Search results for "Activity"
showing 10 items of 7178 documents
[39] Lipoperoxyl radical-scavenging activity of vitamin A and analogs in homogeneous solution
1994
Publisher Summary This chapter describes the assay method for determining the reactivity of all- trans -retinol and other natural and synthetic retinoids, with radicals generated by reaction of the lipid-soluble azo initiator 2,2 ' -azobis(2,4-dimethylvaleronitrile) (AMVN) with methyl linoleate. The chapter discusses the general principles for measuring antioxidant activity. The oxidation of linoleic acid methyl ester (LAME) is the simplest model for studying the oxidation of polyunsaturated lipids and has been widely adopted to evaluate antioxidant activity. Because linoleic acid has two double bonds, peroxidation occurs at the bisallylic hydrogens and generates conjugated diene hydroperox…
Transport, stability, and biological activity of resveratrol
2011
Numerous studies have reported interesting properties of trans-resveratrol, a phytoalexin, as a preventive agent of several important pathologies: vascular diseases, cancers, viral infections, and neurodegenerative processes. These beneficial effects of resveratrol have been supported by observations at the cellular and molecular levels in both cellular and in vivo models, but the cellular fate of resveratrol remains unclear. We suggest here that resveratrol uptake, metabolism, and stability of the parent molecule could influence the biological effects of resveratrol. It appears that resveratrol stability involves redox reactions and biotransformation that influence its antioxidant properti…
Flavanones in Citrus fruit: structure-antioxidant activity relationships
2005
Epidemiological surveys have shown an inverse relationship between the intake of fruit and the incidence of coronary heart disease and some type of cancer. Data found in the literature regarding the flavonoids in general while this study focuses on flavanones, a subclass of flavonoids which occurs in Citrus fruit. The aim of this work is to elucidate the antioxidant or pro-oxidant behaviours of some common flavanones and to determine their activity–structure relationships as antioxidant using the crocin bleaching inhibition assay. The compounds studied were regarding both the aglycon form and the glycoside form. Data evidence that the substitution of the 7th OH group of the flavanones by a …
Acetogenins from Annonaceae
1997
In 1982, Jolad et al. isolated uvaricin, a new antitumor agent, from the roots of Uvaria acuminata (Annonaceae), a bis-tetrahydrofuranoid fatty acid lactone (1) related to polyketides or acetogenins. However, it contained a number of original structural characteristics, particularly a linear acetogenin, a bis-tetrahydrofuran pattern flanked by hydroxyls and a terminal unsaturated lactone. Two years later, Dabrah and Sneden (2, 3 and Cortes et al. (4) described four new products presenting the same structural characteristics. Because these products formed a new class of natural compounds, and are only found in species belonging to the family of Annonaceae, they are commonly called acetogenin…
Oxygen atom transfer catalysis by dioxidomolybdenum(VI) complexes of pyridyl aminophenolate ligands
2021
Abstract A series of new cationic dioxidomolybdenum(VI) complexes [MoO2(Ln)]PF6 (2–5) with the tripodal tetradentate pyridyl aminophenolate ligands HL2-HL5 have been synthesized and characterized. Ligands HL2-HL4 carry substituents in the 4-position of the phenolate ring, viz. Cl, Br and NO2, respectively, whereas the ligand HL5, N-(2-hydroxy-3,5-di-tert-butylbenzyl)-N,N-bis(2-pyridylmethyl)amine, is a derivative of 3,5-di-tert-butylsalicylaldehyde. X-ray crystal structures of complexes 2, 3 and 5 reveal that they have a distorted octahedral geometry with the bonding parameters around the metal centres being practically similar. Stoichiometric oxygen atom transfer (OAT) properties of 5 with…
Influence of some aromatic and aliphatic compounds on the rate of photodegradation of phenol in aqueous suspensions of TiO2
1995
Abstract The influence of 3-nitrophenol, 4-nitrophenol, pentachlorophenol, ethanol, 2-propanol, ethanoic acid and ethanedioic acid on the photodegradation rate of phenol in an aqueous suspension of TiO2 (anatase) irradiated in the near-UV region was investigated. Binary mixtures of organic compound and phenol in molar ratios of 1:1 and 10:1 were used for the photoreactivity experiments performed in a batch reactor. The mineralization rate of all the mixtures was also monitored by measuring the total organic carbon (TOC) concentration. The reactivity results indicate that the photodegradation rate of phenol is mainly determined by the total amount of aromatic substrates present in the reacti…
Well-Defined Multi-Amino-Functional and Stimuli-Responsive Poly(propylene oxide) by Crown Ether Assisted Anionic Ring-Opening Polymerization
2017
Multi-amino-functional poly(propylene oxide) (PPO) copolymers were synthesized by the anionic ring-opening copolymerization (AROP) of N,N-diethyl glycidyl amine (DEGA) and propylene oxide (PO). A solvent free synthesis route using potassium counterions and crown ether for the AROP enabled controlled (co)polymerization with full conversion. The strategy provided access to PPO-b-PDEGA block copolymers, statistical PPO-co-PDEGA copolymers, and, for the first time, PDEGA homopolymer. Molecular weights in the range of 1400 to 4200 g/mol (Mn) and dispersities (Mw/Mn) below 1.1 were obtained. Both the kinetics and resulting microstructure of the statistical copolymerization were investigated by in…
Cyclodextrins in polymer chemistry: Influence of methylated β-cyclodextrin as host on the free radical copolymerization reactivity ratios of isoborny…
1999
Methylated β-cyclodextrin (me-β-CD) was used to complex the hydrophobic monomers isobornyl acrylate (1) and butyl acrylate (2) yielding the water-soluble host/guest complexes isobornyl acrylate/me-β-CD (1a) and butyl acrylate/me-β-CD (2a). The included monomers were copolymerized in water by free-radical mechanism and the kinetics were studied. In order to evaluate these results, the corresponding uncomplexed monomers 1 and 2 were also copolymerized in organic solution. The reactivity ratios of 1a and 2a (r1a = 0.3, r2a = 1.7) differ significantly from the reactivity ratios of the corresponding uncomplexed acrylates 1 and 2 in organic solution (r1 = 1.3, r2 = 1.0). In addition, we found tha…
Water-soluble polysaccharides from Opuntia stricta Haw. fruit peels: Recovery, identification and evaluation of their antioxidant activities
2015
Abstract Opuntia stricta Haw. is considered as one of the most common cactus plant growing in Tunisia. Extracting valuable compounds from its fruit peel, considered as by-product, is drawing more and more attention, making it on the verge of commercialization. Water-soluble polysaccharides were extracted from Opuntia stricta Haw. peels, and their chemical composition assessed using thin layer chromatography. The antioxidant activities of the extracted polysaccharides were assessed using 2,2-diphenyl-1-picrylhydrazyl free radical scavenging activity, total antioxidant activity and reducing power capacity. The extraction yield of water-soluble polysaccharides was 7.53±0.86%. The chemical comp…
Towards the Next Generation of Lochmann-Schlosser Superbases: A Potassium Neopentyl/Alkoxy Aggregate used in the Tetra-Functionalization of Ferrocene
2018
Lochmann-Schlosser superbases are formed by mixing alkyllithium with potassium alkoxides. These reagents could prove their synthetic usefulness and reliability in many reactions over five decades. However, despite many efforts, the real source of the exceptional reactivity remained a secret. The seemingly manageable system of four components (lithium, potassium atoms, alkyl groups, and alkoxy groups) and their interaction is obscured by poor solubility and fierce reactivity. Recent progress was achieved by using neopentyllithium, leading to alkane-soluble aggregates with varying lithium/potassium content and a flexible alkyl/alkoxy ratio. Herein, we isolated two new alkane-soluble alkyl/alk…