Iain Larmour, web science writer – Page 2 – Chemical Communications Blog

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Just Mix – Zeolitic Imidazolate Framework Synthesis

14 Oct 2014

Zeolitic-imidazolate frameworks (ZIFs) are a sub-class of metal-organic frameworks (MOFs) with a wide range of potential uses including: CO2 capture, storage, catalysis, sensing and biomedicine. Unfortunately their synthesis often requires additives or reaction activation, and if they can be made without these it often requires long reaction times or results in low yields, neither of which is ideal for a substance with such wide potential uses.

To overcome this bottleneck in ZIF synthesis, Roland Fischer and his team from the Inorganic Chemistry department in Ruhr Universitat Bochum in Germany have developed a rapid room temperature synthesis approach. I am a great believer in developing approaches that can be carried out at room temperature and pressure and this is one such elegant solution. The authors produce nanocrystals of ZIFs in a very narrow size distribution by careful selection of the precursors and the solvents they are dissolved in. The solutions are then mixed and stirred to create the ZIF crystals; it really is that elegant.

ZIF crystals showing very narrow size distribution

The authors then used these crystals to fabricate thin films on quartz crystal microbalances and used this device to detect volatile organic solvents. This demonstration leads the way into exploring other uses of these ZIFs – after all, they can now be easily made. But to find out which solvent and precursors you need to use, you’ll have to read the paper today!

To read the details, check out the ChemComm article in full:
Rapid room temperature synthesis of zeolitic-imidazolate framework (ZIF) nanocrystals
Min Tu, Christian Wiktor, Christoph Rosler and Roland Fischer
Chem. Commun., 2014, 50, 13258-13260
DOI: 10.1039/C4CC06491G

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Optimising multi-enzyme reactions – enabling enzymatic encoding

10 Sep 2014

The ability to mimic cascade and linked enzyme reactions has potential applications for disease diagnosis and pharmaceutical manufacturing, to name just two. However, the optimisation of the ratios of the interacting enzymes can be a time consuming step when carried out using standard solution based enzyme assays. With the problem becoming exponentially more difficult with the number of enzymes in the system, Jun Ge and Zheng Liu of the Department of Chemical Engineering at Tsinghua University, with colleagues, have looked to overcome this hurdle by developing a simple, fast and high throughput method based on ink-jet printing.

The team replaced the colour inks in a standard inkjet printer with enzyme and substrate solutions. The ratio of these solutions could be controlled by varying the overall colour that was printed. Optimisation of cascade and coupled enzymatic reactions could be carried out rapidly and inexpensively compared to the standard solution based method.

Enzymatic encryption, decoding and deletion of information

Precise two-dimensional control of enzyme placement via ink-jet printing also raises the possibility of creating 2D codes with enzymatic encryption built in, as the figure demonstrates. I don’t want to give the secret of this encryption technique away so you’ll have to read the paper today.

To read the details, check out the ChemComm article in full:

Ink-jet printing an optimal multi-enzyme system
Yifei Zhang, Fengjiao Lyu, Jun Ge, Zheng Liu
Chem. Commun., 2014, Accepted Article
DOI: 10.1039/C4CC06158F

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Strutting Their Stuff – Enantiopure Struts in MOFs

21 Jun 2014

The introduction of chirality into Metal Organic Frameworks (MOFs) produces the possibility of them being used as solid supports for chiral chromatography. This chirality can be introduced through the use of pillar[5]arene struts where the pendant functional groups can be controlled to alter the overall properties. However, the incorporation of planar chirality into homochiral MOFs is a relatively unexplored phenomenon.

Homochiral MOFs which contain enantiopure active domains

In this Communication Fraser Stoddart, from Northwestern University, and his team report the production of homochiral MOFs which contain enantiopure pillar[5]arene active domains. This required the development of an efficient route to the large-scale production of racemic pillar[5]arene derivatives. However, to discover the secret you will have to read the ChemComm article – access is free* for a limited time only!

To read the details, check out the Chem Comm article in full:

Enantiopure pillar[5]arene active domains within a homochiral metal-organic framework

Nathan L. Strutt, Huacheng Zhang and J. Fraser Stoddart

DOI: 10.1039/C4CC02559H

Interested in MOFs? Why not take a look our Chem Soc Rev MOFs Web collection – reviews are added to this collection as and when they are published.

*Access is free through a registered RSC account – click here to register

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Printable Nanoscale Catalysts with Controlled Nano-morphologies

05 Jun 2014

Nanoscale metal rings and dots could find potential use in a wide range of applications including catalysis. However, the impact the morphology differences have must be unambiguously ascertained before they can be used in practical applications. For this to be achieved there needs to be a simple and efficient fabrication process that can create arrays of nanoscale metal rings or dots for study.

Won Bae Kim and team, from the School of Materials Science and Engineering at the Gwangju Institute of Science and Technology, report such a method in their new ChemComm paper. They make use of the powerful transfer printing technique, but importantly have created suitable stamps that can generate ring or dot arrays. These stamps use one dimensional carbon nanostructures that are supported within the hexagonal pores of anodic aluminium oxide, the tip shapes being controlled by ion milling conditions. After loading with a suitable catalytic metal they are then used in transfer printing onto indium tin oxide substrates.

SEM images of nanoring and nanodot stamps showing the supported one dimensional carbon structures within the AAO pores.

The team demonstrate the catalytic ability of the printed metal ring and dot arrays by studying methanol oxidation in acidic solution with platinum structures and carbon monoxide electrooxidation in alkaline solution with gold structures. With this approach they were able to study the effect of morphology on the catalytic activity – to find out which was better, rings or dots, you will have to read the ChemComm article today!

To read the details for free* check out the Chem Comm article in full:

Transfer printing of metal nanoring and nanodot arrays for use in catalytic reactions

Sang Ho Lee, Sung Mook Choi, Seungha Yoon, Huisu Jeong, Gun Young Jung, Beong Ki Cho and Won Bae Kim

DOI: 10.1039/C4CC02939A

*Access is free untill Friday 4th July through a registered RSC account – click here to register

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Mind the gap – Enhancing intercalation of luminescent aggregates

17 Sep 2013

Particular molecules, which are not luminescent in solution, can luminesce intensely upon molecular aggregation; this is known as aggregation-induced emission (AIE). AIE luminogens are used widely as efficient electroluminescent materials, sensitive chemosensors, and as bioprobes. The main cause of the AIE effect is the restriction of intramolecular rotation. Therefore it can be promoted by introducing the molecules into inorganic materials with a rigid skeleton such as α-zirconium phosphate layers.

Jihong Yu and colleagues from Jilin University in China have published a method describing the intercalation of a quaternary tetraphenylethene (TPEN) cation, an AIE chromophore, into α-zirconium phosphate. At first glance, this does not seem to be too difficult a task– after all, the TPEN has two permanent positive charges on either end suitable to interact with the negatively charged phosphate layers. But, in this case, size does matter. The chromophore is almost three times larger than the distance between phosphate layers, more than a tight fit!

Stretching the layers of α-zirconium phosphate by preintercalation of butylamine before introduction of the chromophore

To overcome this problem, Yu and colleagues carried out a preintercalation step with butylamine before performing a cation exchange step to place the TPEN chromophore within the phosphate layers. Ultimately, they stretched the layer before putting the final molecule inside, just like you would stretch a pair of shoes in an effort to make them fit before placing your sensitive feet inside.

The intercalated product was found to be highly emissive in the blue region of the electromagnetic spectrum and was readily internalized by cells. The system also showed good biocompatibility, suggesting that it would make an excellent base for fluorescent labels in future biomedical imaging applications.

To read the details, check out the HOT Chem Comm article in full:

AIE cation functionalized layered zirconium phosphate nanoplatelets: ion-exchange intercalation and cell imaging

Dongdong Li, Chuanlong Miao, Xiaodan Wang, Xianghui Yu, Jihong Yu and Ruren Xu
Chem. Commun., 2013, 49, Accepted Manuscript
DOI: 10.1039/C3CC45041D

Iain Larmour is a guest web writer for ChemComm. He has researched a wide variety of topics during his years in the lab including nanostructured surfaces for water repellency and developing nanoparticle systems for bioanalysis by surface enhanced optical spectroscopies. He currently works in science management with a focus on responses to climate change. In his spare time he enjoys reading, photography and art.

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A cloak of many carbons

28 Jun 2013

Catalysts can be exceedingly useful in the real world, from treating our car’s exhaust fumes to creating fertilisers. There are many ways to make catalysts and even multiple ways to make the same catalyst. The path that you choose to a catalyst can have a significant impact on the quality of the end product.

Eloy del Rio and team from the Structure and Chemistry of Nanomaterials group at the University of Cadiz in Spain have investigated ceria-based oxide-supported gold catalysts for carbon monoxide oxidation. The routine for depositing the metal phase onto the oxide support and the subsequent catalyst activation step can ultimately affect the activity of the catalyst. Catalysts prepared by deposition-precipitation with urea followed by activation under oxidising conditions result in significantly more activity than those prepared under reducing conditions.

Variation in catalyst activity under oxidising and reducing activation protocols.

This had previously been observed by others, but the reason for the difference was never discussed. The authors set out to find out why the activity differed. They used a suite of nano-analytical and nano-structural techniques to probe the catalysts, finding that the catalyst prepared under reducing conditions had a coat of amorphous carbon which severely hampered the catalyst activity. This could be removed by a re-oxidation treatment that burnt away the carbon layer and produced an active catalyst similar to the one produced under oxidising conditions.

The precipitating agent used in the synthesis can also influence the resulting activities of catalysts prepared via the deposition-precipitation method. No difference between oxidising and reducing activations is observed when sodium carbonate is used in place of urea.

To read the details, check out the ChemComm article in full:

Dramatic effect of redox pre-treatments on the CO oxidation activity of Au/Ce_0.50Tb_0.12Zr_0.38O_2-x catalysts prepared by deposition-precipitation with urea: a nano-analytical and nano-structural study
E. del Rio, M. López-Haro, J.M. Cies, J.J. Delgado, J.J. Calvino, S. Trasobares, G. Blanco, M.A. Cauqui and S. Bernal
Chem. Commun., 2013, 49, Accepted Manuscript
DOI: 10.1039/C3CC42051e

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It’s getting hot in here…

22 May 2013

Stimuli-responsive nanoparticles are the focus of much current research, and what could be better than a nanoparticle that responds to one stimulus? A nanoparticle which responds to two or three.

Xianmao Lu and his team have coupled plasmonic silver nanoparticles to magnetic iron oxide nanoparticles and wrapped both in a thermoresponsive polymer – poly(n-isopropylacrylamide).

When illuminated by sunlight the silver nanoparticles absorb the light and convert it to heat. The increase in temperature causes the polymer wrapping to collapse and reduces steric repulsion between the nanoparticle dimers leading to clustering.

Sunlight induced clustering of Magnetic-Plasmonic Heterodimers.

This clustering enhances the magnetic separation of the very small dimers from the solution (the nanoparticles are less than 9 nm each). When you’ve caught the nanoparticles and are done with them, you can turn the lights off and they will re-disperse.

Don’t worry if you live in a cloudy part of the world, you can use a solar simulator to induce the clustering. It would probably be easier to turn off than the sun, too.

To read the details, check out this HOT Chem Comm article in full:
Thermoresponsive Nanoparticles + Plasmonic Nanoparticles = Photoresponsive Heterodimers: Facile Synthesis and Sunlight-Induced Reversible Clustering
Hui Han, Jim Yang Lee and Xianmao Lu
Chem. Commun., 2013, 49, Accepted Manuscript
DOI: 10.1039/C3CC42273A

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Nitrogen-containing graphene-like structures: Theory and experiment combine to reveal active sites

09 Apr 2013

There is significant interest in nitrogen-containing electrocatalysts, driven by the need to find cost-effective and efficient material solutions for replacing platinum in polymer electrolyte membrane fuel cells. However, the active sites of non-platinum group metal, oxygen reduction reaction electrocatalysts have been contentious for over 50 years.

Fortunately researchers are agreed that Metal(Me)-N_x centres may serve as possible active sites but whether it is Me-N₂ or Me-N₄ remains unresolved. X-ray Photoelectron Spectroscopy (XPS) would be the ideal technique to answer this question if it didn’t rely on the use of reference spectra; none exist for the Me-N₂ species which makes it less than ideal.

Fitting of DFT calculated curves to experimental results.

Kateryna Artyushkova, Plamen Atanassov and their team have overcome this problem by using density functional theory (DFT) to calculate the binding energy shifts of the species. Calculating the binding energy shifts, rather than just the binding energies, allows the team to overcome the challenges associated with DFT calculations including; treatment of the core electrons and the poorly screened Coulomb potential near the nucleus.

Once validated, the DFT output can be used as input for XPS curve fitting. This has revealed rearrangement around Cobalt-N_x centres in an oxidizing atmosphere and supports the understanding of these catalysts as vacancy-and-substitution defects in a graphene-like matrix.

This work demonstrates the synergy between experiment and theory which allows critical information to be extracted that might otherwise remain hidden.

For more, read this ChemComm article in full:

Density functional theory calculations of XPS binding energy shift for nitrogen-containing graphene-like structures
K. Artyushkova, B. Kiefer, B. Halevi, A. Knop-Gericke, R. Schlogl and P. Atanassov
Chem. Commun., 2013, 49, 2539-2541
DOI: 10.1039/C3CC40324F

Iain Larmour is a guest web-writer for ChemComm. He has researched a wide variety of topics during his years in the lab including nanostructured surfaces for water repellency and developing nanoparticle systems for bioanalysis by surface enhanced optical spectroscopies. He currently works in science management with a focus on responses to climate change. In his spare time he enjoys reading and photography.

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Liquid crystal relaxation controlled by dopant kinetics

20 Jan 2013

Liquid crystals are an area of intense interest due to their potential use in smart materials such as displays. Cholesteric liquid crystals are of particular interest due to their helical nature and their ability to selectively reflect light over a narrow range of wavelengths. This range can be modified by the inclusion of photo-responsive dopants.

Dopants include overcrowded alkenes which undergo a stable to unstable (cis–trans) transition upon irradiation with UV light. This results in an unwinding and eventual inversion of the cholesteric helix. This is accompanied by a red-shift of the reflection band which then returns close to the original position. However, the handedness of the helix has changed, and therefore the polarization of the light has also changed.

Helix inversion of a cholesteric liquid crystal.

An important parameter with all liquid crystals is their relaxation step which needs to be suitable for the envisioned application. Nathalie Katsonis and her team have studied cholesteric liquid crystals doped with overcrowded alkenes in an effort to find a general paradigm correlating relaxation kinetics with the rate of helix inversion.

In their recent Communication, Katsonis’ group shows that the helix relaxation kinetics are fully determined by the kinetics of the light-sensitive dopants. The relaxation of the dopants from unstable to stable is unperturbed by the liquid crystalline environment.

On the other hand, the presence of the dopants can dramatically accelerate helix inversion. Therefore the inversion can be time-programmed by judicious choice of the dopant. This opens up the great potential of fine tuning cholesteric liquid crystals for smart materials with sophisticated functions.

For more, read this ‘HOT’ Chem Comm article in full:

Time-programmed helix inversion in phototunable liquid crystals

Sarah J. Aßhoff, Supitchaya Iamsaard, Alessandro Bosco, Jeroen J. L. M. Cornelissen, Ben L. Feringa and Nathalie Katsonis

Chem. Commun., 2013, Advance Article

DOI: 10.1039/C2CC37161H

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Lewis acidity of metal ions investigated in the gas phase

03 Oct 2012

In aqueous solutions metal ions can promote acidity via the hydrolysis reaction. This is measured by a hydrolysis constant, which has previously been correlated to the ratio of the ion’s charge to size. Unfortunately lead and tin stubbornly refuse to fit this correlation; additional factors must be at work.

Anthony Stace and team investigated further by studying the minimum number of water molecules needed to stabilise a dication complex in the gas phase against spontaneous hydrolysis (called Coulomb fission in the gas phase). They found an extraordinarily good correlation between the number of water molecules required and the metal ion’s hydrolysis constant in aqueous solution.

What about those stubborn dications, lead and tin? They fit within the trend, requiring a surprising 11 and 26 water molecules to stabilise them respectively. This work suggests that Lewis acidity of metal ions is determined, in part, by the requirement that the ions remain fully solvated.

Plot of acidity constant against minimum number of water molecules required to stabilise the complex against Coulomb fission.

To find out more, download the ChemComm article today.

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