Pyridinones Are Not Antioxidants As Shown by Kinetics of Free Radical Autoxidation, but They Prevent Radical Oxidations Catalyzed by Toxic Heavy Metals

Three 2-methyl-3-hydroxypyridinones, 1-methyl-, <b>1</b>; 1-(4-methoxy)­phenyl-, <b>2</b>; and 1-(4-dimethylamino)­phenyl-, <b>3</b>, were discovered not to possess strong antioxidant properties contrary to literature reports. These pyridinones were not active chain-breaking antioxidants toward peroxyl radicals generated from styrene or methyl oleate initiated by azobis-2-methylpropylnitrile (AIBN) in solution compared to known phenolic antioxidants, 2,2,5,7,8-pentamethyl-6-hydroxychroman (PMHC) or 2,6-di-<i>tert</i>-butyl-4-methoxyphenyl (DBHA). Pyridinone <b>2</b> exhibited weak antioxidant activity in cumene, <i>k</i>_inh = 1.3 × 10³ M^–1 s^–1, compared to 2,6-di-<i>tert</i>-butyl-4-methylphenol (BHT), <i>k</i>_inh = 4.3 × 10³ M^–1 s^–1. The pyridinones were not active antioxidants during lipid peroxidation initiated by azobis-2-amidinopropane·2HCl (ABAP) in aqueous–lipid dispersions of 0.50 M sodium dodecyl sulfate (SDS) micelles where <b>2</b> did not inhibit peroxidation of methyl oleate at pH 7.0 or 4.0, while BHT exhibited effective suppression of oxygen uptake. In addition, <b>2</b> did not exhibit any cooperative antioxidant effect in combination with Trolox during inhibited peroxidation of linoleic acid in micelles. Pyridinones were effective <i>preventative</i> antioxidants in aqueous–lipid dispersions against reactions initiated by heavy metal ions, notably copper; for example, <b>2</b> blocked peroxidation of linoleic acid initiated by Cu ions in SDS micelles. In particular, both <b>2</b> and <b>3</b> were active in preventing the rapid <i>pro-oxidation</i> effects, “spikes”, of very rapid oxygen uptake when phenolic antioxidants PMHC or Trolox were added to peroxidations initiated by Cu²⁺. A proposal is given to account for such pro-oxidant effects

Synthesis and Surface Investigations of N-Substituted 2,5-Dithio-7-azabicyclo[2.2.1]heptanes on Gold Surfaces

The reaction of various primary amines and 2,5-dihydroxy-1,4-dithiane in the presence of a catalytic amount of Mg­(II) in distilled water provided a series of N-substituted 2,5-dithia-7-azabicyclo[2.2.1]­heptanes. The adsorption profiles of the sulfur-containing heterocycles on gold surfaces have been explored by time-of-flight secondary ion mass spectrometry (TOF-SIMS), X-ray photoelectron spectroscopy (XPS), and electrochemistry. SIMS data indicated that these novel bicyclic sulfides interact with gold surfaces favorably, independent of the N-substitution, with minimal fragmentation. An XPS study revealed the three component core levels of S 2p with binding energies at 161, 162, and 163 eV, indicating a combination of the bound and unbound sulfur species. Using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), we found the efficient adsorption of heterocycles onto gold and the formation of densely packed films for alkyl and phenyl analogues. However, the adsorption and film packing properties were greatly compromised by an N<i>-</i>pyridyl substitution. The findings indicate that the surface behavior of N-substituted 2,5-dithia-7-azabicyclo[2.2.1]­heptanes varies with respect to the N-substitution and the nature of the substituent, suggesting that the adsorption profiles and the film packing of bicyclic sulfides on gold surfaces are highly dependent on the binding interface and the molecular orientation

Donor- and/or Acceptor-Substituted Expanded Radialenes: Theory, Synthesis, and Properties

The synthesis of donor- (D) and/or acceptor (A)-expanded [4]­radialenes has been developed on the basis of readily available dibromoolefin (<b>7</b>), tetraethynylethene (<b>10</b> and <b>20</b>), and vinyl triflate (<b>12</b>) building blocks. The successful formation of D/A radialenes relies especially on (1) effective use of a series alkynyl protecting groups, (2) Sonogashira cross-coupling reactions, and (3) the development of ring closing reactions to form the desired macrocyclic products. The expanded [4]­radialene products have been investigated by spectroscopic (UV–vis absorption and emission) and quantum chemical computational methods (density functional theory and time dependent DFT). The combined use of theory and experiment provides a basis to evaluate the extent of D/A interactions via the cross-conjugated radialene framework as well as an interpretation of the origin of D/A interactions at an orbital level