1,721,072 research outputs found
Novel antioxidant bioinspired phenolic polymers and their applications in packaging
No full textPolymers of natural polyphenols have so far received little attention as bioavailable, biocompatible antioxidants for different applications e.g. in packaging and related technologies. Expected advantages with respect to the monomers would include lower volatility (with reduced adverse effects), greater chemical stability under processing conditions and lower tendency to be released from the polymer into the contact medium (food, water, etc.).
Herein we report data on the synthesis, structural characterization and antioxidant properties of two novel bioinspired phenolic polymers prepared by horseradish/H2O2 oxidation of tyrosol (polyTYR) and caffeic acid methyl ester (polyCAME). The materials, obtained in 80-85% yields, were subjected to structural characterization by solid state CPMAS NMR, mass spectrometry and gel permeation chromatography (GPC). ESI(-)/MS and NMR analysis indicated that polyTYR was a mixture of regular oligomers up to the undecamer with heptamer as the most abundant, all featuring units linked through C-C bonds. GPC showed an average molecular weight of 1862 Da with a polydispersity index of 1.64. ESI(-)/MS of polyCAME showed oligomers up to at least the decamer stage, peaking at the tetramer. Analysis of the clusters of the pseudomolecular ion peaks and the presence of CH carbons due to O-substituted benzylic positions in NMR spectra suggested a structure including dihydrobenzofuran units. Both PolyTYR and polyCAME exhibited antioxidant properties in the 2,2-diphenyl-1-picrylhydrazyl (DPPH) and ferric reducing/antioxidant power (FRAP) assays and proved to be efficient hydroxyl radical scavengers in a Fenton reaction assay. The potential of PolyCAME as stabilizer toward polyethylene (PE) thermal and photo-oxidative degradation was also evaluated. PolyCAME exhibited high stability toward decarboxylation and oxidative degradation during the thermal processes associated with PE film preparation. Characterization of PE films by thermal methods, photo-oxidative treatments combined with chemiluminescence and FTIR spectroscopy and mechanical tests indicated a significant effect of polyCAME on PE durability as shown for example by the increase of the Oxidative Induction Time (OIT).1The synthesized phenolic biopolymers are thus proposed as novel easily accessible, eco-friendly and biocompatible materials for a sustainable approach in packaging and other applications.
1) Ambrogi, V.; Panzella, L.; Persico, P.; Cerruti, P.; Lonz, C. A.; Carfagna, C.; Verotta, L.; Caneva, E.; Napolitano, A.; d'Ischia, M. Biomacromolecules 2014, 15, 302-310
Stereochemical Control in CO/p-Methylstyrene Copolymerization Catalyzed by a-Diimine Pd(II) Complexes
No full text
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
From atactic to isotactic CO/p-methylstyrene copolymerizations by proper modifications of Pd(II) catalysts bearing achiral a-diimines
No full textThe Effect of the Prepolymer Composition on the Environmental Aging of Epoxy Based Resins
No full textComputational Overview of a Pd-Catalyzed Olefin Bis-alkoxycarbonylation Process
Full text linkA comprehensive density functional theory analysis is reported for the one-pot bis-alkoxycarbonylation reaction of olefins to form succinic acid esters by action of the catalyst (N-N)Pd(TFA)2 (N-N = bis(2,6-dimethylphenyl)-2,3-dimethyl-1,4-diazabutadiene, TFA- = CF3CO2-). The selective and efficient process involves alkene (H2C=CHR), CO, methanol, and p-benzoquinone (BQ) molecules as reactants. The catalytic mechanism, previously proposed on the basis of available experimental and literature data, is critically revised here. A plethora of optimized intermediates and transition states and their correlating energy profiles allow a step by step reconstruction of the entire cycle, highlighting key mechanistic aspects, such as the role of the R substituent in the olefin. One of its effects is determined by the presence of a 2e- donor group, which, depending on its power, may affect the catalysis up to its total inhibition. As another aspect, the key diester product forms through a reductive elimination step (Pd(II) → Pd(0) transformation) that excludes the previously proposed attainment of a Pd(II)-hydride complex. Finally, the paper illustrates the action of the sacrificial BQ oxidant in the restoration of the original Pd(II) catalyst, as found for other strictly related cases. The energy profile indicates that the rate-determining step occurs in the initial part of the reaction, given a +29.6 kcal mol-1 energy barrier, associated with a methoxo migration into an adjacent CO ligand. The result foreshadows a rather slow activation of the catalyst and a long duration of the cycle
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