Biological dissolution and activity of the Allende meteorite

Abstract

This paper reports on the effect of the Allende meteorite on the integrity of biological material and addresses the question whether it can induce cell damage via oxidative stress and cell mortality. The reaction mechanisms addressed herein are studied using electron-paramagnetic resonance spectroscopy (EPR), high-resolution transmission electron microscopy, scanning electron microscopy and energy dispersive spectroscopy, high-resolution X-ray diffraction, and the assays for thiobarbituric acid reactive substances (TBARS) and cell viability using 3-(4,5)-dimethylthiazol-2-yel-2,5-diphenyltetrazolium bromide (MTT bromide). As determined by the TBARS assay, Allende specimens induced cell damage via oxidative stress. The contents of TBARS in suspensions containing 1000 ppm of Allende and Fe 1– x S were 6.8 ± 0.7 and 5.8 ± 0.6 nmol/mg protein, respectively. EPR experiments conducted on reaction mixtures containing Allende, 5,5-dimethyl-1-pyrroline- N -oxide (DMPO), and H 2 O 2 showed a quartet signal, a 1:2:2:1 intensity, and hyperfine coupling constants corresponding to a N = 1.49 mT and a H = 1.49 mT, a signature of the DMPO-OH adduct. The intensity of the signal depended on the concentration of the solids in suspension, while the formation of DMPO-OH was limited by H 2 O 2 . Experiments were conducted to test for the production of the DMPO-OH adduct from ferric ions, and the plausible generation of HO • . The role of ethanol (CH 3 CH 2 OH) as scavenger of HO • in Allende-DMPO suspensions was addressed. Results showed a six-line spectra, with hyperfine coupling constants a N = 15.8 G, a H = 22.6 G, and g = 2.0059, consistent with the formation of the DMPO-CH(OH)-CH 3 adduct, but not DMPO-OCH 2 CH 3 . We explain these findings as the result of formation of HO • onto (or in proximity to) the mineral surface, with CH 3 CH 2 OH competing with DMPO for HO ∞ , and ferric iron playing a lesser role in DMPO transformation. Our findings are congruent with reported radical-scavenging experiments for pyrite under anoxic conditions, concluding the formation of HO ∞ at surface defect sites. Experiments conducted in Allende–desferrioxamine B(DFO-B) suspensions showed the inhibition of the formation of HO • , by means of decreases in the DMPO-OH adduct signal, accounted for by the reaction between Fe(II) and HO • to form Fe(III) and competing reaction mechanisms at the structural Fe centers, confirming that the production of HO ∞ radicals is associated with iron centers and contributes to mineral dissolution. Small-sized magnetite domains present were recognized as catalytic sites for the production of HO ∞ radicals. The γ-Fe 3 O 4 domains present in the Allende matrix exhibited a submicron range, an elongated-hexagonal habit, and a high degree of crystallinity, supporting the presence of biogenic γ-Fe 3 O 4 . Cell viability was found to be susceptible to the distribution and atomic environment of structural Fe.