Dp. Hessler et al., SOLVENT ISOTOPE EFFECT ON THE RATE CONSTANTS OF SINGLET-OXYGEN QUENCHING BY EDTA AND ITS METAL-COMPLEXES, Helvetica Chimica Acta, 77(3), 1994, pp. 859-868
The reactivity of singlet oxygen (O-2((1) Delta(g),)) with edta and it
s metal complexes with Al3+, CU2+, Fe3+, and Mn2+ was investigated. Th
e emission of singlet oxygen at 1270 nm in D2O was measured in order t
o determine the quenching efficiency of edta and edta-metal complexes
for different metal/edta ratios. The sum of the rate constants (k(r) k(q)) of the chemical reaction between singlet oxygen and the accepto
r (k(r)) and of the physical quenching of singlet oxygen by the accept
or (k(q)) was obtained by a Stern-Volmer analysis. Measurements of the
oxygen consumption in H2O were used to determine quantum yields of th
e sensitized photooxidation, and the combined results of these experim
ents allowed the determination of k(r) and k(q) separately. A strong i
sotope effect was observed between the deuterated and the hydrogenated
solvents. This effect was shown to be independent of the analytical p
rocedure used. The isotope effect, as well as the reactivity of edta a
nd its metal complexes, depend markedly on the complexed metal ion.