| | 41 | Author
| Jacek Wierzchowski, M. Arian Szczęśniak, D. Avid Shugar | Requires 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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| default:Reihe_C/35/ZNC-1980-35c-0878.pdf | | | | Identifier
| ZNC-1980-35c-0878 | | | | Volume
| 35 | |
| 42 | Author
| IouriE. Borissevitcha+, ChristianeP F Borgesa++, GalinaP. Borissevitcha+++, VictorE. Yushmanova+, SoniaR W Louroh, Marcel Tabaka | Requires 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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| 51 | |
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