Search results for " oxidation"

Photoelectrochemical and EPR features of polymeric C 3 N 4 and O-modified C 3 N 4 employed for selective photocatalytic oxidation of alcohols to alde…

2019

Four different C 3 N 4 specimens have been prepared, a bulk one (MCN), a thermally etched (MCN-TE), a solid prepared by hydrothermally treating MCN with H 2 O 2 (MCN-H 2 O 2 ) and a polymeric carbon nitride-hydrogen peroxide adduct (MCN-TE-H 2 O 2 ). The principal aim of this work was to correlate the capability of the prepared material to generate reactive oxygen species (ROS), under irradiation, with their photocatalytic activities in terms of conversion and selectivity for partial oxidation reactions. Photoelectrochemical studies revealed that MCN-TE represented the best material in terms of photoconductivity, whereas MCN-H 2 O 2 was defective and evidenced a poor mobility of carriers. E…

Oxidative changes in Sicilian extra virgin olive oil under heating treatment detected by FTIR spectroscopy, viscosimetry and time-resolved luminescen…

2007

2015

Oxidative stress is thought to be one of the main mediators of neuronal damage in human neurodegenerative disease. Still, the dissection of causal relationships has turned out to be remarkably difficult. Here, we have analyzed global protein oxidation in terms of carbonylation of membrane proteins and cytoplasmic proteins in three different mammalian species: aged human cortex and cerebellum from patients with or without Alzheimer's disease, mouse cortex and cerebellum from young and old animals, and adult rat hippocampus and cortex subjected or not subjected to cerebral ischemia. Most tissues showed relatively similar levels of protein oxidation. However, human cortex was affected by sever…

Effect of Substituents on Partial Photocatalytic Oxidation of Aromatic Alcohols Assisted by Polymeric C3N4

2019

In the present work we scrutinize the effect of substituents in the phenyl ring of the benzyl alcohol on its photo-oxidation to the corresponding benzaldehyde driven by polymeric carbon nitride photocatalyst in aqueous medium. It has been established that electron donating (ED) substituents in para- and ortho-position with respect to the CH2OH-group promote the reactivity of the substrate without compromising the selectivity towards benzaldehyde formation, maintaining it in the range of 84–98 %, if compared to the unsubstituted molecule. The same observation is true for meta-substituted benzyl alcohol with an electron withdrawing (EW) group. On the other hand, the presence of ED-group in me…

Stabilisation of LDPE cross-linked in the presence of peroxidesII. FTIR study of chemical changes taking place in the LDPE–dicumyl peroxide–Irganox 1…

2000

Abstract The chemical changes taking place in the systems: LDPE–Irganox 1081, LDPE–dicumyl peroxide and LDPE–Irganox 1081–dicumyl peroxide, after homogenisation (in a rolling mill at 130°C) and after homogenisation and cross-linking (at 180°C and 5.0 MPa for 20 min) were investigated by FTIR. It was found that the OH groups in Irganox 1081 were in a bound form, and were most probably linked to the sulphur co-ordination centre. Further, the presence of dicumyl peroxide without Irganox 1081 in LDPE resulted in the formation of hydroperoxide groups at a temperature of 130°C, which were replaced by free hydroxy and carbonyl groups of a ketonic type after cross-linking. Simultaneous addition of …

Water oxidation catalyzed by molecular di- and nonanuclear Fe complexes: importance of a proper ligand framework.

2016

The synthesis of two molecular iron complexes, a dinuclear iron(III,III) complex and a nonanuclear iron complex, based on the di-nucleating ligand 2,2-(2-hydroxy-5-methyl-1,3-phenylene)bis(1H-benzo[d]imidazole-4-carboxylic acid) is described. The two iron complexes were found to drive the oxidation of water by the one-electron oxidant [Ru(bpy)(3)](3+). Funding Agencies|Knut and Alice Wallenberg Foundation; Swedish Research Council [621-2013-4872]; Carl Trygger Foundation; DFG (Metal Sites in Biomolecules: Structures, Regulation and Mechanisms) [IRTG 1422]; Swedish Energy Agency

Enhanced susceptibility of cholesteryl sulfate-enriched low density lipoproteins to copper-mediated oxidation

1995

AbstractCholesteryl sulfate (CS) is a minor component of cell membranes, also present in lipoproteins, and its exact function is unknown. Since oxidation of low density lipoproteins (LDL) is thought to be an important determinant of atherogenesis, we investigated the influence of CS enrichment on copper-mediated oxidation of LDL. CS was found to act as a pro-oxidant, as measured by lipid oxidation parameters. The results also suggest that these effects were dependent on the sulfate group since pure cholesterol or cholesteryl acetate did not promote Cu2+-mediated oxidation. Our findings imply that CS may affect the oxidizability and hence the potential atherogenicity of LDL.

Pro-oxidant effects of 7-hydroperoxycholest-5-en-3β-ol on the copper-initiated oxidation of low density lipoprotein

1995

AbstractIn low density lipoproteins (LDL) supplemented with aged cholesterol and oxidized in the presence of Cu2+, an increase of the lipid oxidation parameters was observed compared with pure cholesterol-enriched LDL. A compound, identified as 7-hydroperoxycholesterol (7HPC), isolated from aged cholesterol and added to LDL, reproduced the above effects. The results indicate that the pro-oxidant effect of 7HPC is dependent on the hydroperoxy group since the corresponding alcohol derivative, 7α-hydroxycholesterol, had no such effect. These data suggest that among the LDL-associated lipid peroxides, cholesterol peroxides may have important implications in the susceptibility of this lipoprotei…

Mechanistic aspects of oxalic acid oxidation by photocatalysis and ozonation

2008

Oxalic acid has been oxidised in acidic aqueous solutions (pH 3) using photocatalysis and ozonation alone or coupled. The simultaneous presence of ozone, titanium dioxide and near UV irradiation increases the oxidation rate of oxalic acid to values greater than those deriving from the single contributions of photocatalysis and ozonation. In particular in the present paper ozonation alone, heterogeneous photocatalysis and also combined ozonation with heterogeneous photocatalysis have been used for the oxidation of oxalic acid at acidic pH in the presence of TiO2 Degussa P25. A likely mechanism, able to explain both the homogeneous and heterogeneous processes, is discussed.

Monitoring of headspace volatiles in milk‐cereal‐based liquid infant foods during storage

2006

The effect of storage (time and temperature) on the evolution of pentanal, hexanal, heptanal and pentane as volatile lipid oxidation products in two liquid ready-to-eat milk-cereal-based infant foods was studied. An SPME-GC method was used to this effect. Samples were stored for 9 months at 25, 30 and 37 °C and tested eight times during this period. Freshly produced infant foods contained pentanal, hexanal and heptanal (mean values: 10.71, 71.5 and 1.2 μg/kg, respectively), which decreased during the first 3 months of storage, although from the fourth month onwards no significant differences among storage times were found. Aldehyde content was inversely proportional to storage temperature. …