Effect of protons and metal ions on the fluorescence properties of a polylysin dendrimer containing twenty four dansyl unitsâ Based on the presentation given at Dalton Discussion No. 3, 9â 11th September 2000, University of Bologna, Italy.
Balzani, Vincenzo; Ceroni, Paola; Gestermann, Sven; Gorka, Marius; Kauffmann, Christopher; Vögtle, Fritz; Balzani Vincenzo; Dipartimento di Chimica â G. Ciamicianâ , Università di Bologna; Ceroni Paola; Dipartimento di Chimica â G. Ciamicianâ , Università di Bologna; Gestermann Sven; Kekulé-Institut für Organische Chemie und Biochemie, Universität Bonn; Gorka Marius; Kekulé-Institut für Organische Chemie und Biochemie, Universität Bonn; Kauffmann Christopher; Kekulé-Institut für Organische Chemie und Biochemie, Universität Bonn; Vögtle Fritz; Kekulé-Institut für Organische Chemie und Biochemie, Universität Bonn
Журнал:
Dalton Transactions
Дата:
2000
Аннотация:
The interaction of protons, Co<sup>2+</sup>, Ni<sup>2+</sup> and Zn<sup>2+</sup> ions (as nitrate salts) with a polylysin dendrimer, D, functionalized in the periphery with 24 5-dimethylamino-1-naphthalenesulfonamido (dansyl) units has been investigated in acetonitrileâ dichloromethane solution. The dendrimer consists of a benzene core branched in the 1, 3, and 5 positions. Each branch starts with a (dialkyl)carboxamide-type moiety and carries (i) six aliphatic amide groups and (ii) eight fluorescent dansyl units. For comparison purposes, the behaviour of a monodansyl reference compound (I) has also been investigated. The absorption spectrum and the fluorescence properties of the dendrimer are those expected for a species containing 24 non-interacting dansyl units. Both for the model compound and for the dendrimer, protonation causes a shift of the absorption and fluorescence bands towards higher energies; for the dendrimer, however, the changes in fluorescence intensity during the acid titration reveal the occurrence of intradendrimer quenching processes, with signal amplification. Addition of Co<sup>2+</sup> or Ni<sup>2+</sup> ions to a basic solution of the model compound I does not cause any effect in the absorption and emission properties, whereas in the case of dendrimer D a strong fluorescence quenching is observed. At low metal ion concentration each metal ion quenches about 9 dansyl units; the fluorescence quenching takes place by a static mechanism involving co-ordination of metal ions in the interior of the dendrimer. Addition of Zn<sup>2+</sup> to a basic solution of the dendrimer causes only a very small decrease in the fluorescence intensity. The co-ordinated Co<sup>2+</sup> and Ni<sup>2+</sup> ions are fully displaced by addition of Zn<sup>2+</sup> or H<sup>+</sup> with revival of the dansyl fluorescence. The results obtained show that a dendrimer can exhibit an unusual co-ordinating ability and sensory signal amplification.
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