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<jats:p>Hydrogen bonds (H-bonds) can be interpreted as a classical electrostatic interaction or as a covalent chemical bond if the interaction is strong enough. As a result, short strong H-bonds exist at an intersection between qualitatively different bonding descriptions, with few experimental methods to understand this dichotomy. The [F-H-F]<jats:sup>−</jats:sup> ion represents a bare short H-bond, whose distinctive vibrational potential in water is revealed with femtosecond two-dimensional infrared spectroscopy. It shows the superharmonic behavior of the proton motion, which is strongly coupled to the donor-acceptor stretching and disappears on H-bond bending. In combination with high-level quantum-chemical calculations, we demonstrate a distinct crossover in spectroscopic properties from conventional to short strong H-bonds, which identify where hydrogen bonding ends and chemical bonding begins.</jats:p>

<jats:title>Recent fluid flow in ancient meteorites</jats:title> <jats:p> Carbonaceous chondritic meteorites are thought to be fragments broken off parent bodies that orbit in the outer Solar System, largely unaltered since their formation. These meteorites contain evidence of reactions with liquid water that was thought to have been lost or completely frozen billions of years ago. Turner <jats:italic>et al.</jats:italic> examined uranium and thorium isotopes in several carbonaceous chondrites, finding nonequilibrium distributions that imply that uranium ions were transported by fluid flow. Because this signature disappears after several half-lives of the radioactive isotopes, the meteorites must have been exposed to liquid within the past million years. The authors suggest that ice may have melted during the impacts that ejected the meteorites from their parent bodies. </jats:p> <jats:p> <jats:italic>Science</jats:italic> , this issue p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6525" page="164" related-article-type="in-this-issue" vol="371" xlink:href="10.1126/science.abc8116">164</jats:related-article> </jats:p>

<jats:title>Potassium and lithium on a white dwarf</jats:title> <jats:p> White dwarfs are dense stellar remnants left when a dying parent star throws off its outer layers. The high gravitational fields should cause heavy elements to rapidly sink below the white dwarf surface. Nevertheless some “polluted” white dwarfs have evidence for those materials on their surface, which is thought to be due to the recent accretion of rocky bodies from a surrounding planetary system. Kaiser <jats:italic>et al.</jats:italic> report a white dwarf with pollution by potassium and lithium. This observation provides a record of the composition of the accreted rocky bodies and of the Galactic lithium abundance when the planetary system formed, billions of years ago. </jats:p> <jats:p> <jats:italic>Science</jats:italic> , this issue p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6525" page="168" related-article-type="in-this-issue" vol="371" xlink:href="10.1126/science.abd1714">168</jats:related-article> </jats:p>

<jats:title>Two-way transmission on mink farms</jats:title> <jats:p> Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a zoonotic virus—one that spilled over from another species to infect and transmit among humans. We know that humans can infect other animals with SARS-CoV-2, such as domestic cats and even tigers in zoos. Oude Munnink <jats:italic>et al.</jats:italic> used whole-genome sequencing to show that SARS-CoV-2 infections were rife among mink farms in the southeastern Netherlands, all of which are destined to be closed by March 2021 (see the Perspective by Zhou and Shi). Toward the end of June 2020, 68% of mink farm workers tested positive for the virus or had antibodies to SARS-CoV-2. These large clusters of infection were initiated by human COVID-19 cases with viruses that bear the D614G mutation. Sequencing has subsequently shown that mink-to-human transmission also occurred. More work must be done to understand whether there is a risk that mustelids may become a reservoir for SARS-CoV-2. </jats:p> <jats:p> <jats:italic>Science</jats:italic> , this issue p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6525" page="172" related-article-type="in-this-issue" vol="371" xlink:href="10.1126/science.abe5901">172</jats:related-article> ; see also p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6525" page="120" related-article-type="in-this-issue" vol="371" xlink:href="10.1126/science.abf6097">120</jats:related-article> </jats:p>

<jats:title>Where they can't breathe</jats:title> <jats:p> Climate warming is causing the expansion of marine oxygen-deficient zones, which are regions in which dissolved oxygen concentrations are so low that many marine animals cannot survive. This phenomenon also might affect the global cycles of carbon, sulfur, nitrogen, and trace metals in the oceans. Raven <jats:italic>et al.</jats:italic> show how ocean anoxia affects microbial sulfur processing in sinking marine particles. They observed cryptic microbial sulfate reduction, which forms organic sulfur that is resistant to acid hydrolysis, a process that could enhance carbon preservation in sediments underlying oxygen-deficient water columns. This may help explain some of the more extreme episodes of organic carbon preservation associated with marine anoxia in Earth's history. </jats:p> <jats:p> <jats:italic>Science</jats:italic> , this issue p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6525" page="178" related-article-type="in-this-issue" vol="371" xlink:href="10.1126/science.abc6035">178</jats:related-article> </jats:p>

<jats:title>PreTCRs use horizontal docking geometry</jats:title> <jats:p> The T cell receptor (TCR) recognizes peptide-bound major histocompatibility complex molecules (pMHCs) and consists of an α chain in association with a β chain. Both chains have hypervariable complementarity-determining regions (CDRs) that inform whether a particular TCR can recognize a given pMHC. To successfully graduate from the thymus, aspiring αβT cells must generate a functional TCR. During one early checkpoint in this process, the β chain is first paired with a preTβ chain to form the preTCR. Li <jats:italic>et al.</jats:italic> used x-ray crystallography to visualize how preTCRs recognize pMHCs. They report that the CDR3 loop of the preTCR β chain contacts the pMHC with a distinctive lateral topography. This is in contrast to the established binding modality of mature TCRs, whereby all three CDR loops on both α and β chains bind in a vertical orientation. These complexes help solve the mystery of how only functionally rearranged β chains using competent CDR3 loops can properly engage with pMHC at the preTCR stage. </jats:p> <jats:p> <jats:italic>Science</jats:italic> , this issue p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6525" page="181" related-article-type="in-this-issue" vol="371" xlink:href="10.1126/science.abe0918">181</jats:related-article> </jats:p>

<jats:title>Tire tread particles turn streams toxic</jats:title> <jats:p> For coho salmon in the U.S. Pacific Northwest, returning to spawn in urban and suburban streams can be deadly. Regular acute mortality events are tied, in particular, to stormwater runoff, but the identity of the causative toxicant(s) has not been known. Starting from leachate from new and aged tire tread wear particles, Tian <jats:italic>et al.</jats:italic> followed toxic fractions through chromatography steps, eventually isolating a single molecule that could induce acute toxicity at threshold concentrations of ∼1 microgram per liter. The compound, called 6PPD-quinone, is an oxidation product of an additive intended to prevent damage to tire rubber from ozone. Measurements from road runoff and immediate receiving waters show concentrations of 6PPD-quinone high enough to account for the acute toxicity events. </jats:p> <jats:p> <jats:italic>Science</jats:italic> , this issue p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6525" page="185" related-article-type="in-this-issue" vol="371" xlink:href="10.1126/science.abd6951">185</jats:related-article> </jats:p>

<jats:title>Two antibodies against flaviviruses</jats:title> <jats:p> Flaviviruses are a group of RNA viruses that include the human pathogens dengue virus, Zika virus, and West Nile virus. The envelope protein (E) on the virus surface has been the target of vaccine development, but problems have arisen with antibodies against E, leading to enhanced infection. Now, Modhiran <jats:italic>et al.</jats:italic> and Biering <jats:italic>et al.</jats:italic> describe two different antibodies that bind to the flavivirus NS1 protein and prevent it from disrupting epithelial cells, which is associated with severe disease. Both antibodies cross-react with multiple flavivirus NS1 proteins. The antibodies reduce viremia and increase survival in mouse models of flavivirus disease. Both papers include structures of NS1 bound to an antibody, which give insight into the protective mechanism. </jats:p> <jats:p> <jats:italic>Science</jats:italic> , this issue p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6525" page="190" related-article-type="in-this-issue" vol="371" xlink:href="10.1126/science.abb9425">190</jats:related-article> , p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6525" page="194" related-article-type="in-this-issue" vol="371" xlink:href="10.1126/science.abc0476">194</jats:related-article> </jats:p>

<jats:title>Two antibodies against flaviviruses</jats:title> <jats:p> Flaviviruses are a group of RNA viruses that include the human pathogens dengue virus, Zika virus, and West Nile virus. The envelope protein (E) on the virus surface has been the target of vaccine development, but problems have arisen with antibodies against E, leading to enhanced infection. Now, Modhiran <jats:italic>et al.</jats:italic> and Biering <jats:italic>et al.</jats:italic> describe two different antibodies that bind to the flavivirus NS1 protein and prevent it from disrupting epithelial cells, which is associated with severe disease. Both antibodies cross-react with multiple flavivirus NS1 proteins. The antibodies reduce viremia and increase survival in mouse models of flavivirus disease. Both papers include structures of NS1 bound to an antibody, which give insight into the protective mechanism. </jats:p> <jats:p> <jats:italic>Science</jats:italic> , this issue p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6525" page="190" related-article-type="in-this-issue" vol="371" xlink:href="10.1126/science.abb9425">190</jats:related-article> , p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6525" page="194" related-article-type="in-this-issue" vol="371" xlink:href="10.1126/science.abc0476">194</jats:related-article> </jats:p>

<jats:p>A weekly roundup of information on newly offered instrumentation, apparatus, and laboratory materials of potential interest to researchers.</jats:p>