Browsing by Author "Miranda-Rojas, Sebastian"

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    Influence of Protonation on Substrate and Inhibitor Interactions at the Active Site of Human Monoamine Oxidase-A
    (2012) Zapata-Torres, Gerald; Fierro Huerta, Angélica; Miranda-Rojas, Sebastian; Guajardo, Carlos; Saez-Briones, Patricio; Salgado, J. Cristian; Celis-Barros, Cristian
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    Palmitic acid and hexadecylamine molecules assdsorbed on titania surface in hybrid composites. Effect of surfactants using density functional theory
    (2017) Orellana, Carlos; Mendizabal, Fernando; Gonzalez, Guillermo; Miranda-Rojas, Sebastian; Barrientos, Lorena
    A complete theoretical characterization of the factors involved in the stabilization of hybrid laminar composites is reported, with the purpose of understanding the main interactions involved in the formation of these types of systems. The models were built using two different surfactants: hexadecylamine (HDA) and palmitic acid (PAc), on a cluster of titania (TiO2) which represents its anatase crystalline phase. We explored the relevance of the titania-surfactant and surfactant-surfactant interactions, and of the protonation state of the palmitic acid in the stabilization of the hybrid laminar composites. The results were rationalized using energy decomposition analysis (EDA) and the non-covalent interaction index (NIC). The interaction energies between HDA and the TiO2 surface without the contribution of the dispersion forces were -25 kcal/mol and -29 kcal/mol for the (1 0 0) and (1 01) surfaces, respectively. These results suggest the formation of a donor-acceptor bond between HDA-TiO2 allowing its stabilization. On the other hand, the interaction energy between PAc and the TiO2 (1 0 1) surface was about -45 kcal/mol without the dispersion term. Thus, the PAc-TiO2 model has a higher covalent character than the HDA-TiO2 interaction, as confirmed by the energy decomposition analyses. The results suggest new hybrid laminar composites which are better when carboxylic acid was used instead of amines. Therefore, the use of surfactants with the carboxyl functional group yielded more stable TiO2 hybrid composites. The interaction energy between surfactant chains was about -13 kcal/mol, confirming the importance of dispersion forces in the stabilization of these types of systems. The study of systems with palmitic acid was complemented by building some anionic models to show the importance of acid protons in those systems. However, when the acidic hydrogens were removed, the interaction energy between the PAc molecules considering the dispersion correction increased to 45 kcal/mol, with a highly repulsive character. These results suggest that the acid hydrogens of the PAc surfactants play a fundamental role in terms of correctly representing the carboxylic acid-TiO2 interface and the stabilization of the laminar hybrid composites. (C) 2017 Elsevier B.V. All rights reserved.
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    The interaction mechanism of polystyrene microplastics with pharmaceuticals and personal care products
    (2023) Cortes-Arriagada, Diego; Miranda-Rojas, Sebastian; Camarada, Maria Belen; Ortega, Daniela E.; Alarcon-Palacio, Victoria B.
    Microplastics (MPs) have been detected in the hydrosphere, with hazardous implications in transporting coexisting water pollutants. Our knowledge about the interaction mechanisms that MPs establish with organic pollutants are still growing, which is essential to understand the adsorption properties of MPs and their relative stability with adsor-bates. Here, we used classical (force field methods) and ab-initio (density functional theory) computational chemistry tools to characterize the interaction mechanisms between Polystyrene-MPs (PS-MPs) and pharmaceuticals/personal care products (PPCPs). Adsorption conformations and energies, thermochemistry, binding, and energy decomposition analyses were performed to obtain the quantitative mechanistic information. Our results show that PS-MPs have per-manent dipoles, increasing the interaction with neutral PPCPs while repelling the charged pollutants; in all cases, a sta-ble physisorption takes place. Moreover, PS-MPs increase their solubility upon pollutant adsorption due to an increase in the dipole moment, increasing their co-transport ability in aqueous environments. The stability of the PS-MPs/ PPCPs complexes is further confirmed by thermochemical and molecular dynamics trajectory analysis as a function of temperature and pressure. The interaction mechanism of high pKa pollutants (pKa > 5) is due to a balanced contri-bution of electrostatic and dispersion forces, while the adsorption of low pKa pollutants (pKa < 5) maximizes the elec-trostatic forces, and steric repulsion effects explain their relative lower adsorption stability. In this regard, several pairwise intermolecular interactions are recognized as a source of stabilization in the PS-MPs/PPCPs binding: hydro-gen bonding, pi-pi, O\\HMIDLINE HORIZONTAL ELLIPSIS pi, and C\\HMIDLINE HORIZONTAL ELLIPSIS pi, C\\ClMIDLINE HORIZONTAL ELLIPSISC\\H and C\\HMIDLINE HORIZONTAL ELLIPSISC\\H interactions. The ionic strength in solution slightly affects the adsorption stability of neutral PPCPs, while the sorption of charged pollutants is enhanced. This mechanistic information provides quantitative data for a better understanding of the interactions between organic pol-lutants and MPs, serving as valuable information for sorption/kinetic studies.
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    Unraveling the Nature of the Catalytic Power of Fluoroacetate Dehalogenase
    (2018) Miranda-Rojas, Sebastian; Fernandez, Israel; Kaestner, Johannes; Toro Labbé, Alejandro; Mendizabal, Fernando