O⁻₂ Decay Catalyzed by Cu²⁺ and Cu⁺ Ions in Aqueous Solutions: A Pulse Radiolysis Study for Atmospheric Chemistry

Abstract

Atmospheric Chemistry / Chemical Kinetics / Pulse Radiolysis / Thansition Metals IonsThe catalytic decay of 0; radicals due to Cu+ and Cu2+ ions in 0, saturated solutions of low ionic strength was studied by pulse radiolysis and computer simulation of the entire reaction mechanism. Phosphate was used as buffer and formate was used to convert OH radicals into 0;. At pH = 6, the very low solubility products of Cu2+ with OH-and PO:-limited the copper concentration to the order of wM. In experiments with [Cu*+]>[O,], the rate constant k(Cu2+ +OF) = (8.0rt0.5).109M-'s-1 was determined. In systems with[O?] * [CuItot, steady state for the copper ions is attained with apparent first-order kinetics, which correlates k(Cu2+ +OF) with k(Cu+ +OF). The 0, decay rate decreased with increasing pH due to Cu2+ complexation with HPOZ-. Correspondingly the pK(CuHP04) was found to be -4.Ok0.2 under the assumption that k(CuHP04+O;)S0.01 *k(Cu2+ +O;). With this value, k(Cu+ +O;) could be determined as (9.4k0.8).lo9 M -' s-' by an iterative procedure. The consequences for the chemistry of atmospheric waters are discussed.

Light‐induced redox cycling of iron in circumneutral lakes

“…respectively, and values for and are taken from Zafiriou et al (1998) andvon Piechowski et al (1993), respectively; see also text. k k 2ϩ…”

“…Furthermore, we have considered reactions of O 2 ·Ϫ with inorganic, dissolved copper species (Sedlak and Hoigné 1993;von Piechowski et al 1993;Zafiriou et al 1998). These reactions (reactions 6 and 7) were, however, only included if they significantly improved the agreement between model and experimental data.…”

Insights into the Role of the Unusual Disulfide Bond in Copper-Zinc Superoxide Dismutase

“…The free copper concentration was determined by plotting the measured rate constant of the buffer solution alone into a standard curve (rate constant versus free copper concentration) or by dividing the difference in rate with and without EDTA by the rate constant for the dismutation of O 2 . by free copper (36). The reported data were averages of five measurements for every pH data point.…”

Enhanced Reactant-Contaminant Contact through the Use of Persulfate In Situ Chemical Oxidation (ISCO)

“…Copper (II) was used to dismutate superoxide (k = 8 x 10 9 M -1 s -1 ) as a means of confirming superoxide generation in base-activated persulfate systems (Piechowski et al, 1993;Zafiriou et al, 1998). The base-activated persulfate decomposition of HCA was repeated using 0.5 M persulfate, 1 M NaOH, 0.5 M H 2 O 2 +HO 2 -, and 2 µM HCA with the addition of 2 µM CuCl 2 to dismutate superoxide.…”

“…These results are consistent with the proposed mechanism of the oxidation of hydroperoxide to superoxide as persulfate is reduced to sulfate anion and sulfate radical; i.e., HCA degradation by superoxide proceeds in proportion to the mass of hydroperoxide added to the system. To distinguish between reduction of HCA by superoxide and reduction of HCA by any alkyl radicals that might be formed in the system, copper (II) was used to dismutate superoxide formed in reaction 7.2.3.4 (Piechowski et al, 1993;Zafiriou et al, 1998) (Figure 7.2.3.8). Without copper addition, the superoxide probe HCA degraded 70% within 5 min.…”