Examinando por Autor "Tiznado, W."
Mostrando 1 - 7 de 7
Resultados por página
Opciones de ordenación
Ítem Antioxidant activity and enzymatic of lichen substances: A study based on cyclic voltammetry and theoretical(Elsevier, 2023-02) Yañez, O.; Osorio, M.; Osorio, E.; Tiznado, W.; Ruíz, L.; García, C.; Nagles, O.; Simirgiotisx, M.; Castañeta, G.; Areche, C.; García-Beltrán, O.The antioxidant activity of nine lichen substances, including methylatrarate (1), methyl haematommate (2), lobaric acid (3), fumarprotocetraric acid (4), sphaerophorin (5), subsphaeric acid (6), diffractaic acid (7), barbatolic acid (8) and salazinic acid (9) has been determined through cyclic voltammetry. The compounds 1–4 presented slopes close to the Nernst constant of 0.059 V, indicating a 2H+/2e− relation between protons and electrons, as long as the compounds 5, 6, 7, 8, and 9 present slopes between 0.037 V and 0.032 V, indicating a 1H+/2e− relation between protons and electrons. These results show a high free radical scavenging activity by means of the release of H+, suggesting an important antioxidant capacity of these molecules. Theoretical calculations of hydrogen bond dissociation enthalpies (BDE), proton affinities (PA), and Proton Transfer (PT) mechanisms, at M06-2x/6-311+G(d,p) level complement the experimental results. Computations support that the best antioxidant activity is obtained for the molecules (3, 4, 5, 6, 7 and 8), that have a carboxylic acid group close to a phenolic hydroxyl group, through hydrogen atomic transfer (HAT) and sequential proton loss electron transfer (SPLET) mechanisms. Additional computations were performed for modelling binding affinity of the lichen substances with CYPs enzymes, mainly CYP1A2, CYP51, and CYP2C9*2 isoforms, showing strong affinity for all the compounds described in this study.Ítem Exploring the potential energy surface of small lead clusters using the gradient embedded genetic algorithm and an adequate treatment of relativistic effects(Royal Society of Chemistry, 2018) Rabanal-León, W.A.; Tiznado, W.; Osorio, E.; Ferraro, F.It is a well-known fact that theoretical methodologies play a crucial role to assure an adequate structural assignment of gas-phase clusters. Particularly, in heavy-element containing clusters the inclusion of relativistic effects (scalar and spin-orbit coupling) can significantly affect their chemistry. Therefore, these effects become the keystone on their structural determination. In our work, the way in which relativistic effects were treated, as well as their influence in the process of an adequate identification of lowest-energy isomer (the global minima-"GM"-energy structure), were evaluated in small lead clusters. The potential energy surfaces of small Pbn (n = 3-10) clusters was explored by means of the gradient embedded genetic algorithm program (GEGA). Subsequently, the most stable isomers were re-optimized incorporating relativistic effects through two different approximations: (i) using relativistic effective core potentials (RECPs) or pseudopotentials, which mimics the scalar and spin-orbit coupling relativistic effects (SR and SO) of the core electrons; and (ii) using relativistic Hamiltonians (with proper all-electron basis sets), like, the zeroth-order regular approximation (ZORA) to the Dirac equation, in which the scalar (SR) and spin-orbit coupling (SOC) relativistic effects were also included. The results evidence that methodologies including SOC effect allow to identify the GM energy structure correctly in all the studied cases. Besides, the GEGA algorithm, using a modest RECP, provides good initial structures that become GM after re-optimization at the SOC level.Ítem Persistent Planar Tetracoordinate Carbon in Global Minima Structures of Silicon-Carbon Clusters(MDPI, 2022-02) Leyva-Parra, L.; Inostroza, D.; Yañez, O.; Cruz, J.; Garza, J.; García, V.; Tiznado, W.Recently, we reported a series of global minima whose structures consist of carbon rings decorated with heavier group 14 elements. Interestingly, these structures feature planar tetracoordinate carbons (ptCs) and result from the replacement of five or six protons (H+ ) from the cyclopentadienyl anion (C5 H5− ) or the pentalene dianion (C8 H62− ) by three or four E2+ dications (E = Si–Pb), respec-tively. The silicon derivatives of these series are the Si3 C5 and Si4 C8 clusters. Here we show that ptC persists in some clusters with an equivalent number of C and Si atoms, i.e., Si5 C5, Si8 C8, and Si9 C9 . In all these species, the ptC is embedded in a pentagonal C5 ring and participates in a three-center, two-electron (3c-2e) Si-ptC-Si σ-bond. Furthermore, these clusters are π-aromatic species according to chemical bonding analysis and magnetic criteria.Ítem Planar Hexacoordinate Carbons: Half Covalent, Half Ionic(John Wiley and Sons Inc, 2021-04) Leyva-Parra, L.; Diego, L.; Yañez, O.; Inostroza, D.; Barroso, J; Vásquez-Espinal, A.; Merino, G.; Tiznado, W.Herein, the first global minima containing a planar hexacoordinate carbon (phC) atom are reported. The fifteen structures belong to the CE3M3+ (E=S–Te and M=Li–Cs) series and satisfy both geometric and electronic criteria to be considered as a true phC. The design strategy consisted of replacing oxygen in the D3h CO3Li3+ structure with heavy and less electronegative chalcogens, inducing a negative charge on the C atom and an attractive electrostatic interaction between C and the alkali-metal cations. The chemical bonding analyses indicate that carbon is covalently bonded to three chalcogens and ionically connected to the three alkali metals. © 2021 Wiley-VCH GmbHÍtem Study of the Differential Activity of Thrombin Inhibitors Using Docking, QSAR, Molecular Dynamics, and MM-GBSA(Public Library of Science, 2015-11) Mena-Ulecia, K.; Tiznado, W.; Caballero, J.Non-peptidic thrombin inhibitors (TIs; 177 compounds) with diverse groups at motifs P1 (such as oxyguanidine, amidinohydrazone, amidine, amidinopiperidine), P2 (such as cyano-fluorophenylacetamide, 2-(2-chloro-6-fluorophenyl)acetamide), and P3 (such as phenylethyl, arylsulfonate groups) were studied using molecular modeling to analyze their interactions with S1, S2, and S3 subsites of the thrombin binding site. Firstly, a protocol combining docking and three dimensional quantitative structure-activity relationship was performed. We described the orientations and preferred active conformations of the studied inhibitors, and derived a predictive CoMSIA model including steric, donor hydrogen bond, and acceptor hydrogen bond fields. Secondly, the dynamic behaviors of some selected TIs (compounds 26, 133, 147, 149, 162, and 177 in this manuscript) that contain different molecular features and different activities were analyzed by creating the solvated models and using molecular dynamics (MD) simulations.We used the conformational structures derived from MD to accomplish binding free energetic calculations using MM-GBSA. With this analysis, we theorized about the effect of van der Waals contacts, electrostatic interactions and solvation in the potency of TIs. In general, the contents reported in this article help to understand the physical and chemical characteristics of thrombin-inhibitor complexes. © 2015 Mena-Ulecia et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.Ítem Theoretical design of stable hydride clusters: isoelectronic transformation in the EnAl4−nH7+n − series(ROYAL SOC CHEMISTRY, 2017) Giraldo, C.; Ferraro, F.; Hadad, C.Z.; Riuz, L.; Tiznado, W.; Osorio, E.New stable hydrogen-rich metallic hydrides are designed by systematic transformations of the stable known Al4H7 − species, carried out by successive isoelectronic substitutions of one aluminum atom by one E-H unit at a time (where E = Be, Mg, Ca, Sr and Ba atoms). Searches on the potential energy surfaces (PESs) of EAl3H8 −, E2Al2H9 −, E3AlH10 − and E4H11 − systems indicate that structural analogues of Al4H7 − become higher energy isomers as the number of E-H units increases. The electronic descriptors: Vertical Electron Affinity (VEA), Vertical Ionization Potential (VIP) and the HOMO-LUMO gap, suggest that the systems composed of EAl3H8 −, E2Al2H9 −, E3AlH10 −, with E = Be and Mg, would be the most stable clusters. Additionally, for a practical application, we found that the Be-H and Mg-H substitutions increase the hydrogen weight percentage (wt%) in the clusters, compared with the isoelectronic analogue Al4H7 −. The good capacity of beryllium and magnesium to stabilize the extra hydrogen atoms is supported by the increment of the bridge-like E-H-Al, 3center-2electron chemical bonds. Finally, explorations on the PESs of the neutral species (using Na+ as counterion) indicate that the NaBe2Al2H9, NaBe3AlH10 and NaMg3AlH10 minimum-energy structures retain the original geometric shapes of the anionic systems. This analysis supports the potential use of these species as building blocks for cluster-assembled hydrides in the gas phase.Ítem Which NICS method is most consistent with ring current analysis? Assessment in simple monocycles(Royal Society of Chemistry, 2018) Báez-Grez, R.; Ruiz, L.; Pino-Rios, R.; Tiznado, W.The aromaticity of benzene, Al4 2- cluster, cyclopropane, borazine and planar cyclooctatetraene (COT) was analyzed according to different strategies based on nucleus-independent chemical shift (NICS) computations. The analysis of NICS-components evolution along the main molecular axis seems to be the most adequate and simplest strategy to predict the aromatic or antiaromatic character of the studied systems. Moreover, the analysis of the σ- and π-electron contributions to the out-of-plane component of NICS (NICSzz) leads to the same qualitative and quantitative conclusions previously obtained by the analysis of the magnetically induced ring current densities. © 2018 The Royal Society of Chemistry.