Chemical Science Blog

Scientists from Switzerland have created a system that mimics the way the human nose recognises scents.

Stefan Matile and colleagues from the University of Geneva made an artificial membrane that can distinguish between a range of odour molecules. Their ‘nose’ uses differential sensing, a form of molecular recognition, to recognise subtle structural differences between the molecules. ‘Our nose works by differential sensing in the membrane and differential sensing has been done almost everywhere except in the membrane,’ says Matile.

The human nose can distinguish over 10,000 different smells using 350 receptors. Smell molecules, known as an odorants, interact with the receptors to create an overall ‘fingerprint’ that is recognised by the brain. Matile’s system works by moving odorants across a lipid bilayer, an artificial cell membrane, using electrostatic interactions. Once across the membrane, this creates a fluorescent response, which is then measured to build up an electronic fingerprint of the smell. The team say they can distinguish a range of commercial perfumes using their nose.

The artificial nose builds up a fingerprint of odour molecules

‘This highlights just how closely related this system is to the human system,’ says Jon Steed, an expert in supramolecular sensing at the University of Durham, Durham, UK, who adds: ‘You can adapt the chemistry to sense whatever you want.’

‘The applications are broad and very promising,’ says Matile. Steed adds that detection of low levels of molecules is important in many areas, for example in the detection of explosives or pollutants. Matile is now studying different forms of membrane transport in the system and how this affects its sensing capability.

Will Dennis

Read the full Edge article for free in Chemical Science.

Scientists in Israel have shown how an iron-based antioxidant could prevent damage in arteries that leads to cardiovascular disease.

Zeev Gross and team from the Israel Institute of Technology, Haifa, say that iron-corrole complex 1-Fe works by binding to the two types of cholesterol in the body to block the damaging effects of reactive oxygen and nitrogen species.

Reactive oxygen and nitrogen species are naturally present in the body. They modify the structures of cholesterol-delivering, or atherogenic, low-density lipoproteins and cholesterol-removing, or anti-atherogenic, high-density lipoproteins. This modification, known as oxidative stress, makes low-density lipoproteins (LDL, or bad cholesterol) more atherogenic and high-density lipoproteins (HDL, or good cholesterol) less anti-atherogenic.

1-Fe binds tightly to lipoproteins and is carried to the arterial wall

Gross’ team found that 1-Fe decomposes the harmful species in a catalytic fashion and binds tightly to the lipoproteins implying that the antioxidant will be carried all the way to the arterial wall, where the oxidative environment prevails. This is in contrast to current dietary antioxidants that are not as efficient against some reactive species and can damage the lipoproteins and the arterial wall.

The team analysed the 1-Fe/LDL and 1-Fe/HDL complexes in human serum. ‘The bipolarity of the complex is responsible for the high affinity of the corrole to lipoproteins in general,’ says Gross, ‘while coordination of the chelated iron(III) ion in 1-Fe with specific amino acid residues is involved in the selectivity to HDL.’

‘These findings will have a major impact on future antioxidant design,’ says Claus Jacob, an expert on catalytic antioxidants from Saarland University, Germany. ‘It is now possible to attach catalytic antioxidants to the targets of oxidative stress, providing perfect protection against the damage caused by reactive species. This is a promising lead for the development of the next generation of multi-functional, smart antioxidants. Such antioxidants are of particular importance in the field of cardiovascular diseases.’

‘Demonstrating the effects and understanding the variables that determine efficiency of catalytic antioxidants may lead to the design of optimal new drug candidates for treating the most severe diseases affecting human health,’ says Gross. He intends to extend his study to look at macrophages (white blood cells), major contributors to the development of atherosclerotic plaques.

Jennifer Newton

For more details, read Gross’ Chemical Science Edge article.

That’s it. British summertime is officially over. So to help us through the cold, dark winter, I’ve collected together some of the hottest Edge articles published in October.

Bright results
Oligomeric tandem terpyridyl platinum(II) complexes display spectacular solvent dependent emission properties and self-aggregating behaviour. What factors govern this strong emissive property? Find out in Chi-Ming Che’s Edge Article.

Catalytic water oxidation
Robert Crabtree and colleagues report a new method for generating an amorphous electrodeposited material, principally consisting of iridium and oxygen, which is a robust and long-lived catalyst for water oxidation, when driven electrochemically.

Forming C-C bonds
A novel method for the direct, amine-catalysed, highly enantioselective α-alkylation of aldehydes has been discovered by Claudio Palomo and colleagues. Find out more about the reaction conditions and mechanism.

Extending cyclopropenium activation
Geminal dichlorocyclopropenes rapidly and efficiently convert oximes to amides at room temperature, with reactivity that far surpasses other organic-based promoters, report Tristan Lambert and colleagues in their Edge article.

Understanding aerobic oxidation
Experimental and computational data provide direct evidence for two parallel mechanistic pathways for O₂ insertion into a Pd–H bond, claim Shannon Stahl and colleagues. Assess the evidence for yourself in their Edge Article.

Gauging electronic dissymmetry
What kinds of environments give rise to effective levels of electronic dissymmetry in metal complexes? Seth Brown and colleagues investigate the behaviour of a series of tetrasubstituted biphenolates with substituents of varying electronic and steric character and shed light on the origins of stereoselectivity in these complexes. Read more…

Easy access to polycyclic ring systems
Daniel Seidel and colleagues report a new 1,6-annulation reaction for azomethine ylides which could find widespread use in alkaloid synthesis.

Catalytic nitrene transfer
Alan Heyduk and colleagues report on the catalytic formation of carbodiimide using zirconium(IV) bearing a redox-active ligand.

If you like the sound of these articles, subscribe to the Chemical Science e-alert to receive details of the latest issues. And if you have some hot science to report, submit to Chemical Science.

UK chemists have discovered a surprising application of a simple uranium complex that is widely used as a starting material in coordination chemistry.

Polly Arnold, at the University of Edinburgh, and colleagues found that the uranium tris(amide) complex UN’’₃ (N’’ = N(SiMe₃)₂) reacts with carbon monoxide gas at room temperature and pressure to give a reductively coupled [OCCO]^2- fragment as the sole product.

Remarkably, as the fragment is sterically protected, it was still active towards another C–C bond forming event: upon warming it reacted with one of the amido ligand C-H groups to give a functionalised enediolate dianion.

Find out more about this fascinating reaction in Professor Arnold’s Chemical Science Edge article.

UK scientists have developed a methodology that reveals the reactivity and reaction mechanisms of small molecular dipositive ions when they collide with neutral molecules, which could shed light on reactions taking place in interstellar media and in planetary upper atmospheres.

Dipositive ions are highly-energetic species because the two positive charges are located close together in a small molecule. This repulsion makes these species kinetically, as well as thermodynamically, unstable causing them to fragment rapidly forming singly-charged ions. Most small molecules can however hold themselves together for a few seconds to allow it to interact with other atoms and molecules to form monopositive ions.

These metastable ions can often be found in the upper atmospheres of planets. Recent modelling data has suggested that the chemistry of planetary upper atmospheres results from a contribution of these dipositive species (CO₂²⁺ on Mars and N₂²⁺ on Earth and Saturn’s moon Titan). The data predicts that the N₂²⁺ ion could be observed optically. Data collected by the Cassini spacecraft show that the atmosphere of Titan is complex and the chemistry of dipositive ions has been proposed as a mechanism for the formation of hydrocarbons and other large molecules, a reason for which Titan has fascinated chemists and astrobiologists for years.

Titan is one of Saturn's sixty-two moons and has been described as having the richest chemistry in the Solar System

Now, Stephen Price and colleagues at University College London, UK, have developed a position-sensitive coincidence technique (PSCO), which detects pairs of ions following individual dipositive ion collisions with neutral molecules and have applied the technique to show that N₂²⁺ reacts with H₂ to form NH⁺ via the initial formation of an [N₂H₂]²⁺ collision complex which fragments to NH₂²⁺ + N, with the NH₂²⁺ then fragmenting to give the observed charged products NH⁺ + H⁺.

‘Detecting both the ions from individual reactive events allows for selectively probing the reactions of dications in the presence of other singly-charged ions. We can then determine the identities and velocities of the two product ions from individual dication reactive events,’ says Price. ‘This is a blue-skies area of research, we study these reactions because they are interesting and unusual and we hope will allow us to understand and predict their influence on the chemistry of planetary ionospheres, cometary atmospheres, interstellar space and fusion plasmas, where modelling currently indicates these species play a chemical role,’ he adds.

Stuart Mackenzie, an expert in physical and theoretical chemistry, at Oxford University, UK, comments ‘[This method] provides exquisite detail on a class of chemical reactions which, although exotic on Earth, may play a key role in extraterrestrial environments and the group explore each conceivable mechanism, which might explain the observations and, Sherlock Holmes-style, dismiss them one-by-one as inconsistent with their data until the only one remaining, however improbable, must be the truth.’

The group plan to explore the chemistry of N₂²⁺ with other neutral molecules and to study the chemistry of other small dications of relevance to ionospheric and plasma chemistry, such as O₂²⁺, CO₂²⁺, NO²⁺ as well as extending the PSCO technique in order to gain more information on the electronic states of the ions involved in the reactions.

Carl Saxton

Read the full story in Price’s Chemical Science Edge article.  If you have your own blue-sky research to report, submit to Chemical Science and be seen with the best.

Scientists in Germany have shed new light on the addition of small molecules to the ubiquitous N-heterocyclic carbenes (NHCs), previously thought to be impossible for NHCs.

Ulrich Siemeling and colleagues have shown that stable NHCs can show strongly enhanced reactivities towards fundamentally important small molecules such as ammonia and carbon monoxide, which is unprecedented for diaminocarbene compounds. The scientists were able to add carbon monoxide to a number of carbene systems, including the simplest stable diaminocarbene, Alder’s C(NiPr₂)₂ ­ to which they added carbon monoxide. This provided a new entry to the important β-lactam ring systems commonly found in antibiotics.

Workhorses taking off: Ferrocene-based N-heterocyclic carbenes undergo reactions with fundamentally important small molecules

This newly discovered reactivity opens the door to an exciting area of synthetically useful carbene chemistry.

Read the Chemical Science Edge article for free online. Have you conquered the impossible? Tell the world by submitting to Chemical Science today.

Metal nanoparticles that can catalyse organic reactions in water can be made using polyelectrolyte nanoreactors, claim scientists. 

Thanks to their ionisable functional groups, polyelectrolytes can change their conformation in water. When there are few other ions in the solution, the chains stretch out because the charged groups on the chains repel each other.

But when Vy Dong, at the University of Toronto, Canada, and colleagues added an acidic palladium (II) chloride solution, the repulsive interactions were screened and the polyelectrolyte chains collapsed into globules around the chloride ions. Subsequent reduction of the palladium (II) ions in this collapsed-globule nanoreactor using sodium borohydride generated polyelectrolyte stabilised palladium nanoparticles that were bench stable for over a year.

The team used the nanoparticles as catalysts in aqueous Suzuki coupling reactions and achieved high yields at loadings as low as 0.01 mol % palladium. They now plan to transfer the counterion-induced collapse strategy to the synthesis of other polyelectrolyte–metal systems.

Read more about this work in Professor Dong’s Chemical Science Edge article.

US chemists have made a metal-organic framework (MOF) that changes from microporous to mesoporous when heated up. This makes it better at accommodating large guest molecules, potentially improving its ability to store and separate gases.

Hong-Cai Zhou, at Texas A&M University, and colleagues propose that the change in porosity is due to partial decarboxylation of the MOF’s ligands.

For more details, read their Chemical Science Edge article. 

You can find out more about MOFs in Metal Organic Frameworks, a Chem Soc Rev themed issue, or see Seth Cohen’s Chemical Science Mini review, Modifying MOFS: new chemistry, new materials.

And if you have some ‘hot’ science to report, submit your research to Chemical Science.