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1.
Toxins (Basel) ; 8(7)2016 07 21.
Artigo em Inglês | MEDLINE | ID: mdl-27455324

RESUMO

Theoretical studies of 8-chloro-9-hydroxy-aflatoxin B1 (2) were carried out by Density Functional Theory (DFT). This molecule is the reaction product of the treatment of aflatoxin B1 (1) with hypochlorous acid, from neutral electrolyzed water. Determination of the structural, electronic and spectroscopic properties of the reaction product allowed its theoretical characterization. In order to elucidate the formation process of 2, two reaction pathways were evaluated-the first one considering only ionic species (Cl⁺ and OH(-)) and the second one taking into account the entire hypochlorous acid molecule (HOCl). Both pathways were studied theoretically in gas and solution phases. In the first suggested pathway, the reaction involves the addition of chlorenium ion to 1 forming a non-classic carbocation assisted by anchimeric effect of the nearest aromatic system, and then a nucleophilic attack to the intermediate by the hydroxide ion. In the second studied pathway, as a first step, the attack of the double bond from the furanic moiety of 1 to the hypochlorous acid is considered, accomplishing the same non-classical carbocation, and again in the second step, a nucleophilic attack by the hydroxide ion. In order to validate both reaction pathways, the atomic charges, the highest occupied molecular orbital and the lowest unoccupied molecular orbital were obtained for both substrate and product. The corresponding data imply that the C9 atom is the more suitable site of the substrate to interact with the hydroxide ion. It was demonstrated by theoretical calculations that a vicinal and anti chlorohydrin is produced in the terminal furan ring. Data of the studied compound indicate an important reduction in the cytotoxic and genotoxic potential of the target molecule, as demonstrated previously by our research group using different in vitro assays.


Assuntos
Aflatoxinas/química , Modelos Químicos , Água/química , Aflatoxinas/toxicidade , Eletrólise , Gases , Ácido Hipocloroso/química , Modelos Moleculares , Estrutura Molecular , Espectroscopia de Prótons por Ressonância Magnética , Soluções , Relação Estrutura-Atividade , Termodinâmica
2.
Molecules ; 18(10): 12820-44, 2013 Oct 16.
Artigo em Inglês | MEDLINE | ID: mdl-24135939

RESUMO

Tonsil Actisil FF, which is a commercial bentonitic clay, promotes the formation of cycloveratrylene macrocycles and benzyl oligomers from the corresponding benzyl alcohols in good yields under microwave heating and infrared irradiation in the absence of solvent in both cases. The catalytic reaction is sensitive to the type of substituent on the aromatic ring. Thus, when benzyl alcohol was substituted with a methylenedioxy, two methoxy or three methoxy groups, a cyclooligomerisation process was induced. Unsubstituted, methyl and methoxy benzyl alcohols yielded linear oligomers. In addition, computational chemistry calculations were performed to establish a validated mechanistic pathway to explain the growth of the obtained linear oligomers.


Assuntos
Bentonita/química , Compostos Macrocíclicos/síntese química , Alcenos/síntese química , Compostos de Benzil/síntese química , Catálise , Simulação por Computador , Compostos Macrocíclicos/química , Micro-Ondas , Modelos Químicos , Modelos Moleculares , Conformação Molecular , Polímeros/síntese química , Teoria Quântica , Solventes , Termodinâmica
3.
J Mol Model ; 19(11): 4823-36, 2013 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-24026575

RESUMO

The interactions of L-aminoglucosidic stereoisomers such as rhodostreptomycins A (Rho A) and B (Rho B) with cations (Mg(2+), Ca(2+), and H(+)) were studied by a quantum mechanical method that utilized DFT with B3LYP/6-311G. Docking studies were also carried out in order to explore the surface recognition properties of L-aminoglucoside with respect to Mg(2+) and Ca(2+) ions under solvated and nonsolvated conditions. Although both of the stereoisomers possess similar physicochemical/antibiotic properties against Helicobacter pylori, the thermochemical values for these complexes showed that its high affinity for Mg(2+) cations caused the hydration of Rho B. According to the results of the calculations, for Rho A-Ca(2+)(H2O)6, ΔH = -72.21 kcal mol(-1); for Rho B-Ca(2+)(H2O)6, ΔH = -72.53 kcal mol(-1); for Rho A-Mg(2+)(H2O)6, ΔH = -72.99 kcal mol(-1) and for Rho B-Mg(2+)(H2O)6, ΔH = -95.00 kcal mol(-1), confirming that Rho B binds most strongly with hydrated Mg(2+), considering the energy associated with this binding process. This result suggests that Rho B forms a more stable complex than its isomer does with magnesium ion. Docking results show that both of these rhodostreptomycin molecules bind to solvated Ca(2+) or Mg(2+) through hydrogen bonding. Finally, Rho B is more stable than Rho A when protonation occurs.


Assuntos
Cátions Bivalentes/química , Magnésio/química , Estreptomicina/análogos & derivados , Cálcio/química , Ligação de Hidrogênio , Modelos Moleculares , Simulação de Acoplamento Molecular , Teoria Quântica , Estereoisomerismo , Estreptomicina/química , Termodinâmica
4.
J Org Chem ; 78(6): 2327-35, 2013 Mar 15.
Artigo em Inglês | MEDLINE | ID: mdl-23419137

RESUMO

The transesterification reaction, and in particular the methanolysis of ethyl acetate with sulfuric acid as catalyst, is used as a model reaction to study the acid-catalyzed nucleophilic addition to a carbonyl group. Continuum solvation methods (SMD and IEF-PCM) and the MPWB1K functional are used. The reaction mechanism is studied in methanol and in acetonitrile as solvents. Our results indicate that the acid-catalyzed addition mechanism is stepwise, and the transition state (TS) is a contact ion-pair. The counteranion of the acid catalyst remains in the reaction site playing an important role in the TS of this reaction. Changes in the reaction kinetics and the ionic/nonionic nature of the TS with the ionizing ability of the solvent and the strength of the acid catalyst are explored. Additional calculations at the CBS-Q3 level of theory reinforce the conclusions of this paper. The results obtained allow the generalization of important ideas regarding the mechanism of the nucleophilic addition to carbonyl groups.

5.
Molecules ; 16(2): 1761-75, 2011 Feb 21.
Artigo em Inglês | MEDLINE | ID: mdl-21339711

RESUMO

Tonsil Actisil FF, a commercial bentonitic clay, promotes the formation of a series of electrophilic-aromatic-substitution products from para-methoxybenzyl acetate in carbon disulfide. The molecules obtained correspond to linear isomeric dimers, trimers, tetramers and a pentamer, according to their spectroscopic data. A clear indication of the title mechanistic pathway for the oligomerization growth was obtained from the analysis of a set of computational-chemistry calculations using the density-functional-theory level B3LYP/6-311++G(d,p). The corresponding conclusions were based on the computed dipole moments, the HOMO/LUMO distributions, and a natural-populations analysis of the studied molecules.


Assuntos
Acetatos/química , Bentonita/química , Modelos Teóricos , Simulação por Computador , Estrutura Molecular
6.
Arch Environ Contam Toxicol ; 59(3): 393-406, 2010 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-20340014

RESUMO

This study involved quantum mechanical calculations to explain the chemical behavior of the lactone ring of aflatoxin B1, which is a carcinogenic hazardous compound. The aflatoxin B1 compound, produced by the fungi Aspergillum flavus, was studied with the B3LYP/6-311+G(d,p) method; its reactivity properties were accounted for by means of the calculated geometrical and electronic parameters. The results obtained indicate that the fused A, B, C, and D rings of aflatoxin adopt a continuous planar conformation. The carbon atom of the lactone group presents a highly electrophilic character, since the population analysis yields a high positive charge for this atom, whereas high negative charges were recorded for both oxygen sites of that group. Thus, in an acidic aqueous medium, the oxygen atoms could be protonated and the carbon site may suffer a nucleophilic attack by water. Accordingly, the OC-O bond length has been lengthened substantially. So it was demonstrated that the lactonic ring of aflatoxin B1 is hydrolyzed under acidic conditions by an acid-acyl bimolecular mechanisms, A(AC)2, suggesting the deletion of its carcinogenic properties.


Assuntos
Aflatoxina B1/química , Carcinógenos/química , Lactonas/química , Aflatoxina B1/toxicidade , Carcinógenos/toxicidade , Elétrons , Fluorescência , Hidrólise , Lactonas/toxicidade , Modelos Teóricos , Estrutura Molecular , Eletricidade Estática , Fatores de Virulência/química
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