Gold nanoparticle-initiated free radical oxidations and halogen abstractions

Abstract

We report on the use of EPR spectroscopy and spin trapping technique to detect free radical intermediates formed in the presence of gold nanoparticles. Phosphine- and amine-protected gold nanoparticles were found to initiate air oxidation of organic substrates containing active hydrogen atoms, such as amines and phosphine oxides. Nanoparticles protected by stronger bound ligands (e.g., thiols) were inactive in these reactions. We also found that gold nanoparticles are able to abstract a halogen atom from the halogenated compounds, presumably due to the high affinity of gold metal for halogens. Reaction of Au nanoparticles with chloroform showed an unusual inverse isotope effect. The trichloromethyl spin adduct was observed when Au nanoparticles were mixed with CDCl(3) but not with CHCl(3). This unexpected behaviour suggests that C-H bond breaking is not the rate-determining step in Au-initiated hydrogen abstraction.

Liquid phase oxidation of cyclohexane using bimetallic Au–Pd/MgO catalysts

“…However, It should be stressed that the spin trapping technique only allows for semi-quantitative determination of the spin adducts detected, and it is not a direct measurement of the actual amount of radical species present in solution. Therefore it is not possible to quantitatively correlate reactivity, or lifetime, of a radical to its correspondent spin adduct, but qualitatively only This is a consequence of various factors such as: the life-time of the spin adduct, the nature of the solvent, temperature, pH and importantly, the efficiency of the capture reaction which is different for each radical [35,36]. For example, literature values comparing the capture of ·OOH versus ·OH species for DMPO in aqueous media at room temepruare and pH close to neutrality indicated kinetics constants in the range of 10 1 and 10 9 M s -1 for ·OOH and ·OH respectively [37].…”

Insights into the Reaction Mechanism of Cyclohexane Oxidation Catalysed by Molybdenum Blue Nanorings

“…However, it should be underlined that the spin trapping technique only allows for semi-quantitative determination of the detected adducts. This is a consequence of the lifetime of the spin adduct, the nature of the solvent, the temperature as well as the efficiency of the capture reaction which is different for each radical [54]. Yet considering these limitations, a quantification of the relative amount of spin adducts is possible and was carried out (table 3) with the aim to estimate differences in peroxyl and alkoxyl radicals concentration for MB and T-MB.…”

On the application potential of gold nanoparticles in nanoelectronics and biomedicine

“…This latter suggestion is strongly supported by the fact that AuNPs themselves, in general, create ROS from dioxygen owing to their high surface/volume ratio (Nel et al 2006) and that the closely related 1.4 nm TPPstabilized gold clusters selectively catalyse the oxidation with O 2 , both in the gas phase (Turner et al 2008) and in solution (Ionita et al 2007). Furthermore, Au 55 clusters reveal a remarkable stability towards oxidation (Boyen et al 2002), which is most likely because of their closed-shell structure, a property that indicates that this cluster is an effective oxidation catalyst (Pina et al 2008).…”

“…Furthermore, Au 55 clusters reveal a remarkable stability towards oxidation (Boyen et al 2002), which is most likely because of their closed-shell structure, a property that indicates that this cluster is an effective oxidation catalyst (Pina et al 2008). Additionally, within the previously mentioned investigations on the selective oxidizing effect of Au 55 , it became apparent that thiol-stabilized AuNPs were inactive in this context, which is most likely due to the strong thiolate-gold bond between the ligand and the nanoparticle's surface (Ionita et al 2007). This result may further explain why upon pre-treatment of the cells with the thiol containing NAC and GSH before incubation with the nanoparticles the toxicity is reduced, i.e.…”