Volume 6 Issue 9, September 2014

They might not be fundamental constants of nature, but atomic weights are one of the foundations on which modern chemistry is built, explains Juris Meija.

Benjamin King and Dieter Schlüter, the corresponding authors of two Articles in this issue that describe single-crystal characterization of two-dimensional polymers, talk to Nature Chemistry about the background, challenges and prospects of their work.

Directed evolution is a powerful tool for the development of improved enzyme catalysts. Now, a method that enables an enzyme, its encoding DNA and a fluorescent reaction product to be encapsulated in a gel bead enables the application of directed evolution in an ultra-high-throughput format.

Two reports demonstrate that with the right molecules and the right crystalline arrangement, it is not only possible to create two-dimensional crystals, but also to separate them into single-molecule-thick sheets — so-called two-dimensional polymers.

Intense laser fields can apply strong forces to molecules, distorting molecular potentials. Now, these effects have been used to precisely control the branching ratios of a polyatomic photodissociation reaction.

Enantiomerically pure head-to-head-to-tail triple-stranded helicates synthesized using a subcomponent self-assembly approach possess high anticancer activities against cancer cell lines without significant damage to DNA and with low toxicity to bacteria.

Halogen bonding connects a wide range of subjects — from materials science to structural biology, from computation to crystal engineering, and from synthesis to spectroscopy. The 1st International Symposium on Halogen Bonding explored the state of the art in this fast-growing field of research.

This Review draws an analogy between acid–base catalysis and redox catalysis. The 'electron is a catalyst' paradigm unifies mechanistically an assortment of synthetic transformations that otherwise have little or no apparent relationship. Various radical cascades catalysed by the electron are discussed.

Two-dimensional synthetic polymers can be produced through solid-state topochemical polymerization, but achieving this through a single-crystal-to-single-crystal transformation has not yet been demonstrated. Now, a fluorinated Y-shaped monomer has been preorganized in a lamellar crystal, which goes through two successive single-crystal-to-single-crystal phototransformations to give a 2D polymer; single-crystal X-ray diffraction has been used to elucidate its structure.

Accessing synthetic two-dimensional polymers that are analogous to graphene is synthetically and analytically challenging. Now, single crystals of a simple-to-make monomer have been grown and then photopolymerized to form layered single crystals of covalently bonded two-dimensional polymer. Much like natural graphite, these crystals can be exfoliated to form thin sheets and single layers of the polymer.

Shaping potential energy surfaces by tailored strong laser pulses has now been shown to be a powerful method for controlling product yields in an ultrafast polyatomic photodissociation reaction. Control over the velocity of the product fragments is also achieved through the generation of light-induced conical intersections and modulating the potentials around them.

Directed evolution has emerged as a powerful tool for the identification of improved enzyme catalysts. Now, gel-shell beads are introduced as compartments that cage an enzyme with its encoding DNA, constituting a new genotype–phenotype linkage. Screening of 10⁷ gel-shell beads by flow cytometry leads to an improved phosphotriesterase bioremediation catalyst.

Water-soluble metallohelices containing an antiparallel head-to-head-to-tail arrangement of strands are reported. This amphipathic functional topology is akin to that of host-defence peptides. The metallohelices show high and selective toxicity to a cancer cell line, causing dramatic changes in the cell cycle without DNA damage. In contrast, there is no significant toxicity to MRSA and Escherichia coli.

Conjugation of DNA to proteins often involves a choice between either expressing recombinant proteins with a specific handle, or labelling wild-type proteins with low site-selectivity. Now preorganization of a DNA–ligand complex to a metal-binding site enables site-selective conjugation of a DNA strand to lysine residues of wild-type proteins and antibodies.

Coupling of carbamates with boronic esters followed by protodeboronation creates a new carbon–carbon bond, leaving behind no trace of the functional groups used to create it. Now, methodology for the protodeboronation of alkyl pinacol boronic esters has been developed and an iterative lithiation–borylation–protodeboronation strategy used in a 14-step stereocontrolled synthesis of hydroxyphthioceranic acid.

Macromolecular functionalization and linking are often facilitated by using ‘click’ chemistries. Now, triazolinediones have been used in ultrafast click reactions under additive-free, ambient conditions for polymer conjugation. Clicking to indoles gives an adduct that is dynamic at elevated temperatures, which produces properties such as polymer-network healing, reshaping and recycling.

Hydrogenases are efficient and promising catalysts for fuel cells; however, they suffer from oxygen sensitivity and deactivation at high potentials. Integration of hydrogenases into redox-active hydrogels provides a redox buffer and a self-activated oxygen-scavenging mechanism. This tandem protection makes the hydrogenase a possible alternative to noble metal catalysts.

The oxygen reduction reaction limits fuel cell performance and currently requires costly electrocatalysts with high platinum content to achieve adequate power densities. Now a silver–cobalt surface alloy electrocatalyst has been developed for the oxygen reduction reaction that is stable in alkaline electrolytes and is more economical than traditional platinum-based materials.

Several solutions to the ‘missing xenon’ problem have been proposed that involve the selective sorption of Xe in minerals found in the Earth. It is now shown that a zeolite, Ag-natrolite, absorbs and retains 28 wt% Xe at 1.7 GPa and 250 °C, conditions found in subsurface Earth, through expulsion of metallic Ag(0).

Thomas Albrecht-Schmitt explains the origin of element 98's striking green glow, and why the future for californium chemistry is just as bright.

The properties of 2D materials, such as graphene, arise not only from their composition but also their sheet-like structures. Synthetic 2D polymers made from well-defined monomers promise to expand the range of such materials, but are very difficult to synthesize. A collection of articles in this Focus highlights some of the latest research in making and characterizing single-crystal synthetic 2D polymers, and also considers the challenges and potential for these materials in the future.