Time-resolved studies of the photodissociation of adenine

A novel time-resolved velocity map ion imaging (TR-VMI) experiment has been constructed and successfully applied to the study of non-statistical dissociation processes. The photodissociation of NH3 following the population of the ν2 ’ = 4 umbrella vibrational mode of the first electronically excited, Ã1A2”, singlet state, was initially studied. It was clearly observed that the N-H dissociation timescale was inversely proportional to kinetic energy released to the H fragment. Assignment of different kinetic energy regions of the TR-VMI transients to corresponding bending vibrational modes (ν2) of the X2B1 state NH2 photoproduct clearly suggests that dissociation into the vibrationless NH2 occurs in < 50 fs. Low kinetic energy channels, show extended dissociation timescales, strongly indicative of adiabatic dissociation to the first electronically excited state of NH2 (Ã2A1). With an aim of modelling the photodissociation dynamics of adenine, the photodissociation of pyrrole, imidazole, 2-methylimidazole, 4-methylimidazole and 2,4-dimethylimidazole following excitation at 200 nm were studied using time-resolved mass spectrometry (TR-MS) and VMI. In all cases ultrafast H elimination was observed in < 130 fs, consistent with direct dissociation via the repulsive 1πσ* potential energy surfaces. The photodissociation of 1- methyimidazole at this wavelength was also studied. Once again ultrafast H elimination was observed, but with greatly reduced yields, strongly suggesting H elimination from the non-heteroatom co-ordinates (C-H) also partaking in the photodissociation dynamics at this wavelength. TR-MS and VMI have also been applied to the study of the photodissociation of adenine, 9-methyladenine and 6-dimethylaminopurine. In all measured kinetic energy spectra a high kinetic energy channel has been observed, strongly suggesting the participation of 1πσ* potential energy surfaces of both the azole and amino co-ordinates in H elimination following excitation at 200 nm. Power dependence studies at 266 nm suggest H elimination, but subsequent TR-MS measurements seem to suggest that this is not due to the participation of the 1πσ* potential energy surfaces at this excitation wavelength

Accessibility do not explain abundance of medium and large-sized mammals in Terra Do Meio, Altamira, Pará, Brazil

The aim of this study was to evaluate the effects of accessibility on hunting pressure by considering the mammal abundance and biomass of two protected areas belonging to different conservation categories -indigenous land and Ecological Station- in the Xingu River basin, eastern Amazon. For doing so, we used linear transection methods (total effort 240 km, in four tracks), camera traps (487 days) and complementary records. We also developed an accessibility coefficient based on the distance between navigable rivers and roads, and the center point of the sampled trails. We used the Simple linear regression test to analyze the effects of this accessibility on the biomass of the sighted species, gathering them in orders. We found 34 species belonging to seven families and six orders. We found no relation between mammal biomass and our accessibility index, which suggests that hunting pressure affects even the most distant studied areas.Nosso objetivo foi analisar os efeitos da acessibilidade sobre a pressão de caça refletida na abundância e biomassa de mamíferos em duas áreas protegidas de diferentes categorias de conservação. Terra indígena e Estação Ecológica, na bacia do rio Xingu, no leste da Amazônia. Para tal, usamos os métodos de transição linear (esforço de 240 km), armadilhas fotográficas (487 dias) e registros complementares. Adicionalmente, desenvolvemos um coeficiente de acessibilidade com base na distância dos rios e estradas navegáveis para o ponto central das trilhas percorridas. Utilizamos regressão linear simples para analisar os efeitos da acessibilidade sobre a biomassa das espécies avistadas (agrupadas em ordens). Encontramos 34 espécies pertencentes a 07 famílias. Não encontramos relação entre a biomassa de mamíferos e nosso índice de acessibilidade, sugerindo que a pressão de caça afeta a área estudada a uma maior distância

Microsatellites for the Amazonian Fish Hypophthalmus marginatus

We isolated 41 and characterized 17 microsatellite loci for evaluating the genetic structure of the Amazonian fish Hypophthalmus marginatus, from the Tocantins and Araguaia River in the Eastern Amazonia. Of the 17 selected microsatellite sequences, 15 were dinucleotide repeats, 9 of which were perfect (5–31 repetitions) and 6 were composite motifs. Among these 17 microsatellites, only two were polymorphic. The average number of alleles (Na) observed in the five examined populations ranged from 3.5 to 4.5, while the average observed heterozygosity (Ho) ranged from 0.3 to 0.6. The allelic frequency was less homogeneous at the locus Hm 5 than that for the Hm 13. Genetic diversity was measured in three upstream and two downstream populations under the influence of the Tucuruí Hydroelectric Dam. Our findings provide evidence for low levels of genetic diversity in H. marginatus of the Tocantis basin possibility related to the Dam construction. The Fst and Rst analysis fits well with migratory characteristics of H. marginatus, suggesting the existence of a gene flow mainly in the upstream or downstream directions. To test the hypothesis that the Dam was responsible for the detected reduction on this species genetic diversity, a large number of genetic markers are recommended, covering geographic distribution range of the fish species

Stem density and growth of Attalea maripa and Astrocaryum aculeatum: implication for arborescent palms distribution across Amazonian forests

This study examines aspects of the stem density and growth of two large arborescent palms Attalea maripa and Astrocaryum aculeatum and discusses their implication for the palm trees distribution in Amazonia. Stem density and growth were investigated through both laboratory measurements and field estimates of growth rates. The densities of stem samples collected within one individual of each studied species were very distinct. The samples of A. maripa stem were more homogeneous in density than those of A. aculeatum, both from the internal to the external, and from the lower to the upper parts of the stem. Field estimates of stem growth rates revealed that A. maripa growth is also more constant through development in height. Short A. aculeatum palms had faster growth rates than A. maripa, as they get taller, stem growth rates are reduced and approach A. maripa rates. The implications for arborescent palms distribution across Amazonian forests are discussed