Enzymatic synthesis of a polymeric antioxidant for efficient stabilization of polypropylene

Antioxidant Activity of Biogenic Cinnamic Acid Derivatives in Polypropylene

Antioxidants (AOs) from natural resources are an attractive research area, as petroleum-based products can be replaced in polymer stabilization. Therefore, novel esters based on the p-hydroxycinnamic acids p-coumaric acid, ferulic acid and sinapic acid were synthesized and their structure properties relationships were investigated. The structures of the novel bio-based antioxidants were verified using NMR and Fourier-transform infrared (FTIR) spectrometry. The high thermal stability above 280 °C and, therefore, their suitability as potential plastic stabilizers were shown using thermal gravimetric analysis (TGA). The radical scavenging activity of the synthesized esters was evaluated by using the 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay. Stabilization performance was evaluated in polypropylene (PP) using extended extrusion experiments, oxidation induction time (OIT) measurements and accelerated heat aging. In particular, the sinapic acid derivative provides a processing stability of PP being superior to the commercial state-of-the-art stabilizer octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate.

Sulfated Oligomers of Tyrosol: Toward a New Class of Bioinspired Nonsaccharidic Anticoagulants

Sulfated phenolic polymers have extensively been investigated as anticoagulant agents in view of their higher bioavailability and resistance to degradation compared to heparins, allowing for increased half-lives. In this frame, we report herein the preparation of sulfated derivatives of tyrosol, one of the most representative phenolic constituents of extra virgin olive oil, by different approaches. Mild sulfation of OligoTyr, a mixture of tyrosol oligomers, that has been reported to possess antioxidant properties and osteogenic activity, afforded OligoTyrS I in good yields. Elemental analysis, NMR, and MALDI-MS investigation provided evidence for an almost complete sulfation at the OH on the phenylethyl chain, leaving the phenolic OH free. Peroxidase/H₂O₂ oxidation of tyrosol sulfated at the alcoholic group (TyrS) also provided sulfated tyrosol oligomers (OligoTyrS II) that showed on structural analysis highly varied structural features arising likely from the addition of oxygen, derived from water or hydrogen peroxide, to the intermediate quinone methides and substantial involvement of the phenolic OH group in the oligomerization. In line with these characteristics, OligoTyrS I proved to be more active than OligoTyrS II as antioxidant in the 2,2-diphenyl-1-picrylhydrazyl (DPPH) and ferric reducing/antioxidant power (FRAP) assays and as anticoagulant in the classical clotting times, mainly in prolonging the activated partial thromboplastin time (APTT). After intraperitoneal administration in mice, OligoTyrS I was also able to significantly decrease the weight of an induced thrombus. Data from chromogenic coagulation assays showed that the anticoagulant effect of OligoTyrS I was not dependent on antithrombin or factor Xa and thrombin direct inhibition. These results clearly highlight how some structural facets of even closely related phenol polymers may be critical in dictating the anticoagulant activity, providing the key for the rationale design of active synthetic nonsaccharidic anticoagulant agents alternative to heparin.

Acid Treatment Enhances the Antioxidant Activity of Enzymatically Synthesized Phenolic Polymers

Phenolic polymers produced by enzymatic oxidation under biomimetic and eco-friendly reaction conditions are usually endowed with potent antioxidant properties. These properties, coupled with the higher biocompatibility, stability and processability compared to low-molecular weight phenolic compounds, open important perspectives for various applications. Herein, we report the marked boosting effect of acid treatment on the antioxidant properties of a series of polymers obtained by peroxidase-catalyzed oxidation of natural phenolic compounds. Both 2,2-diphenyl-1-picrylhydrazyl (DPPH) and ferric reducing/antioxidant power (FRAP) assays indicated a remarkable increase in the antioxidant properties for most phenolic polymers further to the acid treatment. In particular, up to a ca. 60% decrease in the EC50 value in the DPPH assay and a 5-fold increase in the Trolox equivalents were observed. Nitric oxide- and superoxide-scavenging assays also indicated highly specific boosting effects of the acid treatment. Spectroscopic evidence suggested, in most cases, that the occurrence of structural modifications induced by the acid treatment led to more extended π-electron-conjugated species endowed with more efficient electron transfer properties. These results open new perspectives toward the design of new bioinspired antioxidants for application in food, biomedicine and material sciences.

Effects of steam explosion pretreatment on the composition and biological activities of tartary buckwheat bran phenolics

Steam explosion (SE) is an efficient technology to disrupt materials for improving their quality. In this study, SE was applied to release phenolics and improve the roughening of tartary buckwheat bran. The results showed that SE promoted the dissolution of phenolics, particularly, the content of the bound fraction was nearly increased by two times (0.36 vs. 0.99 mg GAE per g DW). The analysis of the phenolic composition showed that SE improved the liberation of bound pyrogallic acid, protocatechuic acid and caffeic acid. The biological activity tests indicated that SE effectively enhanced the oxygen radical absorbance capacity (ORAC) in vitro of the extract of bound phenolics by 270%. It also improved the cellular antioxidant activity (CAA) in vitro of the extract of free phenolics by 215%. Furthermore, SE showed potential in improving the antiproliferative activity of the total phenolic extract against Caco-2 cells as well as the bound phenolic extract against HepG2 cells in vitro.

Synthesis and antioxidant activities of phenolic Schiff base monomers and polymers

In this work, synthesis, characterization, and antioxidant activities of two Schiff base monomers (1 and 2) and their corresponding oxidation products (3 and 4) were reported. The monomers were prepared by condensation of 8-amino-2-naphthol with 2,4-dihydroxybenzaldehyde and 3,4-dihydroxybenzaldehyde, and then, they were oxidized to in alkaline medium by NaOCl to obtain the corresponding oxidation products. The compounds 1–4 were characterized by various spectral techniques. The analysis results indicated that the oxidation products had a chain structure consisting of randomly ordered phenylene and oxyphenylene units. In vitro antioxidant activities of 1–4 were evaluated against a ABTS cation radical and a DPPH free radical and compared with standard natural antioxidants, vitamin C (ascorbic acid), and vitamin E (α-tocopherol). The ferric reducing antioxidant power and ferrous-ion chelating activities of 1–4 were also determined.

Disentangling structure-dependent antioxidant mechanisms in phenolic polymers by multiparametric EPR analysis

Excellent and selective correlations between the electron-transfer (ET) or hydrogen atom transfer (HAT) capacity (DPPH and lipid peroxidation inhibition assays) and EPR indices of π-electron spin delocalization delineate specific structural determinants of antioxidant activity in biomimetic phenolic polymers.

Natural Phenol Polymers: Recent Advances in Food and Health Applications

Natural phenol polymers are widely represented in nature and include a variety of classes including tannins and lignins as the most prominent. Largely consumed foods are rich sources of phenol polymers, notably black foods traditionally used in East Asia, but other non-edible, easily accessible sources, e.g., seaweeds and wood, have been considered with increasing interest together with waste materials from agro-based industries, primarily grape pomace and other byproducts of fruit and coffee processing. Not in all cases were the main structural components of these materials identified because of their highly heterogeneous nature. The great beneficial effects of natural phenol-based polymers on human health and their potential in improving the quality of food were largely explored, and this review critically addresses the most interesting and innovative reports in the field of nutrition and biomedicine that have appeared in the last five years. Several in vivo human and animal trials supported the proposed use of these materials as food supplements and for amelioration of the health and production of livestock. Biocompatible and stable functional polymers prepared by peroxidase-catalyzed polymerization of natural phenols, as well as natural phenol polymers were exploited as conventional and green plastic additives in smart packaging and food-spoilage prevention applications. The potential of natural phenol polymers in regenerative biomedicine as additives of biomaterials to promote growth and differentiation of osteoblasts is also discussed.

Powering tyrosol antioxidant capacity and osteogenic activity by biocatalytic polymerization

Oxidative polymerization of tyrosol afforded a mixture of oligomers (OligoTyr) which proved to be more active than tyrosol as antioxidant and as stimulator of alkaline phosphatase (ALP) activity when loaded into polylactic acid (PLA) scaffolds.