CrystEngComm Blog

It gives us great pleasure to assemble a series of issues of CrystEngComm that celebrates 2014 as the International Year of Crystallography (IYCr2014).

Since its inception in 1999, CrystEngComm has been the go-to journal for publishing the highest-quality work in crystal engineering. It was the first online-only journal of the Royal Society of Chemistry and was among the very first to spur and foster an online scientific community.

During the last 15 years, CrystEngComm has witnessed and ushered explosive growth in the field of crystal engineering, as demonstrated by the increase in number of articles published from 9 in 1999 to 1325 in 2013. Indeed, the field of crystal engineering itself now has a highly-successful Gordon Research Conference (GRC) devoted to the subject. Clearly, the launch of CrystEngComm has supported crystal engineering and its numerous sub-areas as the field has developed.

A celebration provides an opportunity to both reflect and look forward. I personally recall travelling as an undergraduate student on a flight to a Chemical Institute of Canada Conference in 1992 and sitting next to a professor who was also travelling to attend the meeting. At that time, I was just beginning to learn how to grow single crystals, as well as collect and solve X-ray data. Our experiments in those days were conducted on a conventional Enraf-Nonius CAD-4 point-detector diffractometer. Data collection times were on the order of days to weeks.

While I had only been a researcher for about one year, in a conversation with the professor I was comfortable enough to remark that, “You really gain a great deal of confidence about chemistry once you have determined a crystal structure”. Clearly, I was already ‘hooked’, at an early stage, by the process of gathering and analysing X-ray data and the insight gained from the X-ray experiment.

Over the past 15 years, CrystEngComm has made many strides scientifically, meaning that we are able to readily draw on an international community to celebrate IYCr2014. To that end, we have assembled a series of issues edited by prominent researchers in crystal engineering that provide a global celebration from regions including:

Each issue contains a series of papers that reflects the wide breath and scope of crystal engineering and modern crystallographic techniques being studied in each region.

Our deepest thanks and gratitude are extended to the Guest Editors (pictures L-R below):

• Michaele Hardie, University of Leeds, UK (CrystEngComm Editorial Board Member)
• Dario Braga, University of Bologna, Italy (first CrystEngComm Scientific Editor)
• Rahul Banerjee, CSIR-National Chemical Laboratory, India (CrystEngComm Associate Editor)
• J. J. Vittal, National University of Singapore, Singapore
• Stuart Batten, Monash University, Australia
• Christer Aakeröy, Kansas State University, USA (CrystEngComm Associate Editor)
• Tomislav Friščić, McGill University, Canada (CrystEngComm Editorial Board Member)

As well as the CrystEngComm staff, for their dedication and hard work to bring such a global effort together.

Guest Editors of IYCr themed issues

All four IYCr14 themed issues have been very successful and I encourage you to take an opportunity to review all of them.

Much change has been realized in crystal engineering and X-ray diffraction during the past two decades. A major change in this regard has been the implementation of charge-coupled device (CCD) detectors, which enable typical data collection times on the order of hours versus days or weeks. The number of structures in the Cambridge Structural Database (CSD) has increased from roughly 200,000 to 700,000 during the time period (one million is coming quickly), which provides the all-important data for crystal engineers to develop improved understandings of structural relationships between solids.

Moreover, with data collection times becoming shorter and shorter, the field of crystal engineering can be expected to deliver even greater insights into the structures and dynamics of crystalline solids. Let us keep each other posted in CrystEngComm.

Leonard R. MacGillivray, Chair, CrystEngComm Editorial Board

Nano-sized crystals (or nanocrystals) have better solubilities and dissolution characteristics than larger crystals do.   Preparation of nanocrystals of drug molecules is therefore of interest to the pharmaceutical industry, particularly in cases where poor solubility is an issue.  However, preparation of crystals of the desired size and crucially, the correct polymorph, is not straightforward.  Problems include the long times required and the unwanted formation of amorphous material. One promising method of nanocrystal preparation  is to grow crystals in pores where the size of the pores limits the size of the crystals formed.

A recent paper in CrystEngComm by Myerson and co-workers reports the growth of three nanocrystals of pharmaceutical ingredients (APIs) – ibuprofen, fenofibrate and griseofulvin – using silica, where the pores of the silica structure provide so-called rigid confinement. The formation process is simple, involving loading of the API into the silica, washing to remove any API adhering to the surface (rather than inside the pores, see diagram below), crystallisation and drying. These steps can be varied to optimise the outcomes.

The nanocrystals exhibit enhanced solubilities and improved stabilities, due to the protection offered from e.g. moisture by the pores. The pores also limit possible reorganisations which would result in undesired crystal forms. The authors also highlight that the samples can be directly formulated into capsules without any additional steps, decreasing the formulation time significantly.

Read the full paper for more information:

Formation of organic molecular nanocrystals under rigid confinement with analysis by solid state NMR
X. Yang, T. C. Ong, V. K. Michaelis, S. Heng, J. Huang, R. G. Griffin and A. S. Myerson
CrystEngComm, 2014, DOI: 10.1039/C4CE01087F, Paper

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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.

A new paper by Behrens and co-workers in CrystEngComm details the modulated syntheses of a Zinc-fumarate MOF in both water and DMF. The authors performed kinetic studies for each synthesis, showing that, contrary to what was expected, the modulator increased the rate of formation of the MOF in DMF.

Modulating agents (usually monocarboxylic acids) are added to a MOF reaction mixture to increase the reproducibility and crystallinity of the final product. In coordination modulation, the modulating agent competes with the organic linkers in binding to the metal centre, preventing the formation of impurities but slowing down the reaction. In this current work, the authors chose formic acid as their modulator and performed in situ energy dispersive x-ray diffraction, which allowed for quantitative kinetic data to be produced.

When the authors carried out the synthesis in water, the modulating agent behaved as expected, decreasing the nucleation and growth rates as the formic acid concentration increased. However, when formic acid was added to the DMF-containing reaction mixture, the rate of growth increased. The authors theorise this occurs due to trace water in their commercial formic acid which they investigated by keeping the formic acid concentration constant but increasing water content. This showed remarkable results, increasing the rate constant by 2 orders of magnitude.

By observing that both the presence of a modulator and the water concentration have a large effect on the crystal formation, the authors added to the body of evidence that successful MOF syntheses are highly dependent on subtle changes in reagents and conditions.

Read the full article to find out more

Insight into the mechanism of modulated syntheses: in situ synchrotron diffraction studies on the formation of Zr-fumarate MOF
Gesa Zahn, Philip Zerner, Jann Lippke, Fabian L. Kempf, Sebastian Lilienthal, Christian A. Schröder, Andreas M. Schneidera and Peter Behrens
CrystEngComm, 2014, 16, 9198-9207

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.

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