Chemical Science Blog

Boronic esters have been used by US scientists to transform the triphenylene core in discotic liquid crystals (DLCs) from electron-rich to electron-deficient.

DLCs are used in electronic devices such as light emitting diodes. They need an electron-rich donor and an electron-poor acceptor. Current electron-poor acceptors have shortcomings including the fact that they can’t form columnar mesophases.

The team incorporated a boronic ester into the triphenylene core, which makes it an electron-poor acceptor and they were able to achieve broad mesophase temperature ranges.

Boronic Esters: A Simple Route to Discotic Liquid Crystals that Are Electron Deficient
Benjamin King and Luke Andrew Tatum
DOI: 10.1039/C2SC20128C

Scientists in Canada have studied the synthetic scope of a new system of [2]rotaxane molecular shuttles based on a templating motif involving a benzimidazolium–crown ether recognition pair.

The template allows an array of molecular shuttles containing macrocyclic crown ethers of varying size and shape to be prepared.

The study also provides the beginnings of a property–structure relationship for molecular shuttling in this rigid, compact [2]rotaxane system. This could aid in the future design of [2]rotaxane molecular shuttles for incorporation into materials such as metal–organic frameworks.

Bis(benzimidazolium) axles and crown ether wheels: a versatile templating pair for the formation of [2]rotaxane molecular shuttles
Stephen J. Loeb, Kelong Zhu, V. Nicholas Vukotic and Nadim Noujeim
DOI: 10.1039/C2SC20986A

US scientists have come up with a general synthetic method to prepare macrocyclic tetracarbenes with first, second and third row transition metals from both sides of the periodic table, using a dimeric silver transmetallating reagent.

The facile synthesis of bidentate and tridentate N-heterocyclic carbenes (NHCs) coupled with their resistance to oxidation has made these chelating ligands an attractive alternative to phosphines for many applications. Despite numerous uses for these strong sigma-donor ligands, one class of chelating NHCs that has not been as thoroughly investigated is tetradentate carbenes.

Link to journal article
Exploiting a Dimeric Silver Transmetallating Reagent to Synthesize Macrocyclic Tetracarbene Complexes
Z Lu, S A Cramer and D M Jenkins
Chem. Sci., 2012, DOI: 10.1039/c2sc20628e

Highly active catalysts for manufacturing bulk and fine chemicals can be made by simply grinding metal acetate salts with pre-formed supports.

Heterogeneous catalysis is a key chemical manufacturing process and lies at the heart of green chemical processes. The use of catalysts can lead to greener reactions when compared to alternative routes. But many routes for making catalysts use halides as a starting point and the halides are difficult to remove from the final material.

UK scientists have prepared supported gold, palladium and gold-palladium catalysts by mixing the metal acetate precursors. The simple, reproducible and scalable preparation method ensures the catalysts prepared are halide free. They found that the removal of the halide from the preparation step and therefore from the final catalyst leads to a significant enhancement in performance compared to previously reported catalysts.

Link to journal article
Physical mixing of metal acetates: a simple, scalable method to produce active chloride-free bimetallic catalysts
S A Kondrat et al
Chem. Sci., 2012, DOI: 10.1039/c2sc20450a

A cylindrical supramolecular complex (yellow) interacting with the central target region of the amyloid beta protein (green, white and red ribbon). Image credit: Xiaogang Qu

Supramolecular chemistry could provide a new avenue in the treatment of Alzheimer’s disease, say scientists in China. The group demonstrates for the first time that supramolecular complexes can inhibit the aggregation of a peptide thought to cause Alzheimer’s disease.

Alzheimer’s disease (AD) is the most common cause of dementia among the elderly and is estimated to affect over 35 million people worldwide, a figure which is expected to triple by 2050. One of the pathological hallmarks of the disease is the polymerisation of amyloid β-peptides (Aβ) into insoluble fibrous protein aggregates known as plaques. Scientists have been trying to develop inhibitors of Aβ aggregation as a therapeutic and preventive strategy for AD treatment. Most reported Aβ inhibitors are small organic molecules or peptides, many of which act non-specifically.

Read the full article in Chemistry World

Link to journal article
Metallosupramolecular Complex Targeting a/ß Discordant Stretch of Amyloid ß Peptide
H Yu et al
Chem. Sci., 2012, DOI: 10.1039/c2sc20372c

The MOF incorporating carboxyl and pyridyl groups within its cavity selectively adsorbs CO2 over ethyne. Image credit: Martin Schröder

UK researchers have designed a metal–organic framework that, unusually, selectively adsorbs CO₂ over ethyne by a dynamic gate-opening mechanism and has potential applications in fuel gas separation.

Metal–organic frameworks, or MOFs, comprise metal clusters or ions complexed to organic ligands, forming an extended crystalline, often porous, structure. The pore sizes can be tuned by careful design, and as such, they are widely investigated for gas storage and separation technologies. However, most MOFs are usually selective to ethyne adsorption over CO₂, limiting their application, as the intermolecular interactions between ethyne and the MOF are stronger.

Now, Martin Schröder at the University of Nottingham, and colleagues, have synthesised a MOF that shows dynamic phase changing behaviour induced by CO₂, inverting the usual selectivity to ethyne.

Read the full article in Chemistry World

Link to journal article
Selective CO₂ uptake and inverse CO₂/C₂H₂ selectivity in a dynamic bifunctional metal–organic framework
W Yang et al
Chem. Sci., 2012, DOI: 10.1039/c2sc20443f

The sensor’s colour changes with different pH. From left to right: pH = 6, 7, 8 and 9

US scientists have developed a pH sensor based on nanocrystal quantum dots designed to be used in a biological pH range. pH is an important factor in monitoring tumour health and the efficacy of anticancer treatments, and the sensor could be injected into tumours to monitor their health in real time.

Nanocrystal-based pH sensors have been reported before as they have attractive properties, but the sensors operate in alkali conditions, making them unsuitable for biological applications. To overcome this problem, Daniel Nocera from the Massachusetts Institute of Technology, Cambridge, and colleagues, tailored their sensor so that it could operate at pHs between 6 and 8 (physiological pH).

Read the full article in Chemistry World

Link to journal article
A Nanocrystal-based Ratiometric pH Sensor for Natural pH Ranges
R C Somers et al
Chem. Sci., 2012, DOI: 10.1039/c2sc20212c

Cyclic paraphenylenes (CPPs), first made in 2008, have potential roles in carbon nanotube synthesis as well as interesting optoelectronic properties and nano-sized cavities. Despite their potential, scientists haven’t explored them much for materials and nano applications because they’ve been really difficult to make at a reasonable scale – 10-15mg is typical – and they are expensive.

Now, scientists in the US have come up with a procedure to make 20g of a common intermediate within a week, which can be used to make gram quantities of cyclic paraphenylenes. They developed a macrocyclisation step that uses a much cheaper palladium source than before (ligand-free), reducing the cost significantly. They also report the first solid-state structure of the supramolecular complex between C60 and [10]CPP, illustrating the perfectly matched convex/concave pi-pi interactions (they describe it as a nanopeapod structure).

Link to journal article
Gram-Scale Synthesis and Crystal Structures of [8]- and [10]CPP, and the Solid-State Structure of C60@[10]CPP
J Xia, J W Bacon and R Jasti
Chem. Sci., 2012, DOI: 10.1039/c2sc20719b