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| Content Provider | World Health Organization (WHO)-Global Index Medicus |
|---|---|
| Author | Petrov, Vesselin Pina, Fernando Diniz, Ana M. Pinheiro, Carlos Parola, A. Jorge |
| Description | Author Affiliation: Diniz AM ( REQUIMTE, Departamento de Química, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, 2829-516 Caparica, Portugal.) |
| Abstract | A symmetric bis(flavylium) constituted by two 7-hydroxyflavylium moieties linked by a methylviologen bridge was synthesized. The thermodynamic and kinetics of the network of chemical reactions involving bis(flavylium) and the model compound 7-hydroxy-4′-methylflavylium was completely characterized by means of direct and reverse pH jumps (stopped flow) and flash photolysis. Both compounds follow the usual pH-dependent network of chemical reactions of flavylium derivatives. The equilibrium species of the model compound are the flavylium cation (acidic species) and the trans-chalcone (basic species) with an apparent $pK′_{a}=2.85.$ In the case of the bis(flavylium) it was possible to characterize by $^{1}H NMR$ spectroscopy three species with different degrees of isomerization: all flavylium, flavylium-trans-chalcone, and all trans-chalcone. Representation of the time-dependent mole fraction distribution of these three forms after a pH jump from equilibrated solutions of all-flavylium cation (lower pH values) to higher pH values, shows that formation of trans-chalcone is not completely stochastic (two independent isomerizations), the isomerization of one flavylium showing a small influence on the isomerization of the other. The radical of the methyl viologen bridge is formed upon reduction of the bis(trans-chalcone) with dithionite. The system is reversible after addition of an oxidant in spite of the occurrence of some decomposition. |
| ISSN | 09476539 |
| e-ISSN | 15213765 |
| Journal | Chemistry - A European Journal |
| Issue Number | 23 |
| Volume Number | 17 |
| Language | English |
| Publisher | Wiley-VCH;ChemPubSoc Europe |
| Publisher Date | 2011-05-27 |
| Publisher Place | Germany |
| Access Restriction | Open |
| Subject Keyword | Chalcone Chemistry Dithionite Flavonoids Chemical Synthesis Oxidants Paraquat Kinetics Magnetic Resonance Spectroscopy Molecular Structure Stereoisomerism Research Support, Non-U.S. Gov't |
| Content Type | Text |
| Resource Type | Article |
| Subject | Organic Chemistry Catalysis |
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