Browsing by Author "Calfuman, Karla"

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    Interpretation and analysis of solvent and physico-chemical parameters of choline-amino acid deep eutectic solvents and their aqueous mixtures over the kinetic response
    (2025) Campodónico, Paola; Calfuman, Karla; Suárez, Cristian; Alcázar, Jackson; Olivares, Belén
    This study underscores the pivotal role of choline-amino acid deep eutectic solvents, [ChCl][AA], in the hydrolysis reaction of p-nitrophenyl laurate (p-NPL), used here as a model reaction to evaluate solvent effects in various aqueous compositions. The [ChCl][AA] analyzed were choline methionine ([ChCl][Met]), and choline proline ([ChCl][Pro]). Hydrolysis reaction was performed both in the absence and presence of the enzyme Candida Antarctica Lipase B (CALB), allowing for detailed examination of how the reaction media influences enzymatic activity. Results indicate that varying solvent compositions significantly affect CALB’s catalytic behavior. A kinetic analysis, along with physicochemical evaluations, supports these findings. Notably, in the non-enzymatic hydrolysis, [ChCl][Met] showed a rate one order of magnitude higher than [ChCl][Pro]. The concentration of the phenolate form also increased with higher molar fractions ( χ ) of [ChCl][AA], implying direct involvement of [ChCl][AA] in phenoxide formation. Conversely, in the enzymatic reaction, [ChCl][Pro] facilitated a rate approximately 3.5 times faster than [ChCl][Met], with rates increasing as χ χ increased. This effect is attributed to the rigid structure of proline, which may induce beneficial conformational changes in CALB. Lineweaver-Burk plots revealed that optimal enzymatic performance occurred in media rich in [ChCl] [Met] ( = 0.85), suggesting that such environments impose structural constraints that stabilize CALB. This stability may arise from the formation of a solvation shell near the [ChCl][AA]. Surface tension data further suggest that at specific compositions, 3D assemblies form, mimicking pure [ChCl][AA] behavior. Overall, this study emphasizes the potential of [ChCl][AA] as green solvents in biocatalysis applications.
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    Mechanism for the SNAr reaction of atrazine with endogenous thiols: experimental and theoretical study
    (Royal Society of Chemistry, 2017) Calfuman, Karla; Gallardo, Sebastian; Contreras, Renato; Tapia, Ricardo; Campodónico, Paola
    Reaction mechanism in aromatic nucleophilic substitution reactions is discussed using kinetic study complemented with quantum chemical calculations. The model system is the reaction of a series of biothiols toward atrazine (ATZ) in aqueous media. The proposed reaction mechanism discloses a non-catalyzed pathway and the presence of a deprotonated (thiolate) nucleophile in water suggests that the reaction mechanism is borderline between a stepwise route and a concerted process. The full analysis of the potential energy surface reinforces the addition/elimination mechanism. Despite of numerous attempts to locate transition structures associated with the leaving group departure were unsuccessful, presumably because this step is extremely fast.

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