Examinando por Autor "Sandoval-Altamirano, Catalina"

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    Ítem
    Electronic and Photophysical Properties of Re I (CO) 3 Br Complexes Modulated by Pyrazolyl-Pyridazine Ligands
    (ACS Omega, 2019-03-04) Saldías, Marianela; Guzmán, Nicolas; Palominos, Franco; Sandoval-Altamirano, Catalina; Gunther, German; Pizarro, Nancy; Vega, Andres
    The direct reaction of a series of substituted (1H-pyrazol-1-yl)pyridazine (L I : 6-(1H-pyrazolyl)pyridazine; L II : 3-chloro-6-(1H-pyrazole-1-yl)-pyridazine; L III : 6-(1H-3,5-dimethylpyrazolyl)pyridazine-3-carboxylic acid; L IV : 3,6-bis-N-pyrazolyl-pyridazine; and L V : 3,6-bis-N-3-methylpyrazolyl-pyridazine) with the bromotricarbonyl(tetrahydrofuran)-rhenium(I) dimer leads to the monometallic complexes [(L X )Re(CO) 3 Br] (I-V), which displays a nonregular octahedral geometry around the Re I center and a fac-isomerism for the carbonyl groups, whereas pyridazine and pyrazolyl rings remain highly coplanar after coordination to rhenium. Cyclic voltammetry shows one irreversible oxidation and one irreversible reduction for each compound as measured in N,N-dimethylformamide. Oxidation ranges from 0.94 V for III to 1.04 V for I and have been attributed to the Re I /Re II couple. In contrast, the reductions are ligand centered, ranging from -1.64 V for II to -1.90 V for III and V. Density functional theory calculations on the vertical one electron oxidized and one electron reduced species, using the gas-phase optimized geometry for the neutral complex confirm this assignment. Compounds I-V show two absorption bands, one around 410 nm (metal-to-ligand charge transfer (MLCT), Re dπ → π∗) and the other at ∼300 nm (intraligand, π → π∗). Excitation at 400 nm at 77 K leads to unstructured and monoexponential emission with large Stokes shift, whose maxima vary between 570 (III) and 636 (II) nm. The quantum yields for these emissions in solution are intensified strongly going from air to argon equilibrated solution. Singlet oxygen quantum yields change from 0.03 (III) to 0.21 (IV). These data are consistent with emission from 3 MLCT. The emission undergoes a bathochromic shift when R 1 is a π-donating group (Cl or N-pyrazolyl) and a hypsochromic shift for a π-acceptor (COOH). The bimolecular emission quenching rate constant by triethylamine (TEA) for II, IV, and V is 1.09, 0.745, and 0.583 × 10 8 M -1 s -1 , respectively. Photolysis in dichloromethane-CO 2 saturated solution with TEA as a sacrificial electron donor leads in all cases to formic acid generation.
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    Ítem
    Photochemistry of P,N-bidentate rhenium(i) tricarbonyl complexes: Reactive species generation and potential application for antibacterial photodynamic therapy
    (Royal Society of Chemistry, 2021-09) Acosta, Alison; Antipán, Javier; Fernández, Mariano; Prado, Gaspar; Sandoval-Altamirano, Catalina; Günther, Germán; Gutiérrez-Urrutia, Izabook; Poblete-Castro, Ignacio; Vega, Andrés; Pizarro, Nancy
    In this work, we describe the photoisomerization of facial rhenium(i) tricarbonyl complexes bearing P,N-bidentate pyridyl/phosphine ligands with different chelating rings and anions: RePNBr, RePNTfO, and RePNNBr, which are triggered under irradiation at 365 nm in solutions. The apparent photodegradation rate constants (kapp) depend on the coordinating ability of the solvent, being lowest in acetonitrile. The kapp value increases as the temperature rises, suggesting a reactive IL excited state thermally populated from the MLCT excited state involved. Using the Eyring equation, positive activation enthalpies (ΔH≠) accompanied by high negative values for the activation entropy (ΔS≠) were obtained. These results suggest whatever the P,N-ligand or anion, the reaction proceeds through a strongly solvated or a compact transition state, which is compatible with an associative mechanism for the photoisomerization. A 100-fold decrease in the log10 CFU value is observed for E. coli and S. aureus in irradiated solutions of the compounds, which follows the same tendency as their singlet oxygen generation quantum yield: RePNBr > RePNTfO > RePNNBr, while no antibacterial activity is observed in the darkness. This result indicates that the generation of singlet oxygen plays a key role in the antibacterial capacity of these complexes. © The Royal Society of Chemistry.