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41Author    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 
42Author    IouriE. Borissevitcha+, ChristianeP F Borgesa++, GalinaP. Borissevitcha+++, VictorE. Yushmanova+, SoniaR W Louroh, Marcel TabakaRequires cookie*
 Title    Binding and Location of Dipyridamole Derivatives in Micelles: the Role of Drug Molecular Structure and Charge  
 Abstract    Binding and localization of the vasodilator and antitumor drug coactivator dipyridamole (D IP) and of its three derivatives, RA14. RA47 and RA25 (D IP D), to cationic (cetyltrimeth-ylammonium chloride), anionic (sodium dodecylsulfate), zwitterionic (N-hexadecyl-N.N-di-methyl-3-ammonio-l-propanesulfonate). and neutral (r-octylphenoxypolyethoxyethanol) m i­ celles was studied using fluorescence, optical absorption and 'H N M R spectroscopy. The analysis of N M R . optical absorption and fluorescence data indicates that the depth of local­ ization of the drugs in the micelles from the surface decreased in the order D IP > RA 14 > RA47 > RA25. The binding constants for the neutral drug forms change in the same order in the range of 1400-3100 m _1 for D IP to 80-300 m _1 for RA25. This order is identical with the reported biological activity of D IP D . For the protonated drugs in zwitterionic or neutral micelles the binding constants are reduced by a factor of 20-75. 
  Reference    Z. Naturforsch. 51c, 578—590 (1996); received March 28/May 31 1996 
  Published    1996 
  Keywords    Dipyridamole and Derivatives, Micelle, Drug Location, Absorption, Fluorescence, N M R 
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 TEI-XML for    default:Reihe_C/51/ZNC-1996-51c-0578.pdf 
 Identifier    ZNC-1996-51c-0578 
 Volume    51