Radical-Trapping and Hydroperoxide-Decomposing Benzoselenazole Antioxidants with Potential Biological Applications against Oxidative Stress.

The synthesis of phenolic benzoselenazoles has been described. These were synthesized from their corresponding diselenides and aldehydes using acetic acid as a catalyst. All compounds have been tested for glutathione peroxidase (GPx)-like antioxidant activity in thiophenol assay.

Near-infrared phosphorescence in a ruthenium(II) complex equipped with a pyridyl-1,2-azaborine ligand.

The 4-methyl-2-(pyridin-2-yl)-2,1-borazaronaphthalene molecule Hazab-py has been successfully used, for the first time, as a ligand in a ruthenium(II) polypyridine complex A (with the formula [Ru(dtbbpy)(azab-py)], where dtbbpy = 4,4'-di--butyl-2,2'-bipyridine). This compound was characterized by NMR spectroscopy and high-resolution mass spectrometry (MS), and its electrochemical and photophysical properties were fully investigated and compared to those of its homoleptic analogue [Ru(dtbbpy)] (B), an archetypical mono-cationic cyclometalated complex C (with the formula [Ru(dtbbpy)(ppy)], where Hppy = 2-phenylpyridine), and the more structurally similar analogue [Ru(dtbbpy)(naft-py)] (D), where the B-N unit of the azaborine ligand is replaced by a standard CC one, resulting in the 2-(naphthalen-2-yl)pyridine ligand (Hnaft-py). The presence of the novel 1,2-azaborine ligand induces a 0.

Long-chain surface-modified red-emitting carbon dots as fluorescent additives for 3D printing vat-photopolymerization.

Carbon dots have recently attracted tremendous scientific attention thanks to their enhanced luminescence properties, photostability and low toxicity. In particular, red-emitting carbon dots (RCDs) are assuming increasing importance in biomedical applications, such as bio-imaging and phototherapy. At the same time, the possibility to create functional and complex objects by means of vat-photopolymerization-based three-dimensional (3D) printing techniques is continuously growing.

Peroxyl Radical Trapping Antioxidant Activity of Essential Oils and Their Phenolic Components.

Essential oils (EOs) are gaining importance as sustainable food antioxidants, but kinetic data on peroxyl radical trapping are missing. Thirteen EOs from 11 botanical species were studied in the inhibited autoxidation of cumene by oxygen-uptake kinetics. EOs of , , , , , , and , containing 23-86% phenolic components by gas chromatography/mass spectrometry (GC-MS) analysis, afforded inhibition rate constants in the order of 10 M s at 30 °C similar to reference butylhydroxytoluene (2,6-di--butyl-4-methylphenol) (BHT).

Pro-aromatic Natural Terpenes as Unusual "Slingshot" Antioxidants with Promising Ferroptosis Inhibition Activity.

Ferroptosis is a cell death mechanism based on extensive cellular membrane peroxidation, implicated in neurodegenerative and other diseases. The essential oil component γ-terpinene, a natural monoterpene with a unique highly oxidizable pro-aromatic 1,4-cyclohexadiene skeleton, inhibits peroxidation of polyunsaturated lipid in model heterogeneous systems (micelles and liposomes). Upon H-atom abstraction, an unstable γ-terpinene-derived peroxyl radical is formed, that aromatizes to p-cymene generating HOO⋅ radicals.

Kinetic study of the reaction of thiophene-tocopherols with peroxyl radicals enlightenings the role of O˙⋯S noncovalent interactions in H-atom transfer.

Three new α-tocopherol thiophene derivatives were efficiently synthesized, characterized and used for the first time as chain-breaking antioxidants for the inhibition of the autoxidation of reference oxidizable substrates. The rate constant of the reaction with alkylperoxyl (ROO˙) radicals and the stoichiometry of radical trapping () for the thiophene-tocopherol compounds were determined by measuring the oxygen consumption during the autoxidation of styrene or isopropylbenzene, using a differential pressure transducer. The measurement of the reaction with ROO˙ radicals in an apolar solvent at 30 °C showed inhibition rate constants () in the order of 10 M s.

Unexpected reactivity of cyclometalated iridium(III) dimers. Direct synthesis of a mononuclear luminescent complex.

A new synthetic method has been developed for the preparation of unexpected emissive iridium(III) complexes (A and B), directly obtained from the established [Ir(ppy)(μ-Cl)] dimer, under reaction conditions in which such compounds are usually considered stable. Complex A ([Ir(ppy)(Oppy)], where Hppy = 2-phenylpyridine and HOppy = 2-(-hydroxyphenyl)pyridine) was obtained from the dimer without the addition of further ancillary ligands in the reaction environment, but in the presence of a basic water environment in 2-ethoxyethanol as solvent at 165 °C. The complex evidences the unexpected insertion of an oxygen atom between the iridium(III) center and the carbon atom of one ppy moiety.

Hydroperoxyl radical (HOO) as a reducing agent: unexpected synergy with antioxidants. A review.

This review highlights the progress made in recent years in harnessing the peculiar chemistry of the hydroperoxyl, or perhydroxyl, radical (HOO) during lipid peroxidation, particularly with regard to its interaction with antioxidants. The HOO radical, the protonated form of superoxide, plays an important role in the propagation and termination of lipid peroxidation in nonaqueous systems. However, differently from alkylperoxyl (ROO) radicals that have only oxidizing ability, HOO has a two-faced oxidizing and reducing activity.

A Pyridyl-1,2-azaborine Ligand for Phosphorescent Neutral Iridium(III) Complexes.

A novel 1,2-azaborine (, 4-methyl-2-(pyridin-2-yl)-2,1-borazaronaphthalene, ) has been synthesized and used for the first time as a B-N alternative to common cyclometalating ligands to obtain neutral phosphorescent iridium(III) complexes (, , , and ) of general formula [Ir(CN)(NNB)], where CN indicates three different cyclometalating ligands (Hppy = 2-phenylpyridine; Hdfppy = 2-(2,4-difluoro-phenyl)pyridine; Hpqu = 2-methyl-3-phenylquinoxaline). Moreover, the azaborine-based complex was compared to the isoelectronic C═C iridium(III) complex , obtained using the corresponding 2-(naphthalen-2-yl)pyridine ligand . Due to the dual cyclometalation mode of such C═C ligand, the isomeric complex was also obtained.

Reaction with ROO• and HOO• Radicals of Honokiol-Related Neolignan Antioxidants.

Honokiol is a natural bisphenol neolignan present in the bark of , whose extracts have been employed in oriental medicine to treat several disorders, showing a variety of biological properties, including antitumor activity, potentially related to radical scavenging. Six bisphenol neolignans with structural motifs related to the natural bioactive honokiol were synthesized. Their chain-breaking antioxidant activity was evaluated in the presence of peroxyl (ROO•) and hydroperoxyl (HOO•) radicals by both experimental and computational methods.

Iridium-Functionalized Cellulose Microcrystals as a Novel Luminescent Biomaterial for Biocomposites.

Microcrystalline cellulose (MCC) is an emerging material with outstanding properties in many scientific and industrial fields, in particular as an additive in composite materials. Its surface modification allows for the fine-tuning of its properties and the exploitation of these materials in a plethora of applications. In this paper, we present the covalent linkage of a luminescent Ir-complex onto the surface of MCC, representing the first incorporation of an organometallic luminescent probe in this biomaterial.

4-Phenyl-1,2,3-triazoles as Versatile Ligands for Cationic Cyclometalated Iridium(III) Complexes.

Five cationic iridium(III) complexes (-) were synthesized exploiting two triazole-based cyclometalating ligands, namely, 1-methyl-4-phenyl-1-1,2,3-triazole () and the corresponding mesoionic carbene 1,3-dimethyl-4-phenyl-1-1,2,3-triazol-5-ylidene (). From the combination of these two ligands and the ancillary one, i.e.

Methods to Determine Chain-Breaking Antioxidant Activity of Nanomaterials beyond DPPH. A Review.

This review highlights the progress made in recent years in understanding the mechanism of action of nanomaterials with antioxidant activity and in the chemical methods used to evaluate their activity. Nanomaterials represent one of the most recent frontiers in the research for improved antioxidants, but further development is hampered by a poor characterization of the ''antioxidant activity'' property and by using oversimplified chemical methods. Inhibited autoxidation experiments provide valuable information about the interaction with the most important radicals involved in the lipid oxidation, namely alkylperoxyl and hydroperoxyl radicals, and demonstrate unambiguously the ability to stop the oxidation of organic materials.

Absolute Antioxidant Activity of Five Phenol-Rich Essential Oils.

Essential oils (EOs) have promising antioxidant activities which are gaining interest as natural alternatives to synthetic antioxidants in the food and cosmetic industries. However, quantitative data on chain-breaking activity and on the kinetics of peroxyl radical trapping are missing. Five phenol-rich EOs were analyzed by GC-MS and studied by oxygen-uptake kinetics in inhibited controlled autoxidations of reference substrates (cumene and squalene).

Nitroxides as Building Blocks for Nanoantioxidants.

Nitroxides are an important class of radical trapping antioxidants whose promising biological activities are connected to their ability to scavenge peroxyl (ROO) radicals. We have measured the rate constants of the reaction with ROO () for a series of 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) derivatives as 5.1 × 10, 1.

SET and HAT/PCET acid-mediated oxidation processes in helical shaped fused bis-phenothiazines.

Helical shaped fused bis-phenothiazines 1-9 have been prepared and their red-ox behaviour quantitatively studied. Helicene radical cations (Hel ) can be obtained either by UV-irradiation in the presence of PhCl or by chemical oxidation. The latter process is extremely sensitive to the presence of acids in the medium with molecular oxygen becoming a good single electron transfer (SET) oxidant.

Hydrogen Atom Transfer from HOO to ortho-Quinones Explains the Antioxidant Activity of Polydopamine.

Melanins are stable and non-toxic biomaterials with a great potential as chemopreventive agents for diseases connected with oxidative stress, but the mechanism of their antioxidant action is unclear. Herein, we show that polydopamine (PDA), a well-known synthetic melanin, becomes an excellent trap for alkylperoxyl radicals (ROO , typically formed during autoxidation of lipid substrates) in the presence of hydroperoxyl radicals (HOO ). The key reaction explaining this peculiar antioxidant activity is the reduction of the ortho-quinone moieties present in PDA by the reaction with HOO .

Excited-State Engineering in Heteroleptic Ionic Iridium(III) Complexes.

Iridium(III) complexes have assumed a prominent role in the areas of photochemistry and photophysics due to the peculiar properties of both the metal itself and the ligand environment that can be assembled around it. Ir(III) is larger, heavier, and bears a higher ionic charge than its analogue and widely used d ions such as Fe(II) and Ru(II). Accordingly, its complexes exhibit wider ligand-field d-d orbital splitting with electronic levels centered on the metal, typically nonemissive and photodissociative, not playing a relevant role in excited-state deactivations.

Synergic antioxidant activity of γ-terpinene with phenols and polyphenols enabled by hydroperoxyl radicals.

Antioxidant 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.

Iridium(III) Complexes with Fluorinated Phenyl-tetrazoles as Cyclometalating Ligands: Enhanced Excited-State Energy and Blue Emission.

Five cationic iridium(III) complexes with fluorinated cyclometalating tetrazole ligands [Ir(dfptrz)L], where Hdfptrz = 5-(2,4-difluorophenyl)-2-methyl-2-tetrazole and L = 2,2'-bypiridine (), 4,4'-di-butyl-2,2'-bipyridine (), 1,10-phenantroline (), 4,4'-bis(dimethylamino)-2,2'-bipyridine (), and -butyl isocyanide (), were prepared following a one-pot synthetic strategy based on a bis-cyclometalated solvato complex obtained via silver(I)-assisted cyclometalation, which was then reacted with the proper ancillary ligand to get the targeted complexes. The X-ray crystal structures of and were determined, showing that the tetrazole ligands are in a trans arrangement with respect to the iridium center. Electrochemical and photophysical properties, along with density functional theory calculations, allowed a full rationalization of the electronic properties of -.

Proton-Sensitive Free-Radical Dimer Evolution Is a Critical Control Point for the Synthesis of Δ-Bibenzothiazines.

The mechanism of the acid-dependent interring dehydrogenation in the conversion of the single-bonded 3-phenyl-2-1,4-benzothiazine dimer to the Δ-bi(2-1,4-benzothiazine) scaffold of red hair pigments is disclosed herein. Integrated chemical oxidation and oxygen consumption experiments, coupled with electron paramagnetic resonance (EPR) analyses and DFT calculations, allowed the identification of a key diprotonated free-radical intermediate, which was implicated in a remarkable oxygen-dependent chain process via peroxyl radical formation and evolution to give the Δ-bi(2-1,4-benzothiazine) dimer by interring dehydrogenation. The critical requirement for strongly acidic conditions was rationalized for the first time by the differential evolution channels of isomeric peroxyl radical intermediates at the 2- versus 3-positions.

Carbazole-Terpyridine Donor-Acceptor Dyads with Rigid π-Conjugated Bridges.

A series of molecules in which 9H-carbazole (electron donor, D) and 2,2':6',2''-terpyridine (electron acceptor, A) are connected through rigid π-conjugated bridges (D-π-A systems) have been synthesized and their photophysical properties examined in detail, with the support of DFT calculations. The bridges are made of different sequences of ethynylene, phenylene, and anthracene groups. The synthetic strategies involve condensation of 2-acetylpyridine with the aromatic aldehyde moiety on different functionalized π-conjugated bridges and couplings with carbazole derivatives.

Magnetic nanoantioxidants with improved radical-trapping stoichiometry as stabilizers for inhibition of peroxide formation in ethereal solvents.

Graphite-coated magnetic cobalt nanoparticles (CoNPs) decorated with hindered phenolic antioxidant analogues of 2,6-di-tert-butyl-4-methylphenol (BHT, E321) provided easily removable nanoantioxidants capable of preventing the autoxidation of organic solvents as tetrahydrofuran (THF).

1-Methyl-1,4-cyclohexadiene as a Traceless Reducing Agent for the Synthesis of Catechols and Hydroquinones.

Pro-aromatic and volatile 1-methyl-1,4-cyclohexadiene () was used for the first time as a valid H-atom source in an innovative method to reduce or quinones to obtain the corresponding catechols and hydroquinones in good to excellent yields. Notably, the excess of 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.

Calibration of Squalene, p-Cymene, and Sunflower Oil as Standard Oxidizable Substrates for Quantitative Antioxidant Testing.

The autoxidation kinetics of stripped sunflower oil (SSO), squalene (SQ), and p-cymene ( p-C) initiated by 2,2'-azobis(isobutyronitrile) at 303 K were investigated under controlled conditions by differential oximetry in order to build reference model systems that are representative of the natural variability of oxidizable materials, for quantitative antioxidant testing. Rate constants for oxidative chain propagation ( k) and chain termination (2 k) and the oxidizability ( k/√2 k) were measured using 2,6-di- tert-butyl-4-methoxyphenol, 2,2,5,7,8-pentamethyl-6-chromanol, BHT, and 4-methoxyphenol as reference antioxidants. Measured values of k (M s)/2 k (M s)/oxidizability (M s) at 303 K in chlorobenzene were 66.