The palladium-catalyzed Tsuji–Trost reaction has been extensively studied under synthetically relevant conditions (millimolar concentrations of substrates and catalyst, aprotic solvents, no additives). Despite the increasing use of the Tsuji–Trost reaction in other areas (e.g., chemical biology), the paucity of kinetic studies at micromolar concentrations of substrates in water has impeded progress. Herein, we show that a fluorescence-based high-throughput method provided massive Eyring plot data and revealed three kinetic regimes. The associated turnover-limiting steps (TLSs) were assigned as the oxidative addition (regime 1; ΔH ⧧ > 0), nucleophilic attack (regime 2; ΔH ⧧ ≈ 0), and association (regime 3; ΔH ⧧ < 0, inverse temperature dependence). A kinetic profile under particular conditions depended on the substrate concentration and reaction temperature. Density functional theory calculations supported these findings. This work indicates that a TLS under dilute conditions may be different from that under synthetically relevant conditions and may provide a path toward the development of faster and more reproducible Tsuji–Trost reactions for synthetic, analytical, and biological applications.
Biodiversity is declining at an alarming rate globally, with freshwater ecosystems particularly threatened. Field-based correlational studies have "ranked" stressors according to their relative effects on freshwater biota, however, supporting cause-effect data from laboratory exposures are lacking. Here, we designed exposures to elicit chronic effects over equivalent exposure ranges for three ubiquitous stressors (temperature: 22−28 °C; pollution [14 component mixture]: 0.05−50 μg/L; invasive predator cue [signal crayfish, Pacifasticus leniusculus]: 25−100% cue) and investigated effects on physiological end points in the pond snail (Lymnaea stagnalis). All stressors reduced posthatch survival at their highest exposure levels, however, highly divergent effects were observed at lower test levels. Temperature stimulated hatching, growth, and reproduction, whereas pollution delayed hatching, decreased growth, reduced egg number/embryo viability, and induced avoidance behavior. The invasive predator cue stimulated growth and reduced embryo viability. In agreement with field-based ranking of stressors, pollution was identified as having the most severe effects in our test system. We demonstrate here the utility of laboratory studies to effectively determine hierarchy of stressors according to their likelihood of causing harm in the field, which has importance for conservation. Finally, we report negative impacts on life-history traits central to population stability (survival/reproduction) at the lowest pollution level tested (0.05 μg/L).
Androgen levels are closely linked with breeding in male amphibians. Development of the nuptial pad is driven by androgens and is believed to have importance for determining mating success in anurans, but this has not been tested in wild populations. We investigated the association between nuptial pad morphology (length, colour) and mating (amplexus) success in wild male common frogs (Rana temporaria) in the UK (Devon in Southern England and central Scotland). Once active breeding had been confirmed, pond water (25 L) was placed in 1–6 replicate mesocosms (66 cm diameter circular, black plastic tubs) in situ. Eight male and two female frogs were placed into each mesocosm, and success observed by identifying the male frog(s) in amplexus. The length of nuptial pads for male frogs observed in amplexus was greater than those that did not achieve amplexus. There was no difference in the absolute dark colour of nuptial pads (determined by red/green/blue analysis, Adobe photoshop©) for male frogs observed in amplexus versus those that did not achieve amplexus. However, within each mesocosm, the nuptial pad was relatively darker for winning male frogs compared to losing male frogs. Overall, 91% of winning male frogs from Devon, and 89% winning male frogs from Scotland, possessed either a longer and/or a darker nuptial pad, compared with frogs that did not achieve amplexus. These data suggest that features of nuptial pad morphology are associated with amplexus (and thus mating) success in male common frogs. Given that nuptial pads have been identified in all anuran amphibian species analysed to date, nuptial pad morphology may contribute to non‐random mating strategies across a broad range of species.
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