CrystEngComm Blog

The quality of protein crystals can sometimes make study of their structure by X-ray crystallography challenging.   Producing higher quality crystals could be facilitated by a better understanding of the crystal growth process.

One method of achieving this  involves inserting a small fluorescent dye into a protein (to form an F-protein) and adding this labelled protein to the crystallising protein.  The distribution, orientation and incorporation efficiency of the F-protein during the growth of the crystals can be studied optically using techniques including polarisation microscopy (see diagram below).

A new paper describes the use of three different F-proteins, each incorporating the dye DY-632-01 NHS ester, to study the crystallisation of the three unlabelled proteins.  This enabled visualisation of the crystal growth habits, symmetry and history as well as the distribution of the F-proteins.

In some cases, the F-proteins are preferentially incorporated into the growing crystal and can act as tracers.  Alternatively, they may not be incorporated at all and provide information about the biophysical factors which affect crystal growth (such as charge distribution and hydrophobicity).

As different F-proteins behave differently during the crystallisation of a given unlabelled protein, repeating the crystallisation experiment with different F-proteins can provide complementary information.

The distribution of F-proteins is not uniform throughout the crystal and authors conclude that that the diffraction quality of the crystal is position dependent. The incorporation of F-proteins may allow areas of higher diffraction quality to be identified.

For more information, read the full paper:

Illuminating protein crystal growth using fluorophore-labelled proteins
Alaa Adawy, Willem J. P. van Enckevort, Elisabeth S. Pierson, Willem J. de Grip and Elias Vlieg
CrystEngComm, 2014, DOI: 10.1039/C4CE01281J

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Gwenda Kyd has a PhD in metallocarborane chemistry from the University of Edinburgh. Other research work includes the spectroscopic study of the structure of glasses and organometallic electron-transfer reactions and the preparation of new inorganic phosphors

The use of fossil fuel-powered vapour compressors for the allocation of hot and cold air makes a significant contribution to global warming. A greener alternative involves reversible adsorption and desorption of a working fluid (often water) in adsorption heat pumps (AHPs) or adsorption chillers (ADCs), concepts originally devised by Michael Faraday in 1848.

The limiting factor when using MOF-based AHPs and ADCs is the rate of heat transfer. In this light, Al-based MOFs provide an attractive target as Al can not only provide a heat-conducting surface, but is also naturally abundant and of low toxicity.

MOFs for heat transfer

In their recent paper in CrystEngComm, de Lange, Gascon and co-workers evaluate a series Al-based MOFs for use in AHPs and ADCs. Of all the materials they tested, the most favourable characteristics were shown by the compound designated CAU-10-H, a material comprised of [Al–OH]²⁺ chains linked together by isophthalic acid, (CAU is Christian-Albrechts-Universität, where the compounds were first developed). 

In the presence of hydrochloric acid, CAU-10-H can be grown directly on to γ-alumina beads or metallic aluminium. These systems show good water adsorption and stability.  Up to 38kJ of heat can be withdrawn in the evaporator of an AHP/ADC per square metre of Al-coated surface, suggesting further study and development of Al-MOFs is worthwhile.

For more details, read the full paper:

Crystals for sustainability – structuring Al-based MOFs for the allocation of heat and cold
M. F. de Lange, C. P. Ottevanger, M. Wiegman, T. J. H. Vlugt, J. Gascon and F. Kapteijn
CrystEngComm, 2014, DOI: 10.1039/C4CE01073F

Gwenda Kyd has a PhD in metallocarborane chemistry from the University of Edinburgh. Other research work includes the spectroscopic study of the structure of glasses and organometallic electron-transfer reactions and the preparation of new inorganic phosphors

Zinc oxide (ZnO) is an important semiconductor material which can be used for gas sensing.  The sensing property relies on an oxidation-reduction reaction on the ZnO surface between the detected gas and surface oxygen molecules which causes the resistance of the sensor to change.  The nature of exposed facets on the sensor is crucial to its performance however, control of the growth, number, and morphology of these features has so far proved difficult.

In their recent paper in CrystEngComm, Xiang, Xu and co-workers report a simple synthesis of ZnO which allows for exposed facet control.  They discovered a two-step hydrothermal synthesis does not require use of any templates or surfactants but achieves structure control simply by adjusting pH.  In this way, hexagonal-pyramids, -prisms, -prismoids and -disks could be formed (see below)/

The authors tested the materials for gaseous ethanol sensing and the sensitivity was found to vary in the order disks > prismoids > prisms > pyramids.  They showed that the sensitivity of the sensors increased with exposure of (0001) crystal planes as these polar facets can provide more active sites for oxygen absorption than other facets, increasing the gas sensor response.   Their new findings are significant for the future development of high performance gas sensors.

For more information, read the full paper:

Evolution of ZnO microstructures from hexagonal disk to prismoid, prism and pyramid and their crystal facet-dependent gas sensing properties
Nan Qin, Qun Xiang, Hongbin Zhao, Jincang Zhang and Jiaqiang Xu
CrystEngComm, 2014, DOI: 10.1039/C4CE00637B

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Gwenda Kyd has a PhD in metallocarborane chemistry from the University of Edinburgh. Other research work includes the spectroscopic study of the structure of glasses and organometallic electron-transfer reactions and the preparation of new inorganic phosphors. She has recently published a book on chemicals from plants.

Cheap and effective storage of renewable energy is a key challenge for consumers in the future. Lithium ion batteries (LIBs) are one class of materials that meet the important requirements of high energy density, low cost, good power capacity and efficient cycling.

Recent research on LIB materials has focused on maximising their favourable properties to bring them closer to commerical use.

A new paper by Jun Liu and co-workers (Central South University, Changsha, China) describes the preparation and testing of a new anode material based on MoO₃ and graphene oxide (GO). The former material is naturally abundant, has good chemical stability and a high storage capability but also exhibits poor conductivity and lithium ion diffusion. GO has good conductivity, a large surface area and is highly stable, making it an attractive material for composite material formation.  

The authors prepared the new material by first synthesising GO and α-MoO₃ nanoribbons before modifying the surface of the latter to produce a positive charge. This allowed the MoO₃ material to assemble onto the GO.  They then applied heat to form the product, α-MoO₃@GNS (GNS refers to graphene nanosheet), and fabricated the material to form an anode.

These robust nanocomposites exhibit greatly enhanced Li transport efficiency compared to other MoO₃-based materials, as well as high electrical conductivity and good cycling efficiency.

The authors concluded that the two components work synergistically to produce the observed properties and suggested the composite as a potential anode material for high performance LIBs.

 To find out more, read the full article:

Graphene nanosheets encapsulated α-MoO₃ nanoribbons with ultrahigh lithium ion storage properties
Pei-Jie Lu, Ming Lei and Jun Liu
CrystEngComm, 2014, DOI: 10.1039/C4CE00252K

Gwenda Kyd has a PhD in metallocarborane chemistry from the University of Edinburgh. Other research work includes the spectroscopic study of the structure of glasses and organometallic electron-transfer reactions and the preparation of new inorganic phosphors.  She has recently published a book on chemicals from plants.

Human kidney stones contain over 200 components, most significantly, anhydrous uric acid (UA, below) and its dihydrate (UAD).  When UAD is present, UA is also, however the reverse isn’t always true. This  suggests the conversion of UAD to UA may be a significant step in the formation of kidney stones.  A deeper understanding of how the stones form could inform strategies to prevent their formation and to disperse them once formed.

A new paper in CrystEngComm looks at the relationship between UAD and UA under physiologically relevant conditions.  The authors studied the behaviour of UAD in aqueous solution at body temperature (37^oC), both at various pHs in the presence of a buffer and in an artificial urine solution. In aqueous solution at acidic pH values, the conversion of UAD occured via a slow dissolution, followed by recrystallization, to form UA over 42 hours. At neutral pH, the final product formed was uric acid monohydrate (UAM), which was obtained either directly or via a UA intermediate. In urine solution, UA formation was much faster (complete in 30 hours) and crystals were much smaller.

The rate limiting step is believed to be the dissolution of UAD, with the timescale of the UA formation explaining why UAD is rarely found in the absence of UA.  Future studies will look at how other urinary components and/or additives can affect UA formation.

For more information, see the full paper:

Solution-mediated phase transformation of uric acid dihydrate
Janeth B. Presores and Jennifer A. Swift
CrystEngComm, 2014, DOI: 10.1039/C4CE00574K

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Gwenda Kyd has a PhD in metallocarborane chemistry from the University of Edinburgh. Other research work includes the spectroscopic study of the structure of glasses and organometallic electron-transfer reactions and the preparation of new inorganic phosphors.  She has recently published a book on chemicals from plants.

Posted on behalf of Josh Campbell, web writer for CrystEngComm 

A new paper in CrystEngComm details the successful synthesis of tungsten oxide (WO₃) mixed amorphous/crystalline nanostructures. These 1D, hexagonal nanorods show electrochromic performances that combine the high optical modulation and quick response times of amorphous WO₃ with the improved stability of crystalline phases.

Researchers synthesised the nanostructures using a two-step hydrothermal process by growing the crystalline core first before the amorphous shell on the rod’s surface. They found that the thickness of the amorphous shells could be varied by altering the length of the second step. They used sodium cations to stop the conversion of the hexagonal WO₃ phase to the monoclinic form encouraging the formation of the rod architectures by promoting growth along the c-axis.

The large surface area of the amorphous shells allowed for rapid bleaching and coloration as most of the electrolyte ions were kept away from the surface of the core. The cores of the structures helped increase the stability of the material by increasing its density and crystallinity.

Getting a balance between amorphous and crystalline properties is important in electrochromic device performance. Materials scientists have studied amorphous WO₃ thin films extensively as they show fast response times and high coloration efficiency. Unfortunately they make for unstable devices due to their disordered structures.

Researchers have since discovered that crystalline WO₃ offers much better stability due to its dense and ordered structure but lacks the performance needed for practical applications. Nanostructures with the best of both worlds may allow increased property control and performance in future devices.

Read the full article for more details: 

Facile synthesis of one-dimensional crystalline/amorphous tungsten oxide core/shell heterostructures with balanced electrochromic properties
Yung-Chiun Her and Chia-Chun Chang
CrystEngComm, 2014, DOI: 10.1039/C4CE00430B 

Josh Campbell is a PhD student, currently at the University of Southampton, UK studying crystal structure prediction of organic semiconductors. He received his BSc from the University of Bradford.