Graphenes as Metal-Free Catalysts with Engineered Active Sites

[EN] This Perspective article highlights how recent discoveries on the activity of defective graphene to promote different organic reactions as metal-free catalysts has led to propose certain substructures present on these defective graphenes as active sites. The sustainability of using as catalysts graphenes obtained from biomass and the possibility to generate active sites by introducing defects on the sheet are the two main characteristics triggering research in this area. Emphasis is made in the need to gain understanding on the nature of the active sites and how this understanding requires the combination of conventional kinetic experiments as well as advanced characterization tools. The relationship between catalysis by graphene and that by organocatalysis has also been remarked.Financial support by the Spanish Ministry of Economy and Competitiveness (Severo Ochoa, Grapas, and CTQ2015-69153-CO2-1) and Generalitat Valenciana (Prometo 2013-014) is gratefully acknowledged. A.P. also thanks the Spanish Ministry of Economy and Competitiveness for a Ramon y Cajal research associate contract.Primo Arnau, AM.; Parvulescu, V.; García Gómez, H. (2017). Graphenes as Metal-Free Catalysts with Engineered Active Sites. The Journal of Physical Chemistry Letters. 8(1):264-278. https://doi.org/10.1021/acs.jpclett.6b01996S2642788

Vapor-Phase Oxidation of Benzyl Alcohol Using Manganese Oxide Octahedral Molecular Sieves (OMS-2)

Vapor-phase selective oxidation of benzyl alcohol has been accomplished using cryptomelane-type manganese oxide octahedral molecular sieve (OMS-2) catalysts. A conversion of 92% and a selectivity to benzaldehyde of 99% were achieved using OMS-2. The role played by the oxidant in this system was probed by studying the reaction in the absence of oxidant. The natures of framework transformations occurring during the oxidation reaction were fully studied using temperature-programmed techniques, as well as in situ X-ray diffraction under different atmospheres

Preparation and characterization of hydrogels with potential for use as biomaterials

Hydrogels have been extensively explored for biomedical applications due to their ability to absorb high water content in its structure, which gives excellent biocompatibility. This work aims at obtaining biocompatible hydrogels with potential for use in increasing the mechanical strength of bone substitutes, or controlled drug release. Poly (N-vinyl-2-pyrrolidone) hydrogels were prepared by free radical polymerization with and without the addition of acrylic acid. Azobisisobutyronitrile and ammonium persulfate were used as initiator and N,N-methylenebisacrylamide was used as the crosslinking agent. The characterization of the hydrogels was performed by thermogravimetric analysis, differential scanning calorimetry, infrared spectroscopy and swelling properties. The results obtained demonstrate different degrees of crosslinking and swelling of up to 490 ± 30%. The different properties of the hydrogels suggest different applications

Hydrogels for Therapeutic Delivery : Current Developments and Future Directions

Hydrogels are attractive materials for the controlled release of therapeutics because of their capacity to embed biologically active agents in their water-swollen network. Recent advances in organic and polymer chemistry, bioengineering and nanotechnology have resulted in several new developments in the field of hydrogels for therapeutic delivery. In this Perspective, we present our view on the state-of-the-art in the field, thereby focusing on a number of exciting topics, including bioorthogonal cross-linking methods, multicomponent hydrogels, stimuli-responsive hydrogels, nanogels, and the release of therapeutics from 3D printed hydrogels. We also describe the challenges that should be overcome to facilitate translation from academia to the clinic and last, we share our ideas about the future of this rapidly evolving area of research

Nuclear Magnetic Resonance Spectroscopy. Carbon-13 Chemical Shifts in Acyclic and Alicyclic Alcohols

The chemical shifts of ^(13)C in a variety of acyclic and alicyclic alcohols have been determined by high resolution nmr spectroscopy with the aid of proton decoupling. It has been found that there are rather good linear relationships between carbon chemical shifts in alcohols and analogously constituted hydrocarbons, wherein a methyl group replaces the hydroxyl group. The linear correlation coefficients for relationships of the general type δ_CROH = Aδ_CRCHa + B are better than 0.98 for shifts of corresponding ɑ (directly attached hydroxyl), β, y, and δ carbons for a variety of primary, secondary, and tertiary acyclic alcohols and cyclohexanols carrying both axial and equatorial substituents. The shifts of the carbons of a number of cycloalkanols have been investigated in hope of providing information about conformations in medium-sized ring compounds

Nuclear Magnetic Resonance Spectroscopy. Effects of Molecular Asymmetry on Carbon-13 Chemical Shifts

A nearby center of molecular asymmetry often induces magnetic nonequivalence of the protons of an isopropyl group (or of a methylene group), and this phenomenon has been the subject of many investigations. We report here the first observance of the effect of molecular asymmetry on the resonances of methyl carbons in isopropyl groups in compounds of the type (CH_3)_2-CH(CH_2)_nCHR_1R-2