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

Manipulation and Tool Use in captive Yellow-Breasted Capuchin Monkeys ( Cebus xanthosternos )

In this short report we test, at an individual level, the prediction that tool use abilities and manipulative tendencies should be correlated, derived from hypotheses in the literature which connect them at a cognitive and evolutionary level. We recorded manipulative events of six captive yellow-breasted capuchin monkeys and later compared these results to their performance in a tool using task. The frequency of time each animal was involved with manipulative events was not correlated to the number of tool-using events displayed by them, even when we analyzed the males only (the most frequent manipulators). This result goes against the idea that tool use in Cebus is a product of both manipulative propensities and tendency to use objects. Most likely, the evolution of tool use in Cebus was due to a complex combination of factors, belonging to various behavioral systems, not only to the foraging one

Manipulation and Tool Use in captive Yellow-Breasted Capuchin Monkeys (Cebus xanthosternos)

In this short report we test, at an individual level, the prediction that tool use abilities and manipulative tendencies should be correlated, derived from hypotheses in the literature which connect them at a cognitive and evolutionary level. We recorded manipulative events of six captive yellow-breasted capuchin monkeys and later compared these results to their performance in a tool using task. The frequency of time each animal was involved with manipulative events was not correlated to the number of tool-using events displayed by them, even when we analyzed the males only (the most frequent manipulators). This result goes against the idea that tool use in Cebus is a product of both manipulative propensities and tendency to use objects. Most likely, the evolution of tool use in Cebus was due to a complex combination of factors, belonging to various behavioral systems, not only to the foraging one

A model for the importance of large arborescent palms in the dynamics of seasonally-dry amazonian forests

In this study we propose a model that represents the importance of large arborescent palms in the dynamics of seasonally-dry Amazonian forests. Specifically, the model is aimed at guiding the investigation of the role of large arborescent palms on forest regeneration and succession. Following disturbance, the high level of luminosity reaching recently formed forest gaps favors the quick proliferation of shade-intolerant lianas that, by casting shade on the crowns of mature forest trees and increasing tree-fall probability, suppress forest succession. Due to their columnar architecture palm trees are, however, not severely affected by vines. As the palms grow, the canopy at the gaps becomes gradually higher and denser, progressively obstructing the passage of light, thus hindering the growth of shade-intolerant lianas and enabling late-successional tree development and forest regeneration. Owing to the long time associated with forest regeneration, the model cannot be tested directly, but aspects of it were examined with field data collected at an Attalea maripa-rich secondary forest patch within a matrix of well-preserved seasonally-dry forest in the Southeastern Amazon. The results indicate that (1) forest disturbance is important for the recruitment of large arborescent palms species, (2) these palms can grow rapidly after an event of disturbance, restoring forest canopy height and density, and (3) secondary forest dominated by palm trees species may be floristically similar to nearby undisturbed forests, supporting the hypothesis that the former has undergone regeneration, as purported in the model

A model for the importance of large arborescent palms in the dynamics of seasonally-dry amazonian forests

In this study we propose a model that represents the importance of large arborescent palms in the dynamics of seasonally-dry Amazonian forests. Specifically, the model is aimed at guiding the investigation of the role of large arborescent palms on forest regeneration and succession. Following disturbance, the high level of luminosity reaching recently formed forest gaps favors the quick proliferation of shade-intolerant lianas that, by casting shade on the crowns of mature forest trees and increasing tree-fall probability, suppress forest succession. Due to their columnar architecture palm trees are, however, not severely affected by vines. As the palms grow, the canopy at the gaps becomes gradually higher and denser, progressively obstructing the passage of light, thus hindering the growth of shade-intolerant lianas and enabling late-successional tree development and forest regeneration. Owing to the long time associated with forest regeneration, the model cannot be tested directly, but aspects of it were examined with field data collected at an Attalea maripa-rich secondary forest patch within a matrix of well-preserved seasonally-dry forest in the Southeastern Amazon. The results indicate that (1) forest disturbance is important for the recruitment of large arborescent palms species, (2) these palms can grow rapidly after an event of disturbance, restoring forest canopy height and density, and (3) secondary forest dominated by palm trees species may be floristically similar to nearby undisturbed forests, supporting the hypothesis that the former has undergone regeneration, as purported in the model