Unraveling the ultrafast dynamics of thermal-energy chemical reactions

In this perspective, we discuss how one can initiate, image, and disentangle the ultrafast elementary steps of thermal-energy chemical dynamics, building upon advances in technology and scientific insight. We propose that combinations of ultrashort mid-infrared laser pulses, controlled molecular species in the gas phase, and forefront imaging techniques allow to unravel the elementary steps of general-chemistry reaction processes in real time. We detail, for prototypical first reaction systems, experimental methods enabling these investigations, how to sufficiently prepare and promote gas-phase samples to thermal-energy reactive states with contemporary ultrashort mid-infrared laser systems, and how to image the initiated ultrafast chemical dynamics. The results of such experiments will clearly further our understanding of general-chemistry reaction dynamics.Comment: 12 pages, 6 figure

The design and development of a time-resolved electron diffractometer for the investigation of molecular dynamics

A time-resolved gas electron diffractometer has been designed and constructed to study the photoinduced dynamics of molecular systems. An ultrafast pulsed electron beam is created by the ionisation of a thin-film gold photocathode, using the third harmonic of a femtosecond Ti:Sapphire laser, and accelerated across a potential of up to 100 kV. Time-averaged diffraction from a polycrystalline platinum sample has been carried out in order to calibrate the apparatus, and the results have been shown to match well with theory. In addition to the design of the apparatus, novel experimental methods and techniques have been implemented, and software for analysing and extracting data has been developed. Other calibration experiments have been carried out, including measuring the diameter of the pulsed electron beam produced, and how this varies as a solenoid magnetic lens acts to focus the beam. An optimal FWHM beam width of 1.2 mm has been observed at the detector for pulses containing 10^4 electrons. The time-zero position between a pump laser and probe electron beam has been found by studying the laser-induced plasma emitted from a copper mesh, and methodologies have been established for grating-enhanced ponderomotive experiments to be carried out to determine the duration of the pulsed electron beam. Extensive electron pulse dynamics simulations, using SIMION and General Particle Tracer, accompany the experimental work. These have allowed for a full and thorough understanding of how both the duration and transverse size of the pulse changes as it propagates through the apparatus with and without the influence of the magnetic lens. It has also allowed for the ultimate time resolution of the apparatus to be determined as 416 fs. Quantum chemical calculations have been carried out for dimethyl disulfide and diethyl disulfide, molecules that readily dissociate along the S–S bond upon excitation using a low-energy ultraviolet light. This has included a full mapping of the reaction potential-energy surface, and study of the molecular dynamics of the molecules in the ground and excited states. These studies have shown that the molecules are suitable candidates for early time-resolved gas electron diffraction studies using the new apparatus

Simulations of the temporal and spatial resolution for a compact time-resolved electron diffractometer

A novel compact electron gun for use in time-resolved gas electron diffraction experiments has recently been designed and commissioned. In this paper we present and discuss the extensive simulations that were performed to underpin the design in terms of the spatial and temporal qualities of the pulsed electron beam created by the ionisation of a gold photocathode using a femtosecond laser. The response of the electron pulses to a solenoid lens used to focus the electron beam has also been studied. The simulated results show that focussing the electron beam affects the overall spatial and temporal resolution of the experiment in a variety of ways, and that factors that improve the resolution of one parameter can often have a negative effect on the other. A balance must, therefore, be achieved between spatial and temporal resolution. The optimal experimental time resolution for the apparatus is predicted to be 416 fs for studies of gas-phase species, while the predicted spatial resolution of better than 2 nm-1 compares well with traditional time-averaged electron diffraction set-ups

2-(4-Chloro­phen­yl)naphtho­[1,8-de][1,3,2]diaza­borinane

The title compound, C16H12BClN2, is one in a series of diaza­borinanes, derived from 1,8-diaminona­phthalene, featuring substitution at the 1, 2 and 3 positions in the nitro­gen-boron heterocycle. The structure deviates from planarity, the torsion angle subtended by the p-chloro­phenyl ring relative to the nitro­gen–boron heterocycle being −44-.3(3)°. The mol­ecules form infinite chains with strong inter­actions between the vacant pz orbital of the B atom and the π-system of an adjacent mol­ecule. The distance between the B atom and the 10-atom centroid of an adjacent naphthalene ring is 3.381 (4) Å. One N-H H atom is weakly hydrogen bonded to the Cl atom of an adjacent mol­ecule. This combination of inter­molecular inter­actions leads to the formation of an infinite two-dimensional network perpendic­ular to the c axis

New County Records of Amphibians and Reptiles from South Texas, USA

Several species of amphibians and reptiles reach their northern range limit in south Texas, USA. Herpetological research in the area, as well as frequent visits from amphibian and reptile enthusiasts, have helped to form a more complete understanding of amphibian and reptile distributions across the region. However, gaps in the recognized distribution of many species remain. Efforts to better document species occurrence are confounded by the lack of public land and the fact that most of south Texas is privately owned, making access to suitable habitat difficult (Schmidly et al. 2001

Species-Specific Effects on Ecosystem Functioning Can Be Altered by Interspecific Interactions

Biological assemblages are constantly undergoing change, with species being introduced, extirpated and experiencing shifts in their densities. Theory and experimentation suggest that the impacts of such change on ecosystem functioning should be predictable based on the biological traits of the species involved. However, interspecific interactions could alter how species affect functioning, with the strength and sign of interactions potentially depending on environmental context (e.g. homogenous vs. heterogeneous conditions) and the function considered. Here, we assessed how concurrent changes to the densities of two common marine benthic invertebrates, Corophium volutator and Hediste diversicolor, affected the ecological functions of organic matter consumption and benthic-pelagic nutrient flux. Complementary experiments were conducted within homogenous laboratory microcosms and naturally heterogeneous field plots. When the densities of the species were increased within microcosms, interspecific interactions enhanced effects on organic matter consumption and reduced effects on nutrient flux. Trait-based predictions of how each species would affect functioning were only consistently supported when the density of the other species was low. In field plots, increasing the density of either species had a positive effect on organic matter consumption (with no significant interspecific interactions) but no effect on nutrient flux. Our results indicate that species-specific effects on ecosystem functioning can be altered by interspecific interactions, which can be either facilitative (positive) or antagonistic (negative) depending on the function considered. The impacts of biodiversity change may therefore not be predictable based solely on the biological traits of the species involved. Possible explanations for why interactions were detected in microcosms but not in the field are discussed

PinR mediates the generation of reversible population diversity in Streptococcus zooepidemicus

Opportunistic pathogens must adapt to and survive in a wide range of complex ecosystems. Streptococcus zooepidemicus is an opportunistic pathogen of horses and many other animals, including humans. The assembly of different surface architecture phenotypes from one genotype is likely to be crucial to the successful exploitation of such an opportunistic lifestyle. Construction of a series of mutants revealed that a serine recombinase, PinR, inverts 114 bp of the promoter of SZO_08560, which is bordered by GTAGACTTTA and TAAAGTCTAC inverted repeats. Inversion acts as a switch, controlling the transcription of this sortase-processed protein, which may enhance the attachment of S. zooepidemicus to equine trachea. The genome of a recently sequenced strain of S. zooepidemicus, 2329 (Sz2329), was found to contain a disruptive internal inversion of 7 kb of the FimIV pilus locus, which is bordered by TAGAAA and TTTCTA inverted repeats. This strain lacks pinR and this inversion may have become irreversible following the loss of this recombinase. Active inversion of FimIV was detected in three strains of S. zooepidemicus, 1770 (Sz1770), B260863 (SzB260863) and H050840501 (SzH050840501), all of which encoded pinR. A deletion mutant of Sz1770 that lacked pinR was no longer capable of inverting its internal region of FimIV. The data highlight redundancy in the PinR sequence recognition motif around a short TAGA consensus and suggest that PinR can reversibly influence the wider surface architecture of S. zooepidemicus, providing this organism with a bet-hedging solution to survival in fluctuating environments

2-Phenyl­naphtho­[1,8-de][1,3,2]diaza­borinane

The title compound, C16H13BN2, is one compound in a series of diaza­borinanes featuring substitution at the 1, 2 and 3 positions in the nitro­gen–boron heterocycle. The title compound is slightly distorted from planarity, with a dihedral angle of 9.0 (5)° between the mean planes of the naphthalene system and the benzene ring. The m-carbon atom of the benzene ring exhibits the greatest deviation of 0.164 (2) Å from the 19-atom mean plane defined by all non-H atoms. The two N—B—C—C torsion angles are 6.0 (3) and 5.6 (3)°. In the crystal, mol­ecules are linked by π–π inter­actions into columns, with a distance of 3.92 (3) Å between the naphthalene ring centroids. Adjacent π-stacked columns, co-linear with the b-axis, are linked by C—H⋯π inter­actions

The Maximizer: Clarifying Merton's Theories of Anomie and Strain

Robert Merton's (1957) theories of anomie and strain are among the most widely examined theories of criminality. Messner and Rosenfeld's (1994) theory of institutional anomie built on Merton's conception of anomie, delineating how specific institutions lead to conditions of anomie and criminality. Cloward and Ohlin's (1961) theory of differential opportunity built upon Merton's strain theory, underscoring the fact that those involved in illegitimate means of opportunity require a set of learned skills as do those involved in legitimate means. In this tradition, the present paper further expands Merton's theories of anomie and strain, suggesting that Merton's categories of conformist and innovator are not mutually exclusive. In fact, some individuals combine both legitimate and illegitimate means of opportunity in pursuit of the American Dream. The Maximizer, the authors suggest, merges elements of both the conformist and the innovator (i.e. legitimate and illegitimate means). The present paper explores the justification for merging legitimate and illegitimate means of opportunity in pursuit of the American Drea

Redox stratification drives enhanced growth in a commercially important deposit-feeding invertebrate: implications for bioremediation and integrated aquaculture.

Effective and affordable treatment of waste solids is a key sustainability challenge for the aquaculture industry. Here, we investigated the potential for a deposit-feeding sea cucumber, Holothuria scabra, to provide a remediation service whilst concurrently yielding a high-value secondary product in a land-based recirculating aquaculture system (RAS). The effect of sediment depth, particle size and redox regime were examined in relation to changes in the behaviour, growth and biochemical composition of juvenile sea cucumbers cultured for 81 d in manipulated sediment systems, describing either fully oxic or stratified (oxic-anoxic) redox regimes. The redox regime was the principal factor affecting growth, biochemical composition and behaviour, while substrate depth and particle size did not significantly affect growth rate or biomass production. Animals cultured under fully oxic conditions exhibited negative growth and had higher lipid and carbohydrate contents, potentially due to compensatory feeding in response to higher microphytobenthic production. In contrast, animals in the stratified treatments spent more time feeding, generated faster growth and produced significantly higher biomass yields (626.89 ± 35.44 g m-2 versus 449.22 ± 14.24 g m-2; mean ± SE). Further, unlike in oxic treatments, growth in the stratified treatments did not reach maximum biomass carrying capacity, indicating that stratified sediment is more suitable for culturing sea cucumbers. However, the stratified sediments may exhibit reduced bioremediation ability relative to the oxic sediment, signifying a trade-off between remediation efficiency and exploitable biomass yield