Nitrogen dioxide is a significant air pollutant and although abatement processes exist, they typically use precious metal catalysts, toxic ammonia and high temperatures. Now, Martin Schröder, Sihai Yang and co-workers have prepared a zinc-based metal–organic framework (MOF) that captures NO2 and promotes its quantitative conversion to HNO3 — an important feedstock for fertilizer production — upon exposure to water. The cover image shows a stylized illustration of NO2 trapped as N2O4 dimers within the pores of the MOF. The MOF can also be fully regenerated by heating and can be reused over ten consecutive cycles.

See Li et al

Prenylated indole alkaloids, such the malbrancheamides, are an important class of secondary metabolites that exhibit potent biological activity. Now, a team led by David H. Sherman and Robert M. Williams have elucidated the complete biosynthetic pathway by which these natural products are made. The synthesis proceeds through a zwitterionic intermediate that undergoes an enantioselective cycloaddition catalysed by the bifunctional enzyme MalC, which acts as both an NADPH-dependent reductase and a Diels–Alderase. The cover image depicts the formation of the bicyclo[2.2.2]diazaoctane scaffold.

See Dan et al

Colibactin is a bacterial genotoxin that is thought to be involved in the formation of colon tumours, as well as enhancing the progression of colorectal cancer by inducing DNA double-strand breaks. The exact species involved in this toxicity and the underlying chemistry have, however, remained controversial. Now Wenjun Zhang, Pei-Yuan Qian and co-workers have identified a macrocyclic colibactin metabolite that can cause double-strand breaks in DNA through a copper-mediated oxidative mechanism. The cover image depicts a stylized representation of this bacterial metabolite cutting DNA.

See Mao et al

It is likely that the volcanic nature of the early Earth meant that liquids were highly saturated with gases and that gas bubbles were common. Now, Dieter Braun and co-workers suggest that gas bubbles subjected to a temperature gradient could have been important sites for the emergence of chemical systems and reaction networks, which could have eventually led to life. Braun and the team showed that molecules aggregate at the gas–water interface and that the accumulation of metal ions and biomolecules can lead to enhanced catalytic activity. The front cover depicts gas bubbles being released in an early-earth ocean.

See Morasch et al

Super-resolved fluorescence microscopy can only interrogate entities that fluoresce. Now, a technique developed by Peng Chen and co-workers that is based on a competition strategy enables quantitative super-resolution visualization of nonfluorescent processes. The cover image is an artistic representation — based on such imaging — showing a single catalyst particle with 12 different degrees of competition between a target nonfluorescent reaction and an auxiliary fluorescent reaction.

See Mao et al

A wide range of fractal objects — such as plants, lungs and snowflakes — exist in nature. Fractal topologies are statistically self-similar over multiple length scales, and possess a high surface area-to-volume ratio, which can provide functional advantages for processes such as molecular trapping and exchange. Now, Sagar D. Khare and co-workers have developed a computationally guided design approach for constructing protein-based fractals. Using engineered proteins as the basic building blocks, the team created fractal structures that assemble in response to phosphorylation. The cover of this issue shows the fractal assemblies imaged using helium ion microscopy.

See Khare et al

The photoinduced ring-opening of 1,3-cyclohexadiene is a prototypical electrocyclic reaction and also provides a model system for understanding photobiological vitamin D generation. Now, Wolf, Wang, Minitti, Martínez and co-workers have used ultrafast electron diffraction to resolve its reaction pathway on the femtosecond timescale and sub-ångström length scale. The cover image is an artist’s visualization of this reaction, showing the photochemical ring-opening of the reactant (top) and the subsequent oscillatory motion between different isomers of the photoproduct 1,3,5-hexatriene.

See Wolf et al

Thiols and phosphines are typically used as ligands to stabilize atomically precise gold nanoclusters, but it has now been shown that N-heterocyclic carbenes (NHCs) can also be used to impart stability to these structures. Hannu Häkkinen, Tatsuya Tsukuda, Cathleen M. Crudden and co-workers have demonstrated that NHC-modified gold nanoclusters can be prepared by simple displacement reactions of phosphines. The addition of a single NHC ligand results in a gold cluster with significantly better stability and improved electrocatalytic performance in the reduction of CO2 to CO (a process shown schematically on the cover of this issue).

See Narouz et al.

This issue marks the 10th anniversary of the launch of Nature Chemistry. The cover features some of our favourite covers from the last decade, including one from each volume of the journal.

See Editorial

The biological function of many proteins requires their assembly into a specific multi-protein structure. Designing artificial protein assemblies is difficult, however, and often relies on the precise redesign of protein–protein interfaces. Now, David W. Taylor, Andrew D. Ellington and colleagues have shown that supercharging green fluorescent protein enables variants of alternating net charge to assemble into a variety of well-defined architectures. The front cover shows a symmetrical 16-mer structure composed of two stacked rings of octamers.

See Simon et al

The ability of some crystalline porous coordination polymers (PCP) to undergo guest-induced reversible structural changes is of great interest for practical applications such as guest separation and storage. Now, using liquid-phase atomic force microscopy, a team led by Nobuhiko Hosono and Susumu Kitagawa has imaged structural transformations occurring at the crystal–solvent interface of a PCP. The surface (illustrated on the cover) was shown to be more flexible than anticipated. It undergoes a sharp, reversible transition between tetragonal and rhombic lattices in the absence and presence of biphenyl guest molecules — even at guest concentrations that are too low to trigger structural transformations of the bulk crystal.

See Hosono et al

The United Nations has proclaimed 2019 to be the International Year of the Periodic Table of Chemical Elements, to coincide with the 150th anniversary of the formulation of this iconic chart. Dmitri Mendeleev is widely credited as the main architect of what has now become the modern periodic table, which has evolved significantly since its inception in 1869. Nevertheless, it represents the collective work of the many scientists who have worked on better understanding the structure and behaviour of a growing number of elements, and on classifying them accordingly. We celebrate the periodic system in this issue with a collection of articles that explore elements of the table.

See Focus