DFT studies of the phenol adsorption on boron nitride sheets

We perform first principles total energy calculations to investigate the atomic structures of the adsorption of phenol (C₆H₅OH) on hexagonal boron nitride (BN) sheets. Calculations are done within the density functional theory as implemented in the DMOL code. Electron-ion interactions are modeled according to the local-spin-density-approximation (LSDA) method with the Perdew-Wang parametrization. Our studies take into account the hexagonal h-BN sheets and the modified by defects d-BN sheets. The d-BN sheets are composed of one hexagon, three pentagons and three heptagons. Five different atomic structures are investigated: parallel to the sheet, perpendicular to the sheet at the B site, perpendicular to the sheet at the N site, perpendicular to the central hexagon and perpendicular to the B-N bond (bridge site). To determine the structural stability we apply the criteria of minimum energy and vibration frequency. After the structural relaxation phenol molecules adsorb on both h-BN and d-BN sheets. Results of the binding energies indicate that phenol is chemisorbed. The polarity of the system increases as a consequence of the defects presence which induces transformation from an ionic to covalent bonding. The elastic properties on the BN structure present similar behavior to those reported in the literature for graphene.     

Habitat preference in the critically endangered yellow‐tailed woolly monkey (Lagothrix flavicauda) at La Esperanza,Peru

Habitat loss is one of the main threats to wildlife. Therefore, knowledge of habitat use and preference is essential for the design of conservation strategies and identification of priority sites for the protection of endangered species. The yellow‐tailed woolly monkey (Lagothrix flavicauda Humboldt, 1812), categorized as Critically Endangered on the IUCN Red List, is endemic to montane forests in northern Peru where its habitat is greatly threatened. We assessed how habitat use and preference in L. flavicauda are linked to forest structure and composition. The study took place near La Esperanza, in the Amazonas region, Peru. Our objective was to identify characteristics of habitat most utilized by L. flavicauda to provide information that will be useful for the selection of priority sites for conservation measures. Using presence records collected from May 2013 to February 2014 for one group of L. flavicauda, we classified the study site into three different use zones: low‐use, medium‐use, and high‐use. We assessed forest structure and composition for all use zones using 0.1 ha Gentry vegetation transects. Results show high levels of variation in plant species composition across the three use zones. Plants used as food resources had considerably greater density, dominance, and ecological importance in high‐use zones. High‐use zones presented similar structure to medium‐ and low‐use zones; thus it remains difficult to assess the influence of forest structure on habitat preference. We recommend focusing conservation efforts on areas with a similar floristic composition to the high‐use zones recorded in this study and suggest utilizing key alimentation species for reforestation efforts.     

A note on Rashevsky's theorem about point-bases in topological biology

A graphG may have more than one point-baseB _G. In a primordial graphP of Rashevsky's (1954) TransformationT, some of the pointbases may consist of nonspecialized points only, and some other pointbases may contains specialized points. In this case, Rashevsky's Theorem (1955a) on point-bases may not hold. The Theorem is certainly true ifall point-bases ofP consists of nonspecialized points. A rigorous proof is given. Some results are derived for the more general case, when point-bases include both kinds of points. A general expression for the point-base ratio of the transformed graphP(T) is obtained. It is shown that with some biologically plausible assumptions Rashevsky's interpretation of the point-base ratio and his conclusions are still true. A few simple Theorems on point-bases of graphs are included in this work.     

Magnetic circular dichroism and electron paramagnetic resonance studies of hydrogenases I and II from Clostridium pasteurianum

The two iron-only hydrogenases (I and II) from Clostridium pasteurianum have been investigated by variable temperature magnetic circular dichroism (MCD) and electron paramagnetic resonance (EPR) spectroscopies. Samples were studied both reduced with dithionite under an atmosphere of H2 and after oxidation with thionine. The results are consistent with four and two [4Fe-4S]1+,2+ (F)-clusters in hydrogenases I and II, respectively. All four F-clusters are reduced and paramagnetic in reduced hydrogenase I, with up to one exhibiting an S = 3/2 ground state and the remainder having conventional S = 1/2 ground states. Both F-clusters have S = 1/2 ground states in reduced hydrogenase II; however, one appears to be only partially reduced under the conditions used for reduction. MCD studies of the oxidized enzymes show no temperature-dependent features in the visible region which can be attributed to the EPR-active S = 1/2 hydrogen-activating cluster, suggesting predominantly oxygen and nitrogen coordination for the iron atoms of this center. However, temperature-dependent MCD transitions arising from a hitherto undetected S greater than 1/2 Fe-S clusters are apparent in both oxidized hydrogenases. Detailed EPR studies of oxidized hydrogenase I revealed resonances from an S = 3/2 species, however, spin quantitation reveals this to be a trace component that is unlikely to be responsible for the observed low temperature MCD spectrum. The nature and origin of these S greater than 1/2 Fe-S clusters are discussed in light of the available spectroscopic data for these and other iron-only hydrogenases.     

Infectivity,viability and effects of Paranosema locustae (Microsporidia) on juveniles of Dichroplus maculipennis (Orthoptera: Acrididae: Melanoplinae) under laboratory conditions

Infectivity and effects on host of a long-term stored aqueous suspension of Paranosema locustae on juveniles of Dichroplus maculipennis, a pest grasshopper in parts of the Pampas and Patagonia, were evaluated. Infections developed in 90–97.8% of treated individuals. Mortality increased with time, reaching highest values at 30–40 days post-inoculation (79.5–100%). Infected nymphs showed significantly slower development.     

Glycans from Fasciola hepatica Modulate the Host Immune Response and TLR-Induced Maturation of Dendritic Cells

Helminths express various carbohydrate-containing glycoconjugates on their surface, and they release glycan-rich excretion/secretion products that can be very important in their life cycles, infection and pathology. Recent evidence suggests that parasite glycoconjugates could play a role in the evasion of the immune response, leading to a modified Th2-polarized immune response that favors parasite survival in the host. Nevertheless, there is limited information about the nature or function of glycans produced by the trematode Fasciola hepatica, the causative agent of fasciolosis. In this paper, we investigate whether glycosylated molecules from F. hepatica participate in the modulation of host immunity. We also focus on dendritic cells, since they are an important target of immune-modulation by helminths, affecting their activity or function. Our results indicate that glycans from F. hepatica promote the production of IL-4 and IL-10, suppressing IFNγ production. During infection, this parasite is able to induce a semi-mature phenotype of DCs expressing low levels of MHCII and secrete IL-10. Furthermore, we show that parasite glycoconjugates mediate the modulation of LPS-induced maturation of DCs since their oxidation restores the capacity of LPS-treated DCs to secrete high levels of the pro-inflammatory cytokines IL-6 and IL-12/23p40 and low levels of the anti-inflammatory cytokine IL-10. Inhibition assays using carbohydrates suggest that the immune-modulation is mediated, at least in part, by the recognition of a mannose specific-CLR that signals by recruiting the phosphatase Php2. The results presented here contribute to the understanding of the role of parasite glycosylated molecules in the modulation of the host immunity and might be useful in the design of vaccines against fasciolosis.     

Carbohydrate constituents of Lessonia trabeculata

D-mannitol was the only low-molecular weight carbohydrate isolated from ethanolic extracts of Lessonia trabeculata blades. After sequential extraction with water, acid and alkali, laminaran, fucose-containing polysaccharides and alginic acid were also isolated. Fucose-containing polysaccharide from the acidic extract was separated into three fractions by ion exchange chromatography. Alginic acid was the major polysaccharide obtained in the sequential extraction.     

Nutrient dynamics within amazonian forests

Summary Relationships between fine root growth, rates of litter decomposition and nutrient release were analysed in a mixed forest on Tierra Firme, a Tall Amazon Caatinga and a Low Bana on podsolized sands near San Carlos de Rio Negro. Fine root growth in the upper soil layers (root mat+10 cm upper soil) was considerably higher in the Tierra Firme forest (1117 g m^-2 yr^-1) than in tall Cattinga (120) and Bana (235). Fine root growth on top of the root mat was stimulated significantly by added N in Tall Caatinga and Low Bana forests, by P in Tierra Firme and Bana forests, and by Ca only in the Tierra Firme forest. Rate of fine root growth in Tierra Firme forest on fresh litter is strongly correlated with the Mg and Ca content of litter. Rate of litter decomposition was inversely related to % lignin and the lignin/N ratio of litter. Litter contact with the dense root mat of the Tierra Firme increased rates of disappearance for biomass, Ca and Mg as compared with litter permanently separated or lifted weekly from the root mat to avoid root attachment. Nitrogen concentration of decomposing litter increased in all forests, net N released being observed only in Caryocar glabrum and Aspidosperma megalocarpum of the Tierra Firme forest after one year of exposure. Results emphasize the differences in limiting nutrients in amazonian forest ecosystems on contrasting soil types: Tierra Firme forests are particularly limited by Ca and Mg, while Caatinga and Bana forests are limited mainly by N availability.