1,721,129 research outputs found
Methods to Measure the Antioxidant Activity of Phytochemicals and Plant Extracts
Full text linkMeasurement of antioxidant properties in plant-derived compounds requires appropriate methods that address the mechanism of antioxidant activity and focus on the kinetics of the reactions involving the antioxidants. Methods based on inhibited autoxidations are the most suited for chain-breaking antioxidants and for termination-enhancing antioxidants, while different specific studies are needed for preventive antioxidants. A selection of chemical testing methods is critically reviewed, highlighting their advantages and limitations and discussing their usefulness to investigate both pure molecules and raw extracts. The influence of the reaction medium on antioxidants' performance is also addressed
Maximizing the reactivity of phenolic and aminic radical-trapping antioxidants: Just add nitrogen!
No full textConspectus Hydrocarbon autoxidation, the archetype free radical chain reaction, challenges the longevity of both living organisms and petroleum-derived products. The most important strategy in sloing this process is via the intervention of radical-trapping antioxidants (RTAs), hich are abundant in nature and included as additives to almost every petroleum-derived product as ell as several other commercial products. Accordingly, a longstanding objective of many academic and industrial scientists has been the design and development of novel RTAs that can outperform natural and industrial standards, such as α-tocopherol, the most biologically active form of vitamin E, and dialkylated diphenylamines, respectively.Some time ago e recognized that attempts to maximize the reactivity of phenolic RTAs had largely failed because substitution of the phenolic ring ith electron-donating groups to eaken the O-H bond and accelerate the rate of H atom transfer to radicals leads to compounds that are unstable in air. e surmised that incorporating nitrogen into the phenolic ring ould render them more stable to one-electron oxidation, enabling their substitution ith strong electron-donating groups. Guided by computational chemistry, e demonstrated that replacing the phenyl ring in very electron-rich phenols ith either 3-pyridyl or 5-pyrimidyl rings leads to phenolic-like RTAs ith good air stability and great reactivity. In fact, rate constants determined for the reactions of some compounds ith peroxyl radicals ere almost 2 orders of magnitude greater than those for α-tocopherol and implied that the reactions proceeded ithout an enthalpic barrier. Folloing extensive thermochemical and kinetic characterization, e took our studies of these compounds to more physiologically relevant media, such as lipid bilayers and human lo density lipoproteins, here the heterocyclic analogues of vitamin E shone, displaying unparalleled abilities to inhibit lipid peroxidation and prompting their current investigation in animal models of degenerative disease. Moreover, e carried out studies of these compounds in several industrially relevant contexts and in particular demonstrated that they could be used synergistically ith less reactive, less expensive, phenolic RTAs.More recently, our attention has turned to the application of these ideas to maximizing the reactivity of diarylamine RTAs that are common in additives to petroleum-derived products, such as lubricating oils, transmission and hydraulic fluids, and rubber. In doing so, e have developed the most reactive diarylamines ever reported. The 3-pyridyl- and 5-pyrimidyl-containing diarylamines are easily accessed using Pd- and/or Cu-catalyzed cross-coupling reactions, and display an ideal compromise beteen reactivity and stability. The most reactive compounds are characterized by rate constants for reactions ith peroxyl radicals that are independent of temperature, implying that-as for the most reactive heterocyclic phenols-these reactions proceed ithout an enthalpic barrier. Unprecedented reactivity as also observed hen hydrocarbon autoxidations ere carried out at elevated temperatures, real-orld conditions here diarylamines are uniquely effective because of a catalytic RTA activity that makes use of the hydrocarbon substrate as a sacrificial reductant. Our studies to date suggest that heterocyclic diarylamines have real potential to increase the longevity of petroleum-derived products in a variety of applications here diphenylamines are currently used
MODULATION OF BIORELEVANT RADICAL REACTIONS BY NON‐COVALENT INTERACTIONS
No full textRadical reactions are involved in a multitude of relevant
processes and their importance is increasingly recognized
in different fields ranging from biochemistry to materials
science.
For instance, radical polymerization accounts for
approximately 45% of world polymer production [1]; on the
other hand, the involvement of transient radical species in
enzyme regulated processes in living organisms has stimulated,
in recent years, enormous research efforts to rationalize
their role in key physiological processes like
mitochondrial respiration and aging [2, 3] or in the pathogenesis
of several diseases [4].
Perhaps the best known example of radical reaction is
hydrocarbon autoxidation, a chain process that affects any
organic material, from food to petrol‐derived chemicals to
human beings, existing under an oxygen‐rich atmosphere [5].
As a consequence, antioxidants and radical‐chain inhibitors
are among the most important compounds used to control
key radical reactions [5]. They act by trapping chain‐carrying
radical species, thereby competing with chain propagation,
as illustrated in Scheme 20.1. Their rational design and use
need to be strictly based on their reactivity with radical
species. Indeed, the understanding of radical reactions and
their role in biology, along with their use and control in
synthetic chemistry or in medicine, requires detailed
knowledge of their kinetics and how it is influenced by the
reaction medium.
In this chapter it will be explained how non‐covalent
interactions control the rates and the products of reactions
that are typical of the radicals involved in autoxidation,
namely, peroxyl (ROO∙), phenoxyl (PhO∙), and alkoxyl
(RO∙) radicals. These radicals are not only of biological
interest, but they are also key intermediates in green synthesis
protocols, which aim at obtaining fine chemicals from
renewable materials under mild conditions. For this reason,
we will illustrate some selected examples of biomimetic radical
reactions that are made possible by the control of these
reactive intermediates by non‐covalent interaction
Anti-tyrosinase and antioxidant activity of meroterpene bakuchiol from Psoralea corylifolia (L.)
Full text linkRapid liquid chromatography-tandem mass spectrometry analysis of 4-hydroxynonenal for the assessment of oxidative degradation and safety of vegetable oils
No full textA novel method for the UHPLC-MS/MS analysis of (E)-4-hydroxynonenal (4-HNE) is described. The method is based on derivatization of 4-HNE with pentafluorophenylhydrazine (1) or 4-trifluoromethylphenylhydrazine (2) in acetonitrile in the presence of trifluoroacetic acid as catalyst at room temperature and allows complete analysis of one sample of vegetable oil in only 21. min, including sample preparation and chromatography. The method involving hydrazine 1, implemented in an ion trap instrument with analysis of the transition m/z 337. →. 154 showed LOD. = 10.9. nM, average accuracy of 101% and precision ranging 2.5-4.0% RSD intra-day (2.7-4.1% RSD inter-day), with 4-HNE standard solutions. Average recovery from lipid matrices was 96.3% from vaseline oil, 91.3% from sweet almond oil and 105.3% from olive oil. The method was tested on the assessment of safety and oxidative degradation of seven samples of dietary oil (soybean, mixed seeds, corn, peanut, sunflower, olive) and six cosmetic-grade oils (avocado, blackcurrant, apricot kernel, echium, sesame, wheat germ) and effectively detected increased 4-HNE levels in response to chemical (Fenton reaction), photochemical, or thermal stress and aging, aimed at mimicking typical oxidation associated with storage or industrial processing. The method is a convenient, cost-effective and reliable tool to assess quality and safety of vegetable oils
Substituted Diarylamines and Use of Same as Antioxidants
No full textA compound of Formula I, Formula IA, Formula IB, or Formula II, or an acid or base addition salt thereof, and use of these compounds as antioxidants. In one embodiment, a compound of Formula II, wherein each of X, Y, and Z are independently a carbon or nitrogen atom; R1 and R2 are each independently a hydrogen or an electron donating group, but are not both hydrogen, and wherein R1, and R2 are each bonded to a carbon atom in their own respective aryl ring
Synergic Antioxidant Activity of γ-Terpinene with Phenols and Polyphenols Enabled by Hydroperoxyl Radicals
Full text linkAntioxidant interactions of γ-terpinene with α-tocopherol mimic 2,2,5,7,8-pentamethyl-6-chromanol (PMHC)
and caffeic acid phenethyl ester (CAPE), used as models, respectively, of mono- and poly-phenols were
demonstrated by differential oximetry during the inhibited autoxidation of model substrates: stripped sunflower
oil, squalene, and styrene. With all substrates, γ-terpinene acts synergistically regenerating the chain-breaking
antioxidants PMHC and CAPE from their radicals, via the formation of hydroperoxyl radicals. The inhibition
duration for mixtures PMHC/γ-terpinene and CAPE/γ-terpinene increased with γ-terpinene concentration, while
rate constants for radical-trapping were unchanged by γ-terpinene, being 3.1 × 106 and 4.8 × 105 M 1s 1 for
PMHC and CAPE in chlorobenzene (30 ◦C). Using 3,5-di-tert-butylcatechol and 3,5-di-tert-butyl-1,2-bezoquinone
we demonstrate that γ-terpinene can reduce quinones to catechols enabling their antioxidant activity. The
different synergy mechanism of γ-terpinene with mono- and poly-phenolic antioxidants is discussed and its
relevance is proven in homogenous lipids using natural α-tocopherol and hydroxytyrosol as antioxidants, calling
for further studies in heterogenous food products
The role of sulfur and heavier chalcogens in the chemistry of antioxidants
No full textSulfur chemistry plays a central role in cellular redox homeostasis and cysteine-derived antioxidants like glutathione are the most abundant in biological systems. Inspired by Nature, the insertion of divalent sulfur as a substituent in phenolic antioxidants, e.g in thiatocopherol, seeking for improved antioxidant performance, has been an important strategy for long time. Replacement of sulfur with heavier chalcogens like Selenium and Tellurium has brought to even more performing antioxidants, able to quench peroxyl radical in a catalytic fashion and to express unusually high reactivity. On the other hand, natural bioactive compounds like plant-derived thiosulfinates (R-S(O)S-R) own their exceptional antioxidant properties to the ability of releasing sulfenic acids, whose antioxidant behavior has only recently been clarified. The chemistry and redox properties of unstable sulfenic acids (R-SOH), and analogous selenenic acids (R-SeOH) have also recently been elucidated, to better understand the properties of chalcogen-based natural antioxidants, and to develop novel bio-inspired compounds. This fascinating chemistry will be reviewed and the most significant achievement will be presented
Measuring Antioxidant Activity in Bioorganic Samples by the Differential Oxygen Uptake Apparatus: Recent Advances
Full text linkThe measure of O2 consumption during the inhibited autoxidation of an easily oxidizable substrate is one of the most reliable and predictive methods to assess antioxidant activity, especially for structure-activity relationship studies, for food and industrial applications. The differential oxygen uptake apparatus described herein represents a powerful and cost-effective way to obtain antioxidant activity from inhibited autoxidation studies. These experiments provide the rate constant and the stoichiometry of the reaction between antioxidants and peroxyl radicals (ROO∙), which are involved in the propagation of radical damage. We show the operation principles and the utility of this instrumentation in the bioorganic laboratory, with regard to the recent advances in this field, ranging from the study of natural antioxidants in biomimetic system, to the use of substrates generating hydroperoxyl radicals, and to the evaluation of novel nanoantioxidants
Antioxidant activity of nanomaterials
Full text linkNanomaterials represent one of the most promising frontiers in the research for improved antioxidants. Some nanomaterials, including organic (i.e. melanin, lignin) metal oxides (i.e. cerium oxide) or metal (i.e. gold, platinum) based nanoparticles, exhibit intrinsic redox activity that is often associated with radical trapping and/or with superoxide dismutase-like and catalase-like activities. Redox inactive nanomaterials can be transformed into antioxidants by grafting low molecular weight antioxidants on them. Herein, we propose a classification of nanoantioxidants based on their mechanism of action, and we review the chemical methods used to measure antioxidant activity by providing a rationale of the chemistry behind them
- …
