,8-tetrahydropterins are the most important derivatives due to their biologicalactivity, e.g., dihydroneopterin (H2Nep) is secreted during the oxidative burst of stimulatedmacrophages [2], dihydrobiopterin (H2Bip) and tetrahydrobiopterin are involved in themetabolism of aminoacids [3]. In addition, H2Bip, biopterin (Bip) and other pterin derivativesaccumulate in the skin of patients affected by vitiligo, a depigmentation disorder, where theprotection against UV radiation fails due to the lack of melanin [4-5].Upon UV-A excitation, unconjugated oxidized pterins present emission bands with maximumaround 450 nm, relatively high fluorescence quantum yields (ФF > 0.10) and fluorescencelifetimes (tF) in the range 2-14 ns. Dihydropterins are more complicated to work withbecause they are unstable in air-equilibrated solutions, undergoing oxidation with a ratedepending on the chemical nature of the substituent [6]. In addition the emission ofdihydropterins is very weak and, and the solutions prepared from chemicals of the highestpurity commercially available are contaminated with small concentrations of oxidizedpterins. For that reason, given that the absorption spectra of dihydropterins and oxidizedpterins are in general more or less superimposed, the emission of the latter is a maininterference in the analysis of the fluorescence of the former.The aim of this work was to investigate the emission properties of dihydropterins in theirneutral forms, in aqueous solutions upon UV-A irradiation. We have chosen for this study 6pterin derivatives: 6-formyldihydropterin (H2Fop), sepiapterin (Sep), dihydrobiopterin(H2Bip), dihydroneopterin (H2Nep), 6-hydroxymethyldihydropterin (H2Hmp) and 6-methyldihydropterin (H2Mep). In particular, we have investigated the emission spectra,determined the FF and tF values, and discussed about the effects of the substituents on theemission properties.References:[1] D. J. Brown, The Chemistry of Heterocyclic Compounds, John Wiley & Sons, New York,1988, 24, 1-42.[2] C. Huber, D. Fuchs and A. Hausen, Journal of Immunology, 1983, 130, 1047-1050.[3] C. A. Nichol, G. K. Smith and D. S. Duch, Annu. Rev. Biochem., 1985, 54, 729-764.[4] K. U. Schallreuter, J. M. Wood, M. R. Pittelkow, M. Gütlich, K. R. Lemke, W. Rödl, N.N. Swanson, K. Hitzemann and I. Ziegler, Science, 1994, 263, 1444-1446.[5] H. Rokos, W. D. Beazley and K. U. Schallreuter, Biochem. Biophys. Res. Commun., 2002,292, 805-811.[6] M. L. Dántola, M. Vignoni, A. L. Capparelli, C. Lorente and A. H. Thomas, Helv. Chim.Acta, 2008, 91, 411-425.