EPR investigation of direct oxyradical scavenging and metal chelation activities of chitosan as an alternative to sulfites in enology

Exposure to dissolved oxygen during the winemaking process adversely affects the sensory properties of wines such as loss of colour, aromatic defects and increase of astringency. For decades the management of juice browning in enology has been managed by adding sulphur dioxide as a powerful antioxidant and antimicrobial agent. However, since sulfites are growingly rejected by consumers because of their chemical nature and known allergenic properties, developing biologically relevant alternatives is an expanding field in enology. Recently chitosan, an abundant biopolymer obtained by deacetylation of chitin from animal or vegetal sources, has been recommended as alternative fining agent in wines, showing antimicrobial, biodegradable and non-allergenic properties. Chitin derivatives also demonstrated metal chelating effects (which slower oxidation in wines), interacting with grape polyphenols such as caftaric acid (whose enzymatic oxidation results in excessive browning [1]), and inhibiting (+)-catechin oxidation in model white wines [2]. Using electron paramagnetic resonance (EPR) techniques involving nitrones spin traps and standard oxyradical generating systems, this study presents for the first time complementary facets of the antioxidant action of chitosan, including direct scavenging of hydroxyl radical (a highly oxidizing species formed during wine oxidation) and chelation of metals (iron and copper). Experiments were conducted in aqueous medium, wine matrix, and commercial white wines, and different chitosans were tested at concentrations (0.1\uf02d2 g/L) allowed by enology regulations. Altogether, EPR data support the preferential use of chitosan as a reliable alternative for the reduction of sulphur dioxide to maintain wine freshness

Structural analysis of urate oxidase in complex with its natural substrate inhibited by cyanide: Mechanistic implications

<p>Abstract</p> <p>Background</p> <p>Urate oxidase (EC 1.7.3.3 or UOX) catalyzes the conversion of uric acid and gaseous molecular oxygen to 5-hydroxyisourate and hydrogen peroxide, in the absence of cofactor or particular metal cation. The functional enzyme is a homo-tetramer with four active sites located at dimeric interfaces.</p> <p>Results</p> <p>The catalytic mechanism was investigated through a ternary complex formed between the enzyme, uric acid, and cyanide that stabilizes an intermediate state of the reaction. When uric acid is replaced by a competitive inhibitor, no complex with cyanide is formed.</p> <p>Conclusion</p> <p>The X-ray structure of this compulsory ternary complex led to a number of mechanistic evidences that support a sequential mechanism in which the two reagents, dioxygen and a water molecule, process through a common site located 3.3 Å above the mean plane of the ligand. This site is built by the side chains of Asn 254, and Thr 57, two conserved residues belonging to two different subunits of the homo-tetramer. The absence of a ternary complex between the enzyme, a competitive inhibitor, and cyanide suggests that cyanide inhibits the hydroxylation step of the reaction, after the initial formation of a hydroperoxyde type intermediate.</p

Partial positive scaling transform: a separability criterion

The problem of constructing a necessary and sufficient condition for establishing the separability of continuous variable systems is revisited. Simon [R. Simon, Phys. Rev. Lett. 84, 2726 (2000)] pointed out that such a criterion may be constructed by drawing a parallel between the Peres' partial transpose criterion for finite dimensional systems and partial time reversal transformation for continuous variable systems. We generalize the partial time reversal transformation to a partial scaling transformation and re-examine the problem using a tomographic description of the continuous variable quantum system. The limits of applicability of the entanglement criteria obtained from partial scaling and partial time reversal are explored.Comment: Submitted for publication to Phys. Lett.

Imaginarios y chilenización: los agentes fiscales chilenos y su visión del espacio y la población andina de la provincia de Tarapacá, norte de Chile 1880-1918

In the 1880’s, the Chilean state annexed the province of Tarapacá into its jurisdiction. This gave rise to a complex process known as chilenization. In this context, Chilean state officials implemented political, economic and cultural devices with the purpose of establishing rapidly the new administration, and transforming this territory and its population into a part of the Chilean nation. Consequently, this article describes and analyzes the imaginary of the Andean space and population, belonging to the Tarapacá province, created by these state agents between the late nineteenth and the early twentieth century.En la década de 1880 el estado chileno incorpora a su soberanía la provincia de Tarapacá, desatando un complejo proceso denominado chilenización. En este contexto, los agentes fiscales chilenos comenzaron a desplegar dispositivos políticos, económicos y culturales enfocados en asentar con rapidez la nueva administración, como el hacer de este territorio y su población parte integral de la nación chilena. Bajo estos términos, en este artículo se describen y analizan los imaginarios que construyeron estos agentes sobre el espacio y la población andina de la provincia de Tarapacá entre fines del siglo XIX y comienzos del XX

Chitosan as an antioxidant alternative to sulphites in oenology: EPR investigation of inhibitory mechanisms

The efficacy against oxidative degradation in model and sulphite-free white wines of two commercial, insoluble chitosans (one being approved for winemaking) were investigated by electron paramagnetic resonance (EPR). Both compounds at various doses significantly inhibited the formation of \u3b1-(4-pyridyl-1-oxide)-N-t-butylnitrone (4-POBN)-1-hydroxyethyl adducts under normal wine storage conditions. Pre-incubation with 2 g/L chitosan followed by filtration had a better effect than adding 50 mg/L sulphur dioxide to the experimental Chardonnay wine on the release of 4-POBN adducts after 6 days of incubation with 100 \u3bcM iron(II). In a relevant photooxidative system acetaldehyde formation was significantly reduced after 6 days of incubation. Parallel EPR tests were performed to assess the importance of metal chelation (iron and copper) versus direct scavenging of hydroxyl radicals on the effect of chitosan. The present data support the potentiality of using biocompatible chitosan as a healthier complement and/or alternative to sulphur dioxide against white wine oxidative spoilage

Ascl1 coordinately regulates gene expression and the chromatin landscape during neurogenesis

The proneural transcription factor Ascl1 coordinates gene expression in both proliferating and differentiating progenitors along the neuronal lineage. Here, we used a cellular model of neurogenesis to investigate how Ascl1 interacts with the chromatin landscape to regulate gene expression when promoting neuronal differentiation. We find that Ascl1 binding occurs mostly at distal enhancers and is associated with activation of gene transcription. Surprisingly, the accessibility of Ascl1 to its binding sites in neural stem/progenitor cells remains largely unchanged throughout their differentiation, as Ascl1 targets regions of both readily accessible and closed chromatin in proliferating cells. Moreover, binding of Ascl1 often precedes an increase in chromatin accessibility and the appearance of new regions of open chromatin, associated with de novo gene expression during differentiation. Our results reveal a function of Ascl1 in promoting chromatin accessibility during neurogenesis, linking the chromatin landscape at Ascl1 target regions with the temporal progression of its transcriptional program

New records of Chondrichthycians species caught in the Cantabrian Sea (southern Bay of Biscay)

Seventeen chondrichthyan species were caught in the Cantabrian Sea (southern Bay of Biscay) during a multidisciplinary survey carried out in the Avile´s canyon system in May 2011. This survey provided the first records of three species (Galeus murinus, Neoraja iberica, and Neoraja caerulea) in these waters, and a further record of Rajella kukujevi. To confirm the identity of these species, the cytochrome c oxidase subunit I (COI) of the specimens was sequenced. Genetic analyses revealed that the DNA sequences of the two Neoraja species were identical in all the specimens analysed. Morphometric analyses, based on 40 characters, showed 3.66% dissimilarity between the two species. The morphometric character that contributed most to this discrepancy was disc width.Versión del editor1,023

Analytic results for Gaussian wave packets in four model systems: I. Visualization of the kinetic energy

Using Gaussian wave packet solutions, we examine how the kinetic energy is distributed in time-dependent solutions of the Schrodinger equation corresponding to the cases of a free particle, a particle undergoing uniform acceleration, a particle in a harmonic oscillator potential, and a system corresponding to an unstable equilibrium. We find, for specific choices of initial parameters, that as much as 90% of the kinetic energy can be localized (at least conceptually) in the `front half' of such Gaussian wave packets, and we visualize these effects.Comment: 22 pages, RevTeX, four .eps figures, to appear in Found. Phys. Lett. Vol. 17, Dec. 200

Specificity of Atonal and Scute bHLH factors: analysis of cognate E box binding sites and the influence of Senseless

The question of how proneural bHLH transcription factors recognise and regulate their target genes is still relatively poorly understood. We previously showed that Scute and Atonal target genes have different E box motifs, suggesting that specific DNA interactions contribute to differences in their target gene specificity. Here we show that Scute and Atonal proteins (in combination with Daughterless) can activate reporter gene expression via their cognate E boxes in a non-neuronal cell culture system, suggesting that the proteins have strong intrinsic abilities to recognise different E box motifs in the absence of specialised cofactors. Functional comparison of E boxes from several target genes and site-directed mutagenesis of E box motifs suggests that specificity and activity require further sequence elements flanking both sides of the previously identified E box motifs. Moreover, the proneural cofactor, Senseless, can augment the function of Scute and Atonal on their cognate E boxes and therefore may contribute to proneural specificity