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<jats:title>Heteroaromatics lured into cycloadditions</jats:title> <jats:p> The Diels-Alder reaction is widely used to produce six-membered carbon rings from alkenes and dienes. Heteroaromatics such as quinolines resemble dienes in principle, but in practice their pairs of double bonds are inert toward cycloadditions because of aromatic stabilization. Ma <jats:italic>et al.</jats:italic> report that by using an iridium photosensitizer, they could excite quinolines and related azaarenes to triplet states, thereby disrupting the aromaticity and enabling intermolecular, Diels-Alder–like reactivity toward alkenes (see the Perspective by Schmidt). The reactions proceeded exclusively at the flanking carbons outside the nitrogen-containing ring. </jats:p> <jats:p> <jats:italic>Science</jats:italic> , this issue p. <jats:related-article issue="6536" page="1338" related-article-type="in-this-issue" vol="371">1338</jats:related-article> ; see also p. <jats:related-article issue="6536" page="1313" related-article-type="in-this-issue" vol="371">1313</jats:related-article> </jats:p>

<jats:title>Carbon cycle history</jats:title> <jats:p> Marine carbon includes organic and inorganic components, both of which must be accounted for to understand the global carbon cycle. Paytan <jats:italic>et al.</jats:italic> assembled a record of stable strontium isotopes ( <jats:sup>88</jats:sup> Sr and <jats:sup>86</jats:sup> Sr) derived from pelagic marine barite and used it to reconstruct changes in the deposition and burial of biogenic calcium carbonate in marine sediments. These data, when combined with measurements of <jats:sup>87</jats:sup> Sr/ <jats:sup>86</jats:sup> Sr, can help to reveal past changes in the sources and sinks of strontium, as well as variations in carbonate deposition that affect the carbon cycle. </jats:p> <jats:p> <jats:italic>Science</jats:italic> , this issue p. <jats:related-article issue="6536" page="1346" related-article-type="in-this-issue" vol="371">1346</jats:related-article> </jats:p>

<jats:title>Cell cycle regulation</jats:title> <jats:p> The hormone cytokinin regulates various aspects of plant development and physiology, largely by managing cell proliferation. Yang <jats:italic>et al.</jats:italic> show that cytokinin promotes nuclear localization of the transcription factor MYB3R4, which activates the expression of two importins and genes that tip the cell into the next phase of the cell cycle. The importins facilitate further MYB3R4 accumulation within the nucleus, accelerating the progression into mitosis. MYB3R4 and the importins dissipate when the nuclear membrane dissolves at prometaphase, so there is only one round of mitotic activation per cell cycle. </jats:p> <jats:p> <jats:italic>Science</jats:italic> , this issue p. <jats:related-article issue="6536" page="1350" related-article-type="in-this-issue" vol="371">1350</jats:related-article> </jats:p>

<jats:title>Dynamic stabilization of an array</jats:title> <jats:p> Large-scale systems comprising one-dimensional chains and two-dimensional arrays of excited atoms held in a programmable optical lattice are a powerful platform with which to simulate emergent phenomena. Bluvstein <jats:italic>et al.</jats:italic> built an array of up to 200 Rydberg atoms and subjected the system to periodic excitation. Under such driven excitation, they found that the array of atoms stabilized, freezing periodically into what looked like time crystals. Understanding and controlling the dynamic interactions in quantum many-body systems lies at the heart of contemporary condensed matter physics and the exotic phenomena that can occur. </jats:p> <jats:p> <jats:italic>Science</jats:italic> , this issue p. <jats:related-article issue="6536" page="1355" related-article-type="in-this-issue" vol="371">1355</jats:related-article> </jats:p>

<jats:title>Perovskite synthesis out in the open</jats:title> <jats:p> Although methods have been developed that create the photoactive black perovskite phase of formamidinium lead iodide (α-FAPbI <jats:sub>3</jats:sub> ), these routes are temperature and humidity sensitive and less compatible with large-scale solar cell production. Hui <jats:italic>et al.</jats:italic> report an alternative route in which vertically aligned lead iodide thin films are grown from the ionic liquid methylamine formate. Nanoscale channels in the films lower the barrier to permeation of formamidinium iodide and enable transformation to α-FAPbI <jats:sub>3</jats:sub> , even at high humidity and room temperature. Solar cells made with these films have power conversion efficiencies as high as 24.1% that display high stability. </jats:p> <jats:p> <jats:italic>Science</jats:italic> , this issue p. <jats:related-article issue="6536" page="1359" related-article-type="in-this-issue" vol="371">1359</jats:related-article> </jats:p>

<jats:title>Mapping nanostructure surface excitations</jats:title> <jats:p> Atomic vibrations (phonons) govern many physical properties of materials, especially those related to heat and thermal transport. They also provide fingerprints of the chemistry of a wide variety of materials, from solids to molecules. The behavior of phonons in nanostructures can be appreciably modified because of confinement effects. Li <jats:italic>et al.</jats:italic> combined several electron microscopy techniques to map out the phonon-polariton excitations across the surface of magnesium oxide nanostructures with high spatial, spectral, and angular resolution. The reconstruction of the surface excitation maps in three dimensions will be useful for understanding and optimizing the properties of the nanostructured materials for advanced functionality. </jats:p> <jats:p> <jats:italic>Science</jats:italic> , this issue p. <jats:related-article issue="6536" page="1364" related-article-type="in-this-issue" vol="371">1364</jats:related-article> </jats:p>

<jats:title>Nanorod alignment for optical asymmetry</jats:title> <jats:p> The high polarizability of chiral nanoassemblies of plasmonic nanoparticles can lead to strong chiral dichroism, but strong light scattering causes the fraction of polarized photons generated, as measured by g-factors, to be much lower than that for chiral liquid crystals. Lu <jats:italic>et al.</jats:italic> used supramolecular interactions of gold nanorods with human islet amyloid peptides to assemble metallic superstructures with unusually high cholesteric order (see the Perspective by Nam and Kim). The long, straight helices increased the g-factor by 4600-fold, and this effect was used to screen small-molecule binding to amyloids. </jats:p> <jats:p> <jats:italic>Science</jats:italic> , this issue p. <jats:related-article issue="6536" page="1368" related-article-type="in-this-issue" vol="371">1368</jats:related-article> ; see also p. <jats:related-article issue="6536" page="1311" related-article-type="in-this-issue" vol="371">1311</jats:related-article> </jats:p>

<jats:title>Targeting the SARS-CoV-2 main protease</jats:title> <jats:p> Vaccines are an important tool in the fight against COVID-19, but developing antiviral drugs is also a high priority, especially with the rise of variants that may partially evade vaccines. The viral protein main protease is required for cleaving precursor polyproteins into functional viral proteins. This essential function makes it a key drug target. Qiao <jats:italic>et al.</jats:italic> designed 32 inhibitors based on either boceprevir or telaprevir, both of which are protease inhibitors approved to treat hepatitis C virus. Six compounds protected cells from viral infection with high potency, and two of these were selected for in vivo studies based on pharmokinetic experiments. Both showed strong antiviral activity in a mouse model. </jats:p> <jats:p> <jats:italic>Science</jats:italic> , this issue p. <jats:related-article issue="6536" page="1374" related-article-type="in-this-issue" vol="371">1374</jats:related-article> </jats:p>

<jats:title>Halting transmission</jats:title> <jats:p> The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spike (S) glycoprotein binds to host cells and initiates membrane fusion and cell infection. This stage in the virus life history is currently a target for drug inhibition. De Vries <jats:italic>et al.</jats:italic> designed highly stable lipoprotein fusion inhibitors complementary to a conserved repeat in the C terminus of S that integrate into host cell membranes and inhibit conformational changes in S necessary for membrane fusion. The authors tested the performance of the lipoproteins as a preexposure prophylactic in a ferret-to-ferret transmission study. Intranasal administration of the peptide 2 days before cohousing with an infected ferret for 24 hours completely protected animals in contact from infection and showed efficacy against mutant viruses. Because ferrets do not get sick from SARS-CoV-2, disease prevention could not be tested in this model. </jats:p> <jats:p> <jats:italic>Science</jats:italic> , this issue p. <jats:related-article issue="6536" page="1379" related-article-type="in-this-issue" vol="371">1379</jats:related-article> </jats:p>

<jats:title>In non-eutherians, a third type of T cell</jats:title> <jats:p> The two established T cell lineages found in jawed vertebrates use either an αβ or a γδ T cell receptor (TCR) to detect antigens. Recently, another type of TCR chain (TCRµ) was found in marsupials and monotremes. Morrissey <jats:italic>et al.</jats:italic> analyzed T cells from the gray short-tailed opossum and uncovered a third lineage resident in the spleen that uses a γµ TCR (see the Perspective by Criscitiello). The authors then characterized the crystal structures of two different γµ TCRs, which exhibited an architecture distinct from αβ or γδ TCRs in which a highly diverse, unpaired immunoglobulin-like variable domain was predicted to be the major antigen recognition determinant. Like camelid VHH and shark IgNAR antibodies, γµ TCRs could potentially inform future nanobody development. </jats:p> <jats:p> <jats:italic>Science</jats:italic> , this issue p. <jats:related-article issue="6536" page="1383" related-article-type="in-this-issue" vol="371">1383</jats:related-article> ; see also p. <jats:related-article issue="6536" page="1308" related-article-type="in-this-issue" vol="371">1308</jats:related-article> </jats:p>