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'Phototautomerism' in keywords Facet   section ZfN Section C  [X]
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1980 (1)
1Author    Jacek Wierzchowski, M. Arian Szczęśniak, D. Avid ShugarRequires cookie*
 Title    Fluorescence Emission Properties of the Cation of 4-Aminopyrazole(3,4-d) pyrimidine, an Adenine Analogue: Evidence for Phototautomerism  
 Abstract    A study has been made of the emission spectra at room temperature, in aqueous and alcoholic media, of 4-aminopyrazolo(3,4-d)pyrimidine (APP) and some o f its methylated derivatives. The cationic forms APPH+, N 2-methyl-APPH+ and N 7-methyl-APPH+ exhibit intense fluorescence un­ der these conditions, the first two exhibiting excitation spectra which differ from the absorption spectra, pointing to the existence o f a tautomeric equilibrium in the ground state. From the shape o f the excitation spectra, and comparisons with methylated analogues in fixed tautomeric forms, it follows that the emission of APPH+ originates exclusively from the species N (2)-H ,N (7)-H +, the other forms being non-fluorescent. The proportion o f the emitting species, calculated from the ex­ citation wavelength dependence o f the quantum yield, is in good agreement with data for the ground state. The emission spectrum of APPH+ in aqueous medium consists o f two bands with /lmax 360 nm and 430 nm, which exhibit identical excitation spectra, but are quenched to different extents by H30 +. The 430 nm emission band is absent in alcoholic media. A similar behaviour is exhibited by N 7-methyl-APPH+, whereas the neutral form o f this analogue exhibits only the 430 nm band. These results indicate that the long wavelength emission band o f APPH+ originates from the rare tautomeric species N(7)-H formed in the excited state by photodissociation o f the N(2)-H proton from the species N(2)-H ,N(7)-H+. This is further confirmed by results obtained with the aid o f the basicity method, as well as by salt efects in non-aqueous media. Consideration is given to the possibility of such processes occurring in other analogues o f nucleic acid derivatives. 
  Reference    Z. Naturforsch. 35c, 878—8 (1980); received July 28 1980 
  Published    1980 
  Keywords    Fluorescence, Phototautomerism, Pyrazolo(3, 4-d)pyrimidines, Adenine Analogues, Protonation Sites 
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 TEI-XML for    default:Reihe_C/35/ZNC-1980-35c-0878.pdf 
 Identifier    ZNC-1980-35c-0878 
 Volume    35