Browsing by Author "Contreras, David"
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- ItemChemiluminescence emission in fenton reaction driven by 1,2-dihydroxybenzenes: Mechanistic approaches using 4-substituted ligands(2021) Romero, Romina; Marquéz, Katherine; Benítez Olivares, Francisca Javiera; Toro Labbé, Alejandro Miguel; Cornejo Ponce, Lorena; Melín, Victoria; Contreras, DavidFenton (F) and Fenton-like (FL) reactions can be amplified by dihydroxybenzenes (DHBs). These compounds chelate and reduce Fe(III), promoting the hydroxyl radical production ((OH)-O-center dot). The products or intermediaries of F and FL reactions driven by DHBs can produce chemiluminescence (CL) with different profiles, depending on the type of DHB involved. In this work, CL produced by F and FL systems driven by different -para substituted DHBs was measured and compared with the reactivity of each system and with the structural parameters of each DHB. CL emission was not related to the reactivity of each studied system but was favored by DHBs substituents with -NHR and -OH groups combined in the branching (NHR-DHBs). PLS multivariate regression models were constructed using computational parameters for each DHB, quinone (Q) and semiquinone (SQ(center dot)) to find the influence of structural and electronic parameters over CL emission. Analysis showed that in NHR-DHBs, the higher CL exhibited could be explained by cycling ability of these compounds. In DHBs with an electron-donor group (EDG) the CL emission would depend only on the stability of the intermediary species generated by DHB and (OH)-O-center dot reaction. While DHBs with electron-withdrawing groups (EWG) showed that CL will increase depending on the stability of the intermediaries by resonance, and by the acidity of the hydroxyl protons of the ring. PLS-SQ(center dot) showed that spin densities were strongly correlated with an increase in CL emission. DHBs with substituents that favor the delocalization of charge in the SQ(center dot) to the ramification would enhance CL emission. Meanwhile, when the delocalization is promoted over the DHB-ring, these systems become more reactive, and the CL emission is disadvantaged by quinone formation.
- ItemImprovement of the BiOI photocatalytic activity optimizing the solvothermal synthesis(2017) Mera, Adriana C.; Moreno, Yanko; Contreras, David; Escalona, Néstor; Meléndrez, Manuel F.; Viswanathan Mangalaraja, Ramalinga; Mansilla, Héctor D.
- ItemThe ferryl generation by fenton reaction driven by catechol(2023) Benítez Olivares, Francisca Javiera; Melin, Victoria; Pérez González, Gabriel; Henríquez, Adolfo; Zarate, Ximena; Schott Verdugo, Eduardo Enrique; Contreras, DavidThe Fenton and Fenton-like reactions are based on the decomposition of hydrogen peroxide catalyzed by Fe(II), primarily producing highly oxidizing hydroxyl radicals (HO∙). While HO∙ is the main oxidizing species in these reactions, Fe(IV) (FeO2+) generation has been reported as one of the primary oxidants. FeO2+ has a longer lifetime than HO∙ and can remove two electrons from a substrate, making it a critical oxidant that may be more efficient than HO∙. It is widely accepted that the preferential generation of HO∙ or FeO2+ in the Fenton reaction depends on factors such as pH and Fe: H2O2 ratio. Reaction mechanisms have been proposed to generate FeO2+, which mainly depend on the radicals generated in the coordination sphere and the HO∙ radicals that diffuse out of the coordination sphere and react with Fe(III). As a result, some mechanisms are dependent on prior HO∙ radical production. Catechol-type ligands can induce and amplify the Fenton reaction by increasing the generation of oxidizing species. Previous studies have focused on the generation of HO∙ radicals in these systems, whereas this study investigates the generation of FeO2+ (using xylidine as a selective substrate). The findings revealed that FeO2+ production is increased compared to the classical Fenton reaction and that FeO2+ generation is mainly due to the reactivity of Fe(III) with HO∙ from outside the coordination sphere. It is proposed that the inhibition of FeO2+ generation via HO∙ generated from inside the coordination sphere is caused by the preferential reaction of HO∙ with semiquinone in the coordination sphere, favoring the formation of quinone and Fe(III) and inhibiting the generation of FeO2+ through this pathway.