1,721,051 research outputs found
Oximetry methods for evaluating the activity of nanoantioxidants (minireview)
No full textNanomaterials are probably the most promising and unexplored frontier in the ongoing research for better antioxidants. Testing the efficacy of these materials however requires significant efforts to improve current protocols. In this minireview, we describe the advantages of the methods based on the detection of oxygen consumption during the autoxidation of an organic substrate. The differential oxygen uptake apparatus is a powerful and cost-effective way to measure antioxidant activity from inhibited autoxidation studies, especially in organic solvents. Besides, electrochemical or optical oxygen probes are specifically designed to quantify dissolved O2 in water, where autoxidations are performed by using micellized linoleate or liposomes as oxidizable substrates. Selected examples of the use of these techniques to rationalize the effect of nanoantioxidants are reported
CHAPTER 11: Vitamin E. Inspired Synthetic Antioxidants
No full textThe search for novel antioxidants inspired by the structure of vitamin E was made possible by rationalization of the physical-chemical properties at the basis of vitamin E bioactivity and has contributed significantly to such rationalization. Hundreds of novel compounds have been synthesized and tested, a representative selection of which (51 molecules) is illustrated and discussed in this chapter, highlighting the structure-activity relationships behind their antioxidant activity. Among them, BO-653, thiatocopherol and related compounds, selenotocopherol and related compounds, tellurophenols, N-tocopherol and related compounds, and Mito-Vitamin E are given special attention. The discussion focuses on the absolute rate constant for trapping peroxyl radicals in solution. When available, the performance in biomimetic models, like the protection of low density lipoproteins, along with the results of in vivo testing for pharmaceutical applications is also addressed. Some of the synthetic analogues largely outperformed the most active natural α-tocopherol, both in model systems and in vivo. However, none of these compounds has yet reached medical practice or is currently approved as a pharmaceutical, which calls for further research
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.[GRAPHICS]
Measuring Antioxidant Activity in Bioorganic Samples by the Differential Oxygen Uptake Apparatus: Recent Advances
No full textThe measure of O-2 consumption during the inhibited autoxidation of an easily oxidizable substrate is one of the most reliableand 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 center dot), 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
Expanding the spectrum of polydopamine antioxidant activity by nitroxide conjugation
Full text linkPolydopamine (PDA) materials are important due to their unique physicochemical properties and their potential as chemopreventive agents for diseases connected with oxidative stress. Although PDA has been suggested to display antioxidant activity, its efficacy is controversial and its mechanism of action is still unclear. Herein, we report that accurately purified PDA nanoparticles in water at pH 7.4 are unable to quench alkylperoxyls (ROO ̇), which are the radicals responsible for the propagation of lipid peroxidation, despite PDA reacting with the model DPPH ̇ and ABTS ̇+radicals. PDA nanoparticles prepared by copolymerization of dopamine with the dialkyl nitroxide 4-NH2TEMPO show instead good antioxidant activity, thanks to the ROO ̇ trapping ability of the nitroxide. Theoretical calculations performed on a quinone-catechol dimer, reproducing the structural motive of PDA, indicate a reactivity with ROO ̇ similar to catechol. These results suggest that PDA nanoparticles have an “onion-like” structure, with a catechol-rich core, which can be reached only by DPPH ̇ and ABTS ̇+, and a surface mainly represented by quinones. The importance of assessing the antioxidant activity by inhibited autoxidation studies is also discussed
Erratum: Synergic Antioxidant Effects of the Essential Oil Component-Terpinene on High Temperature Oil Oxidation (ACS Food Sci. Technol. (2022) 2:1 (180−186) DOI: 10.1021/acsfoodscitech.1c00399)
No full textThe x-Axis labeling of Figure 1B in the original publication (mg/mL) was incorrect. Instead, the correct label is %. This erroneous picture did not influence our findings. We regret that we did not find this error during the submission procedure and galley proofs. Figure 1B and the caption has been corrected as follows: Figure 1. (A) Oxygen consumption during the oxidation of stripped sunflower oil (SSO, 2 g) at 130 °C: without any additive (a), with γ-terpinene (1%, w/w) (b); with α-Tocopherol (0.1%, w/w) (c); with α-tocopherol (0.1%, w/w) and γ-Terpinene (1%, w/w) (d). (B) Duration of the induction period of α-Tocopherol 0.1% on increasing γ-Terpinene concentration (%, w/w). (C) Concentration of hydroperoxides in stripped sunflower oil before (SSO) and after heating at 130 °C for 10.000 s without antioxidants (SSO(H)), with α-tocopherol 0.1%, w/w (SSO(H)+Toc), and with α-Tocopherol 0.1%, w/w and γ-Terpinene 1%, w/w (SSO(H)+Toc+g-T)
Antioxidant activity of nanomaterials
No full textNanomaterials 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
1-Methyl-1,4-cyclohexadiene as a Traceless Reducing Agent for the Synthesis of Catechols and Hydroquinones
No full textPro-aromatic and volatile 1-methyl-1,4-cyclohexadiene (MeCHD) was used for the first time as a valid H-atom source in an innovative method to reduce ortho or para quinones to obtain the corresponding catechols and hydroquinones in good to excellent yields. Notably, the excess of MeCHD and the toluene formed as the oxidation product can be easily removed by evaporation. In some cases, trifluoroacetic acid as a catalyst was added to obtain the desired products. The reaction proceeds in air and under mild conditions, without metal catalysts and sulfur derivatives, resulting in an excellent and competitive method to reduce quinones. The mechanism is attributed to a radical reaction triggered by a hydrogen atom transfer from MeCHD to quinones, or, in the presence of trifluoroacetic acid, to a hydride transfer process
Quantitative role of far-infrared emission on diabatic forcing of the middle and upper troposphere in clear and cloudy conditions
No full textChain-breaking antioxidant activity of hydroxylated and methoxylated magnolol derivatives: The role of H-bonds
No full textChemical modification of magnolol, an uncommon dimeric neolignan contained in Magnolia genus trees, provides a unique array of polyphenols having interesting biological activity potentially related to radical scavenging. The chain-breaking antioxidant activity of four new hydroxylated and methoxylated magnolol derivatives was explored by experimental and computational methods. The measurement of the rate constant of the reaction with ROO center dot radicals (k(inh)) in an apolar solvent showed that the introduction of hydroxyl groups ortho to the phenolic OH in magnolol increased the k(inh) value, being 2.4 x 10(5) M-1 s(-1) and 3.3 x 10(5) M-1 s(-1) for the mono and the dihydroxy derivatives respectively (k(inh) of magnolol is 6.1 x 10(4) M-1 s(-1)). The di-methoxylated derivative is less reactive than magnolol (k(inh) = 1.1 x 10(4) M-1 s(-1)), while the insertion of both hydroxyl and methoxyl groups showed no effect (6.0 x 10(4) M-1 s(-1)). Infrared spectroscopy and theoretical calculations allowed a rationalization of these results and pointed out the crucial role of intramolecular H-bonds. We also show that a correct estimation of the rate constant of the reaction with ROO center dot radicals, by using BDE(OH) calculations, requires that the geometry of the radical is as close as possible to that of the parent phenol
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