High-throughput preparation of alkyl 4-aryl substituted-2-methyl-6-thioxo-1,4,5,6-tetrahydropyridine-3-carboxylates under microwave irradiation

17 p.-1 fig.-2 tab.An efficient high-throughput synthesis of 4-aryl substituted 1,4,5,6-tetrahydro-2-methyl-6-thioxopyridine-3-carboxylates 5a-p was developed by using Lawesson’s reagent, a very effective thionating reagent for carbonyl compounds, under conventional conditions and microwave irradiation. In order to gain a better understanding of the structure of the heterocycles obtained, theoretical calculations at the ab initio level were carried out.The part of this work carried out in Barcelona was partially supported by CICYT (CTQ2009-07758), the Generalitat de Catalunya (2009SGR 1024), the Institute for Research in Biomedicine, and the Barcelona Science Park. This work was also supported by the MICINN of Spain (project CT2008-00795/BQU and Consolider-Ingenio 2010C-07-25200).Peer reviewe

Full Mechanism of Zeolite Dealumination in Aqueous Strong Acid Medium: Ab Initio Periodic Study on H‑Clinoptilolite

Periodic quantum-chemistry methods as implemented in the Crystal14 code were considered to study the mechanism of the dealumination of H-clinoptilolite in aqueous acid medium. A series of models consisting of the primitive cell of a monoaluminated structure of HEU (heulandite) framework type together with water molecules and HCl as catalyzer were considered. Stable and transition state structures together with their relative Gibbs free energy values were computed at the hybrid density functional theory (DFT) level of theory with dispersion correction (PBE0-D2) employing atomic basis sets. Four different steps for the mechanism have been considered. Each of them corresponds to the hydrolysis of the bonds that connect the Al atom with the framework providing as final product Al­(OH)₃ adsorbed on a silanol nest. Results show that the free reaction energy for the whole acid dealumination is about −49 kJ mol^–1. The crucial way the HCl intervents in the reaction is studied in detail, and the polar nature of most intermediates strongly suggests they are significantly stabilized by a solvation-like effect of the aqueous medium

Natural and Sodium Clinoptilolites Submitted to Acid Treatments: Experimental and Theoretical Studies

International audienceIn the present work, the effect of acid treatments on the structure of a natural and sodium exchanged clinoptilolite was evaluated using experimental and theoretical methods. The results demonstrated the good stability of the samples submitted to HCl treatments, although it was proven that aluminum was extracted from the framework. It was verified that the sodium clinoptilolite (AZ) is more resistant than its natural form (NZ) to the acid treatment since the aluminum extraction is smaller and the percent of estimated crystallinity is higher in AZ. An increase in the micropore volume, as well as the creation of new narrow micropores, wasalso verified. The simulation results indicated that the aluminum at T2 position is the easiest to remove during the dealumination process, and it was also noted that, during dealumination, different slabs are formed in the structure, creating a framework like a clay. Calculations suggested that the stability of the dealuminated frameworks was related to attractive and repulsive interactions, which take place between the species involved in the dealumination process. Our work demonstrates that sodium modification is an essential step to obtain a structurally stable acidic natural clinoptilolite

Density functional theory based-study of 5-fluorouracil adsorption on β-cristobalite (1 1 1) hydroxylated surface: The importance of H-bonding interactions

Silica-based mesoporous materials have been recently proposed as an efficient support for the controlled release of a popular anticancer drug, 5-fluorouracil (5-FU). Although the relevance of this topic, the atomistic details about the specific surface-drug interactions and the energy of adsorption are almost unknown. In this work, theoretical calculations using the Vienna Ab-initio Simulation Package (VASP) applying Grimme’s—D2 correction were performed to elucidate the drug–silica interactions and the host properties that control 5-FU drug adsorption on -cristobalite (1 1 1) hydroxylated surface. This study shows that hydrogen bonding, electron exchange, and dispersion forces are mainly involved to perform the 5-FU adsorption onto silica. This phenomenon, revealed by favorable energies, results in optimum four adsorption geometries that can be adopted for 5-FU on the hydroxylated silica surface. Silanols are weakening in response to the molecule approach and establish H-bonds with polar groups of 5-FU drug. The final geometry of 5-FU adopted on hydroxylated silica surface is the results of H-bonding interactions which stabilize and fix the molecule to the surface and dispersion forces which approach it toward silica (1 1 1) plane. The level of hydroxylation of the SiO2 (1 1 1) surface is reflected by the elevated number of hydrogen bonds that play a significant role in the adsorption mechanisms.Fil: Simonetti, Sandra Isabel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Física del Sur. Universidad Nacional del Sur. Departamento de Física. Instituto de Física del Sur; Argentina. Universidad Tecnológica Nacional. Facultad Regional Bahía Blanca; ArgentinaFil: Díaz Compañy, Andres Carlos Daniel. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas; ArgentinaFil: Pronsato, Maria Estela. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Física del Sur. Universidad Nacional del Sur. Departamento de Física. Instituto de Física del Sur; ArgentinaFil: Juan, Alfredo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Física del Sur. Universidad Nacional del Sur. Departamento de Física. Instituto de Física del Sur; ArgentinaFil: Brizuela, Graciela Petra. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Física del Sur. Universidad Nacional del Sur. Departamento de Física. Instituto de Física del Sur; ArgentinaFil: Lam, Anabel. Universidad de La Habana; Cub

Natural and Sodium Clinoptilolites Submitted to Acid Treatments: Experimental and Theoretical Studies

In the present work, the effect of acid treatments on the structure of a natural and sodium exchanged clinoptilolite was evaluated using experimental and theoretical methods. The results demonstrated the good stability of the samples submitted to HCl treatments, although it was proven that aluminum was extracted from the framework. It was verified that the sodium clinoptilolite (AZ) is more resistant than its natural form (NZ) to the acid treatment since the aluminum extraction is smaller and the percent of estimated crystallinity is higher in AZ. An increase in the micropore volume, as well as the creation of new narrow micropores, was also verified. The simulation results indicated that the aluminum at T2 position is the easiest to remove during the dealumination process, and it was also noted that, during dealumination, different slabs are formed in the structure, creating a framework like a clay. Calculations suggested that the stability of the dealuminated frameworks was related to attractive and repulsive interactions, which take place between the species involved in the dealumination process. Our work demonstrates that sodium modification is an essential step to obtain a structurally stable acidic natural clinoptilolite