The oxidative dissolution of silver nanoparticles (AgNPs) plays an important role in the synthesis of well-defined nanostructured materials, and may be responsible for their activities in biological systems. In this study, we use stopped-flow spectrophotometry to investigate the kinetics and mechanism of the oxidative dissolution of AgNPs by H(2)O(2) in quasi-physiological conditions. Our results show that the reaction is first order with respect to both [Ag(0)] and [H(2)O(2)], and parallel pathways that involve the oxidation of H(2)O(2) and HO(2)(-) are proposed. The order of the reaction is independent of the size of the AgNPs (approximately 5-20 nm). The rate of dissolution increases with increasing pH from 6.0 to 8.5. At 298 K and I=0.1 M, the value of k(b) is five orders of magnitude higher than that of k(a) (where k(a) and k(b) are the rate constants for the oxidative dissolution of AgNPs by H(2)O(2) and HO(2)(-), respectively). In addition, the effects of surface coating and the presence of halide ions on the dissolution rates are investigated. A possible mechanism for the oxidative dissolution of AgNPs by H(2)O(2) is proposed. We further demonstrate that the toxicities of AgNPs in both bacteria and mammalian cells are enhanced in the presence of H(2)O(2), thereby highlighting the biological relevance of investigating the oxidative dissolution of AgNPs.
We have recently reported a kinetic and mechanistic study on oxidative dissolution of silver nanoparticles (AgNPs) by H(2)O(2). In the present study, the parameters that govern the dissolution of AgNPs by O(2) were revealed by using UV/Vis spectrophotometry. Under the same reaction conditions (Tris-HOAc, pH 8.5, I=0.1 M at 25 °C) the apparent dissolution rate (k(app)) of AgNPs (10±2.8 nm) by O(2) is about 100-fold slower than that of H(2)O(2). The reaction rate is first-order with respect to [Ag(0)], [O(2)], and [Tris](T), and inverse first-order with respect to [Ag(+)] (where [Ag(0)]=total concentration of Ag metal and [Tris](T)=total concentration of Tris). The rate constant is dependent on the size of AgNPs. No free superoxide (O(2)(-)) and hydroxyl radical (·OH) were detected by trapping experiments. On the basis of kinetic and trapping experiments, an amine-activated pathway for the oxidation of AgNPs by O(2) is proposed.
The kinetics of the reduction of cis-[Ru VI L(O) 2 ] 2ϩ (L = N,N,NЈ, diazaoctane-1,8-diamine) by [Ni(tacn) 2 ] 2ϩ (tacn = 1,4,7-triazacyclononane) and [Fe(H 2 O) 6 ] 2ϩ have been studied in aqueous acidic solutions. Both reactions have the following stoichiometry: 2M II ϩ cis-[Ru VI L(O) 2 ] 2ϩ ϩ 2H ϩ 2M III ϩ cis-[Ru IV L(O)(OH 2 )] 2ϩ (M = Ni or Fe). Two distinct steps were observed for both reactions and these are assigned to Ru VI Ru V and Ru V Ru IV . Both steps are first order in [Ru VI ] and [M II ]. For the reduction by [Ni(tacn) 2 ] 2ϩ , the activation parameters (I = [H ϩ ] = 0.1 mol dm Ϫ3 ) for the first step are ∆H ‡ = 13.4 ± 1.0 kJ mol Ϫ1 and ∆S ‡ = Ϫ111 ± 10 J mol Ϫ1 K Ϫ1 ; for the second reaction, ∆H ‡ = 28.5 ± 1.5 kJ mol Ϫ1 and ∆S ‡ = Ϫ110 ± 10 J mol Ϫ1 K Ϫ1 . The rate constant for the first step is independent of acid concentration, an outer-sphere mechanism is proposed and a selfexchange rate of 2 × 10 4 dm 3 mol Ϫ1 s Ϫ1 for the cis-[Ru VI L(O) 2 ] 2ϩ /cis-[Ru V L(O) 2 ] ϩ couple is estimated using the Marcus cross-relation. The rate constant of the second step increases with [H ϩ ] and it reaches saturation at high [H ϩ ].A mechanism involving a pre-equilibrium protonation of cis-[Ru V L(O) 2 ] ϩ followed by outer-sphere electron transfer is proposed. For the reduction by [Fe(H 2 O) 6 ] 2ϩ , rate constants for both steps are independent of acid concentration in the range of pH = 1-3. The activation parameters (I = 1.0 mol dm Ϫ3 , pH = 1.0) for the first step are ∆H ‡ = 32.5 ± 1.5 kJ mol Ϫ1 and ∆S ‡ = Ϫ52.5 ± 7 J mol Ϫ1 K Ϫ1 ; while for the second step, ∆H ‡ = 17.3 ± 1.2 kJ mol Ϫ1 and ∆S ‡ = Ϫ140 ± 13 J mol Ϫ1 K Ϫ1 . An outer-sphere mechanism is proposed for the first step and an inner-sphere mechanism is proposed for the second step.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.