África Yebra-Rodríguez

Black soiling of an architectural limestone during two-year term exposure to urban air in the city of Granada (S Spain).

A two-year term aging test was carried out on a building limestone under different urban conditions in the city of Granada (Southern Spain) to assess its Cultural Heritage sustainability. For this purpose stone tablets were placed vertically at four sites with contrasting local pollution micro-environments and exposure conditions (rain-sheltered and unsheltered). The back (rain-sheltered) and the front (rain-unsheltered) faces of the stone tablets were studied for each site. The soiling process (surface blackening) was monitored through lightness (ΔL*) and chroma changes (ΔC*). Additionally atmospheric particles deposited on the stone surfaces and on PM10 filters during the exposure time were studied through a multianalytical approach including scanning electron microscopy (SEM-EDX), transmission electron microscopy (TEM) and micro-Raman spectroscopy. The identified atmospheric particles (responsible for stone soiling) were mainly soot and soil dust particles; also fly ash and aged salt particles were found. The soiling process was related to surface texture, exposure conditions and proximity to dense traffic streets. On the front faces of all stones, black soiling and surface roughness promoted by differential erosion between micritic and sparitic calcite were noticed. Moreover, it was found that surface roughness enhanced a feedback process that triggers further black soiling. The calculated effective area coverage (EAC) by light absorbing dust ranged from 10.2 to 20.4%, exceeding by far the established value of 2% EAC (limit perceptible to the human eye). Soiling coefficients (SC) were estimated based on square-root and bounded exponential fittings. Estimated black carbon (BC) concentration resulted in relatively similar SC for all studied sites and thus predicts the soiling process better than using particulate matter (PM10) concentration.

High dietary intake of retinol leads to bone marrow hypoxia and diaphyseal endosteal mineralization in rats

Vitamin A (retinol) is the only molecule known to induce spontaneous fractures in laboratory animals and we have identified retinol as a risk factor for fracture in humans. Since subsequent observational studies in humans and old animal data both show that high retinol intake appears to only have small effects on bone mineral density (BMD) we undertook a mechanistic study of how excess retinol reduces bone diameter while leaving BMD essentially unaffected. We fed growing rats high doses of retinol for only 1 week. Bone analysis involved antibody-based methods, histology, pQCT, biomechanics and bone compartment-specific PCR together with Fourier Transform Infrared Spectroscopy of bone mineral. Excess dietary retinol induced weakening of bones with little apparent effect on BMD. Periosteal osteoclasts increased but unexpectedly endosteal osteoclasts disappeared and there was a reduction of osteoclastic serum markers. There was also a lack of capillary erythrocytes, endothelial cells and serum retinol transport protein in the endosteal/marrow compartment. A further indication of reduced endosteal/marrow blood flow was the increased expression of hypoxia-associated genes. Also, in contrast to the inhibitory effects in vitro, the marrow of retinol-treated rats showed increased expression of osteogenic genes. Finally, we show that hypervitaminotic bones have a higher degree of mineralization, which is in line with biomechanical data of preserved stiffness in spite of thinner bones. Together these novel findings suggest that a rapid primary effect of excess retinol on bone tissue is the impairment of endosteal/marrow blood flow leading to hypoxia and pathological endosteal mineralization.

Contribution of the Microbial Communities Detected on an Oil Painting on Canvas to Its Biodeterioration

In this study, we investigated the microbial community (bacteria and fungi) colonising an oil painting on canvas, which showed visible signs of biodeterioration. A combined strategy, comprising culture-dependent and -independent techniques, was selected. The results derived from the two techniques were disparate. Most of the isolated bacterial strains belonged to related species of the phylum Firmicutes, as Bacillus sp. and Paenisporosarcina sp., whereas the majority of the non-cultivable members of the bacterial community were shown to be related to species of the phylum Proteobacteria, as Stenotrophomonas sp. Fungal communities also showed discrepancies: the isolated fungal strains belonged to different genera of the order Eurotiales, as Penicillium and Eurotium, and the non-cultivable belonged to species of the order Pleosporales and Saccharomycetales. The cultivable microorganisms, which exhibited enzymatic activities related to the deterioration processes, were selected to evaluate their biodeteriorative potential on canvas paintings; namely Arthrobacter sp. as the representative bacterium and Penicillium sp. as the representative fungus. With this aim, a sample taken from the painting studied in this work was examined to determine the stratigraphic sequence of its cross-section. From this information, “mock paintings,” simulating the structure of the original painting, were prepared, inoculated with the selected bacterial and fungal strains, and subsequently examined by micro-Fourier Transform Infrared spectroscopy, in order to determine their potential susceptibility to microbial degradation. The FTIR-spectra revealed that neither Arthrobacter sp. nor Penicillium sp. alone, were able to induce chemical changes on the various materials used to prepare “mock paintings.” Only when inoculated together, could a synergistic effect on the FTIR-spectra be observed, in the form of a variation in band position on the spectrum.

Chemical Purity of Shewanella oneidensis-Induced Magnetites

Magnetite is a common iron oxide produced both inorganically and biogenically. Biologically-induced magnetite is often originated, under appropriate conditions, as a result of the Fe3+ reduction by dissimilatory iron reducing bacteria, which are usually found in anoxic environments or at the oxic-anoxic interface. Such a Fe3+ bioreduction occurs upon this cation acting as an electron acceptor of an anaerobic respiration, thus creating favorable conditions for magnetite precipitation. This biologically-induced magnetite is an important biomineral in the environments inhabited by iron reducing bacteria. The presence of a variety of cations may influence both the biomineralization process and the resulting biomineral, however this phenomenon has not been investigated extensively. In the present study, we study the effect on the magnetite biomineralization process of the presence of calcium, magnesium and manganese in the culture medium where Shewanella oneidensis lives. We also test the incorporation of these cations into the crystalline structure of inorganic and biogenic magnetite induced by S. oneidensis. According to our findings, manganese ions likely become incorporated into the crystal structure of biologically produced magnetites, while magnesium ions are incorporated in inorganic magnetites, and calcium ions are excluded from the crystal structure of both inorganic and biotic magnetites. We hypothesize that the incorporation of cations into magnetite depends not only on the relative cation radii, but also on the mechanisms of magnetite formation.

Effect of calcination temperature of a copper ferrite synthesized by a sol-gel method on its structural characteristics and performance as Fenton catalyst to remove gallic acid from water

A copper ferrite synthesized by a sol-gel combustion method was calcined at different temperatures up to 800°C, determining changes in its structural characteristics and magnetic measurements and studying its catalytic performance in gallic acid removal by Fenton reaction. The main objective was to study the effect of the calcination temperature of copper ferrite on its crystalline phase formation and transformation, activity and metal ion leaching. The cubic-to-tetragonal transformation of the spinel occurred via its reaction with the CuO phase, displacing Fe3+ ions in B (octahedral) sites out of the spinel structure by the following reaction: 2Fe3+B+3CuO→Fe2O3+3Cu2+B. The catalysts showed superparamagnetic or substantial superparamagnetic behaviour. At higher calcination temperatures, catalyst activity was lower, and Cu ion leaching was markedly decreased. There was no Fe ion leaching with any catalyst. The as-prepared catalyst showed better catalytic performance than a commercial copper ferrite. Leached Cu ions acted as homogeneous catalysts, and their contribution to the overall removal mechanism was examined. Cu2O present in the as-prepared catalysts made only a small contribution to their activity. Finally, the reutilization of various catalysts was studied by performing different catalytic cycles.

Thermooxidative degradation of injection-moulded sepiolite/polyamide 66 nanocomposites

Abstract Clay/polymer nanocomposites (CPN) exhibit improved technical properties compared to their microand macro-counterparts. Nevertheless, thermal degradation of CPN may limit the applicability of these hybrid materials. In this paper accelerated ageing (110°C and 150°C) was performed in injection moulded pure polyamide 66 (PA66-S-0 samples) and polyamide 66 reinforced with 5 wt.% sepiolite (PA66-S-5 samples) CPN. Polymer degradation was monitored by the amount of newly formed carbonyl bonds. The carbonyl indices obtained indicate that degradation occurs to a greater extent as the temperature of the ageing process increases. Moreover, the degradation increases with time at the highest treatment temperature (150°C). On the other hand, the occurrence of carbonaceous silicates in the nanocomposite samples at high temperatures yields greater thermal stability of sepiolite/PA66 nanocomposites compared to pure PA66. Furthermore, the sepiolite nanofibres maintain their position in the reticulated semicrystalline structure. In agreement with those results, differential scanning calorimetry and X-ray diffraction analyses show that the motion of the amide groups in the polymer chains are constrained by the well dispersed sepiolite.