Quenching of Singlet Molecular Oxygen (1O2) by Azide Anion in Solvent Mixtures¶

Abstract

The azide ion is a strong physical quencher of singlet molecular oxygen (1O2) and is frequently employed to show involvement of 1O2 in oxidation processes. Rate constants (kq) for the quenching of 1O2 by azide are routinely used as standards to calculate kq values for quenching by other substrates. We have measured kq for azide in solvent mixtures containing deuterium oxide (D2O), acetonitrile (MeCN), 1,4‐dioxane, ethanol (EtOH), propylene carbonate (PC), or ethylene carbonate (EC), mixtures commonly used for many experimental studies. The rate constants were calculated directly from 1O2 phosphorescence lifetimes observed after laser pulse excitation of rose bengal (RB), used to generate 1O2. In aqueous mixtures with MeCN and carbonates, the rate constant increased nonlinearly with increasing volume of organic solvent in the mixtures. kq was 4.78 × 108M−1 s−1 in D2O and increased to 26.7 × 108 and 27.7 × 108M−1 s−1 in 96% MeCN and 97.7% EC/PC, respectively. However, in EtOH/D2O mixtures, kq decreased with increasing alcohol concentration. This shows that a higher solvent polarity increases the quenching efficiency, which is unexpectedly decreased by the proticity of aqueous and alcohol solvent mixtures. The rate constant values increased with increasing temperature, yielding a quenching activation energy of 11.3 kJ mol−1 in D2O. Our results show that rate constants in most solvent mixtures cannot be derived reliably from kq values measured in pure solvents by using a simple additivity rule. We have measured the rate constants with high accuracy, and they may serve as a reliable reference to calculate unknown kq values.

Identification of Ros Produced by Photodynamic Activity of Chlorophyll/Cyclodextrin Inclusion Complexes

“…Analogous indications have been obtained in this article by means of the use of different ROS quenchers (NaN 3 , DABCO, L‐histidine, SOD) in agreement with procedures suggested in the literature (riferimenti vari). In general, in the case of 1 O 2 quenchers , a significative decrease in the lifetime of singlet oxygen with different quenching rate constants is observed. Whereas, superoxide dismutase is known to catalyze the following dismutation reaction O 2 ˙ ● with quenching of superoxide anion species and H 2 O 2 production.…”

Determination of Singlet Oxygen and Electron Transfer Mediated Mechanisms of Photosensitized Protein Damage by Phosphorus(V)porphyrins

“…Thus, the effect of NaN 3 , a physical quencher of 1 O 2 , 26 on the photosensitized HSA damage by P(V)porphyrins for 30 min was examined ( Figure 5). In this figure, the relative HSA damage (D HSA ), which is determined to be 100% in the absence of NaN 3 , is presented.…”

Neutrophils Generate Microparticles during Exposure to Inert Gases Due to Cytoskeletal Oxidative Stress

“…When cell suspensions were exposed to air plus 690 kPa of N 2 in the presence of 2 mM azide or 1 mM ascorbate, agents that quench singlet O 2 , fluorescence was inhibited by 93.8 Ϯ 2.2% (n ϭ 3, p Ͻ 0.05) and 91.1 Ϯ 2.8% (n ϭ 6, p Ͻ 0.05), respectively (37,38). A comparable magnitude of inhibition occurred with similar studies carried out using argon (data not shown).…”