Mechanism of Interaction of γ-Halogenated Salts of Pyrylium and Benzopyrylium with Aromatic Amines

Stoichiometry and kinetics of reactions of 2,6-diphenyl-4-chloropyrylium, 4-chloroflavylium, 4-bromoflavylium, and 4-iodoflavylium perchlorates with nucleophiles N,N-dimethylaniline and n-phenylenediamine are studied using cyclic voltammetry and spectroscopy. Nucleophilic substitution in these compounds proceeds via the formation of a charge-transfer complex, which converts into a radical ion pair as a result of the electron transfer. Heterolytic clevage of the C–Hal bond occurs at the stage of pyranyl (flavanyl) radical.     

2,6-Di-tert-butylphenols and phenoxyl radicals with metal—metal bonds

-Aryl trans-bistriphenylphosphine complexes based on 2,6-di-tert-butylphenol containing Pt—SnCl₃, Pt—GeCl₃ groups were synthesized. Oxidation of these compounds gives the corresponding phenoxyl radicals, which were studied by ESR spectroscopy. The transformation of the diamagnetic complexes to the paramagnetic state is accompanied by cleavage of the Pt—Sn, Pt—Ge bonds and by elimination of SnCl₂, GeCl₂.     

Redox Activation of Hydrogen Sulfide,Thiols, and Sulfur in Electrosynthesis of Organic Di- and Polysulfides

Russian Journal of General Chemistry - A novel and efficient method for the synthesis of biologically active organic di-, tri- and tetrasulfides has been proposed. Different methods of redox...     

Antiradical activity of morpholine- and piperazine-functionalized triphenylantimony(V) catecholates

The antiradical activity of the functionalized triphenylantimony(V) catecholates Ph₃Sb[4-O(CH₂CH₂)₂N-3,6-DBCat] (I), Ph₃Sb[4,5-Piperaz-3,6-DBCat] (II), and Ph₃Sb[4-PhN(CH₂CH₂)₂N-3,6-DBCat] (III) (where [4-O(CH₂CH₂)₂N-3,6-DBCat]^2?, [4,5-Piperaz-3,6-DBCat]^2?, and [4-PhN(CH₂CH₂)₂N-3,6-DBCat]^2? are the dianionic ligands 3,6-di-tert-butyl-4-(morpholin-1-yl)-, 3,6-di-tert-butyl-4,5-(piperazine-1,4-diyl)-, and 3,6-di-tert-butyl-4-(4-phenylpiperazin-1-yl)catecholates, respectively) was studied in reactions with the diphenylpicrylhydrazyl radical during autooxidation of unsaturated fatty (oleic and linoleic) acids with lipid peroxidation of Russian sturgeon (Acipenser gueldenstaedti B.) sperm and human blood erythrocytes in vitro as examples. The EC₅₀ and n _DPPH values obtained indicate the high antiradical activity of complexes II and III in the reactions with the stable radical. On the whole, complexes I–III inhibit the lipid peroxidation in both model (oxidation of unsaturated fatty acids) and in vitro experiments. The inhibiting effects of the complexes are comparable with and even, in some cases, higher than those of the known antioxidant ionol.     

Triphenylantimony(V) Catecholates of the Type (3-RS-4,6-DBCat)SbPh3-Catechol Thioether Derivatives: Structure,Electrochemical Properties,and Antiradical Activity

A new series of triphenylantimony(V) 3-alkylthio/arylthio-substituted 4,6-di-tert-butylcatecholates of the type (3-RS-4,6-DBCat)SbPh₃, where R = n-butyl (1), n-hexyl (2), n-octyl (3), cyclopentyl (4), cyclohexyl (5), benzyl (6), phenyl (7), and naphthyl-2 (8), were synthesized from the corresponding catechol thioethers and Ph₃SbBr₂ in the presence of a base. The crystal structures of 1, 2, 3, and 5 were determined by single-crystal X-ray analysis. The coordination polyhedron of 1–3 is better described as a tetragonal pyramid with a different degree of distortion, while that for 5- was a distorted trigonal bipyramid (τ = 0.014, 0.177, 0.26, 0.56, respectively). Complexes demonstrated different crystal packing of molecules. The electrochemical oxidation of the complexes involved the catecholate group as well as the thioether linker. The introduction of a thioether fragment into the aromatic ring of catechol ligand led to a shift in the potential of the “catechol/o-semiquinone” redox transition to the anodic region, which indicated the electron-withdrawing nature of the RS group. The radical scavenging activity of the complexes was determined in the reaction with DPPH radical.     

Trialkylantimony(V) o-amidophenolates: Electrochemical transformations and antiradical activity

The electrochemical transformations and antiradical activity of trialkylantimony(V) o-amidophenolate derivatives, (AP)SbR₃ (AP = 4,6-di-tert-butyl-N-(2,6-diisopropylphenyl)-o-amidophenolate); R = CH₃ (I), C₂H₅ (II), and C₆H₁₁ (III), are studied. The electrochemical oxidation of compounds I–III proceeds successively to form mono- and dicationic forms of the complexes. The presence of the donor hydrocarbon groups at the antimony(V) atom shifts the oxidation potentials to the cathodic range and decreases the stability of the monocationic complexes formed in electrochemical oxidation. The second anodic process is irreversible and accompanied by o-iminoquinone decoordination. The antiradical activity of compounds I–III is studied in the reaction with the diphenylpicrylhydrazyl radical and oleic acid autooxidation. The values obtained for indices EC₅₀ and IC₅₀ indicate the antiradical activity of the studied compounds. Complexes I–III were found to be the efficient inhibitors of oleic acid oxidation and act as efficient destructors of hydroperoxides.     

Penta- and hexacoordinate antimony(V) compounds with the tridentate O,N,O-donor ligand: Electrochemical transformations and antiradical activity

The electrochemical transformations and antiradical activity of penta- and hexacoordinate antimony(V) complexes I–V containing the tridentate O,N,O-donor ligand, N,N-bis(di-3,5-tert-butyl-2-hydroxyphenyl)amine, are studied. The oxidation of hexacoordinate triarylantimony(V) compounds R₃Sb(Cat-NH-Cat) (I–III) leads to the formation of neutral paramagnetic intermediates Ia–IIIa. Two anodic reversible one-electron stages are observed for pentacoordinate complexes R′₂Sb(Cat-N-Cat) (IV, V). The possibility of the formation of stable paramagnetic species in electrochemical oxidation is a reason for the antiradical activity of the complexes. The study of the reactions of compounds I–V with the electrogenerated superoxide radical anion, diphenylpicrylhydrazyl radical, peroxy radicals, and hydroperoxides formed by the autooxidation of unsaturated fatty acids (oleic, linoleic) shows that all complexes exhibit a pronounced antiradical activity. The highest effect is observed for compounds I, IV, and V characterized by the prolonged action.     

Synthesis and antioxidant activity of new hydroxy derivatives of chalcones

New hydroxy derivatives of chalcones obtained via a condensation of 3-acetyl-2H-chromen-2-one with 2,4-dihydroxy- and 4-hydroxy-benzaldehydes and via an aldol crotonic condensation of methyl N-(4-acetylphenyl)carbamate with 4-hydroxy-3,5-di(tert-butyl)benzaldehyde have been isolated and characterized. A wide range of promising biological activity of the synthesized compounds, including the radical scavenging and antioxidant ones, was predicted by the in silico method. The anti- and pro-oxidant activities in model systems of peroxidation of cis-9-octadecenoic (oleic) acid and lipids from the liver homogenate of tilapia were estimated in vitro. The presence of sterically hindered hydroxy groups and a chromene moiety provides the prolonged antioxidant activity of new hydroxy derivatives of chalcones.

     

New dioxygen-inert triphenylantimony(v) catecholate complexes based on <Emphasis Type="Italic">o</Emphasis>-quinones with electron-withdrawing groups

New triphenylantimony(v) catecholate complexes were synthesized by oxidative addition of sterically hindered o-benzoquinones containing electron-withdrawing substituents in different positions of the carbon ring to triphenylantimony. The complexes were characterized using IR spectroscopy, NMR spectroscopy, and cyclic voltammetry. The oxygen-inertness of the complexes is shown by NMR spectroscopy and electrochemical studies. The introduction of electron-withdrawing substituents to the catecholate ligand shifts the first oxidation potential of the complexes to the electropositive region and thus deactivates the triphenylantimony(v) catecholate complexes in the reaction with molecular oxygen.