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At least 163 records · Page 9Linked to original sources
PubMed2007

Strategies to stabilize new oxides in the Sr(n+1)(CoTa)(n)O(3n+1) Ruddlesden-Popper homologous series.

Two new oxides of the Ruddlesden-Popper series have been isolated and structurally characterized in the Sr-Co-Ta-O system. X-ray and electron diffraction and high-resolution electron microscopy show that polycrystalline Sr(3)CoTaO(7) constitutes the n=2 member of a new Sr(n+1)(CoTa)(n)O(3n+1) homologous series, the essential feature of which is the existence of two connected Co/Ta octahedral layers, separated by Sr atoms. Sr(2)CoTaO(6), the n=infinity member of the series, shows a particular short-range ordering of Co and Ta at the octahedral sites leading, as shown by high-resolution electron microscopy, to the disordered intergrowth of simple and double perovskite type domains. Strategies to stabilize new oxides of this series are discussed.

Journal Article↗
PubMed2001

Modification of the levels of polyphenols in wort and beer by addition of hexamethylenetetramine or sulfite during mashing.

The effects of addition of hexamethylenetetramine (HMT) or sulfite during mashing on the polyphenol content and oxidative stability of wort and beer have been evaluated in a series of laboratory mashings and pilot brews. HMT reduced the concentration of catechin, prodelphinidin B-3, and procyanidin B-3 in wort and beer, whereas the concentration of ferulic acid was unaffected. Sulfite had only a minor effect on the concentration of phenolics in wort and beer. Addition of HMT or sulfite during mashing increased the oxidative stability of the beer slightly as judged by the tendency of formation of radicals (ESR spin trapping technique), although sensory analysis gave identical flavor acceptance scores to beers produced from untreated and HMT-treated wort and lower scores to beer from sulfite-treated wort. No difference in the oxidative stability of the differently treated sweet worts could be detected as judged by the rate of formation of radicals. HMT addition during mashing has thus been demonstrated to be a valuable experimental tool to control the level of polyphenols in wort and for producing brews with various levels of polyphenols from a single malt.

Beer↗
PubMed2003

Polar oxide interface stabilization by formation of metallic nanocrystals.

In situ x-ray photoelectron spectroscopy and ex situ transmission electron microscopy and diffraction studies of a model Fe3O4(111)/MgO(111) polar oxide interface exclude stabilization by interface faceting, reconstruction, or by formation of a continuous interfacial layer with altered stoichiometry, and uncover stabilization by dominant formation of metallic Fe(110) nanocrystals. The iron nanocrystals nucleate both at the interface and within the magnetite film and grow in a Nishiyama-Wasserman orientation relationship with a bimodal size distribution related to twinning. Minority magnetite nanocrystals were also observed, growing in the less polar (100) orientation than the magnetite (111) film. Electron transfer and bond hybridization mechanisms are likely at the metal/oxide and oxide/oxide interfaces and remain to be explored.

Journal Article↗
PubMed1999

Glutathione peroxidase activity, TBARS, and alpha-tocopherol in meat from chickens fed different diets.

This study investigated the effect of feeding broilers with diets differing in dietary fat source (lard, sunflower oil, olive oil) and vitamin E (basal vs supplemented with 200 mg of alpha-tocopheryl acetate/kg) on meat lipid oxidative stability. The diets differed by their degree of unsaturation and included the natural antioxidant alpha-tocopherol (vitamin E). Glutathione peroxidase (GSHPx) activity was measured in raw meat and ranged from 3.62 to 8.06 nmol NADPH/min/mg protein. The enzyme activity was influenced by the degree of unsaturation of the diet. Capillary gas chromatography analyses showed that dietary alpha-tocopherol accumulated in the muscle tissue and contributed to a better oxidative stability of the raw and cooked meat. Thigh meat alpha-tocopherol levels ranged from 2.73 to 3.62 microg/g in unsupplemented chickens whereas levels from 8.69 to 13.37 microg/g were observed in the thigh meat from alpha-tocopherol supplemented animals. The inclusion of olive oil and alpha-tocopherol in the animal diet gave lower thiobarbituric acid reactive substance (TBARS) values and lower GSHPx activity. High correlations were found between the parameters studied. The results suggest that the glutathione peroxidase activity could be used as an indicator of the meat oxidative stability. A negative relationship was observed between GSHPx activity and tissue alpha-tocopherol levels, and a positive relationship was evidenced between TBARS and antioxidant enzyme activity.

Animal Feed↗
PubMed1997

The influence of the sample preparation on plasma protein adsorption patterns on polysaccharide-stabilized iron oxide particles and N-terminal microsequencing of unknown proteins.

The in vivo organ distribution of i.v. injected drug carriers is strongly influenced by the adsorption of plasma proteins after i.v. injection, e.g. uptake by the mononuclear phagocytic system (MPS). 2-D PAGE could be established to analyze plasma protein adsorption patterns on polysaccharide-stabilized aqueous iron oxide dispersions used as contrast agents in Magnetic Resonance Imaging (MRI). After incubation in human plasma, centrifugation, a washing procedure and a solubilization step were carried out to obtain the proteins adsorbed onto these ultrasmall particles (65 nm in diameter). Patterns of adsorbed proteins were analyzed in dependence on the washing medium used, i.e. highly purified water, phosphate buffered saline and Krebs buffer pH 7.4. Conductivity and composition of the washing medium influenced the adsorption of IgG onto the particles, but had little effect on the other proteins present. IgG was strongly reduced when using the relatively high conductive buffers. The more stabilizing polysaccharide was desorbed the larger was the total amount of adsorbed proteins. Appearance of two unknown chains of spots in the range of appr. 92 kDa, accounting for appr. 10% and 2% of the overall detected protein amount, was observed only when using Krebs buffer during the washing process. Performing N-terminal microsequencing one unknown chain of spots could be identified as a dimer of fibrinogen gamma chains.

Adsorption↗
PubMed1998

The influence of the sample preparation on plasma protein adsorption patterns on polysaccharide-stabilized iron oxide particles and N-terminal microsequencing of unknown proteins.

The in vivo organ distribution of i.v. injected drug carriers is strongly influenced by the adsorption of plasma proteins after i.v. injection, e.g. uptake by the mononuclear phagocytic system (MPS). 2-D PAGE could be established to analyze plasma protein adsorption patterns on polysaccharide-stabilized aqueous iron oxide dispersions used as contrast agents in Magnetic Resonance Imaging (MRI). After incubation in human plasma, centrifugation, a washing procedure and a solubilization step were carried out to obtain the proteins adsorbed onto these ultrasmall particles (65 nm in diameter). Patterns of adsorbed proteins were analyzed in dependence on the washing medium used, i.e. highly purified water, phosphate buffered saline and Krebs buffer pH 7.4. Conductivity and composition of the washing medium influenced the adsorption of IgG onto the particles, but had little effect on the other proteins present. IgG was strongly reduced when using the relatively high conductive buffers. The more stabilizing polysaccharide was desorbed the larger was the total amount of adsorbed proteins. Appearance of two unknown chains of spots in the range of appr. 92 kDa, accounting for appr. 10% and 2% of the overall detected protein amount, was observed only when using Krebs buffer during the washing process. Performing N-terminal microsequencing one unknown chain of spots could be identified as a dimer of fibrinogen gamma chains.

Adsorption↗
PubMed2005

Stability of spray-dried tuna oil emulsions encapsulated with two-layered interfacial membranes.

omega-3 Fatty acids have numerous health benefits, but their addition to foods is limited by oxidative rancidity. Spray-drying tuna oil-in-water emulsion droplets with a coating of lecithin and chitosan multilayer system could produce emulsion droplet interfacial membranes that are cationic and thick, both factors that can help control lipid oxidation. Physicochemical and oxidative stability of the spray-dried emulsions were determined as a function of storage temperature and relative humidity (RH). The combination of ethylenediaminetetraacetic acid (EDTA) and mixed tocopherols was able to increase the oxidative stability of dried emulsions. Lipid oxidation was more rapid during storage at low relative humidity (11% and 33% compared to 52% RH). At high moisture, physical modifications in the sample were observed, including reduced dispersibility and formation of brown pigments. Sugar crystallization or Maillard products produced at the higher humidities may have inhibited oxidation. Overall, spray-dried tuna oil-in-water emulsions stabilized by lecithin-chitosan membranes were more oxidatively stable than bulk oils and thus have excellent potential as an omega-3 fatty acid ingredient for functional foods.

Animals↗
PubMed2006

Transition metal oxides: extra thermodynamic stability as thin films.

The oxides of many transition metals wet their own metal surface. The adhesion energy at this interface (E(adh,ox/m)) provides extra stabilization, which lowers the O2 pressure required for oxide stability as a thin film below that required for bulk-oxide stability by the factor exp[(2gamma(g/ox) - E(adh,ox/m))/(tN(ox)RT)], where gamma(g/ox) is the surface energy of the oxide, t is the oxide film thickness, and N(ox) is the oxygen concentration in the bulk oxide (moles O2 per volume). For oxide films only approximately 1 nm thick, this correction can be many orders of magnitude. This may extend to other compounds.

Journal Article↗
PubMed2000

Nitric oxide (NO.) stabilizes whereas nitrosonium (NO+) enhances filopodial outgrowth by rat retinal ganglion cells in vitro.

Recent observations suggest that nitric oxide (NO(.)) can increase or decrease growth cone motility. Here, these apparently paradoxical results are explained by distinct actions of different NO-related species. Filopodial morphology of 223 rat retinal ganglion cells was monitored under computer-enhanced video microscopy in the presence of NO synthase (NOS) substrates or inhibitors, donors of specific NO-related species, and membrane-permeant cyclic nucleotide analogs. Physiological NOS activity induced filopodial outgrowth, whereas inhibition of NOS stabilized filopodia. Similar to NOS, nitrosonium (NO(+) transfer) and peroxynitrite (ONOO(-)), which can regulate the activity of growth-associated proteins by S-nitrosylation and oxidation, respectively, induced filopodial outgrowth. In contrast, NO(.), which stimulates guanylate cyclase to increase cGMP, stabilized filopodial activity. Thus disparate NO-related species may offer a dynamic process of filopodial growth regulation.

Animals↗
PubMed1997

Nitric oxide decreases stability of mRNAs encoding soluble guanylate cyclase subunits in rat pulmonary artery smooth muscle cells.

Nitric oxide stimulates soluble guanylate cyclase (sGC) to convert GTP to the intracellular second messenger cGMP. In rat pulmonary artery smooth muscle cells, sGC is an obligate heterodimer composed of alpha1 and beta1 subunits. We investigated the effect of NO donor compounds on sGC subunit gene expression in rat pulmonary artery smooth muscle cells. Sodium nitroprusside and S-nitroso-glutathione decreased sGC subunit mRNA and protein levels, as well as sGC enzyme activity. 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one, an sGC inhibitor, blocked the effect of sodium nitroprusside on sGC subunit gene expression, whereas 8-bromo cGMP decreased subunit mRNA levels, demonstrating that NO-mediated decrease in sGC subunit mRNA levels is cGMP-dependent. sGC subunit mRNA levels decreased more rapidly in rat pulmonary artery smooth muscle cells exposed to NO than in cells exposed to actinomycin D, suggesting that NO decreases sGC subunit mRNA stability. Actinomycin D and cycloheximide blocked the ability of NO to decrease sGC subunit mRNA levels. These results demonstrate that NO decreases sGC subunit mRNA stability via a transcription- and translation-dependent mechanism.

Animals↗
PubMed2005

NF-kappa B-mediated MyoD decay during muscle wasting requires nitric oxide synthase mRNA stabilization, HuR protein, and nitric oxide release.

Muscle wasting (cachexia) is a consequence of chronic diseases, such as cancer, and is associated with degradation of muscle proteins such as MyoD. The cytokines tumor necrosis factor alpha and gamma interferon induce muscle degeneration by activating the transcription factor NF-kappaB and its target genes. Here, we show that a downstream target of NF-kappaB is the nitric oxide (NO) synthase gene (iNos) and suggest that NO production stimulates MyoD mRNA loss. In fact, although cytokine treatment of iNos(-/-) mice activated NF-kappaB, it did not trigger MyoD mRNA degeneration, demonstrating that NF-kappaB-mediated muscle wasting requires an active iNOS-NO pathway. The induced expression of iNOS by cytokines relies on both transcriptional activation via NF-kappaB and increased mRNA stability via the RNA-binding protein HuR. Moreover, we show that HuR regulates iNOS expression in an AMP-activated protein kinase (AMPK)-dependent manner. Furthermore, AMPK activation results in HuR nuclear sequestration, inhibition of iNOS synthesis, and reduction in cytokine-induced MyoD loss. These results define iNOS and HuR as critical players in cytokine-induced cachexia, establishing them as potential therapeutic targets.

Animals↗
PubMed2005

Model system for testing the efficacy of antioxidants in muscle foods.

The objective of this research was to study the effect of the antioxidants, delta-tocopherol, butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT), tertiary butylhydroquinone (TBHQ), and propyl gallate in a model system of lean muscle and canola oil and to compare the effects with those in minced herring. Two carrier solvents with different dielectric constants (epsilon), ethanol (epsilon = 24) and oil (epsilon= 2), were used. Oxidation was measured using thiobarbituric acid reactive substances (TBARS) and sensory analysis. In both the lean muscle-canola oil model system and in herring muscle, the hydrophilic antioxidants, propyl gallate and TBHQ, were more effective in providing oxidative stability than the lipophilic antioxidants, delta-tocopherol and BHT. The oxidative stability of a cod muscle-canola oil system in the presence of propyl gallate, and delta-tocopherol was not affected by the dielectric constant of the carrier solvent, while BHA was more effective as an antioxidant when added in the polar solvent ethanol.

Animals↗
PubMed2000

Discrete reduction of type I collagen thermal stability upon oxidation.

The oxidation of acid-soluble calf skin collagen type I caused by metal-dependent free radical generating systems, Fe(II)/H2O2 and Cu(II)/H2O2, was found to bring down in a specific, discrete way the collagen thermal stability, as determined by microcalorimetry and scanning densitometry. Initial oxidation results in splitting of the collagen denaturational transition into two components. Along with the endotherm at 41 degrees C typical for non-oxidized collagen, a second, similarly cooperative endotherm appears at 35 degrees C and increases in enthalpy with the oxidant concentration and exposure time, while the first peak correspondingly decreases. The two transitions at 35 and 41 degrees C were registered by densitometry as stepwise increases of the collagen-specific volume. Further oxidation results in massive collagen destruction manifested as abolishment of both denaturational transitions. The two oxidative systems used produce identical effects on the collagen stability but at higher concentrations of Cu(II) in comparison to Fe(II). The discrete reduction of the protein thermal stability is accompanied by a decrease of the free amino groups, suggestive of an oxidation attack of the side chains of lysine residues. Since the denaturation temperature of collagen shifts from above to below body temperature (41 degrees C-35 degrees C) upon oxidation, it appears important to account for this effect in a context of the possible physiological implications of collagen oxidation.

Animals↗
PubMed2002

Stability of virgin olive oil. 2. Photo-oxidation studies.

Virgin olive oil samples with similar oxidative stabilities and fatty acid compositions were exposed to 12100 lx (25 +/- 1 degrees C) in closed bottles until bleached. The observed low changes in the substrate and polar phenols were related to oxygen availability. HPLC monitoring showed that pheophytin agradual degradation (> 90%) was accompanied by a considerable alpha-tocopherol loss (22-35%) due to the reaction of the latter with singlet oxygen. No changes were recorded for carotenoids, which acted as physical quenchers and light filters. Squalene loss was confined (4-12%). Complementary experiments on the activity of pheophytin a, using olive oil models, indicated a concentration dependence, enhanced by oxygen availability. In closed bottles, the degradation rate constant was higher at low amounts of pheophytin a. Squalene was preferentially consumed to protect alpha-tocopherol. An urgent change in the practice of packaging is needed to preserve the precious characteristics of the product during commercialization.

Chlorophyll↗
PubMed2003

The mechanism of oxidative stress stabilization of the thromboxane receptor in COS-7 cells.

The 8-iso-prostaglandin F(2alpha), a prostanoid produced in vivo by cyclooxygenase-independent free-radical-catalyzed lipid peroxidation, acts as a partial agonist on the thromboxane receptor (TXA(2)R) and is a potent vasoconstrictor in the oxidatively stressed isolated perfused rat heart. We hypothesized that the response in the isolated heart may be due to augmentation of TXA(2)R density, which may be initiated by the presence of oxidative radicals. Previous studies have shown that TXA(2)R density is increased during atherosclerosis on both the medial and intimal smooth muscle layers in human coronary arteries. Here we describe the effect of oxidative stress on TXA(2)R. The thromboxane A(2) receptor beta isoform (TXA(2)Rbeta) was transiently expressed in COS-7 cells. Immunofluorescence suggested that the presence of H(2)O(2) increased translocation of TXA(2)Rbeta from the endoplasmic reticulum (ER) to the Golgi complex. H(2)O(2) treatment also increased binding of a TXA(2)R antagonist ([(3)H]SQ29548) to membranes. Degradation kinetics of TXA(2)Rbeta following cycloheximide treatment, a protein synthesis inhibitor, suggested not only that TXA(2)Rbeta is a short-lived protein predominantly localized to the ER but also that TXA(2)Rbeta degradation is modulated in the presence of H(2)O(2). Our results indicate that oxidative stress induces maturation and stabilization of the TXA(2)Rbeta protein probably by intracellular translocation. Importantly, these observations also suggest that TXA(2)Rbeta levels are modulated by ER-associated degradation and controlled by the efficiency of transport to post-ER compartments. Stabilization of the TXA(2)Rbeta by translocation from a degradative compartment, i.e. the ER, can account for the augmentation of receptor density observed in vivo.

Animals↗
PubMed2006

Effect of dry honey on the shelf life of packaged turkey slices.

The development of off-flavors from oxidation reactions in cooked turkey products is a common problem and results in a less desirable, rancid flavor. Various strategies have been evaluated to minimize this off-flavor development, including vacuum and modified atmosphere packaging, feeding antioxidants to animals, and use of antioxidants in the final product. A natural protein-sugar reaction called the Maillard reaction produces a brown pigment, flavors, and antioxidants. This research tested the addition of honey to turkey breast meat before processing to retard production of oxidation products related to off-flavor. Three levels (0, 5, 15%) of dry honey were mixed with raw turkey breast meat pieces, then the mixture was stuffed into casing and cooked. The cooking process facilitated the Maillard reaction and the development of an antioxidative effect. The cooked chubs were then cooled, sliced, and vacuum-packaged as individual slices. The slices were refrigerated and tested for color, flavor, oxidative rancidity, and microbial growth over 11 wk. Sensory panelists detected increased sweetness and no negative flavor impact on acceptability for turkey with added honey. The addition of honey enhanced the oxidative stability of the meat, as indicated by lower TBA values, hexanal content, and oxidative stability index. Honey did impart a slightly darker color with lower lightness values but had no effect of redness and yellowness values.

Animals↗
PubMed2002

The extraordinary ability of guanidinate derivatives to stabilize higher oxidation numbers in dimetal units by modification of redox potentials: structures of Mo(2)(5+) and Mo(2)(6+) compounds.

Full characterization of the first homologous series of dimolybdenum paddlewheel compounds having electronic configurations of the types sigma(2)pi(4)delta(x), x = 2, 1, 0, and Mo-Mo bond orders of 4, 3.5, and 3, respectively, has been accomplished with the guanidinate-type ligand hpp (hpp = the anion of 1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidine). Essentially quantitative oxidation of Mo(2)(hpp)(4), 1, by CH(2)Cl(2) gives Mo(2)(hpp)(4)Cl, 2. The halide in 2 can be replaced by reaction with TlBF(4) to produce Mo(2)(hpp)(4)(BF(4)), 3. Further oxidation of 2 by AgBF(4) produces Mo(2)(hpp)(4)ClBF(4), 4. The change from bond order 4 (in 1) to 3.5 in Mo(2)(hpp)(4)Cl is accompanied by an increase in the Mo-Mo bond length of 0.061 to 2.1280(4) A. A further increase of 0.044 A in the Mo-Mo distance to 2.172(1) A is observed as the bond order decreases to 3 in 4. At the same time, the Mo-N distances decrease smoothly as the oxidation state of the Mo atoms increases. Electrochemical studies have shown two chemically reversible processes at very negative potentials, E(1)(1/2)= -0.444 V and E(2)(1/2)= -1.271 V versus Ag/AgCl. These correspond to the processes Mo(2)(6+/5+) and Mo(2)(5+/4+), respectively. The latter potential is displaced by over 1.5 V relative to those of the Mo(2)(formamidinate)(4) compounds and the first one has never been observed in such complexes. Thus, in surprising contrast to previously observed behavior of the dimolybdenum unit, when it is surrounded by the very basic guanidinate ligand hpp, there is an extraordinary stabilization of the higher oxidation numbers of the molybdenum atoms.

Journal Article↗