Tag Archives: Au

Gold glue?

If you’re hoping for gold flecks in your glue, this is not going to satisfy you, given that it’s all at the nanoscale. An August 7, 2019 news item on Nanowerk briefly describes this gold glue (Note: A link has been removed),

It has long been known that gold can be used to do things that philosophers have never even dreamed of. The Institute of Nuclear Physics of the Polish Academy of Sciences in Cracow has confirmed the existence of ‘gold glue’: bonds involving gold atoms, capable of permanently bonding protein rings. Skilfully used by an international team of scientists, the bonds have made it possible to construct molecular nanocages with a structure so far unparalleled in nature or even in mathematics (Nature, “An ultra-stable gold-coordinated protein cage displaying reversible assembly”).

Caption: The ‘impossible’ sphere, i.e. a molecular nanocage of 24 protein rings, each of which has an 11-sided structure. The rings are connected by bonds with the participation of gold atoms, here marked in yellow. Depending on their position in the structure, not all gold atoms have to be used to attach adjacent proteins (an unused gold atom is marked in red). Credit: Source: UJ, IFJ PAN

An August 6, 2019 Polish Academy of Sciences press release (also on EurekAlert but published August 7, 2019), which originated the news item, expands on the theme,

The world of science has been interested in molecular cages for years. Not without reason. Chemical molecules, including those that would under normal conditions enter into chemical reactions, can be enclosed within their empty interiors. The particles of the enclosed compound, separated by the walls of the cage from the environment, have nothing to bond with. These cages can be therefore be used, for example, to transport drugs safely into a cancer cell, only releasing the drug when they are inside it.

Molecular cages are polyhedra made up of smaller ‘bricks’, usually protein molecules. The bricks can’t be of any shape. For example, if we wanted to build a molecular polyhedron using only objects with the outline of an equilateral triangle, geometry would limit us to only three solid figures: a tetrahedron, an octahedron or an icosahedron. So far, there have been no other structural possibilities.

“Fortunately, Platonic idealism is not a dogma of the physical world. If you accept certain inaccuracies in the solid figure being constructed, you can create structures with shapes that are not found in nature, what’s more, with very interesting properties,” says Dr. Tomasz Wrobel from the Cracow Institute of Nuclear Physics of the Polish Academy of Sciences (IFJ PAN).

Dr. Wrobel is one of the members of an international team of researchers who have recently carried out the ‘impossible’: they built a cage similar in shape to a sphere out of eleven-walled proteins. The main authors of this spectacular success are scientists from the group of Prof. Jonathan Heddle from the Malopolska Biotechnology Centre of the Jagiellonian University in Cracow and the Japanese RIKEN Institute in Wako. The work described in Nature magazine took place with the participation of researchers from universities in Osaka and Tsukuba (Japan), Durham (Great Britain), Waterloo (Canada) and other research centres.

Each of the walls of the new nanocages was formed by a protein ring from which eleven cysteine molecules stuck out at regular intervals. It was to the sulphur atom found in each cysteine molecule that the ‘glue’, i.e. the gold atom, was planned to be attached. In the appropriate conditions, it could bind with one more sulphur atom, in the cysteine of a next ring. In this way a permanent chemical bond would be formed between the two rings. But would the gold atom under these conditions really be able to form a bond between the rings?

“In the Spectroscopic Imaging Laboratory of IFJ PAS we used Raman spectroscopy and X-ray photoelectron spectroscopy to show that in the samples provided to us with the test nanocages, the gold really did form bonds with sulphur atoms in cysteines. In other words, in a difficult, direct measurement, we proved that gold ‘glue’ for bonding protein rings in cages really does exist,” explains Dr. Wrobel.

Each gold atom can be treated as a stand-alone clip that makes it possible to attach another ring. The road to the ‘impossible’ begins when we realize that we don’t always have to use all of the clips! So, although all the rings of the new nanocages are physically the same, depending on their place in the structure they connect with their neighbours with a different number of gold atoms, and thus function as polygons with different numbers of vertices. 24 nanocage walls presented by the researchers were held together by 120 gold atoms. The outer diameter of the cages was 22 nanometres and the inner diameter was 16 nm.

Using gold atoms as a binder for nanocages is also important due to its possible applications. In earlier molecular structures, proteins were glued together using many weak chemical bonds. The complexity of the bonds and their similarity to the bonds responsible for the existence of the protein rings themselves did not allow for precise control over the decomposition of the cages. This is not the case in the new structures. On the one hand, gold-bonded nanocages are chemically and thermally stable (for example, they withstand hours of boiling in water). On the other hand, however, gold bonds are sensitive to an increase in acidity. By its increase, the nanocage can be decomposed in a controlled way and the contents can be released into the environment. Since the acidity within cells is greater than outside them, gold-bonded nanocages are ideal for biomedical applications.

The ‘impossible’ nanocage is the presentation of a qualitatively new approach to the construction of molecular cages, with gold atoms in the role of loose clips. The demonstrated flexibility of the gold bonds will make it possible in the future to create nanocages with sizes and features precisely tailored to specific needs.

Here’s a link to and a citation for the paper.

An ultra-stable gold-coordinated protein cage displaying reversible assembly by Ali D. Malay, Naoyuki Miyazaki, Artur Biela, Soumyananda Chakraborti, Karolina Majsterkiewicz, Izabela Stupka, Craig S. Kaplan, Agnieszka Kowalczyk, Bernard M. A. G. Piette, Georg K. A. Hochberg, Di Wu, Tomasz P. Wrobel, Adam Fineberg, Manish S. Kushwah, Mitja Kelemen, Primož Vavpetič, Primož Pelicon, Philipp Kukura, Justin L. P. Benesch, Kenji Iwasaki & Jonathan G. Heddle Nature volume 569, pages438–442 (2019) Issue Date: 16 May 2019 DOI: https://doi.org/10.1038/s41586-019-1185-4 Published online: 08 May 2019

This paper is behind a paywall.

Gold sheets that are two atoms thick

The gold sheets in question are effectively 2D. I’m surprised they haven’t named them ‘goldene’ as everything else that’s 2D seems to have an ‘ene’ suffix (e.g. graphene, germanene, tellurene).

Of course, these gold sheets are not composed of single atoms but of two according to an August 6, 2019 news item on Nanowerk,

Scientists at the University of Leeds [UK] have created a new form of gold which is just two atoms thick – the thinnest unsupported gold ever created.

The researchers measured the thickness of the gold to be 0.47 nanometres – that is one million times thinner than a human finger nail. The material is regarded as 2D because it comprises just two layers of atoms sitting on top of one another. All atoms are surface atoms – there are no ‘bulk’ atoms hidden beneath the surface.

Caption: Image shows gold nanosheets that are just two atoms thick Credit: University of Leeds

I’m pretty sure they’ve added colour to those images and not just in the background; they’ve likely added a gold colour to the gold.

An August 6, 2019 University of Leeds press release (also on EurekAlert), which originated the news item, gives some insight into the scientists’ ambitions and some technical details about the work,

The material could have wide-scale applications in the medical device and electronics industries – and also as a catalyst to speed up chemical reactions in a range of industrial processes.

Laboratory tests show that the ultra-thin gold is 10 times more efficient as a catalytic substrate than the currently used gold nanoparticles, which are 3D materials with the majority of atoms residing in the bulk rather than at the surface.

Scientists believe the new material could also form the basis of artificial enzymes that could be applied in rapid, point-of-care medical diagnostic tests and in water purification systems.

The announcement that the ultra-thin metal had been successfully synthesised was made in the journal Advanced Science.

The lead author of the paper, Dr Sunjie Ye, from Leeds’ Molecular and Nanoscale Physics Group and the Leeds Institute of Medical Research, said: “This work amounts to a landmark achievement.

“Not only does it open up the possibility that gold can be used more efficiently in existing technologies, it is providing a route which would allow material scientists to develop other 2D metals.

“This method could innovate nanomaterial manufacturing.”

The research team are looking to work with industry on ways of scaling-up the process.

Synthesising the gold nanosheet takes place in an aqueous solution and starts with chloroauric acid, an inorganic substance that contains gold. It is reduced to its metallic form in the presence of a ‘confinement agent’ – a chemical that encourages the gold to form as a sheet, just two atoms thick.

Because of the gold’s nanoscale dimensions, it appears green in water – and given its shape, the researchers describe it as gold nanoseaweed.

Images taken from an electron microscope reveal the way the gold atoms have formed into a highly organised lattice. Other images show gold nanoseaweed that has been artificially coloured. The images are available for download: https://drive.google.com/drive/folders/

Professor Stephen Evans, head of the Leeds’ Molecular and Nanoscale Research Group who supervised the research, said the considerable gains that could be achieved from using these ultra-thin gold sheets are down to their high surface-area to volume ratio.

He said: “Gold is a highly effective catalyst. Because the nanosheets are so thin, just about every gold atom plays a part in the catalysis. It means the process is highly efficient.”

Standard benchmark tests revealed that gold nanoscale sheets were ten times more efficient than the gold nanoparticles conventionally used in industry.

Professor Evans said: “Our data suggests that industry could get the same effect from using a smaller amount of gold, and this has economic advantages when you are talking about a precious metal.”

Similar benchmark tests revealed that the gold sheets could act as highly effective artificial enzymes.

The flakes are also flexible, meaning they could form the basis of electronic components for bendable screens, electronic inks and transparent conducting displays.

Professor Evans thinks there will inevitably be comparisons made between the 2D gold and the very first 2D material ever created – graphene, which was fabricated at the University of Manchester in 2004.

He said: “The translation of any new material into working products can take a long time and you can’t force it to do everything you might like to. With graphene, people have thought that it could be good for electronics or for transparent coatings – or as carbon nanotubes that could make an elevator to take us into space because of its super strength.

“I think with 2D gold we have got some very definite ideas about where it could be used, particularly in catalytic reactions and enzymatic reactions. We know it will be more effective than existing technologies – so we have something that we believe people will be interested in developing with us.”

Here’s a link to and a citation for the paper,

Sub‐Nanometer Thick Gold Nanosheets as Highly Efficient Catalysts by Sunjie Ye, Andy P. Brown, Ashley C. Stammers, Neil H. Thomson, Jin Wen, Lucien Roach, Richard J. Bushby, Patricia Louise Coletta, Kevin Critchley, Simon D. Connell, Alexander F. Markham, Rik Brydson, Stephen D. Evans. Advnaced Science https://doi.org/10.1002/advs.201900911 First published: 06 August 2019

This paper is open access.

Unusual appetite for gold

This bacterium (bacteria being the plural) loves gold, which is lucky for anyone trying to develop artificial photosynthesis.From an October 9, 2018 news item on ScienceDaily,

A bacterium named Moorella thermoacetica won’t work for free. But UC Berkeley [University of California at Berkeley] researchers have figured out it has an appetite for gold. And in exchange for this special treat, the bacterium has revealed a more efficient path to producing solar fuels through artificial photosynthesis.

An October 5, 2018 UC Berkeley news release by Theresa Duque (also on EurekAlert but published on October 9, 2018), which originated the news item, expands on the theme,

M. thermoacetica first made its debut as the first non-photosensitive bacterium to carry out artificial photosynthesis (link is external) in a study led by Peidong Yang, a professor in UC Berkeley’s College of Chemistry. By attaching light-absorbing nanoparticles made of cadmium sulfide (CdS) to the bacterial membrane exterior, the researchers turned M. thermoacetica into a tiny photosynthesis machine, converting sunlight and carbon dioxide into useful chemicals.

Now Yang and his team of researchers have found a better way to entice this CO2-hungry bacterium into being even more productive. By placing light-absorbing gold nanoclusters inside the bacterium, they have created a biohybrid system that produces a higher yield of chemical products than previously demonstrated. The research, funded by the National Institutes of Health, was published on Oct. 1 in Nature Nanotechnology (link is external).

For the first hybrid model, M. thermoacetica-CdS, the researchers chose cadmium sulfide as the semiconductor for its ability to absorb visible light. But because cadmium sulfide is toxic to bacteria, the nanoparticles had to be attached to the cell membrane “extracellularly,” or outside the M. thermoacetica-CdS system. Sunlight excites each cadmium-sulfide nanoparticle into generating a charged particle known as an electron. As these light-generated electrons travel through the bacterium, they interact with multiple enzymes in a process known as “CO2 reduction,” triggering a cascade of reactions that eventually turns CO2 into acetate, a valuable chemical for making solar fuels.

But within the extracellular model, the electrons end up interacting with other chemicals that have no part in turning CO2 into acetate. And as a result, some electrons are lost and never reach the enzymes. So to improve what’s known as “quantum efficiency,” or the bacterium’s ability to produce acetate each time it gains an electron, the researchers found another semiconductor: nanoclusters made of 22 gold atoms (Au22), a material that M. thermoacetica took a surprising shine to.

A single nanocluster of 22 gold atoms

Figure: A single nanocluster of 22 gold atoms – Au22 – is only 1 nanometer in diameter, allowing it to easily slip through the bacterial cell wall.

“We selected Au22 because it’s ideal for absorbing visible light and has the potential for driving the CO2 reduction process, but we weren’t sure whether it would be compatible with the bacteria,” Yang said. “When we inspected them under the microscope, we discovered that the bacteria were loaded with these Au22 clusters – and were still happily alive.”

Imaging of the M. thermoacetica-Au22 system was done at UC Berkeley’s Molecular Imaging Center (link is external).

The researchers also selected Au22 ­– dubbed by the researchers as “magic” gold nanoclusters – for its ultrasmall size: A single Au22nanocluster is only 1 nanometer in diameter, allowing each nanocluster to easily slip through the bacterial cell wall.

“By feeding bacteria with Au22 nanoclusters, we’ve effectively streamlined the electron transfer process for the CO2 reduction pathway inside the bacteria, as evidenced by a 2.86 percent quantum efficiency – or 33 percent more acetate produced within the M. thermoacetica-Au22 system than the CdS model,” Yang said.

The magic gold nanocluster is the latest discovery coming out of Yang’s lab, which for the past six years has focused on using biohybrid nanostructures to convert CO2 into useful chemicals as part of an ongoing effort to find affordable, abundant resources for renewable fuels, and potential solutions to thwart the effects of climate change.

“Next, we’d like to find a way to reduce costs, improve the lifetimes for these biohybrid systems, and improve quantum efficiency,” Yang said. “By continuing to look at the fundamental aspect of how gold nanoclusters are being photoactivated, and by following the electron transfer process within the CO2 reduction pathway, we hope to find even better solutions.”

Co-authors with Yang are UC Berkeley graduate student Hao Zhang and former postdoctoral fellow Hao Liu, now at Donghua University in Shanghai, China.

Here’s a link to and a citation for the paper,

Bacteria photosensitized by intracellular gold nanoclusters for solar fuel production by Hao Zhang, Hao Liu, Zhiquan Tian, Dylan Lu, Yi Yu, Stefano Cestellos-Blanco, Kelsey K. Sakimoto, & Peidong Yang. Nature Nanotechnologyvolume 13, pages900–905 (2018). DOI: https://doi.org/10.1038/s41565-018-0267-z Published: 01 October 2018

This paper is behind a paywall.

For lovers of animation, the folks at UC Berkeley have produced this piece about the ‘gold-loving’ bacterium,

Golden nanoglue

This starts out as a graphene story before taking an abrupt turn. From a June 5, 2018 news item on Nanowerk,

Graphene has undoubtedly been the most popular research subject of nanotechnology during recent years. Made of pure carbon, this material is in principle easy to manufacture: take ordinary graphite and peel one layer off with Scotch tape. The material thus obtained is two-dimensional, yielding unique properties, different from those in three-dimensional materials.

Graphene, however, lacks one important property, semiconductivity, which complicates its usage in electronics applications. Scientists have therefore started the quest of other two-dimensional materials with this desired property.

Molybdenum disulfide, MoS2 is among the most promising candidates. Like graphene, MoS2 consists of layers, interacting weakly with one another. In addition to being a semiconductor, the semiconducting properties of MoS2 change depending on the number of atomic layers.

A June 5, 2018 University of Oulu press release, which originated the news item,  gives more detail about the work,

For the one or few layer MoS2 to be useful in applications, one must be able to join it to other components. What is thus needed is such a metallic conductor that electric current can easily flow between the conductor and the semiconductor. In the case of MoS2, a promising conductor is provided by nickel, which also has other desired properties from the applications point of view.

However, an international collaboration, led by the Nano and molecular systems research unit at the University of Oulu has recently discovered that nanoparticles made of nickel do not attach to MoS2. One needs gold, which ‘glues’ the conductor and the component together. Says docent Wei Cao of NANOMO: “The synthesis is performed through a sonochemical method.” Sonochemistry is a method where chemical reactions are established using ultrasound. NANOMO scientist Xinying Shi adds: “The semiconductor and metal can be bridged either by the crystallized gold nanoparticles, or by the newly formed MoS2-Au-Ni ternary alloy.”

The nanojunction so established has a very small electrical resistivity. It also preserves the semiconducting and magnetic properties of MoS2. In addition, the new material has desirable properties beyond those of the original constituents. For example, it acts as a photocatalyst, which works much more efficiently than pure MoS2. Manufacturing the golden nanojunction is easy and cheap, which makes the new material attractive from the applications point of view.

Here’s a link to and a citation for the paper,

Metallic Contact between MoS2 and Ni via Au Nanoglue by Xinying Shi, Sergei Posysaev, Marko Huttula, Vladimir Pankratov, Joanna Hoszowska, Jean‐Claude Dousse, Faisal Zeeshan, Yuran Niu, Alexei Zakharov, Taohai Li. Small Volume 14, Issue22 May 29, 2018 1704526 First published online: 24 April 2018 https://doi.org/10.1002/smll.201704526

This paper is behind a paywall.

There is a pretty illustration of the ‘golden nanojunctions’,

Golden nanoglue (Courtesy of the University of Oulu)

Create gold nanoparticles and nanowires with water droplets.

For some reason it took a lot longer than usual to find this research paper despite having the journal (Nature Communications), the title (Spontaneous formation …), and the authors’ names. Thankfully, success was wrested from the jaws of defeat (I don’t care if that is trite; it’s how I felt) and links, etc. follow at the end as usual.

An April 19, 2018 Stanford University news release (also on EurekAlert) spins fascinating tale,

An experiment that, by design, was not supposed to turn up anything of note instead produced a “bewildering” surprise, according to the Stanford scientists who made the discovery: a new way of creating gold nanoparticles and nanowires using water droplets.

The technique, detailed April 19 [2018] in the journal Nature Communications, is the latest discovery in the new field of on-droplet chemistry and could lead to more environmentally friendly ways to produce nanoparticles of gold and other metals, said study leader Richard Zare, a chemist in the School of Humanities and Sciences and a co-founder of Stanford Bio-X.

“Being able to do reactions in water means you don’t have to worry about contamination. It’s green chemistry,” said Zare, who is the Marguerite Blake Wilbur Professor in Natural Science at Stanford.

Noble metal

Gold is known as a noble metal because it is relatively unreactive. Unlike base metals such as nickel and copper, gold is resistant to corrosion and oxidation, which is one reason it is such a popular metal for jewelry.

Around the mid-1980s, however, scientists discovered that gold’s chemical aloofness only manifests at large, or macroscopic, scales. At the nanometer scale, gold particles are very chemically reactive and make excellent catalysts. Today, gold nanostructures have found a role in a wide variety of applications, including bio-imaging, drug delivery, toxic gas detection and biosensors.

Until now, however, the only reliable way to make gold nanoparticles was to combine the gold precursor chloroauric acid with a reducing agent such as sodium borohydride.

The reaction transfers electrons from the reducing agent to the chloroauric acid, liberating gold atoms in the process. Depending on how the gold atoms then clump together, they can form nano-size beads, wires, rods, prisms and more.

A spritz of gold

Recently, Zare and his colleagues wondered whether this gold-producing reaction would proceed any differently with tiny, micron-size droplets of chloroauric acid and sodium borohydide. How large is a microdroplet? “It is like squeezing a perfume bottle and out spritzes a mist of microdroplets,” Zare said.

From previous experiments, the scientists knew that some chemical reactions proceed much faster in microdroplets than in larger solution volumes.

Indeed, the team observed that gold nanoparticle grew over 100,000 times faster in microdroplets. However, the most striking observation came while running a control experiment in which they replaced the reducing agent – which ordinarily releases the gold particles – with microdroplets of water.

“Much to our bewilderment, we found that gold nanostructures could be made without any added reducing agents,” said study first author Jae Kyoo Lee, a research associate.

Viewed under an electron microscope, the gold nanoparticles and nanowires appear fused together like berry clusters on a branch.

The surprise finding means that pure water microdroplets can serve as microreactors for the production of gold nanostructures. “This is yet more evidence that reactions in water droplets can be fundamentally different from those in bulk water,” said study coauthor Devleena Samanta, a former graduate student in Zare’s lab and co-author on the paper.

If the process can be scaled up, it could eliminate the need for potentially toxic reducing agents that have harmful health side effects or that can pollute waterways, Zare said.

It’s still unclear why water microdroplets are able to replace a reducing agent in this reaction. One possibility is that transforming the water into microdroplets greatly increases its surface area, creating the opportunity for a strong electric field to form at the air-water interface, which may promote the formation of gold nanoparticles and nanowires.

“The surface area atop a one-liter beaker of water is less than one square meter. But if you turn the water in that beaker into microdroplets, you will get about 3,000 square meters of surface area – about the size of half a football field,” Zare said.

The team is exploring ways to utilize the nanostructures for various catalytic and biomedical applications and to refine their technique to create gold films.

“We observed a network of nanowires that may allow the formation of a thin layer of nanowires,” Samanta said.

Here’s a link and a citation for the paper,

Spontaneous formation of gold nanostructures in aqueous microdroplets by Jae Kyoo Lee, Devleena Samanta, Hong Gil Nam, & Richard N. Zare. Nature Communicationsvolume 9, Article number: 1562 (2018) doi:10.1038/s41467-018-04023-z Published online: 19 April 2018

Not unsurprisingly given Zare’s history as recounted in the news release, this paper is open access.

Surgery on nanoparticles?

Chemists performed “surgery” on a 23-gold-atom nanoparticle according to a June 12, 2017 news item on Nanowerk (Note: A link has been removed),

A team of chemists led by Carnegie Mellon University’s [CMU] Rongchao Jin has for the first time conducted site-specific surgery on a nanoparticle. The procedure, which allows for the precise tailoring of nanoparticles, stands to advance the field of nanochemistry.

The surgical technique developed by Qi Li, the study’s lead author and a 3rd year graduate student in the Jin group, will allow researchers to enhance nanoparticles’ functional properties, such as catalytic activity and photoluminescence, increasing their usefulness in a wide variety of fields including health care, electronics and manufacturing. The findings were published in Science Advances (“Molecular “surgery” on a 23-gold-atom nanoparticle”).

Here’s an image the researchers have provided,

Caption: Carnegie Mellon chemists used a two-step metal exchange method to remove two S-Au-S staples from the surface of a nanoparticle. Credit: Carnegie Mellon University

A June 12, 2017 CMU press release (also on EurekAlert), which originated the news item, provides more details about the research,

“Nanochemistry is a relatively new field, it’s only about 20 years old. We’ve been racing to catch up to fields like organic chemistry that are more than 100 years old,” said Jin, a chemistry professor in the Mellon College of Science. “Organic chemists have been able to tailor the functional groups of molecules for quite some time, like tailoring penicillin for better medical functions, for example. We dreamed that we could do something similar in nanoscience. Developing atomically precise nanoparticles has allowed us to make this dream come true.”

In order to make this “nano-surgery” a reality, researchers needed to begin with atomically precise nanoparticles that could be reliably produced time after time. Jin’s lab has been at the forefront of this research. Working with gold nanoparticles, he and his team have developed methods to precisely control the number of atoms in each nanoparticle, resulting in uniformly-sized nanoparticles with every batch. With reliably precise particles, Jin and colleagues were able to identify the particles’ structures, and begin to tease out how that structure impacted the particles’ properties and functionality.

With these well-defined nanoparticles in hand, Jin’s next step was to find a way to surgically tailor the particles in order to learn more about­ – and hopefully enhance – their functionality.

In their recent study, Jin and colleagues performed nano-surgery on a gold nanoparticle made up of 23 gold atoms surrounded by a protective surface of ligands in staple-like motifs. Using a two-step metal exchange method, they removed two S-Au-S staples from the particle’s surface. In doing this they revealed the structural factors that determine the particle’s optical properties and established the role that the surface plays in photoluminescence. Significantly, the surgery increased the particle’s photoluminescence by about 10-fold. Photoluminescence plays a critical role in biological imaging, cancer diagnosis and LED technology, among other applications.

Jin and coworkers are now trying to generalize this site-specific surgery method to other nanoparticles.

Here’s a link to and a citation for the paper,

Molecular “surgery” on a 23-gold-atom nanoparticle by Qi Li, Tian-Yi Luo, Michael G. Taylor, Shuxin Wang, Xiaofan Zhu, Yongbo Song, Giannis Mpourmpakis, Nathaniel L. Rosi, and Rongchao Jin. Science Advances 19 May 2017: Vol. 3, no. 5, e1603193 DOI: 10.1126/sciadv.1603193

This paper is open access.

Stabilizing a carbon-gold complex (gold carbene shines green)

If you find carbon bonds and catalysis interesting, this is the posting for you. A July 8, 2014 news item on Nanowerk highlights research at Heidelberg University (Germany; Note: A link has been removed),

With a chemical “trick”, scientists at Heidelberg University have succeeded in isolating a stable gold carbene complex. Chemist Prof. Dr. Bernd F. Straub and his team are the first to have created the basis for directly examining the otherwise unstable gold-carbon double bond. Prof. Straub explains that highly reactive gold carbene molecules play an important role in landmark catalysing processes taking place at high speed. The research findings have been published in the German and the international edition of Angewandte Chemie (“Isolation of a Non-Heteroatom-Stabilized Gold–Carbene Complex”).

A July 8, 2014 Heidelberg University press release, which originated the news item, describes the catalytic process in general and the specific complex created by the researchers,

Chemical reactions can be accelerated with the aid of catalysts; consequently materials and pharmaceuticals can be manufactured from the raw materials of nature. The study of gold compounds in catalytic processes has proved particularly intensive and successful, according to Prof. Straub. “In numerous scientific studies in the last ten years, experts have been proposing gold carbenes as essential short-lived intermediates in catalytic reactions,” the Heidelberg researcher explains. However, with their high reactivity they escape detailed study: hardly has a gold carbene fragment consisting of the elements gold and carbon emerged – Au for aurum and C for carbon – when it continues to react.

In order to first create a stable complex and isolate a gold carbene structure for research, the two elements were “lured into a cage like a hungry tiger with a bait,” says Matthias Hussong, who is working on his doctoral dissertation in Prof. Straub’s team. The researchers first shielded the gold and carbon from its environment by surrounding them with low-reactive, space-filling chemical groups. Then the two elements were bonded in a carefully planned step – and so the Au=C fragment was “caught” in the gold carbene complex.

The chemists were able to impart “an amazing stability” to the gold carbene, says Prof. Straub – and at the same time to make it literally visible. “Almost all gold complexes are colourless, while the ‘stable’ gold carbene is emerald green,” states the scientist, who heads a research group at Heidelberg University‘s Institute of Organic Chemistry. Further Heidelberg studies showed that gold in its compounds is more than a “soft proton”, as the chemical behaviour of gold had been described to date.

If the gold fragment is replaced by a “real” proton, e.g. the nucleus of hydrogen, the lightest element, this analogous protonated carbene displays a reddish purple colour. “The gold in the gold carbene complex behaves differently from a proton – that is very clear to the eye,” states Prof. Straub. He and his team are now continuing to explore the understanding of gold catalysis, with the aim of using these findings to make catalytic processes more efficient.

Here’s a link to and a citation for the paper,

Isolation of a Non-Heteroatom-Stabilized Gold–Carbene Complex by  M. Sc. Matthias W. Hussong, Dr. Frank Rominger, Petra Krämer, and Prof. Dr. Bernd F. Straub. Angewandte Chemie DOI: 10.1002/anie.201404032 Article first published online: 20 JUN 2014

© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

This paper is behind a paywall.

All the talk of emerald green reminded me of Angelina Jolie,

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The earrings can be found here.