Volume 5 Issue 2, February 2013

A new biocompatible near-infrared fluorescent probe enables super-resolution imaging of cellular proteins in live cells using a range of different labelling techniques.

The ability of the water surface to donate or accept protons critically influences vital processes in chemistry and biology, but intense disagreement persists regarding this property. Researchers show new evidence that the air side of the air/water interface is more basic than the aqueous one.

Comparing how cyclopropanated polymers with different backbones behave when stretched with an atomic force microscope reveals that it is not only the strained rings that influence the mechanochemical response, but that the structure of the polymer backbone itself is far from innocent in this regard.

No longer held in Bürgenstock or the preserve of stereochemists, the Bürgenstock conference on stereochemistry is much more than its name suggests. The diverse range of subjects discussed at the meeting highlights the fundamental importance of chemistry in other scientific disciplines ranging from molecular biology to materials science.

It is well known that donation of electron density from a metal atom back into an empty orbital on a coordinating ligand, such as an alkene, weakens the π bond. Now, it has been shown that in a metal–diborene complex, π-backdonation involves bonding π-orbitals on the ligand and leads to B–B bond strengthening.

Selective gas uptake in zeolites often relies on size — hosts accommodate guests that are small enough to fit into their pores. Now, a zeolite containing cations that function as molecular trapdoors allows guest-selective, size-inverse separations that could help with carbon capture and hydrogen purification.

Creating useful feedstocks from methane is impeded by over-oxidation when O₂ is used as the oxidant. Now, gaseous sulfur has been shown to be a promising 'soft' oxidant for the selective conversion of methane to ethylene.

An artificial transfer hydrogenase, based on the incorporation of a biotinylated iridium-piano-stool complex in streptavidin, is shown to be fully compatible with a range of biocatalysts. The location of the active metal centre inside the protein scaffold efficiently prevents mutual inactivation processes and enables the concurrent interplay with oxidative enzymes.

Combinations of enzymatic and chemo-catalysis can result in powerful synthetic transformations. Here, encapsulation of Au(I) or Ru(II) within a supramolecular assembly prevents diffusion of the organometallic complexes into solution where they can compromise the activity of an enzyme. This strategy has been applied to tandem reactions employing supramolecular host–guest complexes and enzymes in the catalysis of organic transformations.

The oxidation of methane to create useful feedstocks is hampered by over-oxidation when using O₂. Now a process using gaseous sulfur as a ‘soft’ oxidant for selective conversion to ethylene over metal sulfide catalysts has been developed. Simulations show that both methane activation and ethylene selectivity is linearly correlated with catalyst metal-sulfur bond strength.

Polymer mechanochemistry can trigger a wide range of often unanticipated reactivity, but the focus of these systems typically falls on the structure of the mechanophore rather than the intervening polymer backbone. Now, it has been shown that a poly(norbornene) backbone has a substantial impact on a mechanochemical ring-opening reaction, despite having only a minor effect on the force-free reaction.

A form of π backbonding is observed in a π-diborene complex of platinum, and confirmed by calculations. This interaction partially fills a bonding π orbital on the diborene ligand, strengthening the B–B bond. That π backbonding can strengthen bonds overturns ingrained notions that π backbonding is exclusively a bond-weakening phenomenon.

The development of a catalytic, mild and atom-economical transformation of alcohols to carboxylic acid salts and hydrogen gas is described. The reaction uses water as a source of oxygen, with a homogenous Ru catalyst at low (0.2 mol%) catalyst loadings in basic aqueous solution.

A hydrindanone-based approach to yohimbinoid natural products has been developed. A judicious choice of reaction conditions — inspired by prior work by the Stork group — allows effective control of the stereochemistry at C3 of the yohimbinoid skeleton. This approach has resulted in the first total syntheses of the C3 epimeric natural products venenatine and alstovenine.

Fluorescent probes for bioimaging need to exhibit bright fluorescence, be biocompatible and offer several alternatives for attachment to biomolecules of interest. Here, a near-infrared silicon–rhodamine fluorophore is introduced that can be coupled to intracellular proteins in live cells and tissues and can be exploited for super-resolution microscopy.

Pyrroles are a highly important class of compounds with a wide variety of applications in biochemistry, pharmacy and materials science. Here, an iridium-catalysed synthesis of pyrroles is described, starting from renewable resources, alcohols that may be derived from lignocellulosic feedstocks and amino alcohols. The reaction proceeds by a condensation reaction that liberates two equivalents of hydrogen gas.

Katharina M. Fromm relates how barium and its ores went from a magical, glowing species that attracted witches and alchemists to components in a variety of compounds that are key parts of modern life.