INVESTIGADORES
BORSARELLI Claudio Dario
artículos
Título:
Exciplex Type Behavior and Partition of 3-Substituted Indole Derivatives in Reverse Micelles Made with Benzylhexadecyldimethylammoniun Chloride (BHDC), Water and Benzene
Autor/es:
C. D. BORSARELLI; S.G. BERTOLOTTI; C.M. PREVITALI
Revista:
PHOTOCHEMISTRY AND PHOTOBIOLOGY
Editorial:
American Society for Photobiology.
Referencias:
Año: 2001 vol. 73 p. 97 - 104
ISSN:
0031-8655
Resumen:
The fluorescence properties of 3-methylindole (MI), 3-indoleacetic acid (IAA), 3-indoleethyltrimethylammonium bromide (IETA), L-tryptophan (Trp), and tryptamine hydrochloride (TA) were studied in reverse micelles solutions made with the cationic surfactant benzylhexadecyldimethylammonium chloride (BHDC) in benzene as a function of the molar ratio water/surfactant R (= [H2O]/[BHDC]). The fluorescence quenching of the model compound MI by benzene in cyclohexane solutions and by BHDC in benzene solutions were also studied in detail. The fluorescence of MI in benzene is characteristic of a charge-transfer exciplex. The exciplex is quenched by the presence of BHDC, due to the interactions of the surfactant ion pairs with the polar exciplex. In reverse micelle solutions at low R values, all the indoles show exciplex type fluorescence. As R increases, the fluorescence behavior strongly depends on the nature of the indole derivative. The anionic IAA remains anchored to the cationic interface and its fluorescence is quenched upon water addition due to the increases of interfaces micropolarity. For IETA, TA, and Trp an initial fluorescence quenching is observed increasing R, but a fluorescence recovery is observed at R > 5, indicating a probe partition between the micellar interface and the water pool. For the neutral MI, the fluorescence changes with R indicate the partition of the probe between the micellar interface and the bulk benzene pseudophase. A simple two-site model is proposed for the calculation of the partition constants K as a function of R. In all cases, the calculation showed that even at the highest R value, about 90% of the indoles molecules remain associated at the micellar interface.
