Porosity in ion-exchanged and acid activated clays evaluated using n-nonane pre-adsorption

The applicability of the n-nonane pre-adsorption method for characterising the porosity in clays is presented. Na-SD, a Na+-exchanged purified bentonite, and materials obtained by Al3+-exchange and acid treatments of Na-SD and SAz-1 were used. Nitrogen adsorption isotherms, at -196 ºC, were determined before and after n-nonane pre-adsorption on each of the samples. In all materials, n-nonane remained adsorbed in ultramicropores after outgassing at 25 ºC. Outgassing at higher temperatures (50, 75 and 200 ºC) removed nonane and ultramicropores became available for nitrogen adsorption. All treatments on Na-SD led to increase in micropore volume. Larger ultramicropore and supermicropore volumes were obtained for Na-SD acid activated with HCl at 95 ºC than for treatments at 25 ºC with HCl or following Al3+-exchange (Al-SD), and increased with increasing acid concentration to 3 M. Activation with 4 M HCl led to the largest pore volume with contribution from mesopores. However, the specific external surface area was the same as that obtained for Na-SD, Al-SD and for most of the other acid activated samples. Treatments at 95 ºC with 1 M and 6 M HCl promoted increase in specific external surface area. The micropore volumes and specific external surface area for SAz-1 treated with 1 M HCl at 95 ºC were larger than those of Al-SAz-1, but lower than those obtained for corresponding materials derived from Na-SD. The n-nonane pre-adsorption method enabled micropore volumes and specific external surface areas to be obtained for all samples.

Análise biogeográfica da dieta de um predador de topo ao longo da região Paleártica

Existem vários estudos sobre a dieta de predadores de topo a uma escala local, mas o estudo da dieta de uma espécie ao longo de diferentes regiões geográficas poderá permitir a deteção de certos padrões e variações ecológicas. Para estudar a variação biogeográfica da dieta do bufo-real (Bubo bubo) ao longo do Paleártico criou-se uma base de dados baseada em 192 estudos. Pretendia-se analisar padrões em macro-escala de descritores da dieta e avaliar o efeito de diferentes condições ambientais, de descritores da paisagem e da disponibilidade de presas. Registaram-se 346813 presas de 698 espécies distintas. As principais presas são os lagomorfos e os roedores, enquanto que as aves constituem importantes presas alternativas. Temperaturas mais elevadas favorecem a diversidade trófica, mas esta diminui com a latitude e a longitude. Os resultados revelam a natureza oportunista do bufo-real e a sua elevada adaptabilidade trófica a diferentes habitats e condições ambientais; Biogeographic analysis of a top predator's diet across the Paleartic Region Summary: There are several studies about top predators' diet at a local scale, but studying a species diet across different geographic regions may allow the detection of certain patterns and variations which might influence its ecological features. We created a database of 192 papers to study the diet of the Eurasian Eagle Owl (Bubo bubo) across the Palearctic region. We analysed large scale biogeographical patterns of diet descriptors in relation to different environmental conditions, including climate, landscape and prey availability. We recorded 346816 preys from 698 different species. The main prey groups are lagomorphs and rodents, whereas birds represent important alternative prey. Higher temperatures favour a higher trophic diversity, which in turn decreases at lower latitudes and longitudes. The results reveal the opportunistic nature of the Eurasian Eagle Owl and its high trophic adaptability to different habitats and environments.

Monitoring pasture variability: optical OptRx® crop sensor versus Grassmaster II capacitance probe

Estimation of pasture productivity is an important step for the farmer in terms of planning animal stocking, organizing animal lots, and determining supplementary feeding needs throughout the year. The main objective of this work was to evaluate technologies which have potential for monitoring aspects related to spatial and temporal variability of pasture green and dry matter yield (respectively, GM and DM, in kg/ha) and support to decision making for the farmer. Two types of sensors were evaluated: an active optical sensor(OptRx®, which measures the NDVI, Normalized Difference Vegetation Index) and a capacitance probe (GrassMaster II which estimates plant mass). The results showed the potential of NDVI for monitoring the evolution of spatial and temporal patterns of vegetative growth of biodiverse pasture. Higher NDVI values were registered as pasture approached its greatest vegetative vigor, with a significant fall in the measured NDVI at the end of Spring, when the pasture began to dry due to the combination of higher temperatures and lower soil moisture content. This index was also effective for identifying different plant species (grasses/legumes) and variability in pasture yield. Furthermore, it was possible to develop calibration equations between the capacitance and the NDVI (R2 = 0.757; p < 0.01), between capacitance and GM (R2 = 0.799; p<0.01), between capacitance and DM (R2 = 0.630; p<0.01), between NDVI and GM (R2=0.745; p < 0.01), and between capacitance and DM (R2=0.524; p<0.01). Finally, a direct relationship was obtained between NDVI and pasture moisture content (PMC, in %) and between capacitance and PMC (respectively, R2 = 0.615; p<0.01 and R2=0.561; p <0.01) in Alentejo dryland farming systems.

Adenine as an organocatalyst for the ring-opening polymerization of lactide: scope, mechanism and access to adenine-functionalized polylactide

Nucleobase-functionalized polymers are widely used in the fields of supramolecular chemistry and self-assembly, and their development for biomedical applications is also an area of interest. They are usually synthesized by tedious multistep procedures. In this study, we assess adenine as an organoinitiator/ organocatalyst for the ring-opening polymerization of lactide. L-Lactide can be quantitatively polymerized in the presence of adenine. Reaction conditions involving short reaction times and relatively low temperatures enable the access to adenine end-capped polylactide in a simple one-step procedure, in bulk, without additional catalyst. DFT calculations show that the polymerization occurs via hydrogen bond catalysis. The mechanism involves (i) a hydrogen bond between the NH9 of adenine and the carbonyl moiety of lactide, leading to an electron deficient carbon atom, and (ii) a second hydrogen bond between the N3 of adenine and the NH2 of a second adenine molecule, followed by a nucleophilic attack of the latter activated amine on the former electron deficient carbon on the monomer. For longer reaction times and higher temperatures, macrocyclic species are formed, and a mechanism involving the imidazole ring of adenine is proposed based on literature studies. Depending on the reaction conditions, adenine can thus be considered as an organoinitiator or an organocatalyst for the ring-opening polymerization of lactide.

Adenine as an organocatalyst for the ring-opening polymerization of lactide: scope, mechanism and access to adenine-functionalized polylactide

Nucleobase-functionalized polymers are widely used in the fields of supramolecular chemistry and self-assembly, and their development for biomedical applications is also an area of interest. They are usually synthesized by tedious multistep procedures. In this study, we assess adenine as an organoinitiator/organocatalyst for the ring-opening polymerization of lactide. L-Lactide can be quantitatively polymerized in the presence of adenine. Reaction conditions involving short reaction times and relatively low temperatures enable the access to adenine end-capped polylactide in a simple one-step procedure, in bulk, without additional catalyst. DFT calculations show that the polymerization occurs via hydrogen bond catalysis. The mechanism involves (i) a hydrogen bond between the NH9 of adenine and the carbonyl moiety of lactide, leading to an electron deficient carbon atom, and (ii) a second hydrogen bond between the N3 of adenine and the NH2 of a second adenine molecule, followed by a nucleophilic attack of the latter activated amine on the former electron deficient carbon on the monomer. For longer reaction times and higher temperatures, macrocyclic species are formed, and a mechanism involving the imidazole ring of adenine is proposed based on literature studies. Depending on the reaction conditions, adenine can thus be considered as an organoinitiator or an organocatalyst for the ring-opening polymerization of lactide.