Chemical Communications Blog

Bacteria vs. bacteria: studying small molecules for microbial competition

30 Jun 2020

Antibiotic resistant bacteria, and the subsequent diseases caused by their infection, are of serious global concern. As more and more bacteria develop antibiotic resistance and jeopardise the current treatments for serious infections, there is a strong imperative to both develop new medicines and to understand these bacterial pathogens. Pseudomonas aeruginosa, Staphylococcus aureus and species from the genus Burkholderia are all such antibiotic resistant bacteria that contribute to various human diseases, and they can pose a serious threat to cystic fibrosis patients through chronic lung infections. These are often polymicrobial infections, meaning that the different bacteria interact by association and can alter the impact of the resulting disease.

P. aeruginosa and Burkholderia generally interact competitively with S. aureus, reducing its viability. This is achieved by the secretion of small molecule respiratory toxins which include 2-alkyl-4(1H)-quinolone N-oxides (AQNOs) by P. aeruginosa or 3-methyl-2-alkyl-4-quinolone N-oxides (MAQNOs) by Burkholderia (see Figure 1). Researchers in Germany and Austria sought to understand the antagonistic interactions of these bacteria and have now reported the synthesis of various representative AQNOs and MAQNOs and investigated their action against S. aureus.

Quinolone derivatives secreted by bacteria

Figure 1: Structures of the quinolone derivatives produced by P. aeruginosa and Burkholderia that act against S. aureus

The researchers approached the synthesis of the AQNOs and MAQNOs by starting with the preparation of the corresponding quinolones, and then converting them to the quinolone N-oxides. They focussed on the C₉ nonyl-/nonenyl- derivatives, NQNOs and MNQNOs, as previous studies showed this alkyl chain length proved the most active against S. aureus. Mass spectrometry and fragmentation was primarily used to characterise the synthesised compounds, and the researchers were able to establish a new library of standards to be used for the identification of quinolones and quinolone N-oxides. This therefore allowed the researchers to quantify the specific quinolone derivatives produced by certain strains of P. aeruginosa and Burkholderia using this standard library, as shown in Figure 2.

Figure 2: Quantification of the quinolones (AQs and MAQs) and quinolone N-oxides (AQNOs and MAQNOs) secreted by P. aeruginosa (strains PAO1 and PA14) and Burkholderia thailandesis using calibration against the established standard library

The researchers then investigated the possible activity of these quinolone derivatives against S. aureus. The activity of S. aureus was measured using a chromogenic assay, by varying concentrations of the quinolone derivatives until a minimum inhibitory concentration (MIC) was reached, with complete respiratory inhibition of the bacteria. The C₉-quinolones (before N-oxidation) showed no inhibition against S. aureus at the highest concentrations tested, but the corresponding quinolone N-oxides (NQNOs and MNQNOs) showed activity against the bacteria. More specifically, unsaturated derivatives were more active, and the MNQNOs, with 3-methylation of the quinolone core, showed the greatest antibiotic activity against S. aureus. These results suggest that the methylated quinolones produced by species of Burkholderia, as well as unsaturared quinolones produced by P. aeruginosa, have an important role in competitive interactions against S. aureus in polymicrobial infections.

To find out more, please read:

Profiling structural diversity and activity of 2-alkyl-4(1H)-quinolone N-oxides of Pseudomonas and Burkholderia

Dávid Szamosvári, Michaela Prothiwa, Cora Lisbeth Dieterich and Thomas Böttcher

Chem. Commun., 2020, 56, 6328-6331

About the blogger:

Dr. Samantha Apps is a Postdoctoral Research Associate in the Lu Lab at the University of Minnesota, USA, and obtained her PhD in 2019 from Imperial College London, UK. She has spent the last few years, both in her PhD and postdoc, researching synthetic nitrogen fixation and transition metal complexes that can activate and functionalise dinitrogen. Outside of the lab, you’ll likely find her baking at home, where her years of synthetic lab training has sparked a passion in kitchen chemistry too.

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Studying Anticancer Agents with XFM

23 Jun 2020

By Alessia Millemaggi.

It turns out that rhenium-based compounds have been showing some promising anticancer activity as they’re stable, allow for real time imaging, structurally diverse, and have low off-site toxicity. The most commonly studied complexes are based around a Re(I) tricarbonyl core with the other three binding sites occupied by ligands of varying complexity. Researchers in the US and Australia developed a tricarbonyl Re isonitrile polypyridyl complex fac-[Re(CO)3(dmphen)(para-tolyl-isonitrile)]+, where dmphen = 2,9-dimethyl-1,10-phenanthro-line, called TRIP for short. TRIP showed promising cytotoxicity and can be imaged using confocal fluorescence microscopy, taking advantage of the emissive metal to ligand charge transfer (MLCT) state. The persistence of the emission indicates that the ligands remain bound to the Re even within cells. The complex’s cytotoxicity stems from its inducement of cells to accumulate misfolded proteins, resulting in apoptosis from the unfolded protein response (UPR). UPR induced cell death is relatively uncommon and led the researchers to find a method to characterize the speciation of TRIP in vitro. They used synchrotron X-ray fluorescence microscopy (XFM) to probe the cellular uptake and distribution of TRIP and an iodo-derivative I-TRIP by looking at elemental signals.

Figure 1. Chemical structures of TRIP and I-TRIP

I-TRIP is particularly well-suited to this type of study, as the iodine provides an additional spectroscopic handle on the isonitrile ligand absent in TRIP. Of course, the researchers had to confirm that I-TRIP possessed similar cytotoxicity and working mechanism to TRIP. Various assays and biological studies showed evidence of comparable cytotoxicity and mechanism, demonstrating that altering the substitution of the isonitrile ligand doesn’t significantly impact the bioactivity of the complex. With that settled, the experiments could move to the synchrotron to probe elemental distributions.

Figure 2. XFM elemental distribution maps of HeLa cervical cancer cells treated with either DMSO (control), TRIP, or I-TRIP.

Cells treated with both TRIP and I-TRIP show a clear Re signal, confirming that they can enter and persist in cells. Critically, the colocalization of the Re and I maps for I-TRIP samples indicate that the isonitrile ligand remains bound as a part of the Re complex inside the cells. This strongly suggests that the Re complex is intact while it induces cell death, adding to the developing mechanistic understanding of their activity. This work shows the utility of XRM as a technique to study the distribution of organometallic complexes in living cells. Additionally, the tunability and stable bioactivity of the Re complexes shows that they’re amenable to study by a wide range of techniques that will allow for further mechanistic probing.

To find out more, please read:

X-Ray fluorescence microscopy reveals that rhenium(I) tricarbonyl isonitrile complexes remain intact in vitro

Chilaluck C. Konkankit, James Lovett, Hugh H. Harris and Justin J. Wilson

Chem. Commun., 2020, 56, 6515-6518

About the blogger:

Dr. Beth Mundy is a recent PhD in chemistry from the Cossairt lab at the University of Washington in Seattle, Washington. Her research focused on developing new and better ways to synthesize nanomaterials for energy applications. She is often spotted knitting in seminars or with her nose in a good book. You can find her on Twitter at @BethMundySci.

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Virtual issue on Aggregation-induced Emission (AIE)

22 Jun 2020

By Harriet Kent, Editorial Assistant.

We’re celebrating the upcoming 20th anniversary of aggregation-induced emission (AIE), a term which was first coined in 2001. We’ve put together a collection of key AIE articles published in RSC journals. Here are the articles in the collection from ChemComm, including the very first AIE article!

Aggregation-induced emission of 1-methyl-1,2,3,4,5-pentaphenylsilole
Ben Zhong Tang et al
Chem. Commun., 2001, 1740–1741

A conical intersection model to explain aggregation induced emission in diphenyl dibenzofulvene
Quansong Lia and Lluís Blancafort
Chem. Commun., 2013, 49, 5966

Diarylboryl-phenothiazine based multifunctional molecular siblings
Kalluvettukuzhy K. Neena, Pakkirisamy Thilagar* et al.
Chem. Commun., 2017, 53, 3641-3644

Aggregation-induced emission in precursors to porous molecular crystals
Zhenglin Zhang, Ognjen Š. Miljanić* et al.
Chem. Commun., 2017,53, 10022-10025

A cyanine-based fluorescent cassette with aggregation-induced emission for sensitive detection of pH changes in live cells
Mingxi Fang, Haiying Liu* et al.
Chem. Commun., 2018,54, 1133-1136

AIE-active micelles formed by self-assembly of an amphiphilic platinum complex possessing isoxazole moieties
Takehiro Hirao,Takeharu Haino* et al.
Chem. Commun., 2020,56, 1137-1140

A self-delivery DNA nanoprobe for reliable microRNA imaging in live cells by aggregation induced red-shift-emission
Zhe Chen, Leilei Tian* et al.
Chem. Commun., 2020,56, 1501-1504

A light-up probe with aggregation-induced emission characteristics (AIE) for selective imaging, naked-eye detection and photodynamic killing of Gram-positive bacteria
Guangxue Feng, Bin Liu* et al.
Chem. Commun., 2015, 51, 12490-12493

Rational design of substituted maleimide dyes with tunable fluorescence and solvafluorochromism
Yujie Xie, Rachel K. O’Reilly et al.
Chem. Commun., 2018,54, 3339-3342

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A precious pairing

18 Jun 2020

By Samantha Apps, Web Writer.

Understanding metal-metal interactions is of fundamental interest to chemists, especially in the design of new materials or catalysts. Heterometallic metal-metal bonding is particularly fascinating, since the unique properties of each metal can be combined or even manipulated, to enhance structural, electronic or even photochemical effects. Gold and platinum are one such pairing of interest and there have already been several applications of AuPt clusters reported for catalysis. However, well-defined, homogeneous AuPt complexes are comparatively under explored, but there is a huge potential for these heterodinuclear complexes to catalyse useful chemical transformations. Research in Germany by Butschke and co-workers now describes the first example of an AuPt complex with a bound olefin, as a valuable, formal Au^+IPt⁰ precursor for further reactivity and chemical transformations (Figure 1).

Figure 1: The new AuPt heterodinuclear complex with Pt-bound olefins (right), and existing examples in the literature with Pt-bound phosphines (left and centre).

The new cationic AuPt complex described in this report differs from the existing literature by the presence of weakly bound olefin ligands (in this case, norbonene/nbe) coordinated to the platinum. The other existing examples have only strongly σ-donating phosphine ligands coordinated to the Pt centre, which increases the overall stability of the complexes and renders them unreactive for further chemistry. In contrast, the nbe ligands are more weakly bound, and have a much lower dissociation energy, creating a more reactive complex which is therefore a valuable precursor to other formal Au^+IPt⁰ complexes. This increased reactivity is reflected in the preparation and subsequent manipulations of the complex, which had to be conducted at low temperatures to prevent decomposition.

Figure 2: The X-ray crystal structure of the new AuPt complex.

The new AuPt heterodinuclear complex prepared in this report was characterised by a range of spectroscopic and structural techniques. Single-crystal X-ray diffraction confirmed the molecular structure of the complex, as shown in Figure 2. A rearrangement of the three axial nbe ligands was observed in the new AuPt complex compared to the [Pt(nbe)₃] platinum precursor; the three olefin ligands are arranged in a spoke-wheel geometry with the bridging methylenes of nbe all pointing in the same direction away from the gold (an ‘up-up-up’ configuration, in comparison to an ‘up-up-down’ arrangement as in the Pt precursor). NMR spectroscopic characterisation also helped to elucidate and confirm the structure. The ¹⁹⁵Pt-NMR resonance of the AuPt complex was particularly noteworthy, showing a similar chemical shift to that of the Pt precursor, which indicates little to no electronic change at Pt⁰ in the new AuPt complex. This was also reflected in the ¹³C NMR resonances for the olefinic carbons, which again, were similar in the AuPt complex and the Pt precursor.

Figure 3: Comparing the new AuPt complex (3) to other systems with fewer bound olefins, in terms of the Au-Pt bond dissociation energy (x-axis) and the overall charge transfer between the Au and Pt (y-axis), according to three different calculations.

The authors then further probed the binding of the gold centre to the platinum, and why there was no apparent significant change in the electronics between the new AuPt complex and the Pt precursor. A comparison to the existing AuPt complexes reported revealed that these are often assigned formally as Au^-IPt^+II, where there is a dative interaction between the Lewis base (Pt) and the Lewis Acid (Au). In contrast, the new AuPt complex in this report is formally assigned as Au^+IPt⁰, where there is considerably less charge transfer in the metal-metal bonding, as shown by DFT calculations (see Figure 3). This formal Au^+IPt⁰ assignment ultimately results in the coordinated nbe olefin ligands having a low dissociation energy (i.e. they are highly labile and susceptible to ligand substitution), which is further supported by DFT calculations and is reflected in the lack of an identifiable electrospray-ionisation mass spectrometry peak for the [M]⁺ ion. Therefore, this new AuPt complex is a desirable precursor for the preparation of other formal Au^+IPt⁰ complexes, which will allow for future reactivity studies on these unusual heterodinuclear systems.

To find out more, please read:

A heterodinuclear, formal Au^+IPt⁰ complex with weakly bound alkene ligands

Lukas D. Ernst, Konstantin Koessler, Andreas Peter, Daniel Kratzert, Harald Scherer and Burkhard Butschke

Chem. Commun., 2020, 56, 5350-5353

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ChemComm Milestones – Malte Fischer

17 Jun 2020

By Harriet Kent, Editorial Assistant.

Malte Fischer recently published his first article as a corresponding author with ChemComm. We wanted to celebrate this exciting milestone by finding out more about Malte and his research. Check out his #ChemComm1st article: B(C6F5)3- and HB(C6F5)2-mediated transformations of isothiocyanates.

We asked Malte a few questions about his experience in the lab and working with ChemComm. Read more below.

What are your main areas of research and what motivated you to take this direction?

I would like to summarize the research I am doing and I am interested in, simply under the term “synthetic chemistry”. Specifically, I mean research within the interfaces of organic chemistry, main group chemistry and organometallic chemistry. I am enthusiastic about the progress – especially in recent years – in synthesis, method development and in the search for applications for new molecules. I am convinced that there will always be a need for effective synthesis routes to access unusual and new molecules and I very much hope that I can contribute to this.

Can you set this article in a wider context?

The article is settled in main group chemistry. During my PhD I became more and more interested in this exciting field of research. Based on the reported results I will continue the research in this field.

What do you hope you and your research can achieve in the coming year?

Despite this difficult time, I am simply looking forward to going back to the laboratory at some point to continue having fun in doing research.

Describe your journey to becoming an independent researcher.

I think the moment when I was able to synthesize and characterize my first molecule unknown in literature (happened during my bachelor thesis) inspired me so much that since then I have had the goal of doing independent research and realizing my own ideas. I am definitely still in the beginning of becoming an independent researcher and I am currently working on laying the foundation for it – and this work has given me a lot of pleasure so far.

What is the best piece of advice you have ever been given?

The best advice was given to me by my parents and I try to live by it as much as possible: Pursue what interests you most and captivates you – the rest will come naturally.

Why did you choose to publish in ChemComm?

ChemComm simply stands for publications of the highest quality and with a large readership from all chemistry sub-disciplines. I am immensely pleased to have become a small part of this journal with my first publication as the corresponding author.

Malte’s Bio:

The publication ‘B(C6F5)3- and HB(C6F5)2-Mediated Transformations of Isothiocyanates’ originates from the phase as a research scientist within the group of Prof. Beckhaus in Oldenburg.

05/2019 – 02/2020 Research Scientist/ PostDoc – Carl von Ossietzky University Oldenburg, Germany. Supervisor: Prof. Dr. Rüdiger Beckhaus

10/2015 – 05/2019 PhD in Chemistry. Carl von Ossietzky University Oldenburg, Germany. Supervisor: Prof. Dr. Rüdiger Beckhaus

10/2013 – 10/2015 Master of Science in Chemistry

10/2010 – 10/2013 Bachelor of Science in Chemistry

Find Malte on Twitter: @FiMalte

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Generating Electricity from Urea Using NiCoMo/Graphene Catalysts

12 Jun 2020

By Tianyu Liu.

Electro-oxidizing urea in water has the dual benefit of generating electricity and treating wastewater. In alkaline media, the sluggish kinetics of the urea oxidation reaction, CO(NH₂)₂ + 6OH^– → N₂↑ + CO₂↑ + 5H₂O + 6e^–, due to its transfer of six electrons demand efficient catalysts to speed up this process.

A research team led by Xiujuan Sun and Rui Ding, both at Xiangtan University, China, used a co-precipitation method to synthesize urea-oxidation catalysts. These catalysts comprised of graphene-anchored nanoparticles of metallic Ni, Co, and Mo, as well as their alloys and hydro/oxides (NCM/G) (Figure 1). NCM/G with the optimal composition displayed a mass activity of 140.9 mA cm^-2 mg_cat^-1 and an onset potential of 1.32 V vs. RHE (current density = 10 mA/cm²). Their results are published in Chemical Communications (DOI: 10.1039/D0CC02132F).

Figure 1. Representative (a) transmission electron microscopy image and (b-f) elemental mappings of the synthesized catalyst.

The catalysts exhibited different catalytic activities dependent on their chemical compositions, which were tunable by varying the moles of the Ni, Co, and Mo precursors. Cyclic voltammograms of various NCM/G all showed markedly increased current density at potentials beyond 0.3 V vs. Ag/AgCl in urea-containing aqueous solutions (Figure 2a), marking their catalytic activity for urea oxidation. Among all the tested catalysts, NCM/G with Ni:Co:Mo = 80:10:10 achieved the largest current density at 0.6 V vs. Ag/AgCl, indicating its highest catalytic activity. Additionally, chronoamperometry demonstrated that increasing the Mo content was beneficial for maintaining catalyst stability, as the current density of NCM/G with the lowest amount of Mo (the black curve in Figure 2b) decayed the fastest. Combining the results of cyclic voltammetry and chronoamperometry, the authors deduced that the optimal molar ratio of Ni:Co:Mo was 80:10:10.

Figure 2. (a) Cyclic voltammograms (scan rate: 1 mV/s) and (b) chronoamperometry (potential: 0.5 V vs. Ag/AgCl) profiles of NCM/G with different Ni, Co, and Mo contents. Electrolyte: 1.0 M KOH + 0.33 M urea in water. The molar ratios of Ni:Co:Mo of NCM/G 90505, 811, and 71515 are 90:5:5. 80:10:10, and 70:15:15, respectively.

The optimization of the chemical composition demonstrated in this work can rationalize the development of high-performance, metallic electrocatalysts for urea oxidation.

For expanded understanding, please read:

Trimetallic NiCoMo/Graphene Multifunctional Electrocatalysts with Moderate Structural/Electronic Effects for Highly Efficient Alkaline Urea Oxidation Reaction

Wei Shi, Xiujuan Sun, Rui Ding, Danfeng Ying, Yongfa Huang, Yuxi Huang, Caini Tan, Ziyang Jia, and Enhui Liu

Chem. Commun., 2020, DOI: 10.1039/D0CC02132F

Tianyu Liu acknowledges Zacary Croft at Virginia Tech, U.S., for his careful proofreading of this post.

About the blogger:

Tianyu Liu obtained his Ph.D. (2017) in Chemistry from the University of California, Santa Cruz, in the United States. He is passionate about the communication of scientific endeavors to both the general public and other scientists with diverse research expertise to introduce cutting-edge research to broad audiences. He is a blog writer for Chem. Comm. and Chem. Sci. More information about him can be found at http://liutianyuresearch.weebly.com/.

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ChemComm Milestones – Rob Woodward

03 Jun 2020

By Harriet Kent, Editorial Assistant.

Rob Woodward recently published his first independent research article with ChemComm. We wanted to celebrate this exciting milestone by finding out more about Rob and his research. Check out his #ChemComm1st article: ‘The design of hypercrosslinked polymers from benzyl ether self-condensing compounds and external crosslinkers’

We asked Rob a few questions about his experience in the lab and publishing with ChemComm. Read more below.

What are the main areas of research in your lab and what motivated you to take this direction?

Our primary research focus is the design and production of new porous organic polymers and carbons for a variety of separation and storage applications. These include solid-state extraction to remove pollutants from water, fractionation of complex mixtures, gas separation and storage, energy storage, and even catalysis. In order to approach such a wide variety of applications, we utilise a class of densely crosslinked porous polymers, known as hypercrosslinked polymers. The key feature of these networks is their simple and robust synthesis, allowing a vast array of aromatic compounds to be used as monomeric building blocks.

Our motivation is to try to use hypercrosslinked polymers to establish a platform for targeted adsorbent design. This would enable the engineering of networks customised to tackle specific problems. For example, if certain chemical functionalities or textural properties are known to be beneficial for a given application, we can envision a sort of ‘plug-and-play’ approach, in which various building blocks are used to produce adsorbents with the desired properties. Hypercrosslinked polymers are generally low-cost and have excellent chemical and thermal stabilities, issues that plague many classes of porous materials. Coupled with tailored design, these features may make hypercrosslinked polymers suitable for a broad range of applications, while remaining technically competitive with leading adsorbents.

Can you set this article in a wider context?

The article represents a new approach to the formation of hypercrosslinked polymers, in which conventional aliphatic crosslinkers are replaced with these benzyl ether aromatic compounds. The synthetic process remains the same, but the textural properties of the resulting polymer can be vastly improved, simply by changing a reagent. These compounds also showed unexpected benefits for hypercrosslinking reactions, allowing better control over the porous properties of networks and for reductions in the amount of catalyst required during synthesis, something currently considered a significant setback for hypercrosslinked polymers.

In a wider context, this work opens new routes to hypercrosslinked polymers where conventional approaches may fail or give poor results, presenting synthetic chemists more options with respect to designing new and improved adsorbents.

What do you hope your lab can achieve in the coming year?

Although I have been building my independent research profile while at Imperial College, I was just very recently appointed to an Assistant Professor position in The University of Vienna’s Faculty of Chemistry. This is really the beginning of my independent academic career with regards to establishing my own lab and research group. So, in all honesty, this year will look like a success to me if we can get the laboratory up and running, begin to build a strong research foundation, and establish a network in Vienna to try to begin some local collaborative work. We do have some exciting work due to come out soon which we hope to build from in the short term, but I won’t say too much about that just yet…

Describe your journey to becoming an independent researcher.

I was awarded both my MChem (2008) and PhD (2013) from The University of Liverpool, which is also my hometown. My PhD focused on the synthesis of responsive polymeric surfactants and colloidal systems. I then took up a short post-doctoral position in Prof. Andy Cooper’s group, where I first worked with porous polymeric materials. In 2014, I moved to London for a position in Imperial College London’s Department of Chemical Engineering in the Polymer and Composite Engineering group. There I started to explore other types of porous polymers, as well as investigating their application to several problems, such as energy storage, biomass treatment, and gas separation and storage. I was lucky to have great supervisors who were supportive of me establishing my own independent work. In 2017, I was awarded the Sir William Wakeham prize by Imperial for my research, which gave me the belief that I could pursue a career in academia. Finally, I was offered the role in Vienna just a few weeks ago! So, I am very excited to get that underway and to continue to explore my chosen research avenues.

What is the best piece of advice you have ever been given?

Tough question! Well, my dad always tells me that sometimes you must be a bit cheeky to get what you want – but I’m not sure how well that would go down with a review panel! I have had many great mentors in my academic life too, all of whom have given me advice that I will take forward. However, my PhD supervisor, Dr. Jonathan Weaver, not only taught me to face my demons head on but also assured me that I was able to. He taught me not to take life too seriously and that fostering happiness in all facets of your life was the key to success. Jon passed away at only 32 years old, before we could finish the PhD together, so his advice and guidance has become very special to me.

Why did you choose to publish in ChemComm?

I definitely envisioned the article as a Communication, a short proof of concept for this new approach to making hypercrosslinked polymers. I chose ChemComm as I know it has a great reputation and a broad readership, making it an ideal platform for me to report my work to researchers around the globe. Furthermore, this is the third article I have published in ChemComm (the first as an independent researcher) and the entire process has always been very smooth and transparent, so I was very happy to return.

Rob obtained his PhD from The University of Liverpool (UK) in 2013, before completing a short post-doctoral position in Prof. Andy Cooper’s group. In 2014 he moved to Imperial College London’s Department of Chemical Engineering, where he joined the Polymer and Composite Engineering group and began to build his independent research profile in the design and application of porous polymers. This year Rob was appointed as an Assistant Professor at the University of Vienna’s Institute of Materials Chemistry, marking the beginning of his independent academic career. Find Rob on Twitter: @robbiewoody

Read Rob’s #ChemComm1st article and others in our new collection ChemComm Milestones – First Independent Articles. Follow us on Twitter for the latest #ChemCommMilestones news.

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Teachable micromotors

27 May 2020

By Alessia Millemaggi.

Micromotors, for the uninitiated aka me, are a specific type of colloidal structure that harvests energy from their environment and turns it into motion. In order for them to be truly effective for possible applications though, they must be able to communicate and coordinate with one another. If you want to make microbots, they can’t just move about all willy-nilly with no regard for each other. Recently, scientists have created a mixed system where one structure sheds silver ions that cause other micromotors to accelerate, an approach that mimics natural systems like bee colonies.

Researchers in China developed a system where photochemically powered micromotors can spontaneously “teach” catalytic micromotors to oscillate without any external influence. The teachers are Janus-type microparticles composed of either polymethylmethacrylate (PMMA) or silicon dioxide particles half coated with silver. Under irradiation with KCl and H₂O₂, the silver can interconvert between Ag(0) and Ag(1), causing the oscillatory motion of the entire particle. In contrast, the two non-oscillatory micromotors, either polystyrene spheres half coated with platinum (PS-PT) or gold-rhodium microrods (Au-Rh), catalytically decompose H₂O₂ to move autonomously in standard Brownian motion. When the two types of micromotors are mixed under UV light, the motion of the non-oscillatory materials changes from random to clearly oscillating (Figure 1). The intensity of the motion change depends on the proximity of the learner to the teacher, with learners closer to the teacher displaying more intense oscillations.

Figure 1. Change in movement of non-oscillating micromotors when exposed to oscillating “teacher” structures.

In fact, the Au-Rh rods will demonstrate more intense oscillations than the PMMA-Ag particles. The researchers propose a mechanism where the PMMA-Ag particles release silver ions as they oscillate, which then deposit onto the Au-Rh rods. The silver increases the catalytic activity of the rods and then, given the operating conditions, undergoes the same redox process that causes oscillation in the PMMA-Ag system.

Figure 2. Proposed mechanism of silver release and adsorption onto Au-Rh rods.

This hypothesized mechanism is supported by the development of oscillatory behavior by the Au-Rh rods in under reaction conditions where the PMMA-Ag particles are replaced by silver ions in solution. The silver on the rod surface isn’t merely adsorbed – it forms into small silver nanoparticles which can be seen via electron microscopy, making a new trimetallic structure. These nanoparticles change the trajectories of the rods, causing them to move in circles. While this system isn’t perfect, the student structures have imperfect memories and cannot teach one another, it provides a strategy for working with groups of micromotors to move towards coordinated motion and further applications.

To find out more, please read:

Non-oscillatory micromotors ‘‘learn’’ to oscillate on-the-fly from oscillating Ag micromotors

Chao Zhou, Qizhang Wang, Xianglong Lv and Wei Wang

Chem. Commun., 2020, Advance Article

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Potassium-Ion Batteries Welcome A New Electrode from Iron Compounds

28 Apr 2020

By Tianyu Liu.

A research team led by Jiang Zhou and Shuquan Liang of Central South University, China, recently identified iron oxyhydroxide (β-FeOOH) as a K-ion battery electrode material. It is reportedly the first iron-oxide-based compound to serve in K-ion batteries. The results have been published in Chemical Communications (DOI: 10.1039/d0cc01009j).

K-ion batteries are a new type of rechargeable battery emerging after Li-ion batteries, the charge-storage functionality of which is associated with the intercalation and de-intercalation of K⁺. Due to the relative abundance of K⁺ to Li⁺, K-ion batteries are poised as a promising alternative to Li-ion batteries.

The researchers made the electrode by a hydrothermal reaction. Specifically, they dispersed Super P® (SP), an electrically conductive additive, into FeCl₃ aqueous solutions. The mixture was then heated at 150 °C for 10 h. The resultant powder (FeOOH-SP), comprised of uniformly mixed, crystalline β-FeOOH nanorods and Super P particles (Fig. 1), was directly used as an electrode material.

Figure 1. Transmission electron microscopy images of (a, b) FeOOH-SP and (c) FeOOH. (d) Elemental mappings of C, Fe, and O in FeOOH-SP.

The authors investigated the electrochemical properties of FeOOH-SP in K-ion batteries. At a current density of 100 mA/g, FeOOH-SP exhibited a stable specific capacity of ~200 mAh/g, approximately double and quadruple that of SP and FeOOH alone, respectively (Fig. 2a). The specific capacity of FeOOH-SP was maintained at ~100 mAh/g when the current density increased to 2000 mA/g (Fig. 2b), showing its fast-charging capability. Additionally, the authors observed that the crystalline β-FeOOH nanorods amorphized upon K⁺ intercalation after being discharged (Fig. 2c). Their crystallinity was only partially restored when being re-charged (Fig. 2d). The loss of crystallinity, however, did not undermine the charge-storage capacity of FeOOH-SP.

Figure 2. (a) Specific capacities of FeOOH-SP, SP, and FeOOH at different charge-discharge cycles. Current density: 100 mA/g. (b) Rate capability of FeOOH-SP. (c, d) Transmission electron microscopy images of (c) discharged and (d) charged FeOOH-SP. Red dashed boxes highlight crystalline regions. The electrolyte was a mixture of ethylene carbonate and diethyl carbonate containing 1 M potassium bis(fluorosulfonyl)imide.

Considering the low-cost of iron oxyhydroxide, FeOOH-SP could reduce the manufacturing cost of K-ion batteries and increase the affordability of electrochemical charge storage devices.

For expanded understanding, please read:

β-FeOOH: A New Anode for Potassium-Ion Batteries

Xiaodong Shi, Liping Qin, Guofu Xu, Shan Guo, Shuci Ma, Yunxiang Zhao, Jiang Zhou, and Shuquan Liang

Chem. Commun., 2020, 56, 3713-3716.

Tianyu Liu acknowledges Zacary Croft at Virginia Tech, U.S., for his careful proofreading of this post.

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Aluminum-Based Liquid Coordination Complexes

28 Apr 2020

By Alessia Millemaggi.

Before I get into the research, I just have to say that I think ionic liquids (ILs) are just cool. An ionic compound that’s a liquid? Mind blown. Not only are they interesting, but those unique properties make them attractive for industrial use. One class of ionic liquids generating research focus is halometallate ionic liquids (HILs), generated by reacting a metal halide and an organic halide salt. In particular, chloro-alluminate ILs have been some of the most promising for applications in industrial acid catalysis and are composed of anionic aluminate species. However, recent work has found mixtures of aluminum chloride and N/O/S donors produce a liquid Lewis acidic compounds, referred to as liquid coordination complexes (LCCs). These LCCs are potential replacements for HILs, as they’re typically easier and cheaper to prepare. Further studies have found ionic species by ²⁷Al NMR, drawing parallels between LCCs and HILs. By combining AlCl₃ and polar organic solvents, researchers in the US screened for novel LCC or HIL reactivity in catalysis.

This straightforward approach allowed researchers to easily tune the ratio of AlCl₃ and solvent to find mixtures with desired properties. They chose the nitrogen donor 1-methylimidazole, N-Mim, and an oxygen donor N-methyl-2-pyrrolidone (O-NMP) as their solvents for testing given their wide availability and relevance to organic chemical reactivity. The selected solvent and AlCl₃ were mixed at room temperature and found in all cases to form heterogenous mixtures. When heated to 100 ^oC mixtures with molar fractions of AlCl₃ between 0.33 and 0.6 formed viscous liquids, many of which became solids at room temperature. These compounds were then crystalized for x-ray crystallographic analysis, where their structures confirmed the association of the aluminum with the nitrogen (Figure 1) or oxygen.

Figure 1. 50% probability ellipsoid plot of AlCl3(N-Mim), showing coordination between the aluminum and nitrogen

In the N-Mim system, ²⁷Al NMR showed the formation of a single aluminum-containing species at AlCl₃ molar fractions of 0.5 and below, with exchange occurring when higher concentrations of N-Mim are present. The O-NMP system proved more challenging to characterize crystallographically, potentially due to the formation of larger oligomeric complexes in the solid phase and increased disorder in the O-NMP ligand. However, ²⁷Al NMR proved insightful and showed the presence of multiple aluminum-containing species, including several different stoichiometries of aluminum-solvent adducts.

Figure 2. Aluminum NMR spectra of aluminum/O-NMP complexes showing speciation over a range of different stoichiometries.

When the two systems were side-by-side compared for Lewis acidity and catalytic activity for the alkylization of benzene, the clear winner was the O-NMP system. The O-NMP-AlCl₃ complex with an aluminum molar fraction of 0.6 was both the most Lewis acidic, determined by an acetonitrile IR probe, and the most catalytically active. It gave full conversion with a selectivity of almost 80%, while the N-Mim complex with the same mole fractions produced only a 32% conversion with no significant increase in selectivity. Complexes with less aluminum showed no signs of catalytic activity and were less Lewis acidic. The high activity of the AlCl₃/O-NMP system can be explained by its possession of both a highly Lewis acidic cation [AlCl₂(O-NMP)₂]⁺ and a highly Lewis acidic anion [Al₂Cl₇]^–, whose presence was identified in the NMR experiments. This work demonstrated a straightforward method to synthesize LCC-based catalysts with high activity, while providing some general guidance on the suitability of O-donor ligands for further study.

To find out more, please read:

Are ionic liquids and liquid coordination complexes really different? – Synthesis, characterization, and catalytic activity of AlCl3/base catalysts

Rajkumar Kore, Steven P. Kelley, Anand D. Sawant, Manish Kumar Mishra and Robin D. Rogers

Chem. Commun., 2020, Advance Article

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