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251.
Enes RF Tomé AC Cavaleiro JA Amorati R Fumo MG Pedulli GF Valgimigli L 《Chemistry (Weinheim an der Bergstrasse, Germany)》2006,12(17):4646-4653
Fullerene derivatives incorporating one or two 3,5-di-tert-butyl-4-hydroxyphenyl groups were synthesized by 1,3-dipolar cycloaddition of azomethine ylides to C(60). The O-H bond dissociation enthalpies (BDEs) of these compounds were estimated by studying, by means of EPR spectroscopy, the equilibration of each of these phenols and 2,6-di-tert-butyl-4-methylphenol (BHT) with the corresponding phenoxyl radicals. The antioxidant activity of the investigated phenols was also determined by measuring the rate constants for their reaction with peroxyl radicals in controlled autoxidation experiments and compared to that recorded under identical experimental settings for [60]fullerene itself and unlinked BHT. The results indicate that linking of the BHT structure to C(60) does not substantially alter the thermochemistry and kinetics of its reaction with peroxyl radicals, but such adducts may behave as interesting bimodal radical scavengers. The inherent rate constant for trapping of peroxyl radicals by C(60) per se (k(inh)=3.1+/-1.1 x 10(2) m(-1) s(-1)) indicates that, contrary to previous reports, [60]fullerene is an extremely weak chain-breaking antioxidant. 相似文献
252.
Amorati R Fumo MG Menichetti S Mugnaini V Pedulli GF 《The Journal of organic chemistry》2006,71(17):6325-6332
A kinetic and thermodynamic investigation of phenols para-substituted with thiyl (SR), sulfinyl (SOR), and sulfonyl (SO(2)R) groups and ortho-substituted with thiyl groups is reported. The effect of the sulfur substituents on the O-H bond dissociation enthalpy values, BDE(O-H), was measured by means of the EPR radical equilibration technique and the reactivity toward peroxyl radicals, k(inh), of these phenolic antioxidants was determined by inhibited autoxidation studies. An inverse correlation between these two parameters was found. A p-SMe substituent decreased the BDE(O-H) value to a lesser extent than a p-OMe group (-3.6 vs -4.4 kcal/mol), whereas the effect of the same groups in an ortho position showed an opposite trend (-0.85 vs -0.2 kcal/mol). The latter result is explained in terms of the different strength of the intramolecular hydrogen bond between the OH proton and the sulfur or oxygen substituents in ortho derivatives. ESI-MS analysis of the products formed by reacting the sulfides with peroxyl radicals from the azoinitiator AIBN revealed the formation of a complex mixture of products, which may play an important role in determining the overall antioxidant activity of the parent compounds. 相似文献
253.
Shanks D Amorati R Fumo MG Pedulli GF Valgimigli L Engman L 《The Journal of organic chemistry》2006,71(3):1033-1038
all-rac-alpha-Selenotocopherol (6c) has been synthesized in 11 steps in 6.6% total yield. Key steps include chloromethylation to approach the persubstituted aromatic 9b and cyclization of alcohol precursor 10 by radical homolytic substitution at selenium to form the selenotocopherol heterocycle. Determination of the OH bond dissociation enthalpy (BDE) of 6c by electron paramagnetic resonance (EPR) equilibration techniques gave a value of 78.1 +/- 0.3 kcal mol(-1), approximately 1 kcal mol(-1) higher than that of alpha-tocopherol. Kinetic studies performed by measuring oxygen uptake of the induced oxidation of styrene in the presence of an antioxidant showed that selenotocopherol (6c) was a slightly poorer inhibitor than alpha-tocopherol, in agreement with the BDE values. In contrast to simpler selenotocopherol analogues, 6c was not regenerable in the presence of a stoichiometric coreductant in a two-phase lipid peroxidation model. 相似文献
254.
Mohammad Movassaghi Grazia Piizzi Dustin S. Siegel Giovanni Piersanti 《Tetrahedron letters》2009,50(39):5489-5878
Observations concerning the synthesis of the core spirocyclic AB-ring system of illudins using an enyne ring closing metathesis (EYRCM) cascade are discussed. Substituent effects, in addition to optimization of the reaction conditions and the olefin tether for the key EYRCM reaction, are examined. 相似文献
255.
Fractional moments have been investigated by many authors to represent the density of univariate and bivariate random variables in different contexts. Fractional moments are indeed important when the density of the random variable has inverse power-law tails and, consequently, it lacks integer order moments. In this paper, starting from the Mellin transform of the characteristic function and by fractional calculus method we present a new perspective on the statistics of random variables. Introducing the class of complex moments, that include both integer and fractional moments, we show that every random variable can be represented within this approach, even if its integer moments diverge. Applications to the statistical characterization of raw data and in the representation of both random variables and vectors are provided, showing that the good numerical convergence makes the proposed approach a good and reliable tool also for practical data analysis. 相似文献
256.
Moscato S Mattii L D'Alessandro D Cascone MG Lazzeri L Serino LP Dolfi A Bernardini N 《Micron (Oxford, England : 1993)》2008,39(5):569-579
Tissue engineering scaffolds should be able to reproduce optimal microenvironments in order to support cell attachment, three-dimensional growth, migration and, regarding fibroblasts, must also promote extracellular matrix production. Various bioactive molecules are employed in the preparation of spongy scaffolds to obtain biomimetic matrices by either surface-coating or introducing them into the bulk composition of the biomaterial. The biomimetic properties of a spongy matrix composed of PVA combined with the natural component gelatine were evaluated by culturing human gingival fibroblasts on the scaffold. Cell adhesion, morphology and distribution within the scaffold were assessed by histology and electron microscopy; viability and metabolic activity as well as extracellular matrix production were analyzed by MTT assay, cytochemistry and immunocytochemistry. Fibroblasts interacted positively with PVA/gelatine. They adhered to the PVA/gelatine matrix in which they had good spreading activity and active metabolism; fibroblasts were also able to produce extracellular matrix molecules (type I collagen, fibronectin and laminin) compared to bi-dimensionally grown cells. The in situ creation of a biological matrix by human fibroblasts together with the ability to produce growth factor TGF-beta1 and the intracellular signal transduction molecule RhoA, suggests that this kind of PVA/gelatine sponge may represent a suitable support for in vitro extracellular matrix production and connective tissue regeneration. 相似文献
257.
M. Grazia Speranza 《European Journal of Operational Research》2018,264(3):830-836
Problems in transportation and logistics had to be tackled long before computers and Operational Research (OR) became available to support decision making. After the first optimization models were developed, OR has substantially contributed in making transportation systems efficient and companies with complex transportation and logistics problems competitive. Over the years, technology has evolved and the same has done OR. In this paper, the history of problems and OR contributions in transportation and logistics will be shortly reviewed together with the evolution of technology. Then, the future trends in this area will be discussed together with potential OR contributions. 相似文献
258.
Baikie T Hardy V Maignan A Francesconi MG 《Chemical communications (Cambridge, England)》2005,(40):5077-5079
A small negative magnetoresistance and metallic-like behaviour has been detected for the first time in a one-dimensional sulfide containing Co2+. 相似文献
259.
Transmission problem in thermoelasticity with symmetry 总被引:2,自引:0,他引:2
Marzocchi Alfredo; Rivera Jaime E. Munoz; Naso Maria Grazia 《IMA Journal of Applied Mathematics》2003,68(1):23-46
In this paper we show the existence, uniqueness and regularityof the solutions to the thermoelastic transmission problem.Moreover, when the solutions are symmetrical we show that theenergy decays exponentially as time goes to infinity, no matterhow small is the size of the thermoelastic part. 相似文献
260.
Grazia Zassinovich Clorinda del Bianco Giovanni Mestroni 《Journal of organometallic chemistry》1981,222(2):323-329
The reduction of prochiral ketones by hydrogen transfer from isopropanol is catalyzed by cationic iridium(I) complexes containing optically active Schiff bases. Optical yields of up to 33% have been obtained. 相似文献