Archive for the ‘Subject Areas’ Category

Shrinking the Size of Hydrogen Evolution Catalysts by Carbon Coating

Hydrogen gas is a zero-emission energy resource promising to replace diminishing fossil fuels. The electrolysis of water is a sustainable way to acquire hydrogen gas, but this non-spontaneous process demands electricity to proceed. Therefore, hydrogen evolution reaction (HER) catalysts are used to reduce the energy cost or overpotential of the electrolysis.

Researchers are pursuing ultrafine nanoparticles as HER catalysts due to their high catalytic activity. For example, the HER catalytic activities of Ru nanoparticles are reportedly 100-200% higher than those of bulk Ru catalysts. Unfortunately, the preparation of well-dispersed nanoparticles is challenging because nanoparticles are prone to aggregate together.

Recently in ChemComm, Fuqiang Chu, Yong Qin and coworkers from Changzhou University, China addressed the challenge. They utilized a Ru-based coordination complex and cyanuric acid as the reactants, and synthesized high-performance HER catalysts composed of ~2 nm Ru nanoparticles uniformly dispersed on graphene sheets. During the thermal annealing step in the synthesis, the ligands of the complex and the cyanuric acid both decompose to nitrogen-doped carbon shells covering the as-formed Ru nanoparticles. These shells serve as spacers that prevent particle aggregation (Figure 1).

Figure 1. An illustration of the synthesis of carbon-coated Ru ultrafine nanoparticles on graphene sheets. Tris(2,2′-bipyrindine) ruthenium dichloride is the precursor of the Ru nanoparticles.

In both the acidic and the alkaline electrolytes, the 2 nm Ru particles (RuNC-2) display lower overpotentials and higher current densities than the 5 nm Ru particles (Figure 2) without the carbon coating (RuNC-5). Remarkably, the 2 nm particles showed comparable performance to the benchmark Pt catalyst in the acidic electrolyte (the red and black curves in Figure 2a).

Figure 2. Linear sweep voltammograms of ~3 nm Pt nanoparticles (PtNC), 2 nm Ru nanoparticles (RuNC-2) and 5 nm Ru nanoparticles (RuNC-5) in (a) 0.5 M H2SO4 and (b) 1 M KOH aqueous solutions.

The concept of the in-situ generation of protective coatings could inspire the synthesis of other ultra-small nanoparticles to potentially push the HER catalytic performance to new heights.

 

To find out more please read:

An Ultrafine Ruthenium Nanocrystal with Extremely High Activity for the Hydrogen Evolution Reaction in Both Acidic and Alkaline Media

Yutong Li, Fuqiang Chu, Yang Liu, Yong Kong, Yongxin Tao, Yongxin Li and Yong Qin

Chem. Commun., 2018, DOI: 10.1039/c8cc08276f

 

About the blogger:

Tianyu Liu obtained his Ph.D. (2017) in Chemistry from University of California, Santa Cruz in the 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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Copper A3 Coupling using a Switchable Homogeneous/Heterogeneous Catalyst

A MOC, I learned this week, is a metal-organic cage. I was familiar with MOMs, MOFs and MOBs, but MOCs were a new one. A MOM (metal-organic material) is a coordination-driven assembly constructed from metal nodes linked by organic ligands. MOMs encompass both MOFs (metal-organic frameworks) and MOCs (metal-organic cages). A MOF is an extended network with the potential for inner porosity, and a MOC is a discrete metal-ligand cluster. And that’s just about as far down the nomenclature rabbit hole I’m willing to go. If you’re keeping up you’ll realise that I forgot one! A MOB is a crowd of graduate students competing for free coffee at the public seminar.

Dong and co-workers at Shandong Normal University designed and prepared a MOM catalyst constructed from copper(II) nodes and a tripodal ligand consisting of a phenylic wheel functionalised with diketones. In chloroform these two components arrange into discrete MOC assemblies containing two tripodal ligands and three copper ions. The copper ions in the cluster are each coordinated to two diketone moieties (in a acetylacetonate-like fashion) in a quasi-square planar arrangement.

Synthesis of the tripodal ligand functionalised with diketone coordinating moieties.

Synthesis of the tripodal ligand functionalised with diketone coordinating moieties.

An interesting property of the material is that it can switch between the MOC form, soluble in halogenated solvents, and an insoluble MOF that assembles upon addition of 1,4-dioxane. 1,4-Dioxane is both an anti-solvent and a ligand; coordination between copper and 1,4-dioxane binds the discrete MOC cages to each other, arranging them into the extended MOF structure. This behaviour can be exploited to prepare a practical catalyst that combines the benefits of both homogeneous and heterogeneous catalysis, namely that homogeneous catalysts are generally more efficient, selective and easier to study, but heterogeneous catalysis are easier to recover and recycle. What better way to solve this problem than with a catalyst that is homogeneous during the reaction conditions, but heterogeneous when it comes to product separation?

Reversible metal-organic cage MOC(top left)-MOF(top right) metal-organic framework transition mediated by the addition of 1,4-dioxane. Coordination bonds between 1,4-dioxane shown (bottom image).

Reversible MOC(top left)-MOF(top right) transition mediated by the addition of 1,4-dioxane. Coordination bonds between 1,4-dioxane shown (bottom image).

The authors used the A3 coupling reaction to demonstrate this concept in a catalytic reaction. The A3 reaction is a transition metal-catalysed, multi-component coupling reaction between aldehydes, alkynes and amines. The products are propargylamines, practical synthetic intermediates for the synthesis of nitrogen heterocycles. The A3 reaction has been extensively studied and can be effected by a wide range of transition metal catalysts. Its versatility makes it a popular choice as a model catalytic reaction to demonstrate innovative ideas in catalytic design – as the authors have done here.

Coordination-driven assemblies have a unique potential for the synthesis of differentially soluble materials, used by the authors for novel catalytic design. Whether this particular metal-ligand combination can be applied to other copper catalysed reactions remains to be seen, nevertheless the principle offers an innovative approach that augments the range of methods striving to bridge the gap between homogeneous and heterogeneous catalysis.

To find out more please read:

Cu3L2 metal-organic cages for A3-coupling reactions: reversible coordination interaction triggered homogeneous catalysis and heterogeneous recovery

Gong-Jun Chen, Chao-Qun Chen, Xue-Tian Li, Hui-Chao Ma and Yu-Bin Dong.
Chem. Commun., 2018, 54, 11550-11553
DOI: 10.1039/c8cc07208f

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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The Birth of a Semiconducting Metal Organic Framework by Sulfur Coordination

Metal organic frameworks (MOFs) are crystalline nanomaterials composed of metal ions or clusters coordinated with organic ligands. Owing to the versatility of their building blocks, MOFs have multiple functionalities and can serve as gas separators, sensors, catalysts, electrode materials etc. Now the structure diversity of MOFs is further enriched by Wu and coworkers from Soochow University, China. Specifically, the researchers synthesized a semiconducting MOF with tetra-coordinated sulfur units. This breakthrough was recently published in ChemComm.

The uniqueness of the synthesized semiconducting MOF (MCOF-89) is its square-planar tetra-coordinated metal-sulfur structure, which is observed in MOFs for the first time. It was believed that putting a sulfur atom next to a metal node of MOFs was extremely difficult, because of the large discrepancy in bonding energy between metal-sulfur bonds and conventional metal-carboxylate bonds. Incorporating sulfur atoms thereby could undermine the structural stability of MOFs.

The authors addressed this challenge by designing a tetra-coordination environment as illustrated in Figure 1. The four manganese-sulfur bonds effectively reinforced the unstable S coordination. MCOF-89 was synthesized via a solvothermal reaction with Mn(CH3COO)2 and thiourea as the Mn and S sources, respectively.

Figure 1. The structure of MCOF-89. The illustration on the left is a three-dimensional lattice structure (the red, green and yellow balls represent oxygen, manganese and sulfur), and the structure on the right shows the Mn-S square-planar tetra-coordination configuration (M = manganese).

The synthesized S-incorporated MOF is a semiconductor with a bandgap of 2.82 eV. Additionally, this MOF is photoactive and is able to generate a photocurrent of ~1.9 µA/cm2 upon light irradiation.

This work exemplifies how molecular design can lead to the discovery of novel MOFs with extraordinary structures. It could also inspire other synthesis protocols toward various metal-chalcogenide-containing MOFs with unexpected properties.

 

To find out more please read:

A Semiconducting Metal-Chalcogenide–Organic Framework with Square-Planar Tetra-Coordinated Sulfur

Huajun Yang, Min Luo, Zhou Wu, Wei Wang, Chaozhuang Xue and Tao Wu

Chem. Commun., 2018, 54, 11272-11275

 

About the blogger:

Tianyu Liu obtained his Ph.D. (2017) in Chemistry from University of California, Santa Cruz in the 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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How do Anions Fight Indoor Organic Contaminants?

Indoor air quality is critical to public health. Chronic exposure to indoor organic contaminants (IOCs), including aldehydes and benzene homologues, substantially increases the risk of having respiratory diseases. In recent years, negative air ions (NAIs) have emerged as promising materials to decompose IOCs. NAIs are negatively charged ions generated via ionizing air. However, the limited understanding of the decomposition reaction mechanisms hinders the safety evaluation and wide adoption of NAI-cleaning.

A group of Chinese researchers led by Jin-Ming Lin of Tsinghua University recently demonstrated in ChemComm a powerful tool to unveil the reaction mechanisms. They built a system integrated with an NAI generator, an IOC sprayer and a mass spectrometer (Figure 1). NAIs containing mostly CO3 were produced by the ionization of air. These anions then mixed and reacted with the sprayer-delivered IOCs in front of the mass spectrometer inlet. All species generated during the reactions were directly brought into the mass spectrometer by inert N2 for characterization.

Figure 1. The experimental set-up of the integrated system.

This device revealed real-time reaction kinetics by identifying the reaction intermediates. The mass spectrum of a common IOC, formaldehyde, when reacted with CO3 is presented in Figure 2a. Two pronounced peaks with mass to charge ratios (m/z) of 45.10 and 60.10 were assigned to HCOO and CO3, respectively. Additionally, the 45.10 peak was only detected when formaldehyde was present (Figure 2b). On the basis of these observations, the authors concluded that the major pathway of formaldehyde degradation by CO3was the reaction between CO3 and the α-H atom of the aldehyde group. With identical instrumentation, the authors also proposed how the reactions between CO3 and benzene homologues or esters may proceed.

Figure 2. (a) The mass spectrum of reaction intermediates between CO3 and 10 ppm formaldehyde. (b) The change of peak intensities of m/z = 60.10 and 45.10 peaks with the operation time. Formaldehyde was present during 7.0-14.0 min.

The results obtained by this study could greatly deepen the understanding of NAI-based chemistry. It could also be useful to investigate kinetics of a broad range of other chemical reactions involving charged reactants.

 

To find out more please read:

Real-Time Characterization of Negative Air Ion-Induced Decomposition of Indoor Organic Contaminants by Mass Spectrometry

Ling Lin, Yu Li, Mashooq Khan, Jiashu Sun and Jin-Ming Li

Chem. Commun., 2018, DOI: 10.1039/c8cc05795h

 

About the blogger:

Tianyu Liu obtained his Ph.D. (2017) in Chemistry from University of California, Santa Cruz in the 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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MOFS, ZMOFS and Automobiles

Mohamed Eddaoudi and co-workers at KAUST have synthesised a porous metal organic framework (MOF) constructed from carboxylic acid-functionalised imidazole linkers coordinated to yttrium and potassium cations. The researchers classified this material as a zeolite-like MOF (ZMOF) due to its topological resemblance to the naturally occurring zeolite mineral analcime.

The material’s architecture, with cylindrical channels and a pore aperture measuring 3.8 x 6.2 Å, promised utility as a molecular sieve, and the authors showed the ZMOF could be used to sort small chain alkanes based on their level of branching. Linear and mono-branched pentanes and butanes were adsorbed by the material for different lengths of time (linear isomers were retained longer than their branched counterparts) allowing kinetic separation, while the di-branched alkane 2,2,4-trimethylpentane was excluded entirely. The authors anticipate that this material could have practical applications in crude oil refining, to upgrade petroleum into more energy-efficient fuels with reduced emissions.

ZMOF zeolite-like metal organic framework crystal structure with analcime (ana) topology showing channels and pore aperture.

ZMOF crystal structure with analcime (ana) topology showing channels and pore aperture.

The petroleum used to power internal combustion engines consists of a mixture of low molecular weight, linear and branched alkanes. The research octane number (RON) is a standard measure of petroleum performance, and indicates how much pressure a fuel can withstand before self-igniting (knocking) in the engine. High compression engines, which are more energy efficient and release less emissions than regular engines, require high RON fuels.

The RON increases with the proportion of branched alkanes, so can be improved by supplementing fuels with branched isomers obtained by catalytic isomerisation. This process generates a mixture of linear and branched alkanes, so the desired products must be isolated via fractional distillation, which is energy intensive. This creates a dilemma: high RON fuels are more energy efficient, but their energy-intensive production reduces the net benefit.

The authors envisaged an energy-efficient strategy for increasing the RON of petroleum fuels: A low RON fuel is pumped into the engine, where it encounters a separation chamber consisting of ZMOF-based membranes. The membrane excludes and redirects di-branched alkanes, which have a very high RON, to the internal combustion engine. The low RON fraction, consisting of mono-branched and linear alkanes, passes through the ZMOF pores to undergo further reforming processes downstream. In other words: low RON fuels go in, but high RON fuels are combusted.

Scheme showing how ZMOF materials could be used to upgrade gasoline by separating alkanes based on their level of branching. zeolite-like metal organic framework petroleum reforming

Scheme showing the RON of common small-chain alkanes and the use of ZMOF membranes in upgrading gasoline by separating alkanes based on their level of branching

In this work the authors show the potential of ZMOFs to maximise the energetic potential and reduce emissions of petroleum based fuels, while also offering a glimpse of the more general strategy of energy-efficient separations of chemically-similar molecules using tailored materials.

To find out more please read:

Upgrading gasoline to high octane number using zeolite-like metal organic framework molecular sieve with ana-topology

M. Infas H. Mohideen, Youssef Belmabkhout, Prashant M. Bhatt, Aleksander Shkurenko, Zhijie Chen, Karim Adil, Mohamed Eddaoudi.
Chem. Commun., 2018, 54, 9414-9417
DOI: 10.1039/c8cc04824j

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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Marbles, Microreactions and Magic Tricks

The reaction vessel is a fixed variable behind every innovative chemical synthesis, material or catalyst. It may be as simple as a round bottom flask or as complex as a single cell, as large as an industrial batch reactor or as small as a test tube.

Yujun Feng and co-workers, at Sichuan University in China, study a different kind of reaction vessel: water droplets. The droplets are ‘liquid marbles’, composed of microlitre volumes of water with fine hydrophobic particles covering their surface. Liquid marbles can be used as reaction vessels to manipulate small liquid volumes, avoiding the use of specialised microfluidics equipment. In this communication the authors show that carbon dioxide can trigger coalescence of droplets containing multiple reagents, in order to perform microscale chemistry. This research could be useful for developing high-throughput assays for procedures that would benefit from remotely controlled induction such as very fast or hazardous reactions.

The authors synthesised CO2-responsive particles composed of a mixture of polystyrene and PDEA: a methacrylate polymer bearing tertiary amine ancillary groups. The amine is vital to the properties of the polymer: when deprotonated the powder is hydrophobic, but exposure to carbon dioxide renders the polymer hydrophilic by transforming the amine into an ammonium bicarbonate salt. Liquid marbles were synthesised with a patch of CO2-responsive polymer powder. The rest of the marble was coated in lycopodium, a moss spore with hydrophobic properties that is not CO2-responsive (trivia: the high fat content of lycopdoium makes it a great flash powder, used by magicians since the middle ages).

A) Liquid marbles with white hydrophobic/hydrophilic CO2-responsive patches and pink (dyed) lycopodium powder. B) Coalescence of two liquid marbles upon CO2 carbon dioxide exposure within one minute. C) Coalescence schematic

A) Liquid marbles with white CO2-responsive patches and pink (dyed) lycopodium powder. B) & C) Photos and schematic of coalescence between two liquid marbles upon CO2 exposure

To realise CO2-induced chemistry, two liquid marbles containing different chemical reagents are placed side by side with the CO2-responsive powder positioned at the interface of the two marbles. Upon exposure to CO2 the responsive powder becomes hydrophilic and disperses into the aqueous solution within the two marbles, causing them to coalesce and the reagents to react within a single vessel. The authors performed several reactions using this method, all with distinct colour changes for rapid analysis: redox (persulfate and iodide, permanganate and persulfate), complexation (starch and iodine), substitution (bromine water and phenol) and chemiluminescence (luminol, peroxide and ferricyanide).

The authors show in this paper that innovations in chemistry needn’t be limited to reactions themselves; the vessel we choose can broaden what is possible on a practical level. On a completely impractical note, remotely controlled microreactions in liquid marbles sounds like a magic trick, resonant with the lycopodium flash powder covering their surface.

To find out more please read:

CO2-triggered microreactions in liquid marbles 

Xinjie Luo, Hongyao Yin, Xian’e Li, Xin Su, Yujun Feng.
Chem. Commun., 2018, Advance Article
DOI: 10.1039/c8cc01786g

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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ChemComm Poster Prize winner for the 2nd Early Career Researchers Meeting of the RSC–Macrocyclic and Supramolecular Chemistry Group

Dr Guillaume De Bo (left) presenting the ChemComm prize to Alexander Elmi (right).

The 2nd Early Career Researchers Meeting of the RSC-Macrocyclic and Supramolecular Chemistry (RSC-MASC) Group took place on 27th July 2018 at the University of Manchester, UK. This one-day symposium was organised by Dr. Guillaume De Bo (University of Manchester) and was attended by PhD students and post-doctoral researchers within the supramolecular field.

The meeting consisted of fifteen selected talks from submitted abstracts, and all attendees were invited to present a poster. The day ended with a plenary lecture by Professor Anthony Davis (University of Bristol) on ‘Biomimetic Carbohydrate Recognition:  The Host-Guest Chemistry of Carbohydrates in Water’.

ChemComm was proud to sponsor this successful symposium. Alexander Elmi (University of Edinburgh) received the ChemComm poster prize for his poster entitledUnderstanding Aromatic Stacking Interactions In Solution’.

 

Congratulations Alexander from everyone at ChemComm!

 

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An enzymatic Rube Goldberg machine: a bioluminescent switch for the detection of uracil DNA-glycosylase

A team of researchers from Shandong Normal University in Jinan, China, have developed a highly sensitive and label-free assay for the detection of uracil-DNA glycosylase, a DNA repair enzyme that removes uracil from DNA molecules. Uracil is an RNA base, and when uracil appears in DNA through deamination of cytosine or misincorporation during DNA synthesis, the error can have mutagenic consequences.

Diminished activity of uracil-DNA glycosylase has been linked to a number of disease states including human immunodeficiency and Bloom syndrome, an inherited disorder associated with an increased risk of cancer (among other symptoms). Developing sensitive methods to quantify uracil-DNA glycosylase would enable early diagnosis of such conditions and improve understanding of the DNA-repair machinery. As a proof-of-concept, the researchers showed that this method could quantify the enzyme in the cell lysate of HeLa cancer cells.

Their method reminds me of Rube Goldberg machines, which achieve a task via a series of connected, mechanical steps. Completion of one step triggers the start of another: such as a line of falling dominos hitting a marble that, in turn, rolls down a track. In this work the action of one enzyme returns a product that is the preferred substrate of another enzyme. At the risk of deviating slightly, one of the more spectacular examples of a Rube Goldberg machine is seen in the music video for OK GO’s ‘this too shall pass’, a single-take shoot of a warehouse sized machine, featuring rolling cars, swinging pianos, flowing water and rolling billiard balls, all to perform the task of (spoiler alert) blasting the band members in the face with coloured paint.

The label-free strategy for detecting uracil-DNA glycosylase results in a bioluminescent signal via tricyclic signal amplification

The strategy starts with the action of uracil-DNA glycosylase and ends with a bioluminescent signal via a cascade of enzymatic reactions

The authors’ strategy involves a series of sequential steps employing seven different enzymes and three nucleic acid probes. It begins with a double stranded DNA probe containing one rogue uracil base: the perfect bait for uracil-DNA glycosylase. The action of this enzyme and two others, in a process involving base excision, DNA backbone cleavage and the addition of thymine-rich sequences, produces a large quantity of single-stranded DNA molecules with long thymine-rich tails. These molecules hybridise with adenine-rich RNA probes to generate RNA-DNA duplexes. An enzyme digests the RNA portion, releasing adenosine monophosphate monomers, which are converted to adenosine triphosphate (ATP), a required energy input to activate firefly luciferase. Luciferase catalyses the oxidation of luciferin to form oxyluciferin, accompanied by a large bioluminescent signal. Thus, uracil-DNA glycosylase is detected with 1-2 orders of magnitude more sensitivity than state-of-the-art fluorescent and luminescent assays.

Unlike conventional Rube Goldberg machines, which are characterised by unnecessary complexity, in this ‘enzymatic Rube Goldberg machine’ each step has a specific purpose and serves to amplify the signal of the last. This is dubbed ‘tricyclic cascade signal amplification’ and it enables highly sensitive detection of the enzyme.

To find out more please read:

Label-free and high-throughput bioluminescence detection of uracil-DNA glycosylase in cancer cells through tricyclic cascade signal amplification

Yan Zhang, Qing-nan Li, Chen-chen Li, Chen-yang Zhang.
Chem. Commun., 2018, 54, 6991-6994
DOI: 10.1039/c8cc03769h

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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ChemComm poster prize winner at the 16th Symposium for Host-Guest and Supramolecular Chemistry

The 16th Symposium for Host-Guest and Supramolecular Chemistry was held on 2 – 3 June 2018 at the Tokyo University of Science in Japan.

This annual symposium covers all aspects of the chemical sciences related to molecular recognition and supramolecular chemistry, including the discussion of topics around intermolecular interactions. The event included a special lecture by Dr Shigeki Sasaki and invited lectures by Dr Takashi Hayashi and Dr Katsuhiko Ariga.

ChemComm is delighted to announce that the ChemComm poster prize was awarded to Hiroshi Koganezawa from the Tokyo University of Science for a poster entitled ‘Synthesis of [2]Rotaxanes with Spirofluorene and Pyrrole Moieties’.

Well done Hiroshi from everyone at ChemComm!

 

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Better Make It A Double

Synthesizing nanomaterials consisting of two-particle pairs, or dimers, is no longer a headache. Hongyu Chen and coworkers from Nanjing Tech University, China recently developed a protocol that can produce gold dimers with a record high yield. This breakthrough is published in Chem. Commun.

Dimers are suitable platforms to study the effects of particle-particle interactions on the electrical and optical properties of the constituent materials. Unfortunately, no conventional synthesis methods to exclusively produce dimers from single particles have been successful. This is because of the uncontrollable particle-aggregation rate that leads to the formation of multi-particle clusters. Therefore, how to couple single particles into dimers without triggering their further aggregation has become a tough nut to crack.

Chen and coworkers found a solution by developing a polymer-assisted method that generates gold dimers with high yield. Firstly, they encapsulated individual gold nanoparticles with polymer shells made of polystyrene-b-poly(acrylic acid). Under optimized conditions, the gold nanoparticles were mostly coupled into dimers (Figure 1), achieving a dimer yield of 65%. This is the highest dimer yield achieved for one-step synthesis methods.

Figure 1. (a) A transmission electron microscopy (TEM) image of the polymer-encapsulated gold single particles. (b) A TEM image and (c) a scanning electron microscopy image of the synthesized gold dimers. All scale bars are 200 nm.

The key to this success is due to three factors: temperature, solvent composition and acid concentration. All these factors can change the strength of the repulsion force among the polymer shells. The force must be meticulously tuned to a level that is weak enough to induce 1-to-1 coupling, but strong enough to prevent 1-to-multiple or multiple-to-multiple aggregation. Through a set of control experiments, the authors identified the optimal conditions to be 60 oC, dimethylformamide/water (v/v)=6:1 and 5 mM of hydrochloric acid.

The method demonstrated herein could be extended to other particles. It may also inspire versatile synthesis strategies towards complex nanostructures with high selectivity.

 

To find out more please read:

Controllable Oligomerization: Defying Step-Growth Kinetics in the Polymerization of Gold Nanoparticles

Xuejun Cheng, Gui Zhao, Yan Lu, Miao Yan, Hong Wang and Hongyu Chen

Chem. Sci., 2018, DOI: 10.1039/C8CC03424A

 

About the blogger:

Tianyu Liu obtained his Ph.D. (2017) in Physical Chemistry from University of California, Santa Cruz in the 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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