Luca Valgimigli

Antioxidant activity of essential oils.

Essential oils (EOs) are liquid mixtures of volatile compounds obtained from aromatic plants. Many EOs have antioxidant properties, and the use of EOs as natural antioxidants is a field of growing interest because some synthetic antioxidants such as BHA and BHT are now suspected to be potentially harmful to human health. Addition of EOs to edible products, either by direct mixing or in active packaging and edible coatings, may therefore represent a valid alternative to prevent autoxidation and prolong shelf life. The evaluation of the antioxidant performance of EOs is, however, a crucial issue, because many commonly used tests are inappropriate and give contradictory results that may mislead future research. The chemistry explaining EO antioxidant activity is discussed along with an analysis of the potential in food protection. Literature methods to assess EOs antioxidant performance are critically reviewed.

Incorporation of Ring Nitrogens into Diphenylamine Antioxidants: Striking a Balance between Reactivity and Stability

The incorporation of nitrogen atoms into the aryl rings of conventional diphenylamine antioxidants enables the preparation of readily accessible, air-stable analogues, several of which have temperature-independent radical-trapping activities up to 200-fold greater than those of typical commercial diphenylamines. Amazingly, the nitrogen atoms raise the oxidation potentials of the amines without greatly changing their radical-trapping (H-atom transfer) reactivity.

Redox chemistry of selenenic acids and the insight it brings on transition state geometry in the reactions of peroxyl radicals.

The redox chemistry of selenenic acids has been explored for the first time using a persistent selenenic acid, 9-triptyceneselenenic acid (RSeOH), and the results have been compared with those we recently obtained with its lighter chalcogen analogue, 9-triptycenesulfenic acid (RSOH). Specifically, the selenenyl radical was characterized by EPR spectroscopy and equilibrated with a phenoxyl radical of known stability in order to determine the O-H bond dissociation enthalpy of RSeOH (80.9 ± 0.8 kcal/mol): ca. 9 kcal/mol stronger than in RSOH. Kinetic measurements of the reactions of RSeOH with peroxyl radicals demonstrate that it readily undergoes H-atom transfer reactions (e.g., k = 1.7 × 10(5) M(-1) s(-1) in PhCl), which are subject to kinetic solvent effects and kinetic isotope effects similar to RSOH and other good H-atom donors. Interestingly, the rate constants for these reactions are only 18- and 5-fold smaller than those measured for RSOH in PhCl and CH3CN, respectively, despite being 9 kcal/mol less exothermic for RSeOH. IR spectroscopic studies demonstrate that RSeOH is less H-bond acidic than RSOH, accounting for these solvent effects and enabling estimates of the pKas in RSeOH and RSOH of ca. 15 and 10, respectively. Calculations suggest that the TS structures for these reactions have significant charge transfer between the chalcogen atom and the internal oxygen atom of the peroxyl radical, which is nominally better for the more polarizable selenenic acid. The higher than expected reactivity of RSeOH toward peroxyl radicals is the strongest experimental evidence to date for charge transfer/secondary orbital interactions in the reactions of peroxyl radicals with good H-atom donors.

Identification and analysis of isothiocyanates and new acylated anthocyanins in the juice of Raphanus sativus cv. Sango sprouts

The freeze-dried sprouts juice of Raphanus sativus (L.) cv. Sango was prepared and analysed for the first time. HPLC analysis of total isothiocyanates, after protein displacement, resulted in 77.8 ± 3.0 μmol/g of dry juice while GC-MS analysis of hexane and acetone extracts showed E- and Z-raphasatin (8.9 and 0.11 μmol/g, respectively) and sulforaphene (11.7 μmol/g), summing up to 20.7 ± 1.7 μmol/g of free isothiocyanates. Sprouts juice contained an unprecedented wealth of anthocyanins and a new fractionation methodology allowed us to isolate 34 mg/g of acylated anthocyanins (28.3 ± 1.9 μmol/g), belonging selectively to the cyanidin family. Analysis was performed by HPLC-PDA-ESI-MS(n) and extended to deacylated anthocyanins and aglycones, obtained, respectively, by alkaline and acid hydrolysis. This study identified 70 anthocyanins, 19 of which have never been described before and 32 of which are reported here in R. sativus for the first time. Sango radish sprouts are exceptional dietary sources of heath-promoting micronutrients.

3-Pyridinols and 5-pyrimidinols: Tailor-made for use in synergistic radical-trapping co-antioxidant systems

Summary The incorporation of nitrogen atoms into the aromatic ring of phenolic compounds has enabled the development of some of the most potent radical-trapping antioxidants ever reported. These compounds, 3-pyridinols and 5-pyrimidinols, have stronger O–H bonds than equivalently substituted phenols, but possess similar reactivities toward autoxidation chain-carrying peroxyl radicals. These attributes suggest that 3-pyridinols and 5-pyrimidinols will be particularly effectiveco-antioxidants when used in combination with more common, but less reactive, phenolic antioxidants such as 2,6-di-tert-butyl-4-methylphenol (BHT), which we demonstrate herein. The antioxidants function in a synergistic manner to inhibit autoxidation; taking advantage of the higher reactivity of the 3-pyridinols/5-pyrimidinols to trap peroxyl radicals and using the less reactive phenols to regenerate them from their corresponding aryloxyl radicals. The present investigations were carried out in chlorobenzene and acetonitrile in order to provide some insight into the medium dependence of the synergism and the results, considered with some from our earlier work, prompt a revision of the H-bonding basicity value of acetonitrile to β2 H of 0.39. Overall, the thermodynamic and kinetic data presented here enable the design of co-antioxidant systems comprising lower loadings of the more expensive 3-pyridinol/5-pyrimidinol antioxidants and higher loadings of the less expensive phenolic antioxidants, but which are equally efficacious as the 3-pyridinol/5-pyrimidinol antioxidants alone at higher loadings.

5-S-lipoylhydroxytyrosol, a multidefense antioxidant featuring a solvent-tunable peroxyl radical-scavenging 3-thio-1,2-dihydroxybenzene motif.

5-S-Lipoylhydroxytyrosol (1), the parent member of a novel group of bioinspired multidefense antioxidants, is shown herein to exhibit potent peroxyl radical scavenging properties that are controlled in a solvent-dependent manner by the sulfur center adjacent to the active o-diphenol moiety. With respect to the parent hydroxytyrosol (HTy), 1 proved to be a more potent inhibitor of model autoxidation processes in a polar solvent (acetonitrile), due to a lower susceptibility to the adverse effects of hydrogen bonding with the solvent. Determination of O-H bond dissociation enthalpies (BDE) in t-butanol by EPR radical equilibration technique consistently indicated a ca. 1.5 kcal/mol lower value for 1 relative to HTy. In good agreement, DFT calculations of the BDEOH using an explicit methanol molecule to mimic solvent effects predicted a 1.2 kcal/mol lower value for 1 relative to HTy. Forcing the geometry of the -S-R group to coplanarity with the aromatic ring resulted in a dramatic decrease in the computed BDEOH values suggesting a potentially higher activity than the reference antioxidant α-tocopherol, depending on geometrical constrains in microheterogeneous environments. These results point to sulfur substitution as an expedient tool to tailor the chain-breaking antioxidant properties of catechol derivatives in a rational and predictable fashion.

Red-Hair-Inspired Chromogenic System Based on a Proton-Switched Dehydrogenative Free-Radical Coupling

In the presence of micromolar peroxides or biometals (Fe(III), Cu(II), V(V) salts), and following a strong acid input, the stable 3-phenyl-2H-1,4-benzothiazine is efficiently converted to a green-blue Δ(2,2)-bi(2H-1,4-benzothiazine) chromophore via dehydrogenative coupling of a 1,4-benzothiazinyl radical. The new system is of potential practical interest for colorimetric peroxide and redox biometal detection.

Antioxidant Supplementation in Health Promotion and Modulation of Aging: An Overview

Reactive oxygen and nitrogen species cause structural and functional alteration to essential biomolecules (lipids, proteins, and nucleic acids) that can be counteracted by antioxidants acting with different mechanisms: preventive, chain breaking, or indirect. The main dietary antioxidants found in fruits and vegetables comprise vitamins, phenolic acids, flavonoids, sulfenic acids, and isothiocyanates (ITCs), whose bioavailability depends on intestinal flora. Epidemiological studies show reduced chronic disease incidence and mortality associated with high dietary intakes of antioxidants. However, clinical trials on single molecules (β-carotene, α-tocopherol, and ascorbic acid) or their combination do not support the usefulness of their supplementation, possibly because of improper selection/combination of representative dietary antioxidants.

Antioxidant Supplementation in Health Promotion and Modulation of Aging

Reactive oxygen and nitrogen species cause structural and functional alteration to essential biomolecules (lipids, proteins, and nucleic acids) that can be counteracted by antioxidants acting with different mechanisms: preventive, chain breaking, or indirect. The main dietary antioxidants found in fruits and vegetables comprise vitamins, phenolic acids, flavonoids, sulfenic acids, and isothiocyanates (ITCs), whose bioavailability depends on intestinal flora. Epidemiological studies show reduced chronic disease incidence and mortality associated with high dietary intakes of antioxidants. However, clinical trials on single molecules (β-carotene, α-tocopherol, and ascorbic acid) or their combination do not support the usefulness of their supplementation, possibly because of improper selection/combination of representative dietary antioxidants.