RESUMO
Deep eutectic solvents (DESs) have been considered "the organic reaction medium of the century" because they can be used as solvents and active catalysts in chemical reactions. However, experimental and theoretical studies are still needed to provide information on the structures of DESs, the kinetics and thermodynamics properties, the interactions between the DESs and the substrates, the effect of water on the DES supramolecular network and its physicochemical properties, and so forth. This information is very useful to understand the essence of the processes that take place in the catalysis of chemical reactions and, therefore, to help in the design of a DES for a specific reaction and sample. This article shows a systematic study of the impact of DES choline chloride/p-toluenesulfonic acid and DES choline chloride/p-toluenesulfonic acid-water in the aza-Michael addition of arylamines to maleimide to obtain aminopyrrolidine-2,5-dione derivatives. The derivatives are obtained under very mild reaction conditions with good yield. The global reaction is exothermic, spontaneous, permitted by enthalpy, and prohibited for entropy. The calculated potential energy surface shows a reaction mechanism of six steps controlled by enthalpy (except the last step that is controlled by entropy). The water incorporated in the supramolecular DES complex stabilizes the transition states and favors the enthalpy-driven binding. A set of H/D exchange NMR experiments validates the transition state existing in the fourth stage of the mechanism.
RESUMO
Three Cu(II) coordination compounds with 4-methyl imidazole were obtained, such as [Cu(C4H6N2)4(NO3)2], [Cu(C4H6N2)4Br2], and [Cu(C4H6N2)4Cl2]. Crystallographic studies confirmed their structural similarity with Cu(II) in the active site of endogenous copper-zinc superoxide dismutase (CuZn-SOD). The superoxide anion radical (O2â¢-) scavenging activity was evaluated by the non-enzymatic experimental assay and followed the trend [Cu(C4H6N2)4(NO3)2] > [Cu(C4H6N2)4Br2] > [Cu(C4H6N2)4Cl2]. The density functional theory and the hard and soft acids and bases principle showed the importance of the electron-deficient character of Cu(II) in the chemical reactivity of the coordination compounds; Cu(II) is the softest site in the molecule and it is preferred for the nucleophilic and radical attacks of the soft O2â¢-. A simple rule was obtained: "the electron-deficient character of Cu(II) is the key index for the O2â¢- scavenging activity and is modulated by the electron-releasing counteranion effect on the coordination compound".
RESUMO
The assertion made by Wu et al. that aromaticity may have considerable implications for molecular design motivated us to use nucleus-independent chemical shifts (NICS) as an aromaticity criterion to evaluate the antifungal activity of two series of indol-4-ones. A linear regression analysis of NICS and antifungal activity showed that both tested variables were significantly related (p < 0.05); when aromaticity increased, the antifungal activity decreased for series I and increased for series II. To verify the validity of the obtained equations, a new set of 44 benzofuran-4-ones was designed by replacing the nitrogen atom of the five-membered ring with oxygen in indol-4-ones. The NICS(0) and NICS(1) of benzofuran-4-ones were calculated and used to predict their biological activities using the previous equations. A set of 10 benzofuran-4-ones was synthesized and tested in eight human pathogenic fungi, showing the validity of the equations. The minimum inhibitory concentration (MIC) in yeasts was 31.25 µg·mL-1 for Candida glabrata, Candida krusei and Candida guilliermondii with compounds 15-32, 15-15 and 15-1. The MIC for filamentous fungi was 1.95 µg·mL-1 for Aspergillus niger for compounds 15-1, 15-33 and 15-34. The results obtained support the use of NICS in the molecular design of compounds with antifungal activity.
Assuntos
Antifúngicos/farmacologia , Benzofuranos/farmacologia , Fungos/efeitos dos fármacos , Antifúngicos/química , Aspergillus niger/efeitos dos fármacos , Aspergillus niger/patogenicidade , Benzofuranos/química , Candida/efeitos dos fármacos , Candida/patogenicidade , Humanos , Testes de Sensibilidade Microbiana , Estrutura Molecular , Pichia/efeitos dos fármacos , Pichia/patogenicidade , Hidrocarbonetos Policíclicos Aromáticos/química , Hidrocarbonetos Policíclicos Aromáticos/farmacologiaRESUMO
Chemical reactivity descriptors of indol-4-ones obtained via density functional theory (DFT) and hard-soft acid-base (HSAB) principle were calculated to prove their contribution in antifungal activity [...].
Assuntos
Antifúngicos/química , Antifúngicos/farmacologia , Indóis/química , Indóis/farmacologia , Modelos Químicos , Modelos Moleculares , Algoritmos , Fungos/efeitos dos fármacos , Testes de Sensibilidade Microbiana , Estrutura Molecular , Eletricidade Estática , Relação Estrutura-AtividadeRESUMO
The chemical synthesis of C60 fullerene in the laboratory is still a challenge. In order to achieve this goal, we propose a synthetic route based on the dimerization between two pentacyclopentacorannulene (C30H10) fragments employing the Diels-Alder cycloaddition reaction. Density functional calculations indicate that a step wise non-concerted dimerization mechanism of C30H10 is favored over a one stage dimerization. The step wise dimerization implies the sequential formation of 2, 4, 6, and 10 new C-C bonds between the two fragments. This leads to the formation of the Diels-Alder cycloadduct C60H20. The results then suggest the synthesis of C60H20 as a precursor for C60. The synthesis of the analogue C60F20 has already been reported.
RESUMO
The methylxanthines have attracted interest due to the changes on their biological activities and physicochemical properties in terms of the number and position of the methyl groups present in the xanthine moiety. We report a theoretical study of the influence of the methyl substituent in the basicity and reactivity of xanthine and its methylated derivatives. Our results provide that when the xanthine increases the number of methyl substituents, the gas phase basicity increases (reactivity to proton increases), and the global hardness decreases. The result is in agreement with the maximum hardness principle (MHP) that states, "at equilibrium, chemical systems are as hard as possible" (Pearson, R.G., J. Chem. Educ., 1987, 64, 561-567, and Parr R.G., Chattaraj P.K., J. Am. Chem. Soc. 1991, 113, 1854-1855). Graphical abstract Xanthine and its methyl derivatives.
RESUMO
The potential energy surface for the first step of the methane oxidation CH4 + O2âCH3 + HO2 was studied using the London-Eyring-Polanyi-Sato equation (LEPS) and the conventional transition-state theory (CTST). The calculated activation energy and rate constant values were in good agreement with the experimental and theoretical values reported in the literature using the shock tube technique and coupled cluster method respectively. The rate equation from CTST, although simple, provides good results to study the H-shift between methane and the oxygen molecules.
RESUMO
The local and condensed Fukui functions as well as the principle of hard and soft acids and bases were used to study the addition of free radicals to the exocyclic and endocyclic double bonds of seven monocyclic monoterpenes of formula C10H16. The results obtained showed that, in general, the most reactive double bond was the one with the most substituents on the double-bonded carbon atoms, and that the reaction of a double bond with an electrophile is a soft-soft interaction. The effects of substituents on the double-bonded carbon atoms and the stabilization of the monoterpenes were interpreted by invoking hyperconjugated structures, which led us to propose a simple rule: the larger the value of the Fukui function for the double bond, the greater the hyperconjugative stabilization and the susceptibility of the double bond to electrophilic attack. In general, our results are in good accordance with relevant experimental and theoretical results published in the literature. Graphical abstract The specific electrophilic addition to monocyclic monoterpenes.
RESUMO
The Brønsted-Lowry and Lewis basicity dichotomy in the elimination vs substitution reaction competition is analyzed in terms of a novel Brønsted-Lowry-Lewis basicity ωp/e. This new index unifies the dichotomy and explains the competition between elimination and substitution mechanisms of alkyl centers with para-substituted phenols.
RESUMO
The simultaneous contributions of proton and electron transfer to the Brønsted-Lowry and Lewis acid-base properties of a set of p-substituted phenols are reported in this work. As a result of the analysis, a novel protophilicity index considered as the second-order energy change of a Brønsted-Lowry base as it is saturated with protons, a combined Brønsted-Lowry-Lewis acidity index (with a corresponding basicity index), and a protofelicity equalization principle (a parallel of the electronegativity equalization principle) are presented.
RESUMO
It has been suggested that pyridine and pyrrole could be patterns for imidazole reactivity studies due to the amine (-NH-) and aza (-Nâ) nitrogen atoms. The analyses of the local and global electronic indexes prove and quantify that imidazole has an intermediate analogy between pyrrole and pyridine.
Assuntos
Imidazóis/química , Piridinas/química , Pirróis/química , Aminas/química , Compostos Aza/química , Estrutura MolecularRESUMO
We evaluate herein the impact of positive charge distribution on the in vitro and in vivo properties of Mn porphyrins as redox modulators possessing the same overall 5+ charge and of minimal stericity demand: Mn(III) meso-tetrakis(trimethylanilinium-4-yl)porphyrin (MnTTriMAP(5+)), Mn(III) meso-tetrakis(N,N'-dimethylpyrazolium-4-yl)porphyrin (MnTDM-4-PzP(5+)), Mn(III) meso-tetrakis(N,N'-dimethylimidazolium-2-yl)porphyrin (MnTDM-2-ImP(5+)), and the ortho and para methylpyridinium complexes Mn(III) meso-tetrakis(N-methylpyridinium-4-yl)porphyrin (MnTM-4-PyP(5+)) and Mn(III) meso-tetrakis(N-methylpyridinium-2-yl)porphyrin (MnTM-2-PyP(5+)). Both Mn(III)/Mn(II) reduction potential and SOD activity within the series follow the order: MnTTriMAP(5+)Assuntos
Manganês/metabolismo
, Metaloporfirinas/farmacologia
, Compostos Organometálicos/farmacologia
, Estresse Oxidativo/efeitos dos fármacos
, Superóxido Dismutase/metabolismo
, Escherichia coli/efeitos dos fármacos
, Escherichia coli/enzimologia
, Cinética
, Metaloporfirinas/química
, Metaloporfirinas/metabolismo
, Compostos Organometálicos/química
, Compostos Organometálicos/metabolismo
, Oxirredução
, Espectrometria de Massas por Ionização por Electrospray
, Relação Estrutura-Atividade