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Ruthenium Currency for a Hydrogen Fuel Economy

02 May 2018

A group of researchers at the Chinese Academy of Sciences and Southwest University want us to kick the fossil fuels habit. Their research comes to us from China, a country using roughly one quarter of the world’s yearly energy consumption, and where the finite nature of fossil fuels is a very real threat to energy supply security. Leading in energy use, China also leads the world in electricity production from renewable sources and investment in clean energy projects.

Hydrogen is considered a viable alternative to fossil fuels as it is energy rich, more so than petrol or ethanol at 39 kWh/kg (petrol: 13 kWh/kg, ethanol: 8.2 kWh/kg), and upon combustion emits only water vapour. However, hydrogen is often obtained from fossil fuels, and it will only be a practical option for the world’s future energy needs if it can be produced from a renewable source.

Preparation of the Ru2P/reduced graphene oxide electrocatalyst for the hydrogen evolution reaction

Preparation of the Ru₂P/reduced graphene oxide catalyst

To this end, water splitting offers a solution. In a water electrolysis cell, hydrogen is produced at the cathode via the hydrogen evolution reaction (HER, 2H⁺ + 2e^– –> H₂), and molecular oxygen is produced at the anode (2H₂O –> O₂ + 4H⁺ + 4e^–). It is ideal in theory, but high energy efficiencies are required to make water splitting viable, and this relies on the development of catalytic electrodes to minimize overpotentials required to drive the reaction. Currently, state of the art HER electrocatalysts use platinum, which is expensive and rare. Furthermore, platinum catalysts are most efficient in an acidic electrolyte and proceed 2-3 times slower in alkaline solutions. On the other hand, the best oxygen evolution catalysts perform better in alkaline environments. Using an alkaline electrolyte has overall advantages as it is less corrosive, thus increasing the stability and lifetime of the electrolytic cell.

The authors have developed a HER catalyst, using ruthenium, with overpotentials and current densities superior to Pt/C in both alkaline and acidic conditions.

DFT calculation to probe the hydrogen adsorption energies on the active catalytic surface of the Ru2P on reduced graphene oxide catalyst.

DFT calculation to probe the hydrogen adsorption energies on the active catalytic surface of the Ru₂P catalyst. a) and b) front and side views of the calculated Ru₂P/reduced graphene oxide surface. c) free energy diagram for the HER with different catalysts.

The electrocatalyst is comprised of small, uniform Ru₂P nanoparticles (~2-4 nm) evenly distributed on reduced graphene oxide sheets. The activity of the prepared catalyst (1.0 mg cm^-2) for the HER was measured in an acidic medium (0.5 M H₂SO₄) and the overpotential to achieve a current density of -10 mA cm^-2 was -22 mV, superior to Pt/C (-27 mV). In an alkaline environment (1.0 M KOH) catalyst performance was enhanced, with an overpotential of -13 mV (29 mV lower than Pt/C). High Faradaic efficiencies of more than 98% were measured in both acidic and alkaline solutions. Additionally, analysis was undertaken to further understand how the structure and composition of the catalyst influences its activity. Double layer capacitance measurements gave clues about the catalyst surface, while theoretical DFT calculations were used to study H-adsorption energies.

There is no way to avoid the reality that ruthenium is also a rare and costly metal, and for this reason may not hold the key to solving our energy woes. However, of real value are the insights gained from probing the structure function relationship of this highly active catalyst, which may guide the synthesis of rationally-designed catalysts using inexpensive and abundant materials.

To find out more please read:

Ultrasmall Ru₂P nanoparticles on graphene: a highly efficient hydrogen evolution reaction electrocatalyst in both acidic and alkaline media

Tingting Liu, Shuo Wang, Qiuju Zhang, Liang Chen, Weihua Hu, Chang Ming Li.
Chem. Commun., 2018, 54, 3343-3346
DOI: 10.1039/c8cc01166d

About the author:

Zoë Hearne is a PhD candidate in chemistry at McGill University in Montréal, Canada, under the supervision of Professor Chao-Jun Li. She hails from Canberra, Australia, where she completed her undergraduate degree. Her current research focuses on transition metal catalysis to effect novel transformations, and out of the lab she is an enthusiastic chemistry tutor and science communicator.

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In-Situ Electron Paramagnetic Resonance Spectroscopy Revealed the Charge Storage Behavior of Activated Carbon

19 Apr 2018

Recently in Chem. Commun., Wang et al. from University of Manchester and Liverpool John Moores University, U.K. demonstrated that in-situ electron paramagnetic resonance (EPR) spectroscopy was a powerful tool to study the charge storage mechanism of activated carbon.

Activated carbon is a type of microporous carbon used for electrodes of supercapacitors (a family of charge-storage devices similar to batteries). Conventional electrochemical testing techniques (e.g. cyclic voltammetry) are able to evaluate the overall performance of electrode materials but are unable to reveal the charge storage mechanism at the atomic level. Understanding the charge storage mechanism is crucial to guide the design and synthesis of electrode materials with improved performance. During the past decade, the development of numerous in-situ probing techniques has allowed materials researchers to explore the microscopic charge-discharge behaviour of supercapacitor electrodes.

In the published paper, in-situ EPR spectroscopy was used to study the electrochemical properties of activated carbon under different external potentials. EPR is very sensitive to electron spins originating from unpaired electrons that are generated upon charging or discharging electrode materials. This characteristic makes EPR a suitable technique for in-situ studies. To carry out the experiments, the authors designed and constructed a capillary three-electrode testing cell (Figure 1a). This cell was placed in an EPR spectrometer and its activated carbon electrode was connected to an external power source (to apply external potentials to the activated carbon electrode). The authors collected the spectra of the activated carbon electrode at selected applied potentials, an example of which is shown in Figure 1b.

Analysis of the obtained spectra offered important information about how the surface of activated carbon changed at different potentials. Specifically, the authors deconvoluted the signal into two components: the narrow signal and the broad signal corresponding to the blue and red curves in Figure 1b, respectively. The peak intensity of the narrow signal increased drastically when charging the electrode, but remained almost unchanged when altering the testing temperature. This observation suggests that the origin of the narrow peaks was the surface-localized electrons. These localized electrons were likely from the oxidized products (i.e. radicals) of carboxylate and alkoxide groups on the surface of the activated carbon, evolved during the charging process. The broad signal was ascribed to electrons located on aromatic units (e.g. graphene domains) and its intensity was found to be proportional to the number of ions electrically adsorbed on the activated carbon surface.

Figure 1. (a) The structure of the self-built capillary three-electrode cell: CE – counter electrode (Pt wire); RE – reference electrode (Ag/AgCl); WE – working electrode (activated carbon). (b) A typical EPR signal (black) that can be deconvoluted into narrow peaks (blue) and broad peaks (red).

This work highlights EPR spectroscopy as a novel tool for in-situ investigation of the charge-storage mechanism of carbon-based supercapacitor electrodes, and could be potentially extended to study other types of materials. The availability of diverse in-situ techniques is expected to provide more in-depth fundamental understanding that will guide researchers to rationally develop electrodes with optimized performance.

To find out more please read:

In-Situ Electrochemical Electron Paramagnetic Resonance Spectroscopy as A Tool to Probe Electric Double Layer Capacitance

Bin Wang, Alistair J. Fielding and Robert A. W. Dryfe

Chem. Commun. 2018, DOI: 10.1039/c8cc00450a

About the blogger:

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

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Synthesis of Maleimide Dyes with Colourful Fluorescent Emissions

18 Apr 2018

A group of researchers based at universities spanning the UK, China and Spain have synthesised a diverse library of fluorescent maleimide dyes with the aim of developing a structure-function relationship, relating substituent effects to the optical properties of such molecules. This work is not only important to build upon fundamental understanding of the fluorescence mechanism, but to develop knowledge that may be used to guide the synthesis of organic fluorophores which demand particular optical properties.

Organic fluorescent molecules are used as tools in many areas such as forensics, genetic analysis, DNA sequencing and biotechnology. Maleimides are commonly used as fluorescent labels for proteins, as they can couple with the thiol groups of cysteine residues. They are suited to this purpose as they are stable, easily functionalised, give strong emissions and do not perturb the protein structure to a large extent.

Molecules fluoresce upon absorption of UV or visible light, elevating an electron from a ground state orbital to a higher-energy orbital and resulting in a singlet excited state. Relaxation to the ground state occurs rapidly (~ 10 ns) with concomitant emission of a photon – this is what we observe as ‘fluorescence’. The emitted photon almost always has a longer wavelength than the absorbed light, a phenomenon known as the ‘Stokes shift’.

Structures of selected amino-halo-maleimides and alkoxy-halo-maleimides synthesised for the study

With three dihalomaleimide precursers in hand (Cl, Br and I) the researchers assembled a library of amino-halo-maleimides, amino-alkoxy-maleimides, and amino-thio-maleimides. They varied the R groups bound to the N, O and S heteroatoms to include aliphatic, phenyl and benzyl examples.

The optical properties of the amino-halo-maleimides in diethyl ether were examined and the emission wavelengths were measured to be 461-487 nm, giving green-blue fluorescence. The fluorescence quantum yields, a measure of the quantity of emitted photons compared to absorbed photons and an indication of emission brightness, decreased with the electronegativity of the halide (Cl: 37%, Br: 30%, I: 8%). Like many fluorescent molecules in solution the compounds exhibited solvafluorochromism: when the polarity of the solvent alters the optical properties. In protic solvents (methanol and water) the fluorescence quantum yields decreased to below 1% and the emission wavelengths increased by 73-109 nm. On the other hand, in non-polar solvents (cyclohexane) the fluorescence quantum yield increased, up to 56% for the chloro analogue.

a) The UV and emission spectra of fluorescent maleimides bearing amino (2a-c) and alkoxy (3a, 3b) substituents. b) The quantum yields of selected amino and alkoxymaleimides. c) The solvafluorochromism effect for three maleimides (2a-c) in various solvents.

Compared to their amino-substituted counterparts, alkoxy-halo-maleimides have lower quantum yields (reduction of 20-25%), indicating the increased electron-donating capacity of the amine substituent is important for fluorescence intensity. Furthermore, the slight decrease in the emission wavelengths of alkoxy-halo-maleimides (458-465 nm) gives them blue fluorescent emissions. Amino-thio-maleimides, with greater electron-donating capacity than both the amino and alkoxy analogues, have increased emission wavelengths (526-564 nm), thus yellow fluorescent emissions.

This study is a worthwhile read for anyone who uses fluorescent molecules in their work, those wishing to understand a little more about the practical principles of fluorescence and all those curious minds who like to form their own hypotheses.

To find out more please read:

Rational design of substituted maleimide dyes with tunable fluorescence and solvafluorochromism

Yujie Xie, Jonathan T. Husband, Miquel Torrent-Sucarrat, Huan Yang, Weisheng Liu, Rachel K. O’Reilly.
Chem. Commun., 2018, 54, 3339 – 3342
DOI: 10.1039/C8CC00772A

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An Industrial Revolution on the Nanoscale

27 Mar 2018

“What are the possibilities of small but movable machines? They may or may not be useful, but they surely would be fun to make”. In December 1959 Richard Feynman addressed the annual meeting of the American Physical Society at Caltech with a talk entitled ‘There’s Plenty of Room at the Bottom’, imploring the scientific community to start thinking small, like ‘entire 24 volumes of the Encyclopaedia Britannica on the head of a pin’ kind of small. Many quote this lecture as when the notion of nanomachines first entered the scientific sphere – with talk of miniature cars, injectable molecular ‘surgeons’ and machines that place atoms side by side to synthesize any molecule imaginable. The lecture reads like the description of the futuristic setting in ‘Back to the Future’, an exploration of possibilities at a time when we fundamentally lacked the tools to make them a reality.

As in ‘Back to the Future’, which predated yet predicted the emergence of mobile-banking technology, video calling and personal drones, Richard Feynman’s plea for scientists to prepare molecular-scale machines has also become a reality, and for their successes in this field Jean-Pierre Sauvage, Sir Fraser Stoddart and Ben Feringa were jointly awarded the Nobel Prize in Chemistry in 2016.

A group of researchers based in London and Singapore have written a feature article introducing both the foundational work in this field and state-of-the-art examples. Nanomachines are single molecules or molecular assemblies on the nanoscale (this review defines a 1 – 100 nm scope) that have the ability to perform ‘useful work’ upon application of an external energy source. To extract work (often in the form of controlled mechanical movement) molecular machines are designed to operate at a thermodynamically far-from-equilibrium state, maintained by an energy input, with movement occurring as the system relaxes towards equilibrium. At the synthetic level, molecules are designed with components which have restricted translational and rotational movements with respect to each other, and the ability to control these movements is key to obtaining the desired function.

A catalytically active rotaxane synthesised by Nolte and co-workers acts as a tiny epoxidising machine , moving along a polybutadiene polymer

The catalytically active rotaxane synthesised by Nolte and co-workers acts as a tiny epoxidising machine, moving along a polybutadiene polymer

One of the first advances towards the synthesis of nanomachines was by the research group of Jean-Pierre Sauvage, who achieved the templated synthesis of catenanes; structures with two circular molecules that are interlocked like two links in a chain. It was subsequently shown that a catenane motor could be prepared, with one ring rotating with respect to the other in a controlled manner. Fraser Stoddart further contributed to the field with ‘rotaxanes’, composite molecules comprising a ring threaded onto an axle. Nanomachines based on rotaxanes have been developed and include switches, shuttles and ‘molecular elevators’. A state-of-the-art example of a catalytically active rotaxane synthesised by Nolte and co-workers in 2003 demonstrates the potential of nanomachines to revolutionise organic synthesis. The rotaxane is constructed with a magnesium-bound porphyrin, which threads onto a polybutadiene polymer (300 kDa, 98% cis) and catalyses the epoxidation of the double bonds (turnover number: 140, cis/trans ratio of the polyepoxide: 1:4).

Ben Feringa’s electric nano-car, a single molecule with four fluorene ‘wheels’ capable of driving across a copper surface

In 2011 Ben Feringa and co-workers synthesized the worlds tiniest electric car using the same design principles they had used to create a spinning motor in 1999. The car is a single molecule with the ability to propel itself across a crystalline copper surface upon activation by a voltage pulse, with 10 pulses moving the car 6 nm across the surface. The car itself is comprised of a central diyne strut bonded at each end to carbazole ‘axles’. Each axle is bound through alkenes to two fluorene ‘wheels’. The key design elements are the alkenes and two chiral methyl substituents on each axle which forces each wheel to twist out of the plane. For one wheel rotation: an electronic excitation induces trans–cis isomerisation of the alkene causing a quarter turn of the wheel such that it sits adjacent to the methyl group. Next, a vibrational excitation induces helical inversion, allowing the wheel to push past the methyl group another quarter turn. Another isomerisation and helical inversion completes a full rotation. Research achievements like these demonstrate mechanical work on the nanoscale, with the vision of achieving movement on the macroscale via synchronised motion.

These examples represent a small subset of those discussed in the feature article review, which not only spans the current scope of molecular-scale machines, but reviews the design principles guiding their development and the possibilities nanomachines represent in the future of scientific research.

To find out more please read:

Artificial molecular and nanostructures for advanced nanomachinery

Elizabeth Ellis, Suresh Moorthy, Weng-I Katherine Chio and Tung-Chun Lee.
Chem. Commun., 2018, Advance Article
DOI: 10.1039/c7cc09133h

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Anchoring Arynes on Graphene with Microwave but No Solvents

15 Feb 2018

Recently in ChemComm, an international team from Italy and Spain reported a non-conventional way to anchor arynes onto graphene surface using microwave. Their developed method is fast, efficient, mild and solvent-free.

Attaching functional groups onto graphene surface, i.e. functionalization, allows the physical and chemical properties of graphene to be fine-tuned, such as electrical conductivity and solubility. Conventional solvent-based functionalization strategies usually involve time-consuming reactions and tedious purification steps. The poor suspension stability of graphene in solvents, particularly in polar organic solvents, greatly hinders the overall functionalization efficiency. Therefore, establishing easy and solvent-free functionalization protocols for graphene is highly needed.

M. Prato, A. Criado and coworkers made a breakthrough in addressing this challenge by developing a microwave-assisted functionalization method. Their method to functionalize graphene consists of cycloaddition reactions between few-layer graphene (FLG) and arynes (Figure 1). These reactions proceed by mixing the dry powder of FLG and arylene anhydrides, the precursors of arynes, followed by rapid heating under microwave irradiation. The whole process is solvent-free and occurs within half a minute. It is also applicable to a variety of arynes (Figure 2).

Figure 1. The schematic illustration of the microwave-assisted functionalization of graphene with arynes. This process can be carried out within half a minute and is solvent-free.

Figure 2. A variety of arynes capable of being anchored on graphene surface. 1~6 represent the arylene anhydrides and f-G(7)~f-G(12) are corresponding arynes attached onto graphene.

The most unique feature of the demonstrated method is the dual role of FLG. In addition to being one of the reactants, FLG is capable of absorbing microwave energy, and enables its surface to rapidly reach high temperatures that significantly accelerate the cycloaddition reactions.

This microwave-assisted functionalization method shows great promise as a stepping stone for the fast and efficient modulation of graphene surface and subsequently, the performance of graphene-based electronics.

To find out more please read:

Microwave-Induced Covalent Functionalization of Few-Layer Graphene with Arynes Under Solvent-Free Conditions

V. Sulleiro, S. Quiroga, D. Peña, D. Pérez, E. Guitián, A. Criado and M. Prato

Chem. Commun. 2018, DOI: 10.1039/C7CC08676H

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Hiding Carbon Dioxide in Oxazolidinones

01 Feb 2018

Sometimes it feels as though the pinnacle of synthetic achievement is represented by 20 step total syntheses (with 10 contiguous stereocentres and 5 fused rings…). The level of chemical complexity that can be fashioned from simple building blocks is undoubtedly impressive, but amid such feats it is important not to lose sight of the elegance and worth of simple chemistry, especially when it aims to play a part in resolving profound challenges. One such challenge, which will increasingly confront future generations, is how to reduce the load of carbon dioxide in the atmosphere. One solution is to ‘fix’ carbon dioxide by integrating it into chemical building blocks of added complexity in a sustainable way.

The porosity and high surface area of metal organic frameworks (MOFs), a class of three-dimensional coordination networks, proffers them as ideal materials for capture and storage of carbon dioxide. A team of researchers have designed a MOF which consumes carbon dioxide in a different way: by transformation into value-added chemicals. The group have developed a catalytic MOF embedded with lewis-acidic copper centres capable of converting aziridines to oxazolidinones by the addition of carbon dioxide. Oxazolidinones are used as auxiliaries in chiral synthesis, and are structural components of some antibiotics.

The MOF, termed MMPF-10, is a metal-metalloporphyrin framework constructed from a copper-bound porphyrin ring chemically modified to incorporate 8 benzoic acid moieties, generating an octatopic ligand. These carboxylic acids groups form a second complex with copper in situ, termed a ‘paddlewheel’ for its appearance, with the formula [Cu₂(CO₂)₄]. The resulting network contains hexagonal channels measuring 25.6 x 15.6 Å flanked by four of each of the two copper complexes. With 0.625 % of the catalyst at room temperature, 1 bar CO₂pressure, and in a solvent free environment, MMPF-10 catalyses the transformation of 1-methyl-2-phenylaziridine to yield 63% of the product.

metal-metalloporphyrin MOF catalyses catalyzes carbon dioxide fixation aziridines to oxazolidinones

Topology of MMPF-10 showing hexagonal channels in a) and c), and pentagonal cavities in b). Turquoise: copper, red: oxygen, grey: carbon, blue: nitrogen.

This work, a simple reaction to prepare oxazolidinones, shows that carbon dioxide can be fixed in specialised synthetic building blocks in a sustainable way. This is the way the first paragraph ended, ‘in a sustainable way’, because the challenge of developing such a reaction is two-fold: it must use carbon dioxide, and the reaction conditions must be sustainable. There will be no beneficial offset if the reaction uses a lot of energy, requires many resources, or generates larges quantities of waste. In this reaction the researchers have remained mindful of developing a mild, solvent-free reaction with low catalyst loading employing an earth abundant metal, reflecting an earnest aim to develop practical and sustainable chemistry.

To find out more please read:

A metal-metalloporphyrin framework based on an octatopic porphyrin ligand for chemical fixation of CO₂ with aziridines

Xun Wang, Wen-Yang Gao, Zheng Niu, Lukasz Wojtas, Jason A. Perman, Yu-Sheng Chen, Zhong Li, Briana Aguila and Shengqian Ma
Chem. Commun., 2018, Advance Article
DOI: 10.1039/c7cc08844b

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Single-Crystalline NiFe-Hydroxide Nanosheets for Catalyzing Oxygen Evolution

29 Jan 2018

A group of scientists led by Prof. Shizhang Qiao has synthesized an oxygen evolution reaction (OER) catalyst combining the merit of low cost, excellent catalytic activity and long lifetime. This OER catalyst is composed of single-crystalline NiFe-hydroxide nanoflakes directly grown on nickel foams. The work has been published recently in ChemComm.

OER, the reaction of producing oxygen gas from water, is an indispensable component of electricity-generation devices using sustainable energy (e.g. fuel cells and photoelectrochemical water splitting cells). OER is usually the bottleneck limiting the overall energy conversion efficiency due to its sluggish kinetics and complex reaction pathways. As such, OER catalysts are needed to accelerate the OER reaction rate. Among the various OER catalysts, noble metal oxides stand out owing to their ultrahigh catalytic activity. However, the “shining” performance is dimmed by their high cost and short lifetime. Thus, obtaining alternatives with comparable OER catalytic activity as well as long-term stability is required to advance the utilisation of sustainable energy.

To address this challenge, the authors turned their attention to a low-cost transition metal, nickel. They developed a hydrothermal method using nickel foams to grow highly crystalline and near-vertically aligned NiFe-hydroxide nanosheets as OER catalysts (Figure 1a). The seamless integration between the hydroxide nanosheets and the nickel substrates reduces the contact resistance and facilitates interfacial electron transfer. The near-vertical orientation (Figure 1b) allows water molecules to fully contact the catalysts. Both of the characteristics render excellent OER catalytic activity. Additionally, the high crystallinity (Figure 1c) ensures the catalysts are robust enough to withstand extensive use without degradation in performance.

Figure 1. (a) The schematic illustration of the synthetic procedures of the NiFe-hydroxide [Fe-Ni(OH)2] nanosheets supported on nickel foams (NF). (b) The scanning electron microscopy image shows the near-vertically aligned nanosheets on a piece of nickel foam. (c) The transmission electron microscopy image reveals the crystallinity of the synthesized catalyst.

The NiFe-hydroxide nanosheets outperform most of the state-of-the-art OER catalysts, including those containing noble metal elements. Specifically, the nanosheets exhibit an onset potential of 1.497 V (Figure 2). The onset potential is a measure of the catalytic activity that equals the magnitude of potential required to yield a current density of 10 mA/cm² (when appreciable amount of oxygen gas is evolved). Outstandingly, the onset potential of the NiFe-hydroxide is the smallest among the catalysts selected for comparison.

Figure 2. The polarisation curves of different OER catalysts. The onset potential is marked by the dotted line in the inset.

The catalytic activity is also highly stable, with no loss in performance after at least 100 h of measurement. Interestingly, the onset potential further shifts to a lower value of 1.465 V after 100 h. The authors attributed this observation to a “self-activation” process that involves the formation and accumulation of nickel oxyhydroxide (NiOOH) on the surface of the nanosheets.

The hydrothermal method demonstrated here could be used to synthesize other cost-effective crystalline catalysts to develop catalysts for reactions beyond OER, such as hydrogen evolution and carbon dioxide reduction.

To find out more please read:

Free-Standing Single-Crystalline NiFe-Hydroxide Nanoflake Arrays: A Self-Activated and Robust Electrocatalyst for Oxygen Evolution

Jinlong Liu, Yao Zheng, Zhenyu Wang, Zhouguang Lu, Anthony Vasileff and Shi-Zhang Qiao

Chem. Commun. 2017, DOI: 10.1039/c7cc08843d

About the blogger:

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

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Shoot the Messenger: Circular DNA-Graphene Oxide Material Targets mRNA in Living Cells

19 Jan 2018

Schematic of the circular DNA cDNA/GO graphene oxide platform fabrication for intracellular mRNA messenger RNA imaging and gene therapy.

Scheme showing how cDNA/GO enters the cell and interacts with mRNA

Did you know that the combined length of DNA in your body’s cells is a number so large that the only references I could find use cosmic distances as a reference? Try twice the diameter of the solar system, or the distance to the moon and back 1500 times. Despite the complexity and infinite detail encountered when studying science, it is often something so simple as size that gives us pause. How can DNA be both uncomprehendingly huge and tiny at the same time?

The major function of DNA is to encode proteins, a process which begins with the transcription of genes into single-stranded messenger RNA (mRNA) molecules. It is mRNA that is directly translated into the strands of amino acids which fold to form proteins.

A team of researchers at Fuzhou University in China have developed a graphene oxide and circularised single-stranded DNA (cDNA/GO) hybrid material capable of penetrating living cells and binding mRNA. The material’s utility is shown in two practical applications: mRNA imaging and nucleotide therapeutics. The authors chose the mRNA of survivin and c-raf kinase as targets, because the enzymes are involved in carcinogenesis, and the mRNA are overexpressed in cancer cells and can be used as biomarkers.

cDNA was chosen for its increased stability over linear single-stranded DNA, which is rapidly degraded in vivo by exonucleases. For mRNA imaging the material is designed with a fluorescent dye coupled to the cDNA. GO was chosen as a hydrophilic delivery scaffold capable of adsorbing cDNA and quenching the dye. When cDNA/GO was incubated with HeLa cells (a cancer cell strain) a time-dependent increase in fluorescence was observed in the cytoplasm. Fluorescence is restored when cDNA encounters the target and desorbs from the GO to form a duplex with the mRNA.

CLSM images acquired for HeLa cells treated with both survivin and c-raf targeted cDNA/GO for duplexed intracellular mRNA imaging

The mRNA of both survivin and c-raf kinase can be imaged in living cells with cDNA/GO.

The researchers also probed whether the material might serve as a therapeutic agent: if formation of the cDNA-mRNA duplex blocks translation it may reduce the load of c-raf kinase and survivin in the cell and influence cancer cell growth. Accordingly, the researchers found that when the HeLa cells were incubated with cDNA/GO, cell proliferation was inhibited in a dose-dependent manner.

This research contributes a robust design which can be applied to diverse mRNA targets because optimisable properties such as stability, bioavailability and selectivity are largely independent of the sequence of nucleotides.

To find out more please read:

Circular DNA: a stable probe for highly efficient mRNA imaging and gene therapy in living cells

Jingying Li, Jie Zhou, Tong Liu, Shan Chen, Juan Li and Huanghao Yang
Chem. Commun., 2018, Advance Article
DOI: 10.1039/C7CC08906F

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Binder-free Integration of Bismuth Nanoflakes onto Nickel Foams for Sodium-ion Batteries

13 Dec 2017

A new type of bismuth-based electrode material for sodium-ion batteries has been synthesized. This electrode consists of bismuth metal nanoflakes seamlessly integrated onto nickel foams. The electrode contains no polymer binders, a crucial component required to retain the structural integrity of most battery electrodes. This binder-free feature improves the amount of charge being stored (i.e. capacity) at fast charging rates.

Sodium-ion batteries are attracting worldwide research efforts as electric energy storage devices, in addition to the prevalent lithium-ion batteries, due to the abundance of sodium. Similar to the preparation of other battery electrodes, fabricating sodium-ion battery electrodes generally requires binders, e.g. polyvinylidene fluoride (PVDF), to hold powdered electrode materials together and glue them to metal supporting substrates. However, the electrically insulating nature of the binders impedes fast electron transport between electrode materials and supporting substrates, consequently degrading the capacity of the batteries at fast charging rates.

Now in ChemComm, researchers from Nankai University & the Collaborative Innovation Center of Chemical Science and Engineering in China demonstrate a bismuth-based electrode material that does not involve a binder. This characteristic is realized by the in-situ growth of bismuth nanoflakes onto nickel foams through a solution-based replacement reaction (Figure 1). Because the nanoflakes grow directly from the nickel foam surface and firmly anchor onto nickel (Figure 2a), the resultant Bi/Ni composite can be directly used as an electrode. Specifically, the bismuth nanoflakes and nickel foam serve as the active material and supporting substrate, respectively.

The Bi/Ni composite exhibited excellent electrochemical performance. It achieved a high capacity of 377.1 mAh/g at a current density of 20 mA/g. Significantly, when the current density increased 100-fold, its capacity could still retain 206.4 mAh/g, which is more than half of the capacity obtained at 20 mA/g (Figure 2b). This outstanding capacity retention is a benefit of the binder-free characteristic that reduces the resistance of electron transport.

The authors then elucidated the working mechanism of the bismuth nanoflakes by in-situ Raman spectroscopy. They concluded that a two-step alloying process was responsible for the charge storage activity.

Figure 1. A schematic illustration showing the synthetic process of the binder-free Bi/Ni electrode. By inserting a piece of nickel foam into an ethylene glycol (EG) solution containing bismuth(III) nitrate, Bi3+ can replace Ni metal, be reduced to Bi metal and deposit on the Ni metal surface.

Figure 2. (a) A scanning electron microscopy image of the bismuth nanoflakes. (b) A plot showing the capacity of the Bi/Ni electrode at different current densities.

The successful synthesis of the binder-free electrode is expected to encourage future works on the design and synthesis of integrated electrode materials to advance the performance of sodium-ion batteries.

To find out more please read:

In situ Synthesis of Bi Nanoflakes on Ni Foam for Sodium-ion Batteries

Liubin Wang, Chenchen Wang, Fujun Li, Fangyi Cheng and Jun Chen

Chem. Commun. 2017, DOI: 10.1039/c7cc08341f

About the blogger:

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

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Creating Defects to Enhance Oxygen Evolution Activity: A Case Study using CoFe Layered Double Hydroxides

23 Nov 2017

A group of scientists recently made a breakthrough in promoting the oxygen evolution activity of metal hydroxides. They developed a simple yet efficient strategy of immersing the metal hydroxides in diluted acid solutions.

The oxygen evolution reaction (OER) is a critical component for solar-driven water splitting that can sustainably acquire a clean fuel — hydrogen gas by solar energy. Certain noble metal oxides, such as iridium dioxide (IrO₂) and ruthenium dioxide (RuO₂), work extremely well for catalyzing OERs. However, their scarcity restricts their potential for large-scale applications. To address the cost bottleneck, inexpensive alternatives such as metal hydroxides are being investigated worldwide. Unfortunately, their performance cannot compete with IrO₂ or RuO₂, partly due to their limited active sites for oxygen evolution. As such, there is a current need to develop strategies to promote the oxygen evolution activity of these metal hydroxides.

Figure 1. A schematic illustration showing the structural change of CoFe layered double hydroxide after being immersed in diluted nitric acid. Acid soaking creates Fe, Co and O defects (represented by V_Fe, V_Co, and V_O in the illustration, respectively) as well as separating the hydroxide layers.

Recently, Zhou et al. from Hunan University and Shenzhen University in China, demonstrated an easy acid-etching method that is capable of significantly improving the oxygen evolution activity of CoFe layered double hydroxide. When the hydroxide comes into contact with the nitric acid, protons remove some Co, Fe and O atoms and leave behind vacancies. These vacancies are named defects (Figure 2). Oxygen gas prefers to evolve at these defects and thus the defective hydroxide exhibits improved oxygen evolution activity. In addition, the nitrate anions can intercalate in between the metal hydroxide layers and break adjacent layers apart, exposing a large number of defect-containing surfaces and thus further boosting the oxygen evolution activity (Figure 1).

Figure 2. Transmission electron microscopy images of untreated CoFe layered double hydroxide (a, b) and acid-etched CoFe layered double hydroxide (c, d). After etching, the hydroxide nanoplates crack (due to layer separation) and surfaces become rough (due to creation of defects).

This method is expected to be applicable for a wide range of other metal hydroxides. The simplicity and efficiency of this method could make oxygen evolution catalysts cost-effective for commercialization.

To find out more please read:

Acid-etched Layered Double Hydroxides with Rich Defects for Enhancing the Oxygen Evolution Reaction

Peng Zhou, Yanyong Wang, Chao Xie, Chen Chen, Hanwen Liu, Ru Chen, Jia Huo and Shuangyin Wang

Chem. Commun. 2017, 53, 11778-11781

About the blogger:

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

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Creating Defects to Enhance Oxygen Evolution Activity: A Case Study using CoFe Layered Double Hydroxides

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