Precise mechanical manipulation of molecules is inherently difficult owing to random thermal motion. Although directed movement on the molecular scale has been achieved, using it to impose specific—especially energetically disfavored—shapes on molecules and construct mechanically interlocked structures remains a fundamental challenge. In this study, we report the synthesis of a catenane enabled by a molecular motor that winds molecular strands into discrete entangled structures, each defined by a specific number of mechanical crossings. Light energy drives unidirectional motor rotation, enabling path-dependent control over a sequence of thermodynamically disfavored yet mechanically distinct and kinetically stable winding states, which are covalently captured and subsequently released to yield a catenane. This machine-directed approach offers a general proof-of-concept strategy for the template-free construction of mechanically interlocked molecules.
物理学Chemistry
Dust-driven droplet freezing explains cloud-top phase in the northern extratropics
粉尘驱动液滴冻结有助解释北半球温带地区的云顶相态
▲ 作者：D. VILLANUEVA, M. STENGEL, C. HOOSE, O. BRUNO, K. JEGGLE, A. ANSMANN, AND U. LOHMANN
Clouds between -39° and 0°C can be topped by a liquid or ice layer, which affects their radiative forcing and precipitation. The cloud-top ice-to-total frequency (ITF) quantifies the occurrence of clouds with an ice top relative to total cloud occurrence, but the factors controlling ITF are poorly understood. Using 35 years of satellite data, we show that in the Northern Hemisphere, between -15° and -30°C, dust aerosol is strongly correlated with ITF in both time and space. Furthermore, we found that the sensitivities of ITF to temperature and dust are in a ratio that agrees with laboratory measurements of droplet freezing, showing that ITF can be attributed to dust aerosol.
Acoustic wave modulation of gap plasmon cavities
间隙等离子体腔的声波调制
▲ 作者：SKYLER P. SELVIN, MAJID ESFANDYARPOUR, ANQI JI, YAN JOE LEE, COLIN YULE, MOHAMMAD TAGHINEJAD, AND MARK L. BRONGERSMA
The important role of metallic nanostructures in nanophotonics will expand if ways to electrically manipulate their optical resonances at high speed can be identified. We capitalized on electrically driven surface acoustic waves and the extreme light concentration afforded by gap plasmons to achieve this goal. We placed gold nanoparticles in a particle-on-mirror configuration with a few-nanometer-thick, compressible polymer spacer. Surface acoustic waves were then used to tune light scattering at speeds approaching the gigahertz regime. We observed evidence that the surface acoustic waves produced mechanical deformations in the polymer and that ensuing nonlinear mechanical dynamics led to unexpectedly large levels of strain and spectral tuning. Our approach provides a design strategy for electrically driven dynamic metasurfaces and fundamental explorations of high-frequency, polymer dynamics in ultraconfined geometries.
High-field superconducting halo in UTe2
UTe2中的高场超导光晕
▲ 作者：SYLVIA K. LEWIN, PETER CZAJKA, COREY E. FRANK, GICELA SAUCEDO SALAS, G. TIMOTHY NOE II, HYEOK YOON, YUN SUK EO, JOHNPIERRE PAGLIONE, ANDRIY H. NEVIDOMSKYY, AND NICHOLAS P. BUTCH
The heavy fermion material UTe2is a candidate topological superconductor that exhibits multiple magnetic field–induced superconducting phases. One such phase exists only at fields greater than 40 tesla, a considerable scale given its critical temperature of only 2 K. Here, we extend measurements of this state with fields outside of the bc crystallographic plane and reveal its core structure: The superconducting phase wraps around the b axis in a halo-like fashion and appears to be stabilized by a field component perpendicular to the magnetic easy axis. This angle dependence points to a multicomponent spin-triplet order parameter with a finite angular momentum of the Cooper pairs. The pairing mechanism remains enigmatic, and UTe2’s specific magnetophilic superconducting tendencies seem incompatible with existing models for field-enhanced superconductivity.
生命科学Life Science
Altered translation elongation contributes to key hallmarks of aging in the killifish brain
鳉鱼大脑衰老关键特征的原因
▲ 作者：DOMENICO DI FRAIA, ANTONIO MARINO, JAE HO LEE, ERIKA KELMER SACRAMENTO, MARIO BAUMGART, SARA BAGNOLI, TILL BALLA, FELIX SCHALK, STEPHAN KAMRAD, AND ALESSANDRO ORI
To get a handle on what falls apart during aging in the brain, Di Fraia et al. turned to the short-lived killifish (see the Perspective by Dionne and Laurent). The authors monitored changes in protein and RNA abundance, protein solubility, post-translational modification, and organelle composition as the fish aged. As organisms age, protein abundance is less closely coupled to transcript abundance. In the fish, this appeared to have less to do with protein stability and was more likely influenced by altered translation. Proteins rich in basic amino acids, a characteristic of RNA and DNA binding proteins, had delays in translation and decreased in abundance. Changes in mitochondrial composition were also noted as likely contributors to loss of function in aging.
Behavior drives morphological change during human evolution
行为驱动了人类进化过程中的形态变化
▲ 作者：LUKE D. FANNIN, CHALACHEW M. SEYOUM, VIVEK V. VENKATARAMAN, JUSTIN D. YEAKEL, CHRISTINE M. JANIS, THURE E. CERLING, AND NATHANIEL J. DOMINY
Dietary shifts and corresponding morphological changes can sometimes evolve in succession, not concurrently—an evolutionary process called behavioral drive. Detecting behavioral drive in the fossil record is challenging because it is difficult to measure behaviors independently from corresponding morphologies. To solve this problem, we focused on a puzzling behavior in the fossil record of some primates: eating graminoid plants. We report carbon and oxygen isotope ratios from fossil cercopithecid monkeys and integrate the data into a view of hominin dietary evolution, finding that changes in graminivorous behavior preceded corresponding changes in dental morphology by ~700,000 years. Decoupling diets and morphologies in time was conducive to determining when and to exploring why dietary changes helped to propel human evolution.
