Mechanostereochemical modulation of polymer mechanical properties.

July 28, 2026| Source: Proceedings of the National Academy of Sciences of the United States of America

Stereochemistry profoundly affects the physical and mechanical properties of polymers, illustrated by the contrast between elastic natural rubber ( cis -polyisoprene) and the stiffer, less extensible gutta-percha ( trans -isomer). Traditional stereochemistry such as tacticity and cis / trans isomerism primarily governs polymer properties based on fixed structural or conformational factors. Herein, by incorporating the mechanostereochemistry concept into polymers, we demonstrate a stereochemistry paradigm wherein dynamic isomers dictate material properties, thereby defining the unprecedented transient-stereostructure-efficacy mechanism. Specifically, we engineer two mechanically interlocked networks based on [ c 2]daisy chains, where force-triggered intramolecular motion generates mechanostereoisomers with distinct geometric configurations: [ c 2]Daisy chain 1 in MIN- 1 contracts into a fisherman's knot, whereas [ c 2]daisy chain 2 in MIN- 2 extends into a loop. Due to reduced network elasticity from the loop structure, MIN- 2 exhibits a lower modulus in large-strain shear measurements and less pronounced strain hardening in tensile tests compared to MIN- 1 . Since these mechanostereoisomers are induced by force, material properties show strain-dependent character: both networks perform similarly under small or no strain, but diverge significantly at large strains. Our work expands the conceptual boundaries of polymer stereochemistry and provides insights for designing high-performance materials through stereochemical control.

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Extensive glacier loss in the coterminous United States.

Glaciers populate the mountain ranges of the western conterminous United States and despite their importance to alpine hydrology, their area and volume change have never been comprehensively evaluated. Our study shows that since the mid-twentieth century about one-quarter of the glaciers have disappeared and the overall area and volume are reduced by one-third. The pattern of glacier shrinkage suggests most glaciers in the conterminous United States are largely maintained by local topographic in

Physical/TechOctober 20, 2026

Reaction-based cryo-EM resolves the continuous conformational spectrum of CTP synthase catalysis.

Capturing enzymes under native turnover conditions remains a grand challenge in structural biology. Here, we develop a reaction-based cryo-electron microscopy (cryo-EM) strategy that directly samples Drosophila melanogaster cytidine triphosphate synthase (CTPS) from actively catalyzing mixtures containing only natural substrates and allosteric effectors. By integrating reaction-based sampling with three-dimensional variability analysis, we resolve a continuous conformational spectrum of CTPS dur

Physical/TechOctober 20, 2026

GTP orchestrates CTP synthase via an allosteric effector-cycling mechanism.

Cytidine triphosphate (CTP), a fundamental building block of RNA, plays vital roles in diverse biological processes. CTP synthase (CTPS) is the only known enzyme for de novo synthesis of CTP. Efficient CTPS catalysis requires guanosine triphosphate (GTP) in a dose-dependent, nonconsumptive manner; however, the precise mechanism by which GTP drives CTP formation remains unclear. Here, we integrate a series of cryo-EM structures of Drosophila melanogaster CTPS captured from actively catalyzing sam

Physical/TechOctober 20, 2026

Antiferromagnetism and tightly bound Cooper pairs induced by kinetic frustration.

Antiferromagnetism and superconductivity are often viewed as competing orders in correlated electron systems. Here, we demonstrate that kinetic frustration in hole motion facilitates their coexistence within the square-lattice repulsive Hubbard model. Combining exact analytical solutions on tailored geometries with large-scale numerical simulations, we reveal a robust pairing mechanism: Holes on opposite sublattices behave as if they carry opposite effective charges due to spin singlet formation

Physical/TechOctober 20, 2026

Coordinated transformations of the labyrinth and occiput during the dinosaur-bird transition.

Evolutionary shape changes of the vertebrate semicircular canals (SCCs) are often ascribed to evolutionary transitions in locomotion, including the origin of flight during the dinosaur-bird transition. However, the potential for transformations of braincase architecture to influence SCC shape independent of sensory-functional adaptation has generally been overlooked. We evaluate the influence of both factors using a large dataset of 146 living and recently extinct crown birds, including taxa rep