Search results for "oxidation"
showing 10 items of 1913 documents
Quinone reduction and redox cycling catalysed by purified rat liver dihydrodiol/3 alpha-hydroxysteroid dehydrogenase.
1992
A highly active preparation of rat liver dihydrodiol/3 alpha-hydroxysteroid dehydrogenase was obtained using a newly developed, rapid purification scheme involving affinity chromatography on Red Sepharose. Depending on the coenzyme present, the purified enzyme was found to catalyse the oxidation of dihydrodiols and steroids or the reduction of substrates with carbonyl or quinone moieties. Using a wide range of synthetic quinones derived from polycyclic aromatic hydrocarbons (PAHs), we observed a pronounced regioselectivity of the quinone reductase activity. Good substrates were the o-quinones of phenanthrene, benz(a)anthracene, chrysene and benzo(a)pyrene with the quinonoid moiety in the K-…
Microwave-assisted chemical modification of g-C3N4 for photoinduced processes: organic degradation, hydrogen production and selective oxidation of al…
2023
g-C3N4 powders were treated by means of the microwave technique in three different aqueous and organic media (HNO3, NaOH and N,N-dimethylformamide). All powders were analyzed by XRD reveling that g-C3N4 maintains its structure. The morphology of the samples was analyzed with scanning electron microscopy, where the micrographs reveals that the modifcation occurs on the surface of the g-C3N4. The photocatalytic activity of the samples was evaluated in the degradation of ciprofoxacin, hydrogen production and for the selective partial oxidation of 4-methoxybenzylalcohol (4-MBA) to its aldehyde. The sample treated with HNO3 (C3N4-HNO3) shows the best photocatalytic performance in the degradation…
Carboxylated-xyloglucan and peptide amphiphile co-assembly in wound healing.
2021
Abstract Hydrogel wound dressings can play critical roles in wound healing protecting the wound from trauma or contamination and providing an ideal environment to support the growth of endogenous cells and promote wound closure. This work presents a self-assembling hydrogel dressing that can assist the wound repair process mimicking the hierarchical structure of skin extracellular matrix. To this aim, the co-assembly behaviour of a carboxylated variant of xyloglucan (CXG) with a peptide amphiphile (PA-H3) has been investigated to generate hierarchical constructs with tuneable molecular composition, structure, and properties. Transmission electron microscopy and circular dichroism at a low c…
Influence of orange cultivar and mandarin postharvest storage on polyphenols, ascorbic acid and antioxidant activity during gastrointestinal digestio…
2017
Polyphenols, ascorbic acid content and antioxidant activity of two sweet oranges (Navel-N and Cara Cara-CC) and mandarin (Clementine-M) as well as their bioaccessibilities were evaluated in pulps and compared to those in fresh juice. Thus, pulps of oranges and mandarins displayed higher hesperidin (HES), narirutin (NAR), total flavonoids (TF), total phenols (TP) and antioxidant activity (AAC) than their corresponding juices. Also, CC products presented higher bioactive compounds content than N ones. Bioaccessibility of bioactive compounds and AAC were higher in pulps of both oranges and mandarin than in their corresponding juices. Oranges (N and CC) pulps and juices presented higher bioacce…
Determination of kinetic parameters of redox reactions using CE‐ICP‐MS: A case study for the reduction of Np(V) by hydroxylamine hydrochloride
2018
The rate constants k of the reduction of 5 × 10-5 M Np(V) to Np(IV) by hydroxylamine hydrochloride (HAHCl) in 1 M HCl have been determined by CE-ICP-MS in the temperature range of ϑ = 30-70°C and with varying concentrations of HAHCl from 1 to 7.2 M. The reaction was found to have (pseudo)first order kinetics with respect to HAHCl. The experimental results for k ranged from 0.0029(1) min-1 (ϑ = 40°C, c(HAHCl) = 3 M) to 0.039(7) min-1 (ϑ = 60°C, c(HAHCl) = 7.2 M). The activation energy of the reaction was determined as EA = (72 ± 10) kJ/mol. These results and a comparison with literature data show that the coupling of CE to ICP-MS provides a powerful analytical tool for the investigation of…
Gas-phase selective oxidation of chloro- and methoxy-substituted toluenes on TiO2–Sepiolite supported vanadium oxides
2009
Abstract Catalytic behaviour of vanadium oxide systems (5–20 wt.% V2O5) supported on TiO2–Sepiolite (with titania loading around the theoretical monolayer, 12 wt.%, 12Ti–Sep) and, as reference, on Sepiolite calcined (Sepc) in the p-substituted toluene derivatives selective oxidation was studied. In all the catalysts studied p-chloro (p-ClBA) and p-methoxybenzaldehyde (p-MeOBA) were the main products. The yields to benzaldehydes obtained with %V/12Ti–Sep are comparable with some of those reported in the literature under similar kinetically controlled experimental conditions (Sp-ClBA = 70% and X = 19% were obtained at 653 K on 20 V/12Ti–Sep). The activity for benzaldehyde derivatives formatio…
Coupling between oxidation kinetics and anisothermal oil flow during deep-fat frying
2021
Deep-fat frying is a cooking technique that has been used continuously since prehistoric times. A domestic deep-fryer heated from the bottom develops significant convection inside the bath cavity. It is responsible for very high heat transfer coefficients and the exposure of the deep-frying oil to the atmospheric oxygen. The continuous conversion of gaseous dioxygen into unstable and reactive hydroperoxides and their subsequent advection throughout the bulk volume is at the origin of the main complaints made of frying which includes issues such as odors, fouling, and generation of several toxic compounds. This study analyzes the coupling between natural convection of triacylglycerols and th…
Intramolecular proton transfer boosts water oxidation catalyzed by a Ru complex
2015
We introduce a new family of complexes with the general formula [Run(tda)(py)2]m+ (n = 2, m = 0, 1; n = 3, m = 1, 2+; n = 4, m = 2, 32+), with tda2– being [2,2′:6′,2″-terpyridine]-6,6″-dicarboxylate, including complex [RuIV(OH)(tda-κ-N3O)(py)2]+, 4H+, which we find to be an impressive water oxidation catalyst, formed by hydroxo coordination to 32+ under basic conditions. The complexes are synthesized, isolated, and thoroughly characterized by analytical, spectroscopic (UV–vis, nuclear magnetic resonance, electron paramagnetic resonance), computational, and electrochemical techniques (cyclic voltammetry, differential pulse voltammetry, coulometry), …
Synthesis and characterization of vanadyl(IV) complexes of Schiff bases derived from anthranilic acid and salicylaldehyde (or its derivatives) or ace…
1997
Anhydrous, dimeric vanadyl(IV) complexes of Schiff bases derived from [1+1] condensation of salicylaldehyde (or its derivatives) and anthranilic acid, have been synthesized from CH3CN and were characterized by elemental analysis, FTIR, EPR, absorption, TGA, cyclic voltammetry and room temperature magnetic susceptibility measurements. These complexes were found to be oxidized by air in polar solvents like MeOH and DMF to V-V products. The E(1/2) values were found to be around 660 mV indicating that the carboxylate group favours vanadyl(IV) binding when compared to the alkoxo-bound vanadium complexes. Oxidative instability of these complexes are dependent on the substituent on the salicylalde…
A novel series of rhenium-bipyrimidine complexes: synthesis, crystal structure and electrochemical properties
2007
Four novel rhenium complexes of formula [ReCl(4)(bpym)] (1), [ReBr(4)(bpym)] (2) PPh(4)[ReCl(4)(bpym)] (3) and NBu(4)[ReBr(4)(bpym)] (4) (bpym = 2,2'-bipyrimidine, PPh(4) = tetraphenylphosphonium cation and NBu(4) = tetrabutylammonium cation), have been synthesized and their crystal structures determined by single-crystal X-ray diffraction. The structures of 1 and 2 consist of [ReX(4)(bpym)] molecules held together by van der Waals forces. In both complexes the Re(iv) central atom is surrounded by four halide anions and two nitrogen atoms of a bpym bidentate ligand in a distorted octahedral environment. The structures of 3 and 4 consist of [ReX(4)(bpym)](-) anions and PPh(4)(+) () or NBu(4)…