Chemical Science Blog

Scientists in Australia, China and Canada have made new photocatalysts that, in the presence of sunlight, can oxidise stable compounds such as toluene using oxygen at room temperature. Oxidation of toluene to commercial chemicals is a major industrial process, but it is conducted under high temperatures and oxygen pressures, or requires recovery of homogeneous cobalt catalysts.

The new photocatalysts work via a mechanism that is different from those of any known photocatalysts: the surface complexes are anchored on the surface of metal hydroxides by chemical bonds and can absorb light generating free radicals on the surface. These then initiate aerobic oxidation of the stable alkyl aromatic molecules. So, they can use sunlight to drive the production of fine organic chemicals in an efficient, green and chemoselective manner.

Link to journal article
Driving Selective Aerobic Oxidation of Alkyl Aromatics by Sunlight on Alcohol Grafted Metal Hydroxides
S Sarina et al
Chem. Sci., 2012, DOI: 10.1039/c2sc20114c

Systems chemistry focuses on achieving controllable outputs from the interactions and reactions of a mixture of chemical components. In this way, researchers hope to mimic biological systems, which utilise highly complex series of interconnected signalling processes and feedback loops to respond to a wide range of external stimuli.

Christoph Schalley’s group in Berlin have reported a fascinating example of supramoleular systems chemistry, using a range of non-covalent interactions and self assembly properties of a simple bis-urea starting molecule. Like many bis-ureas, 1 was found to form an organogel due to hydrogen bonding interactions between the urea groups on adjacent molecules. Disrupting these interactions reverses the gel formation, leaving a sol phase. In this case, the authors found three different chemical input signals to switch the gel to a sol: adding chloride anions to hydrogen bond to the urea groups, adding potassium cations to bind within the crown ether groups, and by adding the ammonium threads 2 (2 equivalents) or 3 (1 equivalent) to form a rotaxane.

Each of these binding processes can also be reversed by chemically removing the guest, regenerating the gel phase. Silver cations were used to precipitate the chloride, a cryptand was added to tightly bind to the potassium, and the rotaxane threads were deprotonated using a base. In this way, a large number of input signals were used to yield a controllable and observable chemical property. These processes were used to construct various logic gates, in which a logic output (the formation or dissolution of a gel phase) resulted from one or more logic inputs (the addition of one or more of the above reagents).

This work uses host guest chemistry to produce real-world, observable results from a large number of chemical input signals. It is an inspiring example of how simple binding processes can be incorporated into complex sequences and systems. You can download the full article here.

Scientists in Japan and Germany have made the first efficient catalyst to enable the synthesis of hindered heterobiaryls by direct C–H coupling.  Hindered biaryls have numerous applications such as catalysts/ligands for asymmetric synthesis and chiral materials, and are often found in biologically active natural products.

Link to journal article
Hindered Biaryls by C-H Coupling: Bisoxazoline-Pd Catalysis Leading to Enantioselective C-H Coupling
K Yamaguchi et al
Chem. Sci., 2012, DOI: 10.1039/c2sc20277h

Scientists in Spain and Italy have used simple and cheap wet lithography to generate highly electrical conductive structures located upon demand on technologically relevant surfaces. The team tested the materials as electrodes in organic field‐effect transistor devices and they say it opens the way to a broad range of potential applications, such as molecular sensors.

Link to journal article
Patterned conductive nanostructures from reversible self-assemble of 1D coordination polymer
D Gentili et al
Chem. Sci., 2012, DOI: 10.1039/c2sc00029f

A highly efficient scandium-catalysed asymmetric epoxidation reaction with hydrogen peroxide as the oxidant has been developed by researchers in China. The Sc(OTf)₃ complex enabled epoxidation of a wide range of alpha,beta-unsaturated ketones and amides in overall excellent yields and enantioselectivites.

The reaction is also compatible with dilute aqueous hydrogen peroxide, increasing the safety and practicality of current reactions.

Link to journal article
Asymmetric Catalytic Epoxidation of alfa, beta-Unsaturated Carbonyl Compounds with Hydrogen Peroxide: Additive-Free and Wide Substrate Scope
Y Chu et al
Chem. Sci., 2012, DOI: 10.1039/c2sc20218b

Cyanine dyes have been widely used for fluorescent sensory applications in both industry and academia. However, they are limited by drawbacks such as a small Stokes shift (up to 20nm) and concentration quenching effect.

Scientists in China have now designed a red emissive hemicyanine dye that overcomes these drawbacks. The dye possesses a large Stokes shift (>185nm) and shows different colours and intensities over a broad pH range (pH 5-14).

The acid/base-switched red/blue emission transition is reversible and can last for many cycles.

Link to journal article
An AIE-active hemicyanine fluorogen with stimuli-responsive red/blue emission: Extending the pH sensing range by “switch + knob” effect
S Chen et al
Chem. Sci., 2012, DOI: 10.1039/c2sc01108e

Scientists in the US have developed a way to detect and differentiate between mixtures of plasticisers within plastic explosives such as Semtex and C4 to provide information for anti-terrorism activities.

The team bound a fluorescent indicator to a plasma protein, which then binds to the plasticisers. A cross-reactive array was used to reveal which plasticisers were present in the explosive mixtures.

Link to journal article
Exploration of Plasticizer and Plastic Explosive Detection and Differentiation with Serum Albumin Cross-Reactive Arrays
M A Ivy et al
Chem. Sci., 2012, DOI: 10.1039/c2sc20083j

Scientists in China have shown that their N-rich zeolite-like metal-organic framework shows high CO₂ uptake, selective gas adsorption and efficient drug delivery.

Find out more:
N-rich zeolite-like metal-organic framework with sodalite topology: high CO₂ uptake, selective gas adsorption and efficient drug delivery
J-S Qin et al, Chem. Sci., 2012, DOI: 10.1039/c2sc00017b