Solvent Isotope Effect on the Rate Constants of Singlet‐Oxygen Quenching by edta and Its Metal Complexes

Abstract

The reactivity of singlet oxygen (02('Ag)) with edta and its metal complexes with A13+, Cu2+, Fe3+, and Mn2+ was investigated. The emission of singlet oxygen at 1270 nm in D,O was measured in order to determine the quenching efficiency of edta and edta-metal complexes for different metal/edta ratios. The sum of the rate constants (kr + kq) of the chemical reaction between singlet oxygen and the acceptor (k,) and of the physical quenching of singlet oxygen by the acceptor (k,) was obtained by a Stern-Volmer analysis. Measurements of the oxygen consumption in H 2 0 were used to determine quantum yields of the sensitized photooxidation, and the combined results of these experiments allowed the determination of k, and k, separately. A strong isotope effect was observed between the deuterated and the hydrogenated solvents. This effect was shown to be independent of the analytical procedure used. The isotope effect, as well as the reactivity of edta and its metal complexes, depend markedly on the complexed metal ion.

Photo-oxidation and Photoreduction of Catechols by Chlorophyll Metabolites and Methylene Blue

“…38 It is a poor 1 O 2 scavenger, though some of its metal complexes (1:1 or 1:2 metal to EDTA) do scavenge at appreciable rates. 39 Further, EDTA would not be expected to react with any intermediate in dopamine oxidation to AC. Therefore, we used it in combination with dopamine, photosensitizer and red light to assess its effects on AC formation.…”

Physical Mechanisms of Generation and Deactivation of Singlet Oxygen

“…On the basis of these observations, the authors suggested that interactions of O 2 ( 1 Δ g ) with the lone electron pair of the amine are responsible for a CT-mediated physical deactivation process. Numerous systematic studies have been carried out since then, and it has been suggested that CT-induced physical quenching represents the main pathway of O 2 ( 1 Δ g ) deactivation by aliphatic and aromatic amines, ,− hydrazines, aliphatic and aromatic mono-, di-, and trisulfides, − phenols, , electron-rich naphthalene, , biphenyl, benzophenone, and benzene ,, derivatives; organic complexes of nickel , and cobalt , and other heavy-atom-containing aromatics; , inorganic anions such as azide, − iodide, bromide or superoxide; and numerous biological compounds, including derivatives of guanosine and vitamin B12, vitamin E, , chlorophylls, porphyrins, hydroxycinnamic acids, ascorbate, and amino acids . It was also suggested that CT effects might play a role in the deactivation of O 2 ( 1 Δ g ) by radicals with excited-state energies higher than 94 kJ mol -1 …”

“…On the basis of these observations, the authors suggested that interactions of O 2 ( 1 ∆ g ) with the lone electron pair of the amine are responsible for a CT-mediated physical deactivation process. Numerous systematic studies have been carried out since then, and it has been suggested that CT-induced physical quenching represents the main pathway of O 2 ( 1 ∆ g ) deactivation by aliphatic and aromatic amines, 127,[172][173][174][175][176][177][178][179][180][181][182][183][184][185][186][187][188] hydrazines, 189 aliphatic and aromatic mono-, di-, and trisulfides, [190][191][192][193][194][195] phenols, 196,197 electron-rich naphthalene, 198,199 biphenyl, 200 benzophenone, 201 and benzene 188,202,203 derivatives; organic complexes of nickel 204,205 and cobalt 206,207 and other heavy-atom-containing aromatics; 208,209 inorganic anions such as azide, [210][211][212] iodide,…”

“…Oliveros and Braun and co-workers 206 studied physical quenching of O 2 ( 1 ∆ g ) by metal complexes of ethylenediaminetetraacetic acid (EDTA). They observed rate constants significantly below the diffusion-controlled limit and an increase in the order…”

The Influence of the Donor Atom on the Chemiluminescence of Eu(III) Ions in the System Eu(II)/(III)-Ligand-H2O2

“…As they are very similar in character we conclude that in the systems containing the ligands used the process of decay of Eu(II) ions is similar to their decay in the fundamental system, OH À ) cannot be a source of detectable CL. Moreover, taking into account the fact that EDTA and its complexes with d-electron metals have been used as quenchers of singlet oxygen [14,15], and regarding the energy levels of singlet oxygen dimols ( 1 O 2 ) 2 and excited Eu(III) ions [5], the long time of emission in systems with cyclic and acyclic aminopolycarboxylic acids is a result of the energy transfer from dimers of singlet oxygen (products of the reaction of recombination of radicals [4,8,9,14]) to the complexed Eu(III) ions, similarly as it happens in the system with azide ions [5].…”