Paz del Angel

Cinnabar-Preserved Bone Structures from Primary Osteogenesis and Fungal Signatures in Ancient Human Remains

The Red Queen remains (700 A.C.) found at Palenque, México, are examples of cinnabar (HgS) application to royal remains during pre-Hispanic times. The Red Queen remains are those of a ca. 30–35-yr-old female and present a striking similarity to the remains of another Mayan woman found at Copan, Honduras. Thus, covering the remains of royal women with HgS may have been a common practice in the Mayan civilization. High resolution microdiffraction and microscopic analysis of the Red Queen remains showed the presence of nanotubular organic minerals comparable in composition and molecular dimensions to collagen fibrils, and in spatial ordering to collagen fiber networks. Fungal structures are rare in the geological record because of poor preservation potential. Micrographs revealed the preservation of fungal signatures, with morphology comparable to parasitic fungal-coral matrix associations, consistent with the idea that fungal remains can be preserved in environments which contain high Hg concentrations. The well-preserved signatures of fungus-animal interactions and primary osteogenesis in the Red Queen remains are attributed to the long-term antibacterial activity of HgS and the association of sulfur components with nanotubular structures.

Biological dissolution and activity of the Allende meteorite

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.

Cracking of n-pentane over ZSM-5 obtained from different seed crystals

The influence of the seed nature upon the crystalline and textural characteristics and the catalytic performance of ZSM-5 samples obtained from different seed crystals has been determined. Differences in catalytic behavior can be related to the size of the crystalline agglomerates obtained.

Electron microscopy characterization of ferrisilicates synthesized with two different silicon sources

Ferrisilicates have been synthesized by isomorphous substitution of Al by Fe using two silicon sources, to determine the influence of the silicon nature. The X-ray results are similar to that of ZSM-5 zeolite, but SEM and TEM show that the samples are different.

Controlling the redox properties of nickel in NiO/ZrO2 catalysts synthesized by sol–gel

NiO–ZrO2 samples were prepared by the sol–gel method adjusting the nickel content to 3 and 10 wt% and varying the calcination temperature from 500 to 700 °C. The solids were characterized by X-ray diffraction, ultraviolet-visible diffuse reflectance spectroscopy (UV-vis DRS), X-ray photoelectron spectroscopy, high resolution transmission electron microscopy (HRTEM) and scanning and transmission electron microscopy (STEM). For the sample with 3 wt% Ni, diffraction lines related to cubic zirconia were only detected when calcined from 500 to 650 °C, a NiO crystalline phase as well as the transition phase from cubic to tetragonal zirconia appeared when calcined at 700 °C. UV-vis DRS and HRTEM results indicated the presence of a highly dispersed NiO phase at the nanometric scale throughout the main zirconia crystalline phase. The NiO crystalline phase was already detected for the sample with 10 wt% nickel content calcined at 500 °C. The NiO–ZrO2 interaction was modified by reducing the hydrolysis rate during synthesis leading to a sample with a high dispersion of Ni throughout ZrO2, thus modifying the reducibility of NiO. The NiO–ZrO2 samples were catalytically tested for the oxidative dehydrogenation of ethane as a model reaction. Prior to reaction, the calcined catalysts were pre-treated in situ under reducing and oxidant atmospheres to study their redox properties. As the NiO–ZrO2 interaction modifies the electronic properties of both nickel oxide and zirconia, ethane conversion and ethylene selectivity were strongly influenced not only by the nickel content and calcination temperature but also by the in situ pre-treatment before reaction. This effect was particularly evident in the sample prepared with a modified hydrolysis rate, which changed the redox properties of the NiO species.

Study of the Formation of WO x Nanostructures Supported on Zirconia Prepared by Different Synthesis Routes

Different synthesis procedures of Pt supported on tungstated zirconia catalysts (Pt/WO x -ZrO 2 ) were investigated with the aim to elucidate the different WO x nanostructures developed on the zirconia surface depending on the preparation route. Pt/WO x -ZrO 2 catalysts were synthesized by the coprecipitation and impregnation methods and pretreated by various procedures such as different calcinations temperatures or the use of reflux. The catalysts characterization was carried out by X-ray diffraction (XRD), Raman spectroscopy, transmission and scanning electron microscopy (TEM, SEM) and nitrogen physisorption, and the catalytic activity was evaluated in the n-hexane isomerization reaction. The results indicate that the development of active sites for isomerization of n-hexane is enhanced by the stabilization of the WO x nanostructures on the surface of zirconia, before the formation of the WO 3 crystallites, and it largely depends on the synthesis method.