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C–H Activation and Sequential Addition to Dienes and Imines: Synthesis of Amines with β-Quaternary Centers and Mechanistic Studies on the Complex Interplay Between the Catalyst and Three Reactants
No full textA Rh(III)-catalyzed sequential C-H bond addition to dienes and in situ formed aldimines was developed, allowing for the preparation of otherwise challenging to access amines with quaternary centers at the beta-position. A broad range of dienes were effective inputs and installed a variety of aryl and alkyl substituents at the quaternary carbon site. Aryl and alkyl sulfonamide and carbamate nitrogen substituents were incorporated by using different formaldimine precursors. Moreover, the in situ formed N-Cbz aldimine from ethyl glyoxylate provided beta,beta-disubstituted alpha-amino esters with high diastereoselectivity. Two rhodacycle intermediates along the catalytic cycle were isolated and characterized by X-ray structural analysis, and the equilibria between the rhodacycle species in the presence of different reactants were determined. Deuterium labeling studies provided additional information to explain the uncommon 1,3-addition selectivity to the conjugated diene. Density functional theory calculations were consistent with the equilibria determined between the rhodacycle intermediates in the presence of different reactants and provided further insight on the transition state structures and energies for key steps in the catalytic cycle
Hands, Fingers, Strings, and Bows: Performance Technique and Analysis in JS Bach\u27s Largo for Solo Violin
No full textIn this article, I draw on public-facing sources and my violinistic experience to show how attention to performance technique illustrates three different relationships between performance and analysis. In the Largo from J.S. Bach’s Sonata No. 3 for Solo Violin (BWV 1005), multiple-stop chords, string-based affordances, and bowings in turn correspond with, contradict, and create new analytical perspectives. I first collate definitions of interpretation and technique as they relate to performance. Interpretation is non-instrument-specific and deals with decoding and expressing musical meaning; technique is instrument-specific and deals with the granular mechanics of sound production. A multiple-stop intensity model shows that changes in a violinist’s multiple-stop-based effort correspond with significant cadential markers. At the local level, the violinistic “feel” of each quadruple stop aligns with expressive aspects of harmony and form. Heinrich Schenker’s performance recommendations for the Largo’s cadences, by contrast, conflict with a violinist’s experience of how the cadences intersect with instrumental affordances. Although the two perspectives may be reconcilable, actual performances support the instrument-grounded perspective. Finally, I draw on basic bowing motions to create an analytical technique of bowing reduction. My reduction of the Largo reveals a recurring bowing-based motive, which in turn elucidates the source of a performative tension I have experienced when playing the movement. This final example reminds us that technique and interpretation—just like performance and analysis—are inevitably entangled
Nutritional convergence in plants growing on gypsum soils in two distinct climatic regions
No full textBackground and Aims: Soil endemics have long fascinated botanists owing to the insights they can provide about plant ecology and evolution. Often, these species have unique foliar nutrient composition patterns that reflect potential physiological adaptations to these harsh soil types. However, understanding global nutritional patterns to unique soil types can be complicated by the influence of recent and ancient evolutionary events. Our goal was to understand whether plant specialization to unique soils is a stronger determinant of nutrient composition of plants than climate or evolutionary constraints.
Methods: We worked on gypsum soils. We analysed whole-plant nutrient composition (leaves, stems, coarse roots and fine roots) of 36 native species of gypsophilous lineages from the Chihuahuan Desert (North America) and the Iberian Peninsula (Europe) regions, including widely distributed gypsum endemics, as specialists, and narrowly distributed endemics and non-endemics, as non-specialists. We evaluated the impact of evolutionary events and soil composition on the whole-plant composition, comparing the three categories of gypsum plants.
Key Results: Our findings reveal nutritional convergence of widely distributed gypsum endemics. These taxa displayed higher foliar sulphur and higher whole-plant magnesium than their non-endemic relatives, irrespective of geographical location or phylogenetic history. Sulphur and magnesium concentrations were mainly explained by non-phylogenetic variation among species related to gypsum specialization. Other nutrient concentrations were determined by more ancient evolutionary events. For example, Caryophyllales usually displayed high foliar calcium, whereas Poaceae did not. In contrast, plant concentrations of phosphorus were mainly explained by species-specific physiology not related to gypsum specialization or evolutionary constraints.
Conclusions: Plant specialization to a unique soil can strongly influence plant nutritional strategies, as we described for gypsophilous lineages. Taking a whole-plant perspective (all organs) within a phylogenetic framework has enabled us to gain a better understanding of plant adaptation to unique soils when studying taxa from distinct regions
The Literary Labour of Ants: Refabulation, Digression, and Utopian Form in Daniel Sada’s \u3ci\u3ePorque parece mentira la verdad nunca se sabe\u3c/i\u3e (1999)
No full textThis essay considers the literary labour carried out by ants in Daniel Sada’s Porque parece mentira la verdad nunca se sabe (1999), considered one of the most significant works of Mexican literature in the last decade of the twentieth century. This essay takes a digressive scene within the novel, in which an ant fable is imagined, as a model of “refabulation”, a rewriting of Western formic, or ant-centred, narratives that attempts to escape the total enclosure of allegory. Sada’s refabulation both registers the fact of ants’ radical alterity and deploys them as the axis for the articulation of a utopian desire for the potential of a collective life organized beyond scarcity, labour, and capitalism. At the same time, the essay suggests that meaningful representations of interspecies interactions might not be found in novelistic narratives per se, but in the digressions often found and contained in its pages
Catechol-Based Colorimetric Sensors for Heavy Metals
No full textHeavy metals can cause major public health issues when the population is exposed to them. Prior research in our lab focused on materials inspired by melanin pigments as heavy metal-binding agents. Melanin pigments contain important functional groups called catechol. Our lab found that coatings formed from the polymerization of catechols on membrane discs can change color when exposed to various metal ions, including toxic metals such as lead and cadmium. This led us to consider developing a reliable and cheap sensor for heavy metal contamination in the water supply. Shortly before we joined the group, the system was optimized to generate large color changes, but many challenges remain to understand the system and ultimately make it practical. In particular, there are significant gaps in our understanding of the structural changes and the chemical basis of metal-ion selectivity. Thus, we have begun focusing on the structural elucidation of the catechol coatings. We have found multiple contributions to the color change that include covalent and temporary noncovalent changes to the material. Depending on the catechol and the metal ion, these effects can be competing or additive towards the overall color change. This presentation will highlight our recent efforts regarding quantitative colorimetry, infrared (IR)/UV/VIS spectroscopy, and most recently, nuclear magnetic resonance (NMR) spectroscopy to understand the system
Unveiling Subduction Dynamics: A Study of Metamorphosed Deep-Sea Sediment at Jenner Beach, California
No full textSubduction zones play a crucial role in seismic activity and volcanism, making them of paramount importance in Earth Sciences. The Franciscan Formation, exposed at the surface, serves as a valuable laboratory for subduction studies. This study examines a previously undescribed sample of metamorphosed deep-sea sediment that was subducted and then returned to the surface at Jenner Beach, California. Our primary objective is to analyze and reconstruct its metamorphic history, explain complex interactions at subduction interfaces, and clarify the role of fluids in shaping Earth\u27s lithosphere and mantle.
Our approach involves conducting Scanning Electron Microscope - Energy Dispersive X-ray Spectrometer mapping to outline mineral distributions and compositions, complemented by thermodynamic modeling to create Equilibrium Assemblage Diagrams. We then use these to reconstruct pressures and temperatures of metamorphism. The presence of garnet, glaucophane, muscovite, epidote, and sphene most closely matches the predicted assemblage at ~500˚ and ~14 kbar, similar to metamorphosed basalts from the same locality. This data indicates that our sample reached depths as far down as 45 km, just above where the melting that forms arc magma occurs. We can utilize this data to examine the geochemical processes crucial in arc formation.
The discovery of the first metaquartzite at Jenner Beach can add to the geological understanding of the region, indicating unique metamorphic conditions. By adding Fe3+ to the model, we hope to refine the conditions of metamorphism. We are seeing this rock form under similar conditions and future studies can use this as a geochemical probe into geochemical processes
Carbon Adsorbent Properties Impact Hydrated Electron Activity and Perfluorocarboxylic Acid (PFCA) Destruction
No full textCarbon-based adsorbents used to remove recalcitrant water contaminants, including perfluoroalkyl substances (PFAS), are often regenerated using energy-intensive treatments that can form harmful byproducts. We explore mechanisms for sorbent regeneration using hydrated electrons (e(aq) -) from sulfite ultraviolet photolysis (UV/sulfite) in water. We studied the UV/sulfite treatment on three carbon-based sorbents with varying material properties: granular activated carbon (GAC), carbon nanotubes (CNTs), and polyethylenimine-modified lignin (lignin). Reaction rates and defluorination of dissolved and adsorbed model perfluorocarboxylic acids (PFCAs), perfluorooctanoic acid (PFOA) and perfluorobutanoic acid (PFBA), were measured. Monochloroacetic acid (MCAA) was employed to empirically quantify e(aq) - formation rates in heterogeneous suspensions. Results show that dissolved PFCAs react rapidly compared to adsorbed ones. Carbon particles in solution decreased aqueous reaction rates by inducing light attenuation, e(aq) - scavenging, and sulfite consumption. The magnitude of these effects depended on adsorbent properties and surface chemistry. GAC lowered PFOA destruction due to strong adsorption. CNT and lignin suspensions decreased e(aq )- formation rates by attenuating light. Lignin showed high e(aq) - quenching, likely due to its oxygenated functional groups. These results indicate that desorbing PFAS and separating the adsorbent before initiating PFAS degradation reactions will be the best engineering approach for adsorbent regeneration using UV/sulfite
Pd/IPrBIDEA-Catalyzed Hydrodefluorination of gem-Difluorocyclopropanes: Regioselective Synthesis of Terminal Fluoroalkenes
No full textDeveloping new strategies to enable chemo- and regioselective reductions is an important topic in chemical research. Herein, an efficient and regioselective Pd/IPrBIDEA-catalyzed ring-opening hydrodefluorination of gem-difluorocyclopropanes to access terminal fluoroalkenes is developed. The success of this transformation was attributed to the use of 3,3-dimethylallyl Bpin as a novel hydride donor. DFT calculations suggest that a direct 3,4\u27-hydride transfer via a 9-membered cyclic transition state is more favorable, which combined with the irreversibility of the reaction enables the unusual selectivity for the less thermodynamically stable terminal alkene isomer. This reaction mode is also applicable to a variety of regioselective allylic and propargyl reductions