Radical Trapping Efficiency Research Articles

Block Copolymers of Polyolefins with Polyacrylates: Analyzing and Improving the Blocking Efficiencies Using MILRad/ATRP Approach.

Despite their industrial ubiquity, polyolefin-polyacrylate block copolymers are challenging to synthesize due to the distinct polymerization pathways necessary for respective blocks. This study utilizes MILRad, metal-organic insertion light-initiated radical polymerization, to synthesize polyolefin-b-poly(methyl acrylate) copolymer by combining palladium-catalyzed insertion-coordination polymerization and atom transfer radical polymerization (ATRP). Brookhart-type Pd complexes used for the living polymerization of olefins are homolytically cleaved by blue-light irradiation, generating polyolefin-based macroradicals, which are trapped with functional nitroxide derivatives forming ATRP macroinitiators. ATRP in the presence of Cu(0), that is, supplemental activators and reducing agents , is used to polymerize methyl acrylate. An increase in the functionalization efficiency of up to 71% is demonstrated in this study by modifying the light source and optimizing the radical trapping condition. Regardless of the radical trapping efficiency, essentially quantitative chain extension of polyolefin-Br macroinitiator with acrylates is consistently demonstrated, indicating successful second block formation.

Kinetic analysis of free radical scavenging in sonochemistry

As an advanced oxidation process, high-power ultrasound produces free radicals in aqueous solution through acoustic cavitation. Whereas radical production inside the cavitation bubble is well understood, radical scavenging outside the bubble is still unexplored quantitatively. In this study, we modeled the behavior of radicals in the scavenging process by solving the diffusion-advection-reaction equations. Using terephthalate as the scavenger, the principal reaction pathways of hydroxyl radicals are identified and the scavenging efficiency is quantified. The analysis shows that among the various reactions competing for hydroxyl radicals, the scavenging by terephthalate is in disadvantage for the small mass diffusivity. It limits the replenishment of scavengers to the reaction zone and compromises radical trapping efficiency. A parametric study puts the maximum radical trapping efficiency below 30%. Our study elucidates the key factor limiting the utilization of ultrasound-induced radicals and paves the way for future efforts to maximize the sonochemical effects.

Efficiency and capacity of antioxidant rich foods in trapping peroxyl radicals: A full evaluation of radical scavenging activity

For the first time a variety of foods, characterized by high antioxidant activity, have been tested for the reactivity by which the system of antioxidants present in these foods competes for peroxyl radicals with poly-unsaturated fatty acids. The oxygraphic method we have used, on the basis of a rigorous kinetic model, permits to obtain the reactivity that is the Peroxyl Radical Trapping Efficiency (PRTE), beyond the Peroxyl Radical Trapping Capacity (PRTC) and to assign to each food characteristic values of these parameters, so facilitating their inter-comparison. In the analyzed foods the PRTE/PRTC ratio spans more than one order of magnitude, so reflecting the quality of antioxidants present in foods. According to the PRTE values and on the basis of the serving size the ranking of antioxidant food efficiency in trapping peroxyl radicals was blueberry>red chicory>coffee>pineapple≈red wine≥orange≈dark chocolate≈apple≥tea>pomegranate.

Influence of Diameter, Length, and Chirality of Single-Walled Carbon Nanotubes on Their Free Radical Scavenging Capability

Density functional theory calculations have been used to model the influence of diameter, length, and chirality of single-walled carbon nanotubes (SWCNT) on their free radical scavenging activity. SWCNTs with wide distributions of different diameter, length, and chirality are proposed to have good free radical scavenging activity in the gas phase and in nonpolar environments. Therefore, they can be used as free radical traps with potential application in environmental and biological systems. In general, thinner tubes are expected to have better antiradical activities. However, the curvature of the tubes seems to modify the antiradical activity of armchair nanotubes. Therefore, for wide distributions of tube diameter, the zigzag SWCNTs are expected to be more efficient for free radical scavenging purposes than the armchair ones. The length of the tubes only has a minor influence on the free radical trapping efficiency of SWCNTs. From the results reported in this work, thin and zigzag nanotubes are recommended as those with the best antiradical activity, regardless of their length.

γ-irradiation of PEGd,lPLA and PEG-PLGA Multiblock Copolymers: II. Effect of Oxygen and EPR Investigation

The purpose of this research was to evaluate how the presence of oxygen can affect irradiation-induced degradation reactions of PEGd,lPLA and PEG-PLGA multiblock copolymers submitted to gamma irradiation and to investigate the radiolytic behavior of the polymers. PEGd,lPLA, PEG-PLGA, PLA, and PLGA were irradiated by using a (60)Co irradiation source in air and under vacuum at 25 kGy total dose. Mw and Mn were evaluated by gel permeation chromatography. The stability study was carried out on three samples sets: (a) polymer samples irradiated and stored in air, (b) polymer samples irradiated and stored under vacuum, and (c) polymer samples irradiated under vacuum and stored in air. The thermal and radiolytic behavior was investigated by differential scanning calorimetry and electron paramagnetic resonance (EPR), respectively. Samples irradiated in air showed remarkable Mw and Mn reduction and Tg value reduction due to radiation-induced chain scission reactions. Higher stability was observed for samples irradiated and stored under vacuum. EPR spectra showed that the presence of PEG units in multiblock copolymer chains leads to: (a) decrease of the radiolytic yield of radicals and (b) decrease of the radical trapping efficiency and faster radical decay rates. It can be concluded that the presence of oxygen during the irradiation process and the storage phase significantly increases the entity of irradiation-induced damage.

Fast and Simple Method for the Simultaneous Evaluation of the Capacity and Efficiency of Food Antioxidants in Trapping Peroxyl Radicals in an Intestinal Model System

A simple oxygraphic method, for which the theoretical and experimental bases have been recently revised, has been successfully applied to evaluate the peroxyl radical chain-breaking characteristics of some typical food antioxidants in micelle systems, among which is a system that reproduces conditions present in the upper part of the digestive tract, where the absorption and digestion of lipids occur. This method permits one to obtain from a single experimental run the peroxyl radical trapping capacity (PRTC, that is, the number of moles of peroxyl radicals trapped by a given amount of food), the peroxyl radical trapping efficiency (PRTE, that is, the reciprocal of the amount of food that reduces to half the steady-state concentration of peroxyl radicals), and the half-life of the antioxidant ( t(1/2)) when only a small fraction of peroxyl radicals reacts with the antioxidants present in foods. Examples of application of the method to various types of foodstuffs have been reported, assessing the general validity of the method in the simple and fast evaluation of the above-reported fundamental antioxidant characteristics of foods.

A method to evaluate capacity and efficiency of water soluble antioxidants as peroxyl radical scavengers

In this paper, we report on a method to evaluate the activity of water soluble and H-atom donor antioxidants as peroxyl radical scavengers in a micelle system reproducing the conditions occurring in the upper small intestine in humans, during digestion and absorption of lipids. This method, which overcomes some of the problems of the total radical trapping antioxidant parameter (TRAP) assays, measures the peroxyl radical trapping capacity ( n) and the peroxyl radical trapping efficiency IC 50 − 1 of antioxidants, that is the number “ n” of peroxyl radicals trapped by one molecule of the studied antioxidant and the reciprocal of the antioxidant concentration that halves the steady-state concentration of peroxyl radicals, respectively. These two fundamental parameters characterizing the radical chain breaking of many water soluble antioxidants, among which dietary polyphenols, can be obtained with relatively good precision from a single experiment, on the basis of a rigorous treatment of the kinetic data.

Major Phytochemicals in Apple Cultivars: Contribution to Peroxyl Radical Trapping Efficiency

Forty-one samples of apples (peel plus pulp), obtained from eight cultivars, were examined for concentration of some important phytochemicals and for antioxidant activity expressed as peroxyl radical trapping efficiency. Five major polyphenolic groups plus ascorbate were identified and quantified by HPLC in the apple varieties. Oligomeric and polymeric proanthocyanidins were found to be about two-thirds of total polyphenols. The antioxidant efficiency of the apple extracts and of representative pure compounds for each group of phytochemicals was measured in a micellar system mimicking lipid peroxidation in human plasma. Although the amount of polyphenols measured by HPLC is similar to that measured by standard methods, the antioxidant efficiency calculated on the basis of the contribution of the pure compounds was lower than the antioxidant efficiency of the apple extracts. The higher efficiency of apples appears to be strictly related to the overwhelming presence of oligomeric proanthocyanidins.

Antioxidant protection of low density lipoprotein by procyanidins: structure/activity relationships

The antioxidant activity of catechins and oligomeric procyanidins against low density lipoproteins peroxidation was studied by means of three distinct methods: cis-parinaric acid fluorescence decay, conjugated-dienes detection, and oxygen consumption. A relationship between the radical trapping efficiency of procyanidins and their structure was investigated. The results indicated that: (i) interflavan linkage type (C4C6 or C4C8) exerts a significant effect upon radical-trapping antioxidant activity of procyanidins. It is suggested that the conformation adopted by each procyanidin in aqueous solution influence their hydrophilic character, hence affecting their interaction with the peroxyl radicals present in aqueous phase and those in LDL particle (lipidic nature); (ii) antioxidant activity increase with the degree of polymerization for the compounds with (−)-epicatechin (epi) as structural unit (epi, dimer B2 (epi–epi) and trimer C1 (epi–epi–epi)); (iii) galloylation increases antioxidant activity of procyanidins, specially in the case of B2-3′′- O-gallate dimer, which revealed the maximal trapping efficiency.

Extraction resistant polymer stabilizers

AbstractA new generation of polysiloxane based polymer stabilizers is examined. The flexibility and versatility of polysiloxane backbones have allowed the development of a family of products that provide outstanding radical trapping efficiency, an unexpected resistance to extraction, and a high degree of compatibility in certain polymeric systems. Functionalization with graftable moieties results in a product that can be chemically bound to the polymer itself. The key to success in this work was optimizing the balance of graft linkages and mobility of the stabilizer chain.

Increasing the performance and permanence of polymer stabilizers

AbstractA new generation of polysiloxane based polymer stabilizers is examined. The flexibility and versatility of polysiloxane backbones have allowed the development of a family of products which provide outstanding radical trapping efficiency, an unexpected resistance to extraction, and a high degree of compatibility in certain polymeric systems. Functionalization with graftable moieties results in a product which can be chemically bound to the polymer itself. The key to success in this work was optimizing the balance of graft linkages and mobility of the stabilizer chain.

Synergistic effects of some phenolic inhibitors used in polyethylene stabilization. I. Lyoluminescence method in studying the synergistic effects of some binary mixtures of phenolic stabilizers

The effectiveness of some combinations of antioxidants as trapping agents for peroxy radicals has been evaluated by the lyoluminescence method. A sample of solid dilauryl peroxide is gamma irradiated to produce peroxy radicals then dissolved in ethylene trichloride, containing the additives under study. Chemiluminescence from recombination of the peroxy radicals is suppressed by the antioxidants and the extent of this suppression is proposed as a method of assessment of radical trapping efficiency.