Free Radical Generation at the Solid/Liquid Interface in Iron Containing Minerals

Abstract

The potential for free radical release has been measured by means of the spin trapping technique on three kinds of iron containing particulate: two asbestos fibers (chrysotile and crocidolite); an iron-exchanged zeolite and two iron oxides (magnetite and haematite). DMPO (5,5'-dimethyl-1-pirroline-N-oxide), used as spin trap in aqueous suspensions of the solids, reveals the presence of the hydroxyl and carboxylate radicals giving rise respectively to the two adducts [DMPO-OH] and [DMPO-CO2], each characterized by a well-defined EPR spectrum. Two target molecules have been considered: the formate ion to evidence potential for hydrogen abstraction in any biological compartment and hydrogen peroxide, always present in the phagosome during phagocytosis. The kinetics of decomposition of hydrogen peroxide has also been measured on all solids. Ferrozine and desferrioxamine, specific chelators of Fe(II) and Fe(III) respectively, have been used to remove selectively iron ions. Iron is implicated in free radical release but the amount of iron at the surface is unrelated to the amount of radicals formed. Only few surface ions in a particular redox and coordination state are active. Three different kinds of sites have been evidenced: one acting as H abstracter, the other as a heterogeneous catalyst for hydroxyl radical release, the third one related to catalysis of hydrogen peroxide disproportionation. In both mechanisms of free radical release, the Fe-exchanged zeolite mimics the behaviour of asbestos whereas the two oxides are mostly inert. Conversely magnetite turns out to be an excellent catalyst for hydrogen peroxide disproportionation while haematite is inactive also in this reaction. The results agree with the implication of a radicalic mechanism in the in vitro DNA damage and in the in vivo toxicity of asbestos.

Analysis of the biological and chemical reactivity of zeolite-based aluminosilicate fibers and particulates.

“…The small amounts of hydroxyl radicals produced relative to the surface iron for all samples show that not all iron species on a zeolite surface are Fenton active. This is supported by results from Fubini and co-workers (55)(56)(57), who have argued that only a few surface iron species on mineral samples are in the right redox and coordination state to be active in the hydroxyl radical generation. This correlates well with the various coordination environments (and their respective abundances) that a zeolite provides for binding iron.…”

Carbon in Intimate Contact with Quartz Reduces the Biological Activity of Crystalline Silica Dusts

“…21 The spectra were recorded with the following instrument setting: scan range, 400 G; receiver gain, 1*10 4 ; microwave power, 10 mW; modulation amplitude, 1G; scan time, 80 s. Three scans were usually performed.…”

In vitro cellular responses to silicon carbide particles manufactured through the Acheson process: Impact of physico-chemical features on pro-inflammatory and pro-oxidative effects

“…This SiC I atypical profile could be explained on the one hand by the presence of crystallized silica (quartz and cristobalite) with high free carbon levels, and on the other hand by its high content of iron impurities (Table 1) Governa et al, 2005;IARC, 1996). It has been well described in the literature that there is a relationship between the presence of surface transition metal ions (especially iron) and cellular responses (Fubini et al, 1995b;Pritchard et al, 1996;Aust et al, 2000), especially for free radical generation (Fubini and Hubbard, 2003;Fenoglio et al, 2001;van Maanen et al, 1999;Turci et al, 2011;Pourchez et al, 2012). Indeed iron is known to be a catalyst in the formation of several reactive oxygen species (Pierre and Fontecave, 1999) (Halliwell and Gutteridge, 1992).…”

“…However, it is interesting to note that both oxidized SiC C1 and SiC F1 particles treated at 1400°C, despite the presence of a silica cristobalite layer around SiC grains, presented a TNFα production equivalent to that of the negative control and significantly lower than their original counterparts. Some studies indicate that cristobalite originated by heating quartz at high temperature (>1300°C), as well heated cristobalite, exhibits higher hydrophobicity and lower amount of surface radicals (Fubini et al, 1995b(Fubini et al, , 1995a) if compared to other cristobalite samples, such as those originated from diatomaceous earth heated at 1000°C. Heated cristobalite also exhibits a lower toxicity in cell free tests .…”

“…Electron paramagnetic resonance (EPR) using the spin-trapping technique (Fubini et al, 1995b) was used to evaluate SiC particle potential to generate free radicals (hydroxyl radical HO • , carboxyl radical COO -) in aqueous suspensions. Each powder (45 mg) was suspended in a buffered solution (0.5M potassium phosphate buffer, pH 7.4) 0.15M of DMPO (5-5'-dimethyl-1-pirroline-Noxide).…”