Over recent years there has been a surge of interest in halogen bonding and in some settings it has emerged as a compelling and complementary alternative to hydrogen bonding for the purposes of self-assembly and molecular recognition. Now, Paul Beer and co-workers have shown that halogen bonding enables rotaxane-based hosts to bind anions more strongly in water than the corresponding hydrogenbonding systems. The cover shows halogen-bonding host rotaxanes binding iodide anions — mediated by iodine–iodide halogen-bonding interactions — in water.Article p1039News & Views p1029IMAGE: KARL HARRISONCOVER DESIGN: ALEX WING

Intercalation of guest molecules or ions in graphite is generally driven by host-guest electron transfer between the intercalant and the layers of carbon. Now, Thomas Mallouk and co-workers have shown that a range of Brønsted acids can form intercalation compounds with graphite without reducing, oxidizing or bonding with the graphene sheets themselves. The cover depicts a phosphoric acid-containing gallery between graphene layers, with acid-base interactions — rather than electron transfer — occurring between the acid and the carbon sheets.Article p957IMAGE: YUANXI WANGCOVER DESIGN: ALEX WING

The success of natural products and their derivatives as drugs has encouraged researchers to seek further inspiration from nature in the discovery of novel bioactive small molecules. Two Articles in this issue describe attempts to mimic aspects of natural-product biosynthesis in the preparation of diverse molecules for screening. The cover is an illustrative metaphor for the connection between nature and drug discovery. The honeycomb, prevalent in nature, represents a vast array of reactions, with the highlighted cells representing those reactions that yield products with specific biological activity.Editorial p841; Interviews p845, 846; News & Views p851; Articles p872, 877 IMAGE: ANDREY KUZMIN/ALAMYCOVER DESIGN: ALEX WING

Making 2D materials from the bottom up in a precise fashion poses significant challenges in terms of both synthesis and characterization. Now, two research groups — led by Benjamin T. King and Dieter Schlüter — have shown that 2D polymers can be formed in a single-crystal-to-single-crystal process, and each step along the way has been characterized by X-ray crystallography. On the cover is a polarized optical microscopy image of a 2D polymer single crystal made by Schlüter and co-workers, showing exfoliation of the layered structure.Editorial p747;Interview p751;News & Views p757;Articles p774779IMAGE: MICHAEL WöRLE AND MAX J. KORYCOVER DESIGN: ALEX WING

The topology of any given metal–organic framework (MOF) is typically determined after it is made, rather than being predicted before its synthesis based on the nature of the building blocks. Now, Mohamed Eddaoudi and colleagues have discovered a new MOF topology (denoted gea), and through an analysis of its components they have replicated the same connectivity in a different MOF. The cover depicts a blueprint for this (3,18) topology as well as the molecular and supermolecular building blocks (MBB and SBB, respectively) used to construct the second framework.

Article p673

IMAGE: V. GUILLERM AND M. EDDAOUDI

COVER DESIGN: ALEX WING

Proteins can adopt many conformations at room temperature, which creates a problem for those trying to find complementary ligands. Now, James S. Fraser, Brian K. Shoichet and colleagues have developed a computational method that represents the conformational behaviour of proteins in docking screens. An artistic impression of the docking of nine newly discovered ligands within a protein binding site is shown on the cover; the panels are arranged in pairs and depict either a prediction of a particular ligand-protein interaction (upper) or the corresponding crystallographic data (lower).Article p575;News & Views p560IMAGE: RYAN G. COLEMAN

Starting from a small-molecule precursor that contains a hexayne unit, Holger Frauenrath and co-workers have shown that functionalized carbon nanosheets can be made at room temperature. The amphiphilic starting material self-assembles into tightly packed monolayers at the air/water interface and the alkyne groups can be crosslinked with one another when exposed to ultraviolet light. The resulting two-dimensional carbon network (shown conceptually on the cover) contains regions of extended π-conjugation (grey shading) and retains the functional groups (red and blue circles) present in the original hexayne.

Article p468; News & Views p463

IMAGE: HOLGER FRAUENRATH, STEPHEN SCHRETTL AND SHAWN KOPPENHOEFER

COVER DESIGN: ALEX WING

The general tendency for actinides to decrease in covalency across the series indicates that californium should form ionic metal-ligand bonds. Now, Thomas Albrecht-Schmitt and co-workers have combined californium with electron-rich polyborate ligands — the coordination geometry of the resulting structure is schematically illustrated on the cover. The bonding involves the 7p, 6d and even 5f orbitals of californium, showing a surprisingly significant covalent character more akin to transition metal bonding than that expected for a late actinide.Article p387IMAGE: EVGENY ALEKSEEVCOVER DESIGN: DENIS MALLET

The dynamics of systems featuring small reaction containers and low reagent concentrations are often affected by the stochastic nature of chemical reactions. This creates both challenges and opportunities for the engineering of cell-scale molecular devices and for understanding complicated naturally occurring biochemical circuits. Now, Elisa Franco, Friedrich C. Simmel and co-workers demonstrate the encapsulation of a synthetic transcriptional oscillating reaction system into cell-sized microemulsion droplets. Great variability in the oscillatory dynamics of the system are observed, which is attributed to partitioning effects. The cover shows a filtered epifluorescence microscopy image of droplets containing the oscillating reaction system.Article p295IMAGE: MAXIMILIAN WEITZCOVER DESIGN: ALEX WING

Copolymers of ethylene and other monomers bearing polar functional groups are typically produced using harsh conditions that make any fine structural control of the resulting material quite difficult. Now, Christophe Detrembleur and co-workers have shown that an organo-cobalt complex can be used to mediate the radical copolymerization of ethylene with polar monomers such as vinyl acetate or acrylonitrile under mild conditions. This approach affords a measure of control over the monomer composition of the final product as well as the distribution of the different monomers in the polymer chain, as shown schematically on the cover.Article p179IMAGE: CHRISTOPHE LEPOTCOVER DESIGN: ALEX WING

Research by Wokyung Sung, Kimoon Kim and co-workers shows that tetraolefins with rigid aromatic cores can be reacted with dithiol linkers to produce hollow micrometre-sized polymer rings. Mechanistic studies suggest that the process begins with the formation of oligomeric patches that roll up to form nanotubes that subsequently curl around to form rings (as shown schematically on the cover). C60 can be encapsulated inside the hollow toroidal structures, which can also serve as templates for the assembly of circular arrays of silver nanoparticles.

Article p97

IMAGE: JIYEONG LEE

COVER DESIGN: ALEX WING

G-protein-coupled receptors lie across cell membranes and transmit messages from the outside of cells — initiated through ligand binding — to the inside. Molecular dynamics simulations have proved helpful in understanding how they work at an atomistic level but are very computationally intensive. Now Kohlhoff, Altman, Pande and co-workers describe an approach to performing and analysing lengthy molecular dynamics simulations, which involves the stitching together of many shorter independent simulations run using Google's Exacycle cloud computing platform. The cover shows an artistic interpretation of a view from the cell exterior of a G-protein-coupled receptor interacting with the partial inverse agonist carazolol.Article p15;News & Views p7IMAGE: THOR LEWISCOVER DESIGN: ALEX WING