Search

Abstract: Irradiation of N-triphenylmethyloxy- or N-diphenylmethyloxy phthalimide is reported to result in the formation of phthalimide N-oxyl radical (PINO), which is able to initiate and propagate oxidative radical chain reactions of hydrocarbons. [Copyright &y& Elsevier]

Abstract: The rearrangement rates of several di-, tri-, tetra- or penta-substituted Z-arylhydrazones of 3-benzoyl-5-phenyl-1,2,4-oxadiazole (1a–18a) into the relevant 2-aryl-4-benzoylamino-5-phenyl-1,2,3-triazoles (1b–18b) have been determined in 1:1 (v:v) dioxane/water in a wide range of pS+ (3.80–12.50) at different temperatures. The kinetic data obtained have been correlated with those previously collected for the rearrangement of ortho-, meta- and para-substituted Z-arylhydrazones (19a–38a) by means of an extension of the linear free-energy relationship (LFER) proposed by Fujita and Nishioka, thus considering steric (Es) and field (Fo) proximity effects in addition to the normal electronic effects (σo,m,p). Excellent correlation coefficients have been calculated (R≥0.999), with susceptibility constants (ρ, δ and f) close to those previously obtained for 19a–38a, when only excluding data for the 2,6-bis-ortho-substituted Z-arylhydrazones 11a and 16–18a, which show a reactivity much higher than foreseeable, evidencing the first case of ‘steric acceleration’ in mononuclear rearrangements of heterocycles. A rationale for such a behaviour is proposed. [Copyright &y& Elsevier]

A study on the regeneration of α-tocopherol (vitamin E) by phenolic co-antioxidants in homogeneous hydrocarbon solution is reported. The behavior of some relevant phenols such as BHA, BHT, and trans-resveratrol appears to be nicely predicted by a model based on the knowledge of kinetic and thermochemical data concerning the various reactants. Despite its good reputation as an antioxidant, trans-resveratrol was found only moderately effective (k[sub inh] = 2.0 × 10[sup 5] M[sup -1] s[sup -1] in chlorobenzene at 303 K) and unable to recycle vitamin E. [ABSTRACT FROM AUTHOR]

A systematic investigation is reported on the regeneration of α-tocopherol (α-TOH) in homogeneous solution by coantioxidants in order to better understand the mechanism and the factors responsible for the effectiveness of this process. The current availability of thermochemical data concerning the reactants involved in the regeneration reactions, as well as a large number of the kinetic constants for the various reactions involved, allowed us to rationalize the experimental observations collected so far. Three limiting cases have been considered. The first case is that of a coantioxidant irreversibly regenerating α-TOH, where the effectiveness of the recycling process depends on the magnitude of the rate constant k[sub r]. The second case is that of a coantioxidant reversibly recycling α-TOH, where regeneration can only be observed if the bond dissociation enthalpy value of the coantioxidant is lower or at least close to that of the O-H bond of α-tocopherol. The third case is that of a catechol derivative (chosen as a model compound for polyphenolic antioxidants), where recycling of α-TOH is feasible even though the BDE value is significantly higher than that of vitamin E. In this case, the driving force for the recycling process is the removal of the semiquinone radical from the catechol derivative by the α-tocopheroxyl radical, which makes the regeneration of α-TOH practically irreversible. [ABSTRACT FROM AUTHOR]

The synthesis and spectroscopic properties of a novel paramagnetic [2]rotaxane is described. This rotaxane is made from molecules having an alkyl chain flanked by 2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPO) groups. Complexation of sebacoyl chloride by α-cyclodextrin followed by reaction with a bulky aminonitroxide resulted in the trapping of the cyclodextrin, threaded by the alkyl chain, thus generating the rotaxane structure. The structure of the paramagnetic [2]rotaxane was fully characterized by ESI-MS, ID and 2D NMR and ESR spectroscopy. [ABSTRACT FROM AUTHOR]

We report a newly developed synthesis of a number of alditol thiacrowns using an eco-friendly and versatile two-step strategy: the regioselective thioallyletherification of a polyhydroxylated alditol followed by a ring closing metathesis using the Grubbs second generation catalyst. This approach allows a series of target thiacrown products to be obtained in acceptable to good yields, from the corresponding α,ω-dithioallylether alditol starting materials featuring either the xylo , ribo , threo , erythro , d - manno or d - gluco configurations. The per- O -acetylated d -mannitol dithioallyether 10 , easily obtained on a large scale using this approach, was selected for evaluation as both an antibacterial and an antioxidant. Although no antibacterial activity was observed for the bacterial strains investigated, compound 10 is shown to be an antioxidant, and able to quench hydrogen peroxide in a stoichiometric fashion. [ABSTRACT FROM AUTHOR]

The synthesis of new unsymmetrical substituted zinc phthalocyanines derivatives has been described; moreover the photodynamic activity of some compounds tested against Candida albicans has been reported. [Copyright &y& Elsevier]