The ability to generate singlet molecular oxygen, O2 (1Δg), and the scavenging activity of two well-known 1,4-dihydropyridines (1,4-DHPs) such asnifedipine (1,4-dihydro-2,6-dimethyl-4-(2-nitrophenyl)-3,5-pyridine-dicarboxylic acid dimethyl ester) and nitrendipine (1,4-dihydro-2,6-dimethyl-4-(3-nitrophenyl)-3,5-pyridine-dicarboxylic acid ethyl methyl ester) is assessed. Results show that nifedipine does not generate O2(1Δg) under our experimental conditions. In contrast, this 1,4-dihydropyridine behaves as a good scavenger of excited oxygen, mainly via physical deactivation with values of the total rate constant ranging from 20.8 × 105M-1 s-1 in dioxane to 93.0 × 105 M-1 s-1 in propylencarbonate. The less favored reactive pathway generates a photooxidation product, which has been isolated and identified by GC-MS as the nitropyridine derivative. Voltammetric experiments also confirm the generation of this oxidation product. On the other hand, nitrendipine yields O2(1Δg), but it is a less efficient scavenger of this species. Rate constants range from 1.88 × 105 M-1 s-1 in ethyl acetate to 15.8 × 105 M-1 s-1 in N,N-dimethylacetamide, the reactive channel being the main O2(Δg) deactivation pathway. Dependence on solvent microscopic parameters of the total rate constant for the reaction between singlet oxygen and 1,4-DHPs permits us to propose a mechanism involving a perepoxide-like encounter complex in the first step of the reaction path.
|Número de páginas||9|
|Publicación||Journal of Photochemistry and Photobiology A: Chemistry|
|Estado||Publicada - 31 oct. 2005|
Áreas temáticas de ASJC Scopus
- Química (todo)
- Ingeniería química (todo)
- Física y astronomía (todo)