Examinando por Autor "Zarate, Ximena"

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    Comparative study of the anchorage and the catalytic properties of nanoporous TiO2 films modified with ruthenium (II) and rhenium (I) carbonyl complexes
    (Elsevier B.V., 2018-02) Oyarzún, Diego P.; Chardon-Noblat, Sylvie; Linarez Pérez, Omar E.; López Teijelo, Manuel; Zúñiga, César; Zarate, Ximena; Shott, Eduardo; Carreño, Alexander; Arratia-Perez, Ramiro
    In this article we study the anchoring of cis-[Ru(bpyC4pyr)(CO)2(CH3CN)2]2+, cis-[Ru(bpy)2(CO)2]2+ and cis-[Ru(bpyac)(CO)2Cl2], onto nanoporous TiO2 employing electropolymerization, electrostatic interaction and chemical bonding. Also, the [Re(bpyac)(CO)3Cl] rhenium(I) complex for chemical anchorage was analyzed. The characterization of TiO2/Ru(II) and TiO2/Re(I) nanocomposite films was performed by field emission scanning electron microscopy (FESEM), electron dispersive X-ray spectroscopy (EDS) and Raman spectroscopy. In addition, for the more stable nanocomposites obtained, the catalytic properties (solar energy conversion and CO2 reduction) were evaluated. The efficiency improvement in redox process derived from the (photo)electrochemical evidence indicates that modified nanoporous TiO2 structures enhance the rate of charge transfer reactions. © 2018 Elsevier B.V.
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    Insights into the selective sensing mechanism of a luminescent Cd(II)-based MOF chemosensor toward NACs: roles of the host–guest interactions and PET processes
    (Springer, 2021-05) Hidalgo-Rosa, Yoan; Mena-Ulecia, Karel; Treto-Suarez, Manuel; Schott, Eduardo; Páez-Hernández, Dayán; Zarate, Ximena
    The structural and photophysical properties of the [Cd2(H2L)2(H2O)5].5H2O (where H4L is the ligand 5,5'-((thiophene-2,5-dicarbonyl)bis(azanediyl))diisophthalic acid labeled as Cd-MOF), as well as the elucidation of the selective turn-off luminescent sensing mechanism toward 4-nitroaniline (pNA) were addressed, using quantum chemical methods. To reach this aim, the structures of the ground state (S0) and first excited state (S1) Cd-MOF/analyte system were assessed. We found that after the interaction a photoinduced electron transfer (PET) from the Cd-MOF to pNA is responsible for the fluorescence quenching in this system. For this purpose, a study was performed based on TD-DFT and multireference calculations to corroborate that an excited state exists with the adequate electronic configuration for PET process in the interacting system Cd-MOF/analyte. Intermolecular interaction between the Cd-MOF and analyte was studied by means of Morokuma–Ziegler energy decomposition analysis, natural orbitals of chemical valence, ab initio molecular dynamics (AIMD) calculations and non-covalent interactions (NCI) index. These results showed that intermolecular interactions via hydrogen bond are considerably strengthened in the excited state for the Cd-MOF/pNA, which favor the non-radiative deactivation channels of the chemosensor. In addition, the overlap of absorption spectra of Cd-MOF and pNA indicates that the loss of fluorescence is also due to internal filter effect (IFE). The most noteworthy aspect of this methodology is to consider the relative energies of the S0 and S1 states of MOF/analyte system to explaining the experimental behavior of Cd-MOF toward 4-nitroaniline, proving to be a robust tool in the accurate elucidation of the sensing mechanism in the MOF chemosensor. Graphical abstract: [Figure not available: see fulltext.] Ab initio methods along with TD-DFT have been used to elucidate the selective turn-off luminescent sensing mechanism of nitroaromatic compounds by a Cd-based metal–organic framework (MOF). The role of the host–guest interaction has been pointed out using different theoretical descriptors. A theoretical protocol is given to get more insights into the MOF design and selectivity for nitroaromatic compounds. © 2021, The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.
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    Ítem
    Quantum chemical elucidation of the turn-on luminescence mechanism in two new Schiff bases as selective chemosensors of Zn2+: Synthesis, theory and bioimaging applications
    (RSC Advances, 2019) Berrones-Reyes, Jessica C.; Muñoz-Flores, Blanca M.; Cantón-Diáz, Arelly M.; Treto-Suárez, Manuel A.; Páez-Hernández, Dayan; Schott, Eduardo; Zarate, Ximena; Jiménez-Pérez, Víctor M.
    We report the synthesis and characterization of two new selective zinc sensors (S,E)-11-amino-8-((2,4-di-tert-butyl-1-hydroxybenzylidene) amino)-11-oxopentanoic acid (A) and (S,E)-11-amino-8-((8-hydroxybenzylidene)amino)-11-oxopentanoic acid (B) based on a Schiff base and an amino acid. The fluorescent probes, after binding to Zn2+ ions, presented an enhancement in fluorescent emission intensity up to 30 times (ϕ = A 50.10 and B 18.14%). The estimated LOD for compounds A and B was 1.17 and 1.20 μM respectively (mixture of acetonitrile : water 1 : 1). Theoretical research has enabled us to rationalize the behaviours of the two selective sensors to Zn2+ synthesized in this work. Our results showed that in the free sensors, PET and ESIPT are responsible for the quenching of the luminescence and that the turn-on of luminescence upon coordination to Zn2+ is mainly induced by the elimination of the PET, which is deeply analysed through EDA, NOCV, molecular structures, excited states and electronic transitions via TD-DFT computations. Confocal fluorescence microscopy experiments demonstrate that compound A could be used as a fluorescent probe for Zn2+ in living cells.
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    Synthesis, characterization and computational studies of (E)-2-{[(2-aminopyridin-3-yl)imino]-methyl}-4,6-di-tert-butylphenol
    (Sociedade Brasileira de Química, 2014) Carreño, Alexander; Vega, Andrés; Zarate, Ximena; Schott, Eduardo; Gacitúa, Manuel; Valenzuela, Ninnette; Preite, Marcelo; Manríquez, Juan M.; Chávez, Ivonne
    (E)-2-{[(2-Aminopyridin-3-yl)imino]-methyl}-4,6-di-tert-butyl-phenol ( 3: ), a ligand containing an intramolecular hydrogen bond, was prepared according to a previous literature report, with modifications, and was characterized by UV-vis, FTIR, 1H-NMR, 13C-NMR, HHCOSY, TOCSY and cyclic voltammetry. Computational analyses at the level of DFT and TD-DFT were performed to study its electronic and molecular structures. The results of these analyses elucidated the behaviors of the UV-vis and electrochemical data. Analysis of the transitions in the computed spectrum showed that the most important band is primarily composed of a HOMO→LUMO transition, designated as an intraligand (IL) charge transfer.