Understanding the effect of mechanical strains on the catalytic activity of transition metals.

The effect of elastic strains on the catalytic activity for the hydrogen evolution reaction (HER) and the oxygen reduction reaction (ORR) was analyzed on thirteen late transition metals: eight (111) surfaces of fcc metals (Ni, Cu, Pd, Ag, Pt, Au, Rh, Ir) and five (0001) surfaces of hcp metals (Co, Zn, Cd, Ru, and Os). The corresponding adsorption energies for the different intermediate reactions up to strains dictated by the mechanical stability limits were previously obtained by means of density functional theory calculations. It was found that the elastic strains can be used to tune the catalytic activity of different metals by reducing the energy barrier of the rate limiting step and even to reach the cusp of the volcano plot. The largest changes in catalytic activity with strain for the HER were found in Pt, Au, and Ir while Co and Ni were very insensitive to this strategy. In the case of the ORR, the catalytic activity of Au could be enhanced by the application of tensile strains while that of Cu, Ni, Pt, Pd, Rh, Co, Ru, and Os was improved by the application of compressive strains. However, the catalytic activity of Ir was rather insensitive to mechanical deformations. Elastic strains were able to modify the rate limiting reaction in Au, Pt, Ag, and Os and it was possible to achieve the cusp of the volcano plot in these metals. Final, mechanical instabilities were attained at small strains in Zn and Cd, which did not lead to significant changes in the catalytic activity for the HER and the ORR. These results provide a framework to systematically investigate the application of elastic strains in the design of new catalysts.

The effect of elastic strains on the adsorption energy of H, O, and OH in transition metals.

The influence of elastic strains on the adsorption of H, O, and OH on the (111) surfaces of 8 fcc (Ni, Cu, Pd, Ag, Pt, Au, Rh, Ir) and on the (0001) surfaces of 3 hcp (Co, Zn, Cd) transition metals was analyzed by means of density functional theory calculations. To this end, surface slabs were subjected to different strain states (uniaxial, biaxial, shear, and a combination of them) up to strains dictated by the mechanical stability limits indicated by phonon calculations. It was found that the adsorption energy followed the predictions of the d-band theory but - surprisingly - the variations in the adsorption energy only depended on the area of the adsorption hole and not on the particular elastic strain tensor applied to achieve this area. The analysis of the electronic structure showed that the applied strains did not modify the shape of the Projected Density of States (PDOS) of the d-orbitals of the transition metals but only led to a shift in the energy levels. Moreover, the presence of the adsorbates on the surfaces led to negligible changes in the PDOS. Thus, the adsorption energies were a function of the Fermi energy which in turn was associated with the change of the area of the adsorption through a general linear law that was valid for all metals. The information in this paper allows the immediate and accurate estimation of the effect of any elastic strain on the adsorption energies of H, O, and OH in 11 transition metals with more than half-filled d-orbitals.

Predictive markers of response to neoadjuvant therapy in rectal cancer.

BACKGROUND: Neoadjuvant therapy followed by radical surgery is the standard treatment in locally advanced rectal cancer. It is important to predict the response because the treatment has side effects and is costly. The aim of this study was to establish the relationship among clinical, pathologic, and molecular biomarkers and the response to neoadjuvant therapy. METHOD: A total of 130 patients with locally advanced mid and low rectal cancer who underwent long-course radiotherapy with 5-FU based chemotherapy followed by radical surgical resection were included in the study. Clinical and pathologic data were collected. Paraffin-embedded sections obtained in diagnostic biopsies were assessed by immunohistochemical staining for molecular markers and classified using a semiquantitative method. Results were related with T-downstaging and tumor regression grade using Mandard scoring system on surgical specimens. RESULTS: Pathologic complete response was found in 19 patients (14.6%), while in another 18 (13.8%) only minor residual disease was seen in the rectal wall. T-downstaging was observed in 63 (48.5%). The average of lymph node retrieval in the surgical specimens was 9.4. Regarding predictive markers of response, there was significant correlation between the expression of B-cell lymphoma 2 (P = 0.005), ß-catenin (P = 0.03), vascular endothelial growth factor (P = 0.048) and apoptotic protease activating factor 1 (P = 0.03), tumor differentiation grade (P < 0.001), and response in the univariate analysis. T-downstaging was associated with vascular endothelial growth factor expression (P = 0.03) and tumor differentiation grade (P < 0.001). Significant parameters found in the multivariate analysis were tumor differentiation grade and Bcl-2 expression. CONCLUSIONS: Pathologic and molecular biomarkers in the diagnostic biopsies may help us predict tumor response to chemoradiation in rectal cancer patients.

Evaluation of the Bioaccessible Fraction of T-2 Toxin from Cereals and Its Effect on the Viability of Caco-2 Cells Exposed to Tyrosol.

The bioaccessibility of mycotoxins is an important factor that has to be considered when assessing the risk they pose to human health. Bioactive compounds like phenolics could play a protective role against the toxic effects of contaminants. In this work, the bioaccessible fraction of the T-2 toxin (T-2) contained in breakfast cereals and its effect on the viability of Caco-2 cells were investigated. Furthermore, the effect of tyrosol (a polyphenol abundant in EVOO) on T-2-induced cytotoxicity was evaluated in the same cell line. After standardized in vitro gastrointestinal digestion, the T-2 toxin was released from T-2-spiked breakfast cereals and further quantified by UHPLC-MS/MS. The bioaccessible fraction of T-2 was 51 ± 4%. The cell viability study was performed by pre-treating the cells for 24 h with tyrosol (25, 50 and 100 µM) and subsequently adding T-2 at 15 nM or by treating the cells with a combination of tyrosol and T-2. In the simultaneous treatment, 25 µM tyrosol prevented the toxic effects produced by the exposure to T-2 at 15 nM; however, cytotoxic effects were observed for the other combinations tested. The pre-treatment of Caco-2 cells with tyrosol did not attenuate the cytotoxic effects caused by exposure to T-2. These results suggest that tyrosol at low concentrations (25 µM) could exert a cytoprotective effect on Caco-2 cells against 15 nM T-2 when administered simultaneously with T-2. However, more studies are required to corroborate this hypothesis.

Effect of Phenolic Extract from Red Beans (Phaseolus vulgaris L.) on T-2 Toxin-Induced Cytotoxicity in HepG2 Cells.

Red beans contain human bioactive compounds such as polyphenols. Several in vitro studies have proposed the natural compounds as an innovative strategy to modify the toxic effects produced by mycotoxins. Hence, in this work, a complete investigation of the polyphenolic fraction of red beans was performed using a Q-Orbitrap high-resolution mass spectrometry analysis. Notably, epicatechin and delphinidin were the most detected polyphenols found in red bean extracts (3.297 and 3.108 mg/Kg, respectively). Moreover, the red bean extract was evaluated against the T-2 toxin (T-2) induced cytotoxicity in hepatocarcinoma cells (HepG2) by direct treatment, simultaneous treatment, and pre-treatment assays. These data showed that T-2 affected the cell viability in a dose-dependent manner, as well as observing a cytotoxic effect and a significant increase in ROS production at 30 nM. The simultaneous treatment and the pre-treatment of HepG2 cells with red bean extract was not able to modify the cytotoxic T-2 effect. However, the simultaneous treatment of T-2 at 7.5 nM with the red bean extract showed a significant decrease in ROS production, with respect to the control. These results suggest that the red bean extract could modulate oxidative stress on HepG2 cells.