Complex chemical reaction networks can be used to form macroscale patterns, but it is very difficult to program such systems to generate reproducible patterns. Now Xi Chen, Andrew D. Ellington and co-workers have created reaction networks based on DNA that can be programmed to transform an input pattern (ultraviolet light) into an output image (fluorescence). The cover image shows a compilation of different two-channel output patterns that were all generated from the same input using 16 different pattern-transformation networks. Article p1000; News & Views p986

IMAGE: STEVEN CHIRIELEISON

COVER DESIGN: ALEX WING

The decoration of surfaces with nanoparticles is typically achieved through deposition, but now John Irvine and co-workers describe a method that gives improved control over particle size, distribution and surface anchorage. They grow nanoparticles at the surface of perovskites through exsolution from the materials' backbones, using variations in non-stoichiometry to tune their properties. The cover shows the scanning electron micrograph of such a surface, in which the metallic nanoparticles have been highlighted with an artificial green colour.Article p916IMAGE: DRAGOS NEAGUCOVER DESIGN: ALEX WING

The cover image shows an artistic impression of large single crystals comprising covalent organic networks. A team led by James Wuest made these materials through the reversible polymerization of organic monomers bearing four tetrahedrally oriented nitroso groups and characterized them using single-crystal X-ray diffraction. Such a modular construction is typically used to build monocrystalline materials held together by non-covalentbonding interactions, but is now also shown to work for covalently bonded analogues.

Article p830; News & Views p810

IMAGE: SOPHIE DUBOIS ONCE UPON A TIME IN THE LAB (ORIGINAL PAINTING: ACRYLIC ON CANVAS, 2012).

COVER DESIGN: ALEX WING

Graphene is a two-dimensional carbon material that has captured the attention of scientists from many different disciplines. Now, Lawrence Scott, Kenichiro Itami and co-workers have made and isolated discrete nanographene compounds that are highly warped because of the inclusion of odd-membered rings. The distortion from planarity of these polycyclic aromatic hydrocarbons perturbs both the optical and electronic properties in comparison with flat systems of a similar size, and they could serve as models to better understand the effect of non-hexagonal defects on the characteristics of larger graphene sheets.Article p739;News & Views p730IMAGE: K. KAWASUMI, Q. ZHANG, Y. SEGAWA, L. T. SCOTT AND K. ITAMI

Antibiotic–resistant bacteria are an increasingly important public health concern and the development of new antibiotic drugs — particularly those that act by new mechanisms — is thus of great importance. Now, Benjamin Davis, Hagan Bayley and co-workers have used a single-molecule electrochemical technique to identify potential blockers of the channel-forming proteins that export capsular polysaccharides, which form part of the bacterial defence system, from the cell. The cover image shows the eight-fold symmetrical cyclodextrinbased inhibitor binding to the octameric channel-forming protein.

Article p651; News & Views p642

IMAGE: LEON HARRINGTON AND LINGBING KONG

COVER DESIGN: ALEX WING

The extent to which protein motions can affect the chemical step of an enzymatic reaction has caused heated debate in recent times. Now, J. Javier Ruiz-Pernía, Iñaki Tuñón and colleagues describe how free-energy surfaces obtained as a function of both a chemical coordinate and an environmental coordinate can be used to explore the role of structure and motion on enzyme chemistry. They studied an SN2 nucleophilic reaction catalysed by a haloalkane dehalogenase from Xanthobacter autotrophicus; the enzyme is schematically represented on the cover.Article p566IMAGE: CARLOS GARCIA-MESEGUERCOVER DESIGN: ALEX WING

The self-assembly of materials is driven by many competing processes. Christopher Murray, Sharon Glotzer and colleagues have now experimentally and computationally studied the self-organization of thin lanthanide fluoride nanoplates at the liquid/air interface. Various twodimensional planar tilings are observed and a simulated example of one such pattern can be seen on the cover. The assembly behaviour can be understood by considering both the directional attractions between the particles, which are caused by patchy ligand coverage, and their shape.

Article p466

IMAGE: MICHAEL ENGEL, JAIME A. MILLAN, SHARON C. GLOTZER (UNIV. MICHIGAN)

COVER DESIGN: ALEX WING

Chemical reactions that proceed inside molecular capsules are often studied in solution. In the gas phase, the energy necessary to trigger inner-phase reactions typically results in the host–guest complex dissociating before the reaction occurs. Now, a team led by Elina Kalenius and Werner Nau have used mass spectrometry to study thermally activated retro-Diels–Alder reactions of guest molecules inside cucurbituril hosts in the gas phase. The cover picture conceptually shows the fate of a macrocyclic complex, from its formation, subsequent cycloelimination of the encapsulated guest, to the extrusion of a fragment.Article p376IMAGE: K. I. ASSAF, R. N. DSOUZA & H. OLSENCOVER DESIGN: ALEX WING

Andrew Cooper and co-workers have shown that porous solids made from molecular organic cages can separate structural isomers of simple aromatic compounds. The host–guest properties of the discrete organic cages in solution (as illustrated conceptually on the cover in the beaker) correlate with the solid-state behaviour (as shown above the beaker). The shape-sorting selectivity arises from the intrinsic structure of the cage-like building blocks, suggesting that different cages could be designed to separate other feedstocks.

Article p276

IMAGE: KIM JELFS AND SAM CHONG

COVER DESIGN: ALEX WING

Robin Hochstrasser and colleagues have used vibrational spectroscopy, X-ray crystallography and simulations to study the role of water in the binding of the anti-AIDS drug rilpivirine to HIV-1 reverse transcriptase. The cover shows a snapshot (taken from molecular dynamics simulations) of rilpivirine within the binding pocket; the carbon, nitrogen, oxygen and hydrogen atoms are shown in cyan, blue, red and white, respectively, and the green surface represents the protein and other associated water molecules. The purple atoms are the nitrogens of the nitrile groups that are used as infrared probes.Article p174;News & Views p152IMAGE: DANIEL G. KURODACOVER DESIGN: ALEX WING

The complementary catalytic reactivities of enzymes and transition-metal complexes often hint at the possibility of useful cascade reactions, but these two classes of catalyst often inactivate one another. A team of researchers from the UK, the Netherlands and Switzerland now report a solution to this important problem, which involves anchoring a metal complex inside a host enzyme (as shown on the cover) to produce a metal catalyst that is compatible with natural enzymes.Article p93IMAGE: CREATED BY V. KöHLER USING PyMOL v.1.3 (SCHRöDINGER LCC); based on PDB ID: 3PK2, M. Dürrenberger et al. Angew. Chem. Int. Ed. 50, 3026–3029 (2011)COVER DESIGN: ALEX WING

The proton-coupled redox reactions of a class of expanded porphyrins known as rosarins have been studied by an international collaboration between researchers based in Korea, Japan, the USA and India. A near-planar 24 π-electron antiaromatic rosarin is reduced in a stepwise manner when treated with HI to first give a non-aromatic 25 π-electron system and then a 26 π-electron aromatic species. Artistic representations of the ortho-phenylene-bridged rosarin used in this study are repeated in the central window of the image shown on the cover.Article p15IMAGES: CATHEDRAL © ISTOCKPHOTO.COM/THINKSTOCK; ROSARIN © ANGEL SYRETTCOVER DESIGN: ALEX WING