Browsing by Author "Alcazar, Jackson J."

Now showing 1 - 6 of 6
  • 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
    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
    Predicting the Adsorption of Amoxicillin and Ibuprofen on Chitosan and Graphene Oxide Materials: A Density Functional Theory Study
    (2021) Anchique, Leonardo; Alcazar, Jackson J.; Ramos-Hernandez, Andrea; Mendez-Lopez, Maximiliano; Mora, Jose R.; Rangel, Norma; Luis Paz, Jose; Marquez, Edgar
    The occurrence, persistence, and accumulation of antibiotics and non-steroidal anti-inflammatory drugs (NSAIDs) represent a new environmental problem due to their harmful effects on human and aquatic life. A suitable absorbent for a particular type of pollutant does not necessarily absorb other types of compounds, so knowing the compatibility between a particular pollutant and a potential absorbent before experimentation seems to be fundamental. In this work, the molecular interactions between some pharmaceuticals (amoxicillin, ibuprofen, and tetracycline derivatives) with two potential absorbers, chitosan and graphene oxide models (pyrene, GO-1, and coronene, GO-2), were studied using the omega B97X-D/6-311G(2d,p) level of theory. The energetic interaction order found was amoxicillin/chitosan > amoxicillin/GO-1 > amoxicillin/GO-2 > ibuprofen/chitosan > ibuprofen/GO-2 > ibuprofen/GO-1, the negative sign for the interaction energy in all complex formations confirms good compatibility, while the size of E-int between 24-34 kcal/mol indicates physisorption processes. Moreover, the free energies of complex formation were negative, confirming the spontaneity of the processes. The larger interaction of amoxicillin Gos, compared to ibuprofen Gos, is consistent with previously reported experimental results, demonstrating the exceptional predictability of these methods. The second-order perturbation theory analysis shows that the amoxicillin complexes are mainly driven by hydrogen bonds, while van der Waals interactions with chitosan and hydrophobic interactions with graphene oxides are modelled for the ibuprofen complexes. Energy decomposition analysis (EDA) shows that electrostatic energy is a major contributor to the stabilization energy in all cases. The results obtained in this work promote the use of graphene oxides and chitosan as potential adsorbents for the removal of these emerging pollutants from water.
  • 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
    Theoretical Calculations of the Multistep Reaction Mechanism Involved in Asparagine Pyrolysis Supported by Degree of Rate Control and Thermodynamic Control Analyses
    (2019) Cervantes, Cristian; Mora, Jose R.; Marquez, Edgar; Torres, Javier; Rincon, Luis; Mendez, Miguel A.; Alcazar, Jackson J.
    A computational study on the mechanisms of reaction for the pyrolysis of asparagine is presented. A density functional theory (DFT) study at the omega B97XD/6-311G(d,p) level was performed to analyze the differences in two reaction mechanisms: (i) the formation of five-membered cyclic products: maleimide and succinimide, and (ii) the more classical, six-membered cyclic products (diketopiperazine species) which are common in the pyrolysis of many other amino acids. The effect of temperature was included in the calculations at 300 degrees C or 625 degrees C, as required. Moreover, a detailed study based on the degree of rate control and thermodynamic control of the proposed mechanism for the formation of maleimide and succinimide is also presented. Results show that, for asparagine, the five-membered ring formation is the preferred process instead of the six-membered cycle (32 kJ/mol of Gibbs free energy difference between them at the first cyclization step); therefore, the polymerization is favored. On the other hand, the rupture of the polymer represents the highest energetic barrier (Delta G(double dagger) = 281 kJ/mol) and the most influential process in the overall rate of the reaction. These results are in good agreement with the experimental evidence.