编译 | 未玖
Nature, 15 June 2023, VOL 618, ISSUE 7965
《自然》2023年6月15日，第618卷，7965期
天文学 Astronomy
Detection of phosphates originating from Enceladus’s ocean
从土卫二海洋中探测到磷酸盐
▲ 作者：Frank Postberg, Yasuhito Sekine, Fabian Klenner, Christopher R. Glein, Zenghui Zou, Bernd Abel, et al.
▲ 链接：
https://www.nature.com/articles/s41586-023-05987-9
▲ 摘要：
土星的卫星土卫二拥有一片全球冰封的海洋。卡西尼号宇宙飞船通过分析卫星低温火山羽流喷射到太空中的物质来研究海洋组成。卡西尼号宇宙尘埃分析仪对富含盐分的冰粒进行了分析，从而推断出海水中的主要溶质（Na+、K+、Cl–、HCO3–、CO32–）及其碱性pH值。
磷是生物必需元素中含量最低的一种，目前尚未在地球以外的海洋中检测到。早期的地球化学模型研究表明，在土卫二海洋和其他冰冷的海洋世界中，磷酸盐可能很稀缺。然而，最近对土卫二海洋矿物溶解度的模拟表明，磷酸盐可能相对丰富。
研究组展示了卡西尼号宇宙尘埃分析仪对土卫二喷射冰粒的质谱分析，显示了磷酸钠的存在。该观测结果及实验室模拟实验表明，在土卫二海洋中，磷较易以正磷酸盐的形式存在，卫星羽流形成海水中的磷浓度至少是地球海洋的100倍。
此外，地球化学实验和建模表明，如此高的磷酸盐丰度可能在土卫二上实现，也可能在原始二氧化碳雪线之外的其他冰冷海洋世界中实现，无论是在寒冷的海底还是在中等温度的热液环境中。在这两种情况下，主要驱动因素可能是在富含碳酸盐或碳酸氢根离子的中等碱性溶液中，磷酸钙矿物比碳酸钙矿物的溶解度更高。
▲ Abstract：
Saturn’s moon Enceladus harbours a global ice-covered water ocean. The Cassini spacecraft investigated the composition of the ocean by analysis of material ejected into space by the moon’s cryovolcanic plume. The analysis of salt-rich ice grains by Cassini’s Cosmic Dust Analyzer enabled inference of major solutes in the ocean water (Na+, K+, Cl–, HCO3–, CO32–) and its alkaline pH. Phosphorus, the least abundant of the bio-essential elements, has not yet been detected in an ocean beyond Earth. Earlier geochemical modelling studies suggest that phosphate might be scarce in the ocean of Enceladus and other icy ocean worlds. However, more recent modelling of mineral solubilities in Enceladus’s ocean indicates that phosphate could be relatively abundant. Here we present Cassini’s Cosmic Dust Analyzer mass spectra of ice grains emitted by Enceladus that show the presence of sodium phosphates. Our observational results, together with laboratory analogue experiments, suggest that phosphorus is readily available in Enceladus’s ocean in the form of orthophosphates, with phosphorus concentrations at least 100-fold higher in the moon’s plume-forming ocean waters than in Earth’s oceans. Furthermore, geochemical experiments and modelling demonstrate that such high phosphate abundances could be achieved in Enceladus and possibly in other icy ocean worlds beyond the primordial CO2 snowline, either at the cold seafloor or in hydrothermal environments with moderate temperatures. In both cases the main driver is probably the higher solubility of calcium phosphate minerals compared with calcium carbonate in moderately alkaline solutions rich in carbonate or bicarbonate ions.
物理学 Physics
Evidence for the utility of quantum computing before fault tolerance
在容错之前证明量子计算的实用性
▲ 作者：Youngseok Kim, Andrew Eddins, Sajant Anand, Ken Xuan Wei, Ewout van den Berg, Sami Rosenblatt, et al.
▲ 链接：
https://www.nature.com/articles/s41586-023-06096-3
▲ 摘要：
量子计算有望在某些问题上提供比经典计算更快的速度。然而，实现其全部潜力的最大障碍是这些系统固有的噪声。针对该挑战，人们广泛接受的解决方案是实现容错量子电路，但当前处理器无法实现。
研究组报道了在有噪声的127量子位处理器上的实验，演示了在超出Brute-Force经典计算范围内测量电路体积的精确期望值，并认为这代表了量子计算在前容错时期的实用性。该实验结果归功于这种规模的超导处理器在相干性和校准方面的进步，以及在如此大的设备上表征和可控操纵噪声的能力。
通过与精确可验证电路的输出进行比较，研究组确定了测量期望值的准确性。在强纠缠状态下，量子计算机提供了正确的结果，而诸如基于纯态的一维（矩阵乘积态，MPS）和二维（等距张量网络态，isoTNS）张量网络方法等主要经典近似都失效了。这些实验展示了实现Near-Term量子应用的基础工具。
▲ Abstract：
Quantum computing promises to offer substantial speed-ups over its classical counterpart for certain problems. However, the greatest impediment to realizing its full potential is noise that is inherent to these systems. The widely accepted solution to this challenge is the implementation of fault-tolerant quantum circuits, which is out of reach for current processors. Here we report experiments on a noisy 127-qubit processor and demonstrate the measurement of accurate expectation values for circuit volumes at a scale beyond brute-force classical computation. We argue that this represents evidence for the utility of quantum computing in a pre-fault-tolerant era. These experimental results are enabled by advances in the coherence and calibration of a superconducting processor at this scale and the ability to characterize and controllably manipulate noise across such a large device. We establish the accuracy of the measured expectation values by comparing them with the output of exactly verifiable circuits. In the regime of strong entanglement, the quantum computer provides correct results for which leading classical approximations such as pure-state-based 1D (matrix product states, MPS) and 2D (isometric tensor network states, isoTNS) tensor network methods break down. These experiments demonstrate a foundational tool for the realization of near-term quantum applications.
化学 Chemistry
Transannular C–H functionalization of cycloalkane carboxylic acids
环烷烃羧酸的跨环C-H*能官**化
▲ 作者：Guowei Kang, Daniel A. Strassfeld, Tao Sheng, Chia-Yu Chen & Jin-Quan Yu
▲ 链接：
https://www.nature.com/articles/s41586-023-06000-z
▲ 摘要：
环状有机分子在天然产物和药物中很常见。事实上，绝大多数小分子药物至少含有一个环状体系，因为环能够控制分子形状，通常提升了口服生物利用度，同时增强了对候选药物活性、特异性和物理性质的控制。因此，直接位点、非对映选择性合成*能官**化碳环极为必要。
原则上，通过C-H活化进行分子编辑为这些化合物合成提供了一个理想途径。然而，环烷烃的区域选择性C-H*能官**化仍颇具挑战，因为在跨环C-H钯化中会遭遇应变。
研究组报道两类配体（即奎宁吡啶酮和磺酰胺吡啶酮）实现了中小型环烷烃羧酸的跨环γ-亚甲基C-H芳基化，环尺寸从环丁烷到环辛烷不等。在存在多个β-C-H键时，实现了优异的γ-区域选择性。
这一进展标志着人们向实现饱和碳环的分子编辑迈出了重要一步，即饱和碳环是一类在合成化学和药物化学中很重要的支架。该方案的实用性通过两步正式合成一系列具有明显生物活性的小分子得以证明，而此前合成需多达11步。
▲ Abstract：
Cyclic organic molecules are common among natural products and pharmaceuticals. In fact, the overwhelming majority of small-molecule pharmaceuticals contain at least one ring system, as they provide control over molecular shape, often increasing oral bioavailability while providing enhanced control over the activity, specificity and physical properties of drug candidates. Consequently, new methods for the direct site and diastereoselective synthesis of functionalized carbocycles are highly desirable. In principle, molecular editing by C–H activation offers an ideal route to these compounds. However, the site-selective C–H functionalization of cycloalkanes remains challenging because of the strain encountered in transannular C–H palladation. Here we report that two classes of ligands—quinuclidine-pyridones (L1, L2) and sulfonamide-pyridones (L3)—enable transannular γ-methylene C–H arylation of small- to medium-sized cycloalkane carboxylic acids, with ring sizes ranging from cyclobutane to cyclooctane. Excellent γ-regioselectivity was observed in the presence of multiple β-C–H bonds. This advance marks a major step towards achieving molecular editing of saturated carbocycles: a class of scaffolds that are important in synthetic and medicinal chemistry. The utility of this protocol is demonstrated by two-step formal syntheses of a series of patented biologically active small molecules, prior syntheses of which required up to 11 steps.
General access to cubanes as benzene bioisosteres
立方烷作为苯生物电子等排体的通用途径
▲ 作者：Mario P. Wiesenfeldt, James A. Rossi-Ashton, Ian B. Perry, Johannes Diesel, Olivia L. Garry, Florian Bartels, et al.
▲ 链接：
https://www.nature.com/articles/s41586-023-06021-8
▲ 摘要：
在保留生物活性的同时，用sp3杂化的生物电子等排体取代苯环通常可以改善候选药物的药代动力学性质。刚性应变框架（如双环[1.1.1]戊烷和立方烷）特别适合，因为环应变赋予高键强度，从而在其C-H键上代谢稳定。
立方烷是理想的生物电子等排体，因其提供了最接近苯的几何匹配。然而，目前药物设计中的所有立方烷，就像几乎所有的苯生物电子等排体一样，仅仅作为单取代或对位取代苯环的替代品。这归因于很难获得1,3-和1,2-二取代的立方烷前体。
由于竞争性金属催化的价异构化，交叉偶联反应与立方烷支架的相容性较差，进一步阻碍了立方烷在药物设计中的应用。研究组报道了分别使用易得的环丁二烯前体和光解C-H羧化反应制备1,3-和1,2-二取代立方烷构建块的便捷途径。
此外还利用铜的缓慢氧化加成和快速还原消除来开发C-N、C-C ( sp 3)、C-C ( sp 2)和C-CF3交叉偶联方案。该研究使所有的立方烷异构体易于加工成候选药物，从而实现邻位、间位和对位取代苯的理想生物电子等排替代。
▲ Abstract：
The replacement of benzene rings with sp3-hybridized bioisosteres in drug candidates generally improves pharmacokinetic properties while retaining biological activity. Rigid, strained frameworks such as bicyclo[1.1.1]pentane and cubane are particularly well suited as the ring strain imparts high bond strength and thus metabolic stability on their C–H bonds. Cubane is the ideal bioisostere as it provides the closest geometric match to benzene. At present, however, all cubanes in drug design, like almost all benzene bioisosteres, act solely as substitutes for mono- or para-substituted benzene rings. This is owing to the difficulty of accessing 1,3- and 1,2-disubstituted cubane precursors. The adoption of cubane in drug design has been further hindered by the poor compatibility of cross-coupling reactions with the cubane scaffold, owing to a competing metal-catalysed valence isomerization. Here we report expedient routes to 1,3- and 1,2-disubstituted cubane building blocks using a convenient cyclobutadiene precursor and a photolytic C–H carboxylation reaction, respectively. Moreover, we leverage the slow oxidative addition and rapid reductive elimination of copper to develop C–N, C–C(sp3), C–C(sp2) and C–CF3 cross-coupling protocols. Our research enables facile elaboration of all cubane isomers into drug candidates, thus enabling ideal bioisosteric replacement of ortho-, meta- and para-substituted benzenes.
地球科学 Earth Science
Hadaean to Palaeoarchaean stagnant-lid tectonics revealed by zircon magnetism
锆石磁学揭示冥古宙—古太古代的滞盖构造
▲ 作者：John A. Tarduno, Rory D. Cottrell, Richard K. Bono, Nicole Rayner, William J. Davis, Tinghong Zhou, et al.
▲ 链接：
https://www.nature.com/articles/s41586-023-06024-5
▲ 摘要：
板块构造是维持地球可居住性的一个基本因素，但其开始时间尚不清楚，年代跨越冥古宙至元古代。板块运动是区分板块构造和滞盖构造的关键诊断，但古地磁测试一直受阻，因为地球上现存最古老的岩石已经变质或变形。
研究组报道了南非巴伯顿绿岩带冥古宙至中太古代的含原生磁铁矿包裹体的单一碎屑锆石的古强度数据。这些数据揭示了始太古代（约39亿年前，即3.9 Ga）到中太古代（约3.3 Ga）的古强度模式，与杰克山地区（JH，西澳大利亚）的原始磁化所定义的几乎一致，进一步证明了所选碎屑锆石的记录保真度。
此外，古场值在3.9 Ga~3.4 Ga之间几乎不变。这表明纬度不变，该观测结果不同于过去6亿年（600 Myr）的板块构造，但由滞盖对流预测。如果生命起源于始太古代，并持续到5亿年后叠层石的出现，那么生命在地球处于滞盖状态时出现，而无需板块构造驱动的地球化学循环。
▲ Abstract：
Plate tectonics is a fundamental factor in the sustained habitability of Earth, but its time of onset is unknown, with ages ranging from the Hadaean to Proterozoic eons. Plate motion is a key diagnostic to distinguish between plate and stagnant-lid tectonics, but palaeomagnetic tests have been thwarted because the planet’s oldest extant rocks have been metamorphosed and/or deformed. Herein, we report palaeointensity data from Hadaean-age to Mesoarchaean-age single detrital zircons bearing primary magnetite inclusions from the Barberton Greenstone Belt of South Africa. These reveal a pattern of palaeointensities from the Eoarchaean (about 3.9 billion years ago (Ga)) to Mesoarchaean (about 3.3 Ga) eras that is nearly identical to that defined by primary magnetizations from the Jack Hills (JH; Western Australia), further demonstrating the recording fidelity of select detrital zircons. Moreover, palaeofield values are nearly constant between about 3.9 Ga and about 3.4 Ga. This indicates unvarying latitudes, an observation distinct from plate tectonics of the past 600 million years (Myr) but predicted by stagnant-lid convection. If life originated by the Eoarchaean, and persisted to the occurrence of stromatolites half a billion years later, it did so when Earth was in a stagnant-lid regime, without plate-tectonics-driven geochemical cycling.
Krill body size drives particulate organic carbon export in West Antarctica
南极西部磷虾的体型大小决定了颗粒有机碳输出
▲ 作者：Rebecca Trinh, Hugh W. Ducklow, Deborah K. Steinberg & William R. Fraser
▲ 链接：
https://www.nature.com/articles/s41586-023-06041-4
▲ 摘要：
海洋表面的碳输出和海洋内部的碳储存对于调节全球气候非常重要。西南极半岛是世界上夏季颗粒有机碳（POC）输出速率最大的地区之一，也是全球变暖速度最快的地区之一。要了解全球变暖如何改变碳储存，有必要首先确定POC输出的模式和生态驱动因素。
研究组表明，南极磷虾（ Euphausia superba ）的体型和生活史周期对POC通量起主导作用，而非其总体生物量或区域环境因子。他们测量了超过21年的POC通量，这是南大洋最长的记录，结果发现年POC通量具有显著的5年周期性，与磷虾体型同步起伏，当磷虾种群以大型个体为主时达到峰值。
磷虾体型大小通过生产和输出大小不同的粪便颗粒来改变POC通量，这些颗粒在总通量中占主导地位。冬季海冰（磷虾的重要栖息地）减少正在引发磷虾种群的变化，这可能会改变该粪便颗粒的输出模式，并导致海洋碳储量的变化。
▲ Abstract：
The export of carbon from the ocean surface and storage in the ocean interior is important in the modulation of global climate. The West Antarctic Peninsula experiences some of the largest summer particulate organic carbon (POC) export rates, and one of the fastest warming rates, in the world. To understand how warming may alter carbon storage, it is necessary to first determine the patterns and ecological drivers of POC export. Here we show that Antarctic krill (Euphausia superba) body size and life-history cycle, as opposed to their overall biomass or regional environmental factors, exert the dominant control on the POC flux. We measured POC fluxes over 21 years, the longest record in the Southern Ocean, and found a significant 5-year periodicity in the annual POC flux, which oscillated in synchrony with krill body size, peaking when the krill population was composed predominately of large individuals. Krill body size alters the POC flux through the production and export of size-varying faecal pellets, which dominate the total flux. Decreases in winter sea ice, an essential habitat for krill, are causing shifts in the krill population, which may alter these export patterns of faecal pellets, leading to changes in ocean carbon storage.