260 research outputs found
Spectroscopic, calorimetric, and catalytic evidences of hydrophobicity on Ti-MCM-41 silylated materials for olefin epoxidations
tHydrophobic Ti-MCM-41 samples prepared by post-synthesis silylation treatment demonstrate to behighly active and selective catalysts in olefins epoxidation by using organic hydroperoxides as oxidizingagents in liquid phase reaction systems. Epoxide yields show important enhancements with increasedsilylation degrees of the Ti-mesoporous samples. Catalytic studies are combined and correlated withspectroscopic techniques (e.g. XRD, XANES, UV-Visible,29Si MAS-NMR) and calorimetric measurementsto better understand the changes in the surface chemistry of Ti-MCM-41 samples due to the post-synthesis silylation treatment and to ascertain the role of these trimethylsilyl groups incorporated inolefin epoxidation. In such manner, the effect of the organic moieties on solids, and both water and gly-col molecules contents on the catalytic activity and selectivity are analyzed in detail. Results show thatthe hydrophobicity level of the samples is responsible for the decrease in water adsorption and, conse-quently, the negligible formation of the non-desired glycol during the catalytic process. Thus, catalystdeactivation by glycol poisoning of Ti active sites is greatly diminished, this increasing catalyst stabilityand leading to practically quantitative production of the corresponding epoxide. The extended use ofthese hydrophobic Ti-MCM-41 catalysts together with organic hydroperoxides for the highly efficientand selective epoxidation of natural terpenes is also exemplified.The authors gratefully acknowledge financial support of Spanish Government (MAT2012-38567-C02-01, Consolider-Ingenio 2010-Multicat CSD-2009-00050 and Severo Ochoa SEV-2012-0267) and Generalitat Valenciana (Project Prometeo). M.E.D. also thanks funds from Spanish Government (CTQ-2011-27550) and CSIC (PIE 2009801063). J.S.A. and F.R.R. acknowledge financial support from MINECO (Projects MAT2013-45008-p and CONCERT Project-NASEMS (PCIN-2013-057), and from Generalitat Valenciana (PROMETEO2009/002).Silvestre Albero, J.; Domine ., ME.; Jorda Moret, JL.; Navarro Villalba, MT.; Rey Garcia, F.; Rodriguez-Reinoso, F.; Corma Canós, A. (2015). Spectroscopic, calorimetric, and catalytic evidences of hydrophobicity on Ti-MCM-41 silylated materials for olefin epoxidations. Applied Catalysis A: General. 507:14-25. https://doi.org/10.1016/j.apcata.2015.09.029S142550
Confinement of a Nonionic Surfactant Membrane Within a Montmorillonite as a New Way to Prepare Organoclay Materials
Reparameterization of RNA χ Torsion Parameters for the AMBER Force Field and Comparison to NMR Spectra for Cytidine and Uridine
A reparameterization of the torsional parameters for the glycosidic dihedral angle, χ, for the AMBER99 force field in RNA nucleosides is used to provide a modified force field, AMBER99χ. Molecular dynamics simulations of cytidine, uridine, adenosine, and guanosine in aqueous solution using the AMBER99 and AMBER99χ force fields are compared with NMR results. For each nucleoside and force field, 10 individual molecular dynamics simulations of 30 ns each were run. For cytidine with AMBER99χ force field, each molecular dynamics simulation time was extended to 120 ns for convergence purposes. Nuclear magnetic resonance (NMR) spectroscopy, including one-dimensional (1D) 1H, steady-state 1D 1H nuclear Overhauser effect (NOE), and transient 1D 1H NOE, was used to determine the sugar puckering and preferred base orientation with respect to the ribose of cytidine and uridine. The AMBER99 force field overestimates the population of syn conformations of the base orientation and of C2′-endo sugar puckering of the pyrimidines, while the AMBER99χ force field’s predictions are more consistent with NMR results. Moreover, the AMBER99 force field prefers high anti conformations with glycosidic dihedral angles around 310° for the base orientation of purines. The AMBER99χ force field prefers anti conformations around 185°, which is more consistent with the quantum mechanical calculations and known 3D structures of folded ribonucleic acids (RNAs). Evidently, the AMBER99χ force field predicts the structural characteristics of ribonucleosides better than the AMBER99 force field and should improve structural and thermodynamic predictions of RNA structures
Obtenção de membranas microporosas a partir de manocompósitos de poliamida 6/argila nacional. Parte 1: influência da presença da argila na morfologia das membranas
Effects of peeling methods on the quality of cubiu fruits
Cubiu (Solanum sessiliflorum Dunal) is an Amazonian Basin native fruit. Its importance comes from its high contents of pectin. Currently, processing technologies are necessary for the substitution of the traditional system (small crops and small-scale processing) for a larger scale system and thus increase the use of biodiversity and promote the implementation of Local Productive Arrangements of agribusiness in the Amazon. This research aims to evaluate the methods of peeling cubiu. Ripe fruits were divided into lots (150 each) and subjected to the following treatments: immersion in 2.5% NaOH boiling solution for 5 minutes, exposure to water vapor, and immersion in water at 96 ºC for 5, 10, 15 and 20 minutes. The peel released during heat treatment and immediately removed under running tap water. In the control treatment, the fruits were manually peeled (unheated) with a stainless steel knife. The treatments were evaluated for completeness and ease of peeling, tissue integrity, texture, and peroxidase activity. The immersion in 2.5% NaOH boiling solution (5 minutes) stood out as the best treatment since it inhibited the enzymatic browning and intensified the natural yellow color of the cubiu fruit and easily and fully peeled the whole fruit more rapidly without damaging its tissues. This treatment was chosen as the most advantageous because it can promote simultaneous peeling and bleaching. Therefore, it is recommended for cubiu industrial processing
Desenvolvimento de nanocompósitos polipropileno/argila bentonita brasileira: I tratamento da argila e influência de compatibilizantes polares nas propriedades mecânicas
A Family of Peroxo-titanate Materials Tailored for Optimal Strontium and Actinide Sorption
Preparação e Caracterização de Nanofibras de Nanocompósitos de Poliamida 6,6 e Argila Montmorilonita
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