Radioisotopes can be very challenging to study because of their scarcity, rapid decay, toxicity or cost. Now, a team led by Gauthier J.-P. Deblonde has shown that only microgram quantities of these isotopes are required to generate radioisotope–polyoxometalate (POM) complexes that can be both spectroscopically and structurally characterized. The image on the cover shows a photograph, taken under ultraviolet light irradiation, of single crystals in crystallography oil of complexes between the rare radioactive 248Cm isotope and polyoxotungstate ligands.

See Colliard et al.

Topologically interesting cyclic polymers can be prepared by metathesis polymerization, but their precise synthesis has suffered from the catalyst’s vulnerability and inseparability. Now, Tae-Lim Choi and colleagues have designed a silica-supported ruthenium catalyst to overcome these limitations. With the help of customized glassware (a cyclic polymer dispenser), the use of this quarantined catalyst enables a continuous circular process of in situ polymerization, polymer separation, and catalyst recovery, giving a scalable process for the synthesis of cyclic polycyclopentene. The cover shows cyclopentene monomers undergoing ring-expansion metathesis polymerization to form cyclic polymers.

See Yoon et al.

During intermolecular Coulombic decay (ICD), photoexcited molecules relax while ionizing their neighbouring molecules. This is usually observed in weakly bound systems — such as clusters and hydrogen-bonded systems — because ICD is efficient when intermolecular interactions are active. Now Sajeev, Aravind and colleagues have shown that ICD can occur between unbound pyridine molecules excited at ambient-light intensities, implying that soft ionization could occur naturally in astrophysical environments that feature such molecules with π-electron systems. The cover depicts this process occurring.

See Barik et al.

Realizing sustainable plastics requires cost-effective production from renewable feedstocks, good materials properties and end-of-life recycling options. Now, a team led by Jeremy S. Luterbacher has taken advantage of the natural structure of sugars to create polymers that may meet these stringent criteria. Trapping the cyclic and oxygen-rich structure of carbohydrates (shown as a white chemical structure on the cover) within the backbone of these materials dramatically simplifies the production from nonedible biomass, leads to useful properties, enables closed-loop chemical recycling from mixed-plastic waste streams and provides a degradation route back to sugars in the presence of water. The 3D-printed leaf shown on the cover is made from this thermoplastic.

See Maker et al.

Macrocycles made up of para-linked phenylene rings (the [n]CPPs) have attracted the attention of researchers because their unique conjugated structures result in interesting physical properties. Their strained topology makes it difficult to extend the aromatic system, but now a team led by Andreas Görling, Konstantin Y. Amsharov and Sabine Maier have shown that a planar π-extended [12]CPP can be produced using a bottom-up on-surface synthesis approach. The resulting nanographene macrocycle, shown on the cover of this issue, features an all-armchair edge, which leads to delocalized electronic states around the entire ring.

See Xiang et al.

The magnetic switching capabilities of transition-metal spin-crossover (SCO) complexes show potential as multifunctional switches for applications in information storage and processing. However, the photo-induced spin-crossover behaviour of Fe(II) complexes is not fully understood and thus not fully exploited. Now, using ultrafast circular dichroism spectroscopy, a symmetry-breaking twisting mode has been observed during the high-spin-state relaxation of FeII(4,4’-dimethyl-2,2’-bipyridine)3 — this molecule is shown on the cover undergoing photoexcitation. The relaxation of the high-spin state is also shown to be retarded through control of its configuration using enantiopure counterions.

See Oppermann et al.

Stability issues currently prevent the practical application of nickel-rich layered oxides as cathodes in next-generation lithium batteries. Now, Kang, Park and colleagues have studied the solid-state synthesis of LiNi0.6Co0.2Mn0.2O2 (NCM622) using multiscale in situ techniques and show that kinetic competition between precursor decomposition and lithiation leads to spatially heterogeneous intermediates and the formation of detrimental defects. The image on the cover depicts the heterogeneous intermediates captured during the synthesis of NCM622 from a precursor mixture of transition-metal hydroxides and lithium hydroxides. The lithium atoms are shown as blue spheres, transition-metal atoms (Ni, Co and Mn) as brown spheres, and hydrogen and oxygen atoms are white and red, respectively.

See Park et al.

Photocatalysis is often limited by the molecular integrity of the photocatalyst and although instability can be managed by replacing the inactive photocatalyst with a new one, repairing the damaged system can be a more cost-effective strategy. Now, Rau, Dietzek-Ivanšić and colleagues have shown that a hydrogen-evolving photocatalyst that contains photoactive and catalytic components connected by an aromatic bridging ligand can be repaired. The bridge is inactivated through hydrogenation, which inhibits intramolecular electron transfer and prevents the system functioning as a photocatalyst. The inactivated bridge can be repaired by reoxidation, however, which restores the photocatalytic function. The cover depicts the photocatalyst working as desired on the left and undergoing bridge repairs on the right.

See Pfeffer et al

Two-dimensional layers of boron atoms have been grown on a variety of surfaces, typically noble metals. Borophene sheets can form different polymorphs with different properties, which is attractive for applications, but for practical use larger flakes with weaker metal–substrate interactions are required. Now, Rongting Wu, Sohrab Ismail-Beigi, Ivan Božović and co-workers have synthesized micrometre-scale single-crystalline borophene on a square-lattice Cu(100) surface. The cover image depicts a continuous transition from the experimental scanning tunnelling microscopy (STM) topography, to the simulated STM image, to the atomic model of this borophene polymorph that adopts a rectangular unit cell.

See Wu et al.

Understanding and controlling the rate at which electrons are transferred across solid–liquid interfaces is critical to developing efficient processes for the interconversion of electrical and chemical energy. Now, Bediako and colleagues have shown that the interfacial electrochemical kinetics of two stacked layers of graphene can be modified by varying the ‘twist’ angle between them, with the greatest enhancement observed near the ‘magic angle’ (~1.1°). The cover depicts an artistic representation of electron transfer from twisted bilayer graphene to Ru(NH3)6 3+ — the redox-active molecule used in these studies.

See Yu et al.

Discovering ligands that modulate the function of biomolecules can be achieved by using DNA-encoded libraries that link the function of a synthetic molecule to an amplifiable nucleic acid tag. Such technologies do not make full use of the principles of Darwinian selection, but now a team led by Nicolas Winssinger has developed a strategy to assemble libraries of macrocyclic-like structures (Dsuprabodies) that undergo iterative cycles of selection, amplification and diversification. The method was validated with selections against streptavidin and used to discover a potent and selective binder for the protein PD-L1. The cover image shows an artistic representation of a suprabody interacting with PD-L1.

See Vummidi et al.

Carbapenems, like meropenem, are antibiotics that are commonly used to treat serious Gram-negative infections. They are, however, prone to hydrolysis by metallo-β-lactamases (MBLs). A multidisciplinary team led by Jürgen Brem and Christopher J. Schofield have now shown that indole-2-carboxylates are inhibitors of MBLs and can restore the in vivo activity of meropenem. These inhibitors show minimal in vivo toxicity and are, therefore, promising candidates for clinical development. The cover image depicts an indole-2-carboxylate binding to an MBL.

See Brem et al.