Browsing by Author "Garcia-Rio, Luis"
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- ItemA comparative study on the cucurbit[7]uril-based indicator displacement assay for methyl Viologen. A theoretical and experimental perspectivePavez Guerrero, Paulina; Fierro Huerta, Angelica Maria; Rojas Guerrero, Mabel Natalia; Garcia-Rio, Luis; Dinamarca-Villarroel, Luis; Fuentealba Patino, Denis Alberto; Droguett Muñoz, Kevin Arturo; Santos Blanco, José Guillermo; Aliaga Miranda, Margarita EllyOne colorimetric and one fluorescent-indicator displacement assay (IDA) were studied to assess their interaction with methyl viologen (MV), an herbicide commercially known as paraquat. The host–guest complexes formed by cucurbit[7]uril (CB[7]) and the 4-nitroaniline (NA) or Berberine (Be) dyes function as colorimetric- and fluorescent-IDA for MV, respectively. The CB[7]@NA and CB[7]@Be complexes were characterized by UV–vis, fluorescence spectroscopy, and dynamic simulations. Isothermal titration calorimetry (ITC) experiments and dynamic simulations were employed to obtain thermodynamic data for the formation of the 1:1 inclusion complexes. Finally, NA is proposed as a reference colorimetric dye for determining CB[7]-binding affinities using competitive host–guest titrations, and the fluorescent-IDA as the best assay proposed, as it exhibits a high binding constant, a good detection limit of 2.7 × 10−6 mol L-1, good linearity in the range from 4 × 10−6 mol L-1 to 3.5 × 10−5 mol L-1, in aqueous solution.
- ItemChanges in Protonation Sites of 3-Styryl Derivatives of 7-(dialkylamino)-aza-coumarin Dyes Induced by Cucurbit[7]uril(2022) Alcazar, Jackson J.; Marquez, Edgar; Garcia-Rio, Luis; Robles-Munoz, Agustin; Fierro, Angelica; Santos, Jose G.; Aliaga, Margarita E.The incorporation of a guest, with different basic sites, into an organized system (host), such as macrocycles, could stabilize, detect, or promote the formation of a certain protomer. In this context, this work aimed to study the influence of cucurbit[7]uril (CB7) on dyes such as 7-(dimethylamino)-aza-coumarins, which have more than one basic site along their molecular structure. For this, three 3-styryl derivatives of 7-(dialkylamino)-aza-coumarin dyes (SAC1-3) were synthesized and characterized by NMR, ESI-HRMS and IR. The spectral behaviour of the SACs in the absence and presence of CB7 was studied. The results showed large shifts in the UV-vis spectrum in acid medium: a hypsochromic shift of approximate to 5400 cm(-1) (SAC1-2) and approximate to 3500 cm(-1) (SAC3) in the absence of CB7 and a bathochromic shift of approximate to 4500 cm(-1) (SAC1-3) in the presence of CB7. The new absorptions at long and short wavelengths were assigned to the corresponding protomers by computational calculations at the density functional theory (DFT) level. Additionally, the binding mode was corroborated by molecular dynamics simulations. Findings revealed that in the presence of CB7 the heterocyclic nitrogen was preferably protonated instead of the dialkylamino group. Namely, CB7 induces a change in the protonation preference at the basic sites of the SACs, as consequence of the molecular recognition by the macrocycle.
- ItemCucurbit[7]uril as a Supramolecular Catalyst in Base-Catalyzed Reactions. Experimental and Theoretical Studies on Carbonate and Thiocarbonate Hydrolysis Reactions(2021) Fierro, Angelica; Garcia-Rio, Luis; Arancibia-Opazo, Sandra; Alcazar, Jackson J.; Santos, Jose G.; Aliaga, Margarita E.Cucurbit[7]uril (CB7) catalyzes the hydrolysis reaction of bis(4-nitrophenyl)carbonate (1) but inhibits that of bis(4-nitrophenyl)thiocarbonate (2). Two relevant CB7 effects are proposed, a base-catalyst mediated by the CB7 portal and an inhibitory role attributed to the lower interaction of the thiocarbonyl group with the solvent in the host cavity, respectively.
- ItemHost–guest interaction of coumarin-derivative dyes and cucurbit[7]uril : leading to the formation of supramolecular ternary complexes with mercuric ions(2015) Aliaga Miranda, Margarita Elly; Garcia-Rio, Luis; Pessego, Marcia; Montecinos Escobar, Rodrigo Andrés; Fuentealba Patiño, Denis Alberto; Uribe, Ivan; Martin-Pastor, Manuel; Garcia-Beltran, Olimpo
- ItemKinetic and mechanistic study of the reactions of aryl chloroformates with quinuclidines(2006) Castro R., Enrique; Aliaga Miranda, Margarita Elly; Campodónico Galdames, Paola Rossana; Leis, J. Ramon; Garcia-Rio, Luis; Santos Blanco, José Guillermo
- ItemLinear relationship between emission quantum yield and Stokes shift in 3-styryl aza-coumarin based dyes in the presence of cyclodextrins(2023) Alcazar, Jackson J.; Garcia-Rio, Luis; Robles, Agustin I.; Dinamarca-Villarroel, Luis; Fierro, Angelica; Santos, Jose G.; Aliaga, Margarita E.The effect of the cyclodextrins inclusion on the Stokes shifts and emission quantum yield of three 3-styryl aza-coumarin dyes (SACs) was experimentally and theoretically studied. Preliminary results show a rela-tionship between the emission quantum yield and the calculated binding constants. Supramolecular inclusion was supported by changes in the fluorescence spectra, high-resolution mass spectrometry and molecular dynamics studies. 2,6-di-O-methyl-b-cyclodextrin (DM -b-CD) presented higher binding constants than b-cyclodextrin (b-CD), along with up to a 6-fold increase in emission quantum yield for the SACs. Additionally, a linear negative correlation was obtained between the Stokes shift and the emis-sion quantum yield. This linear and empirical relationship was explained by the action of a unique intramolecular rotation and charge transfer phenomenon in the dyes, which was modulated by cyclodex-trins, and supported by calculations based on density functional theory.(c) 2023 Elsevier B.V. All rights reserved.
- ItemSupramolecular Control of Reactivity toward Hydrolysis of 7-Diethylaminocoumarin Schiff Bases by Cucurbit[7]uril Encapsulation(2021) Alcazar, Jackson J.; Geue, Niklas; Valladares, Veronica; Canete, Alvaro; Perez, Edwin G.; Garcia-Rio, Luis; Santos, Jose G.; Aliaga, Margarita E.A series of aromatic Schiff bases, featuring 7-diethylamino-coumarin and with five different substituents at an adjacent phenyl ring, were synthesized and characterized. With the aim of assessing the stability of these dyes in acidic medium, their hydrolysis reactions were kinetically studied in the absence and presence of the macrocycle cucurbit[7]uril (CB[7]). Our results are consistent with a model containing three different forms of substrates (un-, mono-, and diprotonated) and three parallel reaction pathways. The pK(a) values and the rate constants were estimated and discussed in terms of the presence of a hydroxyl group at the ortho position and electron-releasing groups on the phenyl ring of the dyes. The kinetic study in the presence of CB[7] led to two different behaviors. Promotion of the reaction by CB[7] was observed for the hydrolysis of the Schiff bases containing only one coordination site toward the macrocycle. Conversely, an inhibitor effect was observed for the hydrolysis of a Schiff base with two coordination sites toward CB[7]. The latter effect could be explained with a model as a function of a prototropic tautomeric equilibrium and the formation of a 2:1 host/guest complex, which prevents the attack of water. Therefore, the kinetic results demonstrated a supramolecular control of the macrocycle toward the reactivity and stability of 7-diethylaminocoumarin Schiff bases in acidic medium.
- ItemSupramolecular kinetic effects by pillararenes: the synergism between spatiotemporal and preorganization concepts in decarboxylation reactions†(2021) Vieira Silveira, Eduardo; Montecinos, Rodrigo; Scorsin, Leandro; Garcia-Rio, Luis; Medeiros, Michelle; Nascimento, Vanessa; Nome, Faruk; Affeldt, Ricardo F.; Micke, Gustavo A.A study about spontaneous decarboxylation reactions of 3-carboxy-1,2-benzisoxazole (CBI) nitrated derivatives (6-NitroCBI and 5,6-DinitroCBI) compared with supramolecular kinetic effects promoted by two cationic pillararenes (P5A and P6A) has been carried out and brings contributions to advance current theories related to supramolecular and enzymatic catalysis/inhibition. A higher energy barrier to spontaneous hydrolysis of 6-NitroCBI relative to that of 5,6-DinitroCBI (Delta Delta G(double dagger) = 2.98 kcal mol(-1)) was determined experimentally, however similar transitions states were observed for both substrates. The host-guest complexes generated catalytic effects up to 7.1-fold on k(obs), except for 6-NitroCBI subset of P5A which is the only system that presented unprecedent inhibitory kinetic effects. The data (kinetics, H-1 NMR titration and molecular dynamic simulations) elucidated the kinetic effects of the four complexes as a result of their geometries, more specifically, by modifying 3 main factors: (1) number of hydrogen bonds between solvent and carboxyl groups of the CBIs, (2) polarization of the O-N bond of the isoxazole ring and (3) reduction of the inductive effect of NO2 groups by field effects. The data from the present study encourage the use of both spatiotemporal and preorganization theories during interpretations related to supramolecular and enzymatic catalysis.