Browsing by Author "Santos, Jose G."

Now showing 1 - 8 of 8
  • No Thumbnail Available
    Item
    Changes 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.
  • No Thumbnail Available
    Item
    Cucurbit[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.
  • No Thumbnail Available
    Item
    Ionic liquids: anion effect on the reaction of O,O-diethyl O-(2,4-dinitrophenyl) phosphate triester with piperidine
    (2015) Pavez, Paulina; Millan, Daniela; Cocq, Cristian; Santos, Jose G.; Nome, Faruk
    The reactions of O,O-diethyl 2,4-dinitrophenylphosphate triester (1) with piperidine in ionic liquids and four conventional organic solvents (COS) were subjected to kinetic and product studies. Analytical techniques (UV-vis and NMR) identified two pathways: nucleophilic attack at the phosphoryl center and at the C-1 aromatic carbon. The nucleophilic rate constants (k(N)(T)) for these parallel reactions were separated into two terms: k(N)(P) and k(N)(Ar) for the corresponding electrophilic centers. Both the rate and the selectivities of the reactions are strongly dependent on the nature of the ionic liquid used, and a good correlation with the solvent acceptor capacity to form hydrogen bonds (beta) was observed. Remarkably, an exclusive attack at the phosphoryl center was found using [Bmim] DCA, [Bmpyrr] DCA and [Bmpy] DCA as the reaction solvents. In contrast, with [Bmim]PF6 as the reaction solvent, attack at the C-1 aromatic was the main path (94%). These results suggest that ionic liquids can be considered to be designer solvents because by an appropriate choice of the anion it is possible to steer the selectivity of this reaction.
  • No Thumbnail Available
    Item
    Linear 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.
  • No Thumbnail Available
    Item
    Nucleofugality hierarchy, in the aminolysis reaction of 4-cyanophenyl 4-nitrophenyl carbonate and thionocarbonate. Experimental and theoretical study
    (2021) Montecinos, Rodrigo; Aliaga, Margarita E.; Pavez, Paulina; Cornejo, Patricio; Santos, Jose G.
    Nucleophilic substitution reactions of the title compounds have been investigated with a series of secondary alicyclic amines in several solvents. The solvent, amine, and electrophilic group effects on kinetics, mechanism and nucleofugality hierarchy are discussed from experimental and theoretical studies. These studies show the mechanistic dependence on the solvent polarity; the theoretical results indicate that the relative polarization of the reactive centres (C=O and C=S) and the stabilization of the nucleofuges are the main factors in the control of the product distribution.
  • No Thumbnail Available
    Item
    Quinolin-2(1H-)-one-isoxazole dye as an acceptor for mild addition of bisulfite in cationic or zwitterionic aqueous micellar solutions
    (2024) Quintero, Guillermo E.; Espinoza, Catalina; Valencia, Jhesua; Insuasty, Daniel; Tiznado, William; Leiva-Parra, Luis; Santos, Jose G.; Perez, Edwin G.; Aliaga, Margarita E.
    (E)-6-Methoxy-1-methyl-3-(2-(3-methyl-4-nitroisoxazol-5-yl)vinyl)quinolin-2(1H)-one dye (MQI) has been synthesized, and its structural and electronic properties have been characterized by employing UV-vis spectroscopy in combination with computational methods. The MQI dye has been assessed as an activated Michael acceptor-type probe toward bisulfite ions. This reaction was kinetically tested in different mild, cationic (cetyltrimethylammonium bromide, cetyltrimethylammonium chloride, and cetylpyridinium bromide), and zwitterionic (N-decyl-N,N-dimethyl-3-ammonio-1-propanesulfonate, N-tetradecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate, and N-hexacyl-N,N-dimethyl-3-ammonio-1-propanesulfonate) micellar solutions at pH similar to 5.5. Both micellar media remarkably allow the addition reactions, increasing the reactivity of MQI towards bisulfite ions, the biggest effects were found in the presence of cationic micelles. The binding constants of MQI with the micelles and the rate constants were determined from kinetic data, which were interpreted on the basis of the pseudophase kinetic model. The kinetic study and the product analysis allow us to highlight the relevant role of the association between MQI dye and the micellized surfactant, allowing efficient nucleophilic addition of bisulfite ions. The findings of this work will be valuable for the use of micellar solutions as an alternative medium to replace the use of toxic solvents to carry out organic reactions to perform nucleophilic addition reactions of bisulfite.
  • No Thumbnail Available
    Item
    Supramolecular 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.
  • No Thumbnail Available
    Item
    The effect of the electrophilic group on the hierarchy of nucleofuges in the aminolysis reactions of thiol- and dithiocarbonates with secondary alicyclic amines: A kinetic and theoretical study
    (2019) Montecinos, Rodrigo; Gazitua, Marcela; Santos, Jose G.
    The aminolysis reactions of O-(4-nitrophenyl) S-aryl dithiocarbonates with different secondary alicyclic amines (SAA) lead to the formation of different 4-nitrophenyl:S-aryl ratios (56:44 and 47:53 for benzenethiol and 4-chlorobenzenethiol, respectively). For the corresponding thiolcarbonates, 4-nitrophenol was the lone product, evidencing the effect of the electrophile moiety on the nucleofugacity hierarchy. The kinetic results show that in the mechanism there are two tetrahedral intermediates: one zwitterionic (T-+/-) and one anionic (T-). As model reactions, the reactions of O-(4-nitrophenyl) S-phenyl thiol- and dithiocarbonates with morpholine were theoretically examined using DFT methods. Theoretical calculations were performed using a continuous solvation model in the absence and presence of one and two explicit water molecules. The microsolvation of T- by one explicit water molecule was predicted as having O-(4-nitrophenyl):S-phenyl distributions of 52:48 and 98:2 for dithiocarbonates and thiolcarbonates, respectively. These results have allowed us to establish that processes such as microsolvation, electronic distribution and the structure of the reactive centers participate in the departure of the leaving groups in the thiolcarbonate and dithiocarbonate aminolysis, although the preferential solvation of these centers seems to have a predominant role in the nucleofuge hierarchy.