Superior antioxidant polymer films created through the incorporation of grape tannins in ethyl cellulose

Agro-wastes represent an abundant and economical source of antioxidant compounds. Extraction and incorporation of antioxidants from these compounds into ethyl cellulose films provides the basis for an active packaging material. Grape tannin extract (GT) incorporation into ethyl cellulose results in hydrogen bonding between polyphenols and ethyl cellulose strands, which allows for the polyphenols to remain active and to be securely incorporated. Incorporation of 0.5 % GT in ethyl cellulose produced a significant increase (p < 0.01) in antioxidant activity while not altering physical or mechanical properties. A higher loading of GT at 3.0 % into ethyl cellulose resulted in further improvement in antioxidant activity (12-fold), while a slight decrease in the tensile properties was noted due to the plasticizing effect of GT as a consequence of disruption of the intermolecular hydrogen bonding.     

Surface oxidability of pure liquid metals and alloys

The analysis of the oxygen-liquid metal interaction is a topic of particular technological interest. A deep knowledge of the kinetics and transport mechanisms involved in the oxidation phenomena is necessary: the effect of oxidation reactions taking place in the gas phase and the evaporation of oxides must be considered.This paper aims to review our works in order to provide a systematic analysis of the oxidation of pure metals and determine the most likely to keeping oxygen-free the surface in a binary alloy.In addition, the upgrading of this theoretical approach, here briefly described, is addressed to give a contribution to a better understanding of the evolution of oxidation phenomena close to the solid-liquid-gas interfaces.     

Polymerization of (E)‐1,3‐Pentadiene and (E)‐2‐methyl‐1,3‐pentadiene with neodymium catalysts: Examination of the factors that affect the stereoselectivity

(E)‐1,3‐Pentadiene (EP) and (E)‐2‐methyl‐1,3‐pentadiene (2MP) were polymerized to cis‐1,4 polymers with homogeneous and heterogeneous neodymium catalysts to examine the influence of the physical state of the catalyst on the polymerization stereoselectivity. Data on the polymerization of (E)‐1,3‐hexadiene (EH) are also reported. EP and EH gave cis‐1,4 isotactic polymers both with the homogeneous and with the heterogeneous system, whereas 2MP gave an isotactic cis‐1,4 polymer with the heterogeneous catalyst and a syndiotactic cis‐1,4 polymer, never reported earlier, with the homogeneous one. For comparison, the results obtained with the soluble CpTiCl₃‐based catalyst (Cp = cyclopentadienyl), which gives cis‐1,4 isotactic poly(2MP), are examined. A tentative interpretation is given for the mechanism of the formation of the stereoregular polymers obtained and a complete NMR characterization of the cis‐1,4‐syndiotactic poly(2MP) is reported. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 3227–3232     

Synthesis of Aminopyridines and Aminopyridones by Cobalt‐Catalyzed [2+2+2] Cycloadditions Involving Yne‐Ynamides: Scope,Limitations, and Mechanistic Insights

An in‐depth study of the cobalt‐catalyzed [2+2+2] cycloaddition between yne‐ynamides and nitriles to afford aminopyridines has been carried out. About 30 nitriles exhibiting a broad range of steric demand and electronic properties have been evaluated, some of which open new perspectives in metal‐catalyzed arene formation. In particular, the use of [CpCo(CO)(dmfu)] (dmfu=dimethyl fumarate) as a precatalyst made possible the incorporation of electron‐deficient nitriles into the pyridine core. Modification of the substitution pattern at the yne‐ynamide allows the regioselectivity to be switched toward 3‐ or 4‐aminopyridines. Application of this synthetic methodology to the construction of the aminopyridone framework using a yne‐ynamide and an isocyanate was also briefly examined. DFT computations suggest that 3‐aminopyridines are formed by formal [4+2] cycloaddition between the nitrile and the intermediate cobaltacyclopentadiene, whereas 4‐aminopyridines arise from an insertion pathway.     

Synthesis and Chemistry of New Central and Planar Chiral Sulfur-Containing Ferrocenyl Compounds

Abstract

Enantiomerically pure 2-hydroxyalkyl, 2-aminoalkyl and 2-iminoalkyl ferrocenyl p-tolylsulfides are easily prepared in good yields and with complete diastereocontrol from (S)-(2-p-tolylthio)ferrocencarboxyaldehyde. 2-Iminoalkyl ferrocenyl derivatives can be used as ligands in asymmetric catalysis and as starting materials for asymmetric Staudinger reaction.     

The Mechanism of 2-Furaldehyde Formation from d-Xylose Dehydration in the Gas Phase. A Tandem Mass Spectrometric Study

The mechanism of reactions occurring in solution can be investigated also in the gas phase by suited mass spectrometric techniques, which allow to highlight fundamental mechanistic features independent of the influence of the medium and to clarifying controversial hypotheses proposed in solution studies. In this work, we report a gas-phase study performed by electrospray triple stage quadrupole mass spectrometry (ESI-TSQ/MS) on the dehydration of d-xylose, leading mainly to the formation of 2-furaldehyde (2-FA). It is generally known in carbohydrate chemistry that the thermal acid catalyzed dehydration of pentoses leads to the formation of 2-FA, but several aspects on the solution-phase mechanism are controversial. Here, gaseous reactant ions corresponding to protonated xylose molecules obtained from ESI of a solution containing d-xylose and ammonium acetate as protonating reagent were allowed to undergo collisionally activated decomposition (CAD) into the triple stage quadrupole analyzer. The product ion mass spectra of protonated xylose are characterized by the presence of ionic intermediates arising from xylose dehydration, which were structurally characterized by their fragmentation patterns. As expected, the xylose triple dehydration leads to the formation of the ion at m/z 97, corresponding to protonated 2-FA. On the basis of mass spectrometric evidences, we demonstrated that in the gas phase, the formation of 2-FA involves protonation at the OH group bound to the C1 atom of the sugar, the first ionic intermediate being characterized by a cyclic structure. Finally, energy resolved product ion mass spectra allowed to obtain information on the energetic features of the d-xylose→2-FA conversion.

One step nanoencapsulation of corrosion inhibitors for gradual release application

The direct application of corrosion inhibitors on metal surfaces is potentially dangerous for the environment and the restoration operators, thus new conservation strategies are mandatory. In this study, two copper corrosion inhibitors, 1H-benzotriazole (BTA) and 5-phenyl-1H-tetrazole (PT), are encapsulated in a silica nanocontainer, for future application in smart coatings, with the aim to reduce the amount of chemicals used in treatments, their dispersion in the environment and the direct exposure of the operators to these chemicals. In particular, composite silica nanocapsules, containing the corrosion inhibitors, are prepared via one-step synthesis, based on mini-emulsion polymerisation processes.The morphology, structure, and texture of these loaded silica nanocontainers are characterised by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and N₂ physisorption (BET/BJH). Micro-Raman spectroscopy (RS) is performed to characterise the composition. UV–visible spectroscopy and thermal analysis (TG/DSC) are performed for the loading and encapsulation efficiency (L%, EE%) study.Synthesised nanocapsules show a core-shell structure and, when loaded with the inhibitors, have size ranging from about 130 to 170 nm and a BET surface area of the order of 800 m²/g. The EE% is maximum in the case of BTA and decreases to ～52% in the case of PT.     

Recent advances in the field of diolefin polymerization with transition metal catalysts

Recent advances in the field of catalysis for 1,3-diene polymerization and in the interpretation of the polymerization mechanism are examined. Catalysts prepared from methylaluminoxanes and soluble transition metal compounds are in general more active than the analogous systems prepared from AlR₃. With some catalysts, however, (e.g. lanthanide systems) a high activity is obtained only when transition metal compounds containing preformed metal-carbon bonds are used. Methylaluminoxanes affect also the stereospecificity of the polymerization. Active and stereospecific systems are obtained from monocyclopentadienyl derivatives of Ti and aluminoxanes. Recent views on the factors that determine stereospecificity are examined. Schemes are presented for the formation of iso- or syndiotactic polymers, with 1,2, cis-1,4 or trans-1,4 structure, from various dienes.