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Organic chemistry students often struggle with reaction mechanisms, particularly in how they are proposed and justified. In this activity targeting second year organic undergraduates, students used infrared spectroscopy (IR) to track the reaction progress of two distinct aldol reactions and used polarimetry to analyze the stereoselectivity of aldol catalysts. Students worked in two pairs, with one focusing on the traditional hydroxide-catalyzed aldol reaction (two units of propionaldehyde combining via an enolate intermediate) and the other focusing on the enantioselective l-proline-catalyzed aldol reaction (propionaldehyde catalyzed by l-proline, showing an iminium intermediate). During the course of the lab period, students used IR spectra showing kinetic data and guided questions to propose and validate the reaction mechanisms. After the pairs of students analyzed their individual reactions, they formed groups of four to further analyze and compare the two mechanisms. This comparison of IR and polarimetry data allowed students to discuss both pathways and consider why chemists use different reaction conditions to reach the same product. The focus of this experiment is to improve the understanding of reaction mechanisms and the process by which scientists propose and justify mechanisms, while giving students practical experience with IR spectroscopy, polarimetry, and intermediate analysis. 

Physical inactivity is a scourge to human health, promoting metabolic disease and muscle wasting. Interestingly, multiple ecological niches have relaxed investment into physical activity, providing an evolutionary perspective into the effect of adaptive physical inactivity on tissue homeostasis. One such example, the Mexican cavefishAstyanax mexicanus,has lost moderate-to-vigorous activity following cave colonization, reaching basal swim speeds ~3.7-fold slower than their river-dwelling counterpart. This change in behavior is accompanied by a marked shift in body composition, decreasing total muscle mass and increasing fat mass. This shift persisted at the single muscle fiber level via increased lipid and sugar accumulation at the expense of myofibrillar volume. Transcriptomic analysis of laboratory-reared and wild-caught cavefish indicated that this shift is driven by increased expression ofpparγ—the master regulator of adipogenesis—with a simultaneous decrease in fast myosin heavy chain expression. Ex vivo and in vivo analysis confirmed that these investment strategies come with a functional trade-off, decreasing cavefish muscle fiber shortening velocity, time to maximal force, and ultimately maximal swimming speed. Despite this, cavefish displayed a striking degree of muscular endurance, reaching maximal swim speeds ~3.5-fold faster than their basal swim speeds. Multi-omic analysis suggested metabolic reprogramming, specifically phosphorylation of Pgm1-Threonine 19, as a key component enhancing cavefish glycogen metabolism and sustained muscle contraction. Collectively, we reveal broad skeletal muscle changes following cave colonization, displaying an adaptive skeletal muscle phenotype reminiscent to mammalian disuse and high-fat models while simultaneously maintaining a unique capacity for sustained muscle contraction via enhanced glycogen metabolism. 

Dynamic covalent Diels–Alder chemistry was combined with multiwalled carbon nanotube (CNT) reinforcement to develop strong, tough and conductive dynamic materials. Unlike other approaches to functionalizing CNTs, this approach uses Diels–Alder bonds between diene pendant groups on the polymer and the CNT surface πσ bonds acting as dienophiles. Experimental and simulation data align with the CNT reinforcement coming from dynamic covalent bonds between the matrix and the CNT surface. The addition of just 0.9 wt% CNTs can lead to an almost 3-fold increase in strength and 6–7 order of magnitude increases in electrical conductivity, and materials with 0.45 wt% CNTs show excellent strength, self-healing and conductivity.