Solvent effects on reactions of singlet molecular oxygen, O-2((1)triangle(g)), with antimalarial drugs
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2004-11-01Metadata
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Lemp Miranda, Else
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Solvent effects on reactions of singlet molecular oxygen, O-2((1)triangle(g)), with antimalarial drugs
Abstract
Detection of O2(1 g) emission, λmax = 1270 nm, following laser excitation and steady-state methods were employed to measure
total reaction rate constants, kT, for the reaction between singlet oxygen and the antimalarial drugs quinine (QU), quinacrine (QC),
chloroquine (CQ) and amodiaquine (AQ) in several solvents. Values for kT range from 0.45 ± 0.03 × 107M−1 s−1 for AQ in benzene to
25.1 ± 0.88 × 107M−1 s−1 for CQ in N,N-dimethylformamide. Analysis of solvent effect on kT for QU, QC, and CQ by using the LSER
formalism indicates that singlet oxygen deactivation by these drugs is accelerated by solvents with large π∗ values and hydrogen bond
acceptor (HBA) properties and is inhibited by hydrogen bond donors (HBD) solvents. This result support the formation of an exciplex
intermediate of charge transfer character, as proposed for reactions of tertiary amines with singlet oxygen, process largely governed by
physical quenching. AQ behaves in a different manner. The LSER equation for this drug shows that kT increases in solvents with large π∗
values and diminishes in HBD solvents. In this case, reaction mechanism probably involves a partially concerted cycloaddition of singlet
oxygen to the aminophenolic ring in position 4.
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URI: https://repositorio.uchile.cl/handle/2250/121701
DOI: DOI: 10.1016/j.jphotochem.2004.05.016
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JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY A-CHEMISTRY Volume: 168 Issue: 1-2 Pages: 91-96 Published: NOV 1 2004
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