Understanding the mechanism of photoinduced DNA damage is important for identifying the molecular origins of diseases caused by light and for the use of light in photodynamic therapies. The one-electron photo-oxidation of guanine is known to be a key process in photoinduced DNA damage when using ruthenium polypyridyl complexes as photosensitizers, however, its dynamics are yet to be fully understood. Now, Christine Cardin, John Kelly, Susan Quinn and colleagues have used a combination of ultrafast time-resolved infrared spectroscopy and X-ray crystallography to study this process, succeeding in defining both the geometry of the reaction site and the rates of individual steps. Ruthenium photosensitizers (orange spheres) bound to DNA are shown on the cover.Article p961IMAGE: JAMES P. HALL AND CHRISTINE J. CARDINCOVER DESIGN: KAREN MOORE

Short amphiphilic foldamers featuring an oligourea backbone with typical amino-acid side chains have been shown to self-assemble in water to form well-defined three-dimensional structures. By changing the sequence of the oligoureas — and hence the arrangement of different side chains when folded into a helical conformation — Gilles Guichard and co-workers are able to programme the system to form either discrete helical bundles containing isolated cavities, or pH-responsive water-filled channels with controllable pore diameters (an example of the latter is shown conceptually on the cover).Article p871;News & Views p858MAIN IMAGE: GAVIN W. COLLIE, CAMERON MACKERETH AND GILLES GUICHARD BACKGROUND IMAGE: AUIMEESRI/THINKSTOCK/ISTOCKCOVER DESIGN: KAREN MOORE

Sometimes it's just as important to break chemical bonds as it is to make them and one area in which this is particularly true is degradable polymers. In a Review Article in this issue, Vianney Delplace and Julien Nicolas discuss approaches to the synthesis of vinyl polymers that can be partially or completely degraded and consider the potential for such materials in biomedical applications.Review Article p771 IMAGE: JULIEN NICOLASCOVER DESIGN: KAREN MOORE

Chemists strive to control the outcome of reactions and it was recently shown that the efficiency of photo-induced electron transfer in a donor–bridge–acceptor compound can be significantly altered by exciting intramolecular vibrations using infrared light. Now, continuing their work on this topic, Anthony Meijer, Julia Weinstein and colleagues have extended and generalized the understanding of this phenomenon by studying its occurrence in several different molecules. The excited-state dynamics of these molecules were monitored using time-resolved infrared (TRIR) spectroscopy and the background of the cover image features a two-dimensional map of a portion of their TRIR data.Article p689News & Views p683IMAGE: M. DELOP ET AL. AND VERTEBRATEGRAPHICS COVER DESIGN: KAREN MOORE

Arynes have been proposed as intermediates in certain chemical transformations for more than a century. Their existence has been confirmed spectroscopically but their short lifetimes and high reactivities present a challenge to their characterization. Now, Niko Pavliček, Diego Peña and colleagues have demonstrated the generation and direct visualization of individual polycyclic aryne molecules on a surface using low-temperature scanning tunnelling microscopy and atomic force microscopy. The molecule shown on the cover is 10,11-diiodonaphtho[1,2,3,4-g,h,i]perylene.Article p623IMAGE: NIKO PAVLICEK, IBM RESEARCH-ZURICHCOVER DESIGN: KAREN MOORE

The accuracy of hybridizationbased approaches for analysing nucleic acids is limited by a probe's specificity — as well as binding the intended target, closely related sequences may also be captured. Now, Juexiao Sherry Wang and David Yu Zhang have shown that simulations of binding kinetics can be used to guide the design of competitive hybridization-probe systems that are highly selective for specific single-nucleotide variants. With this approach, they have developed probes that, when combined with PCR amplification, can detect variant alleles at concentrations as low as 1% in human genomic DNA.Article p545IMAGE: CINDY THAUNGCOVER DESIGN: KAREN MOORE

If one of the hydrogen atoms on each carbon of a cyclohexane ring is replaced with a fluorine atom, it is possible to produce nine different isomers of 1,2,3,4,5,6-hexafluorocyclohexane. The highest-energy isomer is one in which all six fluorines are located on the same face of the cyclohexane ring. Now, a team of researchers at the University of St Andrews led by David O’Hagan have made this all-cis isomer in a 12-step procedure starting from myo-inositol. This facially polarized hydrofluorocarbon is predicted to have a high molecular dipole (μ = 6.2 D), the largest identified so far for any aliphatic or aromatic organic compound that is not ionic.Article p483;News & Views p467IMAGE: NEIL S. KEDDIECOVER DESIGN: KAREN MOORE

The self-assembly of ordered molecular arrays on surfaces has received a lot of attention, but fractals are particularly challenging patterns to replicate. Now, a team of researchers led by Yongfeng Wang, Michael Gottfried and Kai Wu have shown how bent oligophenyls with a bromine atom at each end can selfassemble into Sierpinski triangle fractals on a silver surface (as shown on the cover). A combination of hydrogen bonding and halogen bonding between the adsorbed molecules guides the formation of the fractal structures, along with other factors such as molecule—substrate interactions and the temperature of the system.Article p389News & Views p370IMAGE: KAI WUCOVER DESIGN: KAREN MOORE

DNA nanotubes are attractive scaffolds for the assembly of complex arrays, and there is great interest in controlling their polydispersity and the sequence of rungs along their backbone. Now, Hanadi Sleiman, Gonzalo Cosa and co-workers have devised a solid-state synthesis to produce surface-grafted robust DNA nanotubes. Different rungs can be incorporated in a stepwise manner and each one is individually addressable. As shown on the cover, each rung is tagged with a fluorescent dye to enable visualization of nanotube growth at the single-molecule level.Article p295IMAGE: MELANIE BURGERCOVER DESIGN: KAREN MOORE

Complex terpene natural products are assembled in nature by reaction cascades that occur inside enzyme pockets that stabilize the cationic intermediates and transition states. Now Qi Zhang and Konrad Tiefenbacher have successfully mimicked this process inside a supramolecular assembly. As shown on the cover, six resorcinarene monomers self-assemble to form a cavity that can encapsulate a geranyl acetate substrate and catalyse its conversion to a variety of cyclic monoterpene natural products.Article p197; News & Views p187IMAGE: JOHANNES RICHERSCOVER DESIGN: ALEX WING

Metal-organic frameworks (MOFs) have attracted increasing attention for the uptake and separation of hydrocarbon mixtures in an effort to develop more efficient industrial processes and routes to cleaner energy. To better understand how hydrocarbons bind in the pores of a particular MOF (NOTT-300), Sihai Yang, Martin Schröder and co-workers have combined scattering and diffraction studies with computational modelling — a visualization of the mobility and binding dynamics of acetylene, ethylene and ethane guests is shown on the cover. It is found that NOTT-300 selectively binds unsaturated hydrocarbons through cooperative supramolecular interactions, but only interacts weakly with ethane.Article p121IMAGE: HAN XUE AND SIHAI YANGCOVER DESIGN: ALEX WING

Some short peptides are known to self-assemble into well-defined nanostructures that may prove useful in applications ranging from food and cosmetics to biomedicine and photonics. Now, Rein Ulijn, Tell Tuttle and co-workers have used a computational approach to predict the self-assembly properties of all 8,000 tripeptides that can be made from the 20 canonical amino acids (as shown conceptually on the cover — the background image is a matrix that represents the aggregation propensity of each tripeptide). The most promising candidates were then studied experimentally, leading to the discovery of new tripeptide hydrogelators (such as KYF) that do not contain protecting groups. Scrabble © JHPhoto/AlamyArticle p30; News & Views p14IMAGE: PIM FREDERIX AND TELL TUTTLECOVER DESIGN: ALEX WING