3,267 research outputs found
Methods to Measure the Antioxidant Activity of Phytochemicals and Plant Extracts
No full textMeasurement 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
Lipid Peroxidation and Antioxidant Protection
No full textLipid peroxidation (LP) is the most important type of oxidative-radical damage in biological systems, owing to its interplay with ferroptosis and to its role in secondary damage to other biomolecules, such as proteins. The chemistry of LP and its biological consequences are reviewed with focus on the kinetics of the various processes, which helps understand the mechanisms and efficacy of antioxidant strategies. The main types of antioxidants are discussed in terms of structure–activity rationalization, with focus on mechanism and kinetics, as well as on their potential role in modulating ferroptosis. Phenols, pyri(mi)dinols, antioxidants based on heavy chalcogens (Se and Te), diarylamines, ascorbate and others are addressed, along with the latest unconventional antioxidant strategies based on the double-sided role of the superoxide/hydroperoxyl radical system
A Sensitivity-Based Approach to Improve Efficiency of Automotive Chassis Architecture
No full textThe strong competition of the automotive market brings the industries to look continuously for more challenging comfort and performance standards. These requirements often contrast with the need for weight reduction related to the restrictive emissions limits. In this scenario, the investments aimed at increasing the structure efficiency (stiffness-to-weight ratio) become fundamental. The objective of this work is to propose a methodology that allows to identify the most important chassis areas in terms of efficiency: The design and research efforts could then be focused on the real determinant parts. This is done through a sensitivity process that works on frame subsystems and then on each component, first varying the material properties and then the thickness (and so the mass). The designing loadcases considered are the torsional stiffness, bending stiffness, modal analysis and frequency response analysis. The results show which are the most important subsystems and components that affects the chassis efficiency and that will have to be re-designed in order to improve the current architecture
Carburacy: Summarization Models Tuning and Comparison in Eco-Sustainable Regimes with a Novel Carbon-Aware Accuracy
No full textGenerative transformer-based models have reached cutting-edge performance in long document summarization. Nevertheless, this task is witnessing a paradigm shift in developing ever-increasingly computationally-hungry solutions, focusing on effectiveness while ignoring the economic, environmental, and social costs of yielding such results. Accordingly, such extensive resources impact climate change and raise barriers to small and medium organizations distinguished by low-resource regimes of hardware and data. As a result, this unsustainable trend has lifted many concerns in the community, which directs the primary efforts on the proposal of tools to monitor models' energy costs. Despite their importance, no evaluation measure considering models' eco-sustainability exists yet. In this work, we propose Carburacy, the first carbon-aware accuracy measure that captures both model effectiveness and eco-sustainability. We perform a comprehensive benchmark for long document summarization, comparing multiple state-of-the-art quadratic and linear transformers on several datasets under eco-sustainable regimes. Finally, thanks to Carburacy, we found optimal combinations of hyperparameters that let models be competitive in effectiveness with significantly lower costs
Graph neural network benchmark per la selezione di contenuto rilevante nella low-resource summarization
No full textNel cuore di questo elaborato vi è G-SEEK, un approccio innovativo presentato recentemente dal team di ricerca del prof. Gianluca Moro, insieme ai dott. Lorenzo Valgimigli e Luca Ragazzi, in un paper dedicato. G-SEEK è stato introdotto come un modello rivoluzionario per la Summarization, progettato specificamente per affrontare le sfide legate alla Summarization di documenti lunghi, combinando tecniche avanzate di elaborazione del linguaggio naturale con metodi di apprendimento automatico. Questo modello si propone come soluzione per la Summarization abstrattiva basata su grafi, avendo la capacità di creare grafi di conoscenza da grandi quantità di testo, fornendo una rappresentazione semantica ricca e compressa dei dati.
In questo lavoro, sono stati esplorati ulteriormente le potenzialità di G-SEEK combinandolo con nuove Graph Neural Networks(GNN). Ogni GNN porta con sé un insieme unico di caratteristiche e tecniche di modellazione, offrendo diverse prospettive sulla semantica dei grafi creati da G-SEEK.Inoltre, per migliorare ulteriormente l'efficacia, sono stati integrati nuovi Large Language Models(LLM).Ogni LLM, sono noti per le loro capacità di elaborazione del linguaggio naturale, hanno fornito un ulteriore strato di comprensione e hanno migliorato significativamente la qualità dei riassunti generati
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
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
No full textThe 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
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