Examinando por Autor "Escobar, Carlos A."
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Ítem 1,2,3-Benzotriazole derivatives adsorption on Cu(1 1 1) surface: A DFT study(Elsevier B.V., 2017-12) Saavedra-Torres, Mario; Escobar, Carlos A.; Ocayo, Fernanda; Tielens, Frederik; Santos, Juan C.In the context of copper corrosion passivation, the adsorption of benzotriazole (BTAH) and its derivatives: 5-Methyl, 5-Amine, 1-Amine, 1-Methyl on a Cu(1 1 1) surface was investigated using periodic density functional (DFT) calculations. The results were contrasted with experimental ASTM protocols. Adsorption of BTAH and radical (BTA●) forms, as well as solvent effect were evaluated. The Cu-N interaction provides stable complexes with adsorption over top sites. Radical forms yielded more stable complex. Their adsorption energies correlate with the substituent position and electronic features. And finally, a strong interaction was obtained when the charge transfer goes from surface to adsorbate. © 2017Ítem Antibacterial Effect of Luma apiculata (DC.) Burret Extracts in Clinically Important Bacteria(International Journal of Microbiology, 2019) Araya-Contreras, Tiare; Veas, Rhonda; Escobar, Carlos A.; Machuca, Pamela; Bittner, MauricioNosocomial infections caused by bacteria are one of the main public health problems. Moreover, the resistance to antibiotics by these bacteria makes it necessary to find new treatments to fight them. Objective. To evaluate the antibacterial activity of Luma apiculata (DC.) Burret extracts on bacteria of clinical importance. Materials and Methods. In this study, extracts were obtained at room temperature by successive extraction of L. apiculata leaves, flowers, and branches and treated separately with solvents of ascending polarity (i.e., hexane, methylene dichloride, ethyl acetate, ethanol, methanol, and water) to extract the compounds depending on their polarity. Then, the extract's antibacterial activity was tested against Staphylococcus aureus, Staphylococcus epidermidis, Staphylococcus saprophyticus, Enterococcus sp, Acinetobacter baumanii, Pseudomonas aeruginosa, and Escherichia coli. Results. The hexane extract of L. apiculata leaves resulted to be active against all bacteria tested. Among them, S. aureus showed to be the more susceptible, showing a minimum inhibitory concentration (MIC) of 120 μg/ml. In addition, a growth curve was performed, and colonies were counted. A decrease in bacterial growth was observed when the hexane extract of L. apiculata leaves was added. Besides, the hexane extracts of L. apiculata flowers resulted to be active against all Gram-positive tested bacteria. However, at higher concentrations, this extract resulted inactive for the Gram-negative bacteria tested. The hexane extract of L. apiculata branches resulted to be inactive in all cases. The extracts obtained treating separately leaves, flowers, or branches with solvents of major polarity than the hexane in a successive extraction of ascending polarity methodology resulted also to be inactive as an antimicrobial against all bacteria tested. Discussion/Conclusion. The hexane extract of L. apiculata leaves showed the lower MIC against S. aureus when compared with extracts obtained from other parts of the plant. The growth curve and the colonies count suggest a bacteriostatic activity of the L. apiculata leaves extract against Staphylococcus aureus.Ítem Chalcone-induced apoptosis through caspase-dependent intrinsic pathways in human hepatocellular carcinoma cells(MDPI AG, 2016-02) Ramirez-Tagle, Rodrigo; Escobar, Carlos A.; Romero, Valentina; Montorfano, Ignacio; Armisén, Ricardo; Borgna, Vincenzo; Jeldes, Emanuel; Pizarro, Luis; Simon, Felipe; Echeverria, CesarHepatocellular carcinoma (HCC) is one of the most commonly diagnosed cancers worldwide. Chemoprevention of HCC can be achieved through the use of natural or synthetic compounds that reverse, suppress or prevent the development of cancer progression. In this study, we investigated the antiproliferative effects and the mechanism of action of two compounds, 2,3,41 -trimethoxy-21 -hydroxy-chalcone (CH1) and 31 -bromo-3,4-dimethoxy-chalcone (CH2), over human hepatoma cells (HepG2 and Huh-7) and cultured mouse hepatocytes (HepM). Cytotoxic effects were observed over the HepG2 and Huh-7, and no effects were observed over the HepM. For HepG2 cells, treated separately with each chalcone, typical apoptotic laddering and nuclear condensation were observed. Additionally, the caspases and Bcl-2 family proteins activation by using Western blotting and immunocytochemistry were studied. Caspase-8 was not activated, but caspase-3 and -9 were both activated by chalcones in HepG2 cells. Chalcones also induced reactive oxygen species (ROS) accumulation after 4, 8 and 24 h of treatment in HepG2 cells. These results suggest that apoptosis in HepG2 was induced through: (i) a caspase-dependent intrinsic pathway; and (ii) by alterations in the cellular levels of Bcl-2 family proteins, and also, that the chalcone moiety could be a potent candidate as novel anticancer agents acting on human hepatomas.Ítem On the reduction of 4-oxo-4h-benzopyran-3-carbaldehydes : global and local electrophilicity patterns(Sociedad Chilena de Química, 2004) Araya Maturana, Ramiro; Heredia Moya, Jorge; Escobar, Carlos A.; Pérez, PatriciaThe theoretical global and local electrophilicity patterns of substituted and chelated 4-oxo-4H-benzopyran-3-carbaldehydes (formylchromones) have been evaluated using the electrophilicity index proposed by Parr et al [J. Am. Chem. Soc. 1999, 121, 1922]. The complexation of formylchromones with aluminum predicts a strong electrophilic character of these compounds against nucleophiles. Local response at the active sites may also be assessed in terms of a global contribution described by the global electrophilicity, and a local contribution described by the variations in electrophilic Fukui function at those sites. The highest local electrophilicity is found at the formyl group of the chelated formylchromones, in spite of that, the highest positive charge is located on the pyrone carbonyl group. This result is consistent with the experimental observed reactivity displayed by 4-oxo-4H-benzopyran-3-carbaldehydes in the presence of 2-propanol and alumina.