CrystEngComm Blog

Successful use of pharmaceutical drugs depends on their delivery and controlled release so that their bioactivity can be harnessed.  This can mediate poor solubility, degradation and other properties of the drug which might otherwise be problematic.  One way to control delivery is to load the drug into a container which allows the compound to be transported to the desired location, to then be released over a suitable time period.  The behaviour of the container is dependent on both the size and the shape, so simple and reliable fabrication techniques are required.

In a recent CrystEngComm article, scientists from China show how such containers can be made which are shaped like lotus leaves and are nano/microsized.  The Co₃O₄ nano/microcontainers can be easily prepared from Co(NO₃)₂.6H₂O by evaporation of the acetone solvent followed by calcining (i.e. heating at below the melting point).   In this process, shown in the diagram below, the large amount of gas bubbles produced are key to determining the shape of the containers, with no other shape-directing agents required.  The size and density of the nano/microlotus-leaf arrays can be controlled by variation of the evaporation time and temperature.

The research team used fluorescein isothiocyanate (FITC) as a model drug to study the controlled drug delivery from the nano/microlotus-leaf arrays.  They found that it could be loaded and released more effectively than for comparable Co₃O₄ microspheres and showed that cells which were treated with the arrays retained over 80% viability even at high concentration — indicating that these microcontainers are a safe delivery vehicle of active compounds to cells.

For more details, see the paper:

Facile bubble-assisted evaporation-induced assembly of high-density arrays of Co₃O₄nano/microlotus leaves: fluorescent properties, drug delivery, and biocompatibility

 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. Currently, she is writing a book on chemicals from plants. 

Posted on behalf of Josh Campbell, web writer for CrystEngComm 

The phenomenon of jumping crystals was first reported in 1983 when it was discovered that heating crystals of (phenylazophenyl)palladiumhexafluoroacetylacetonate caused not only a polymorphic transition, but also the sample to literally “jump” off the heat source.  Since then, mechanically responsive materials research has blossomed due to potential applications in medical devices, actuators and electronic sensors. Most research in the field has focussed on molecular scale movement (typically using rotaxanes or catenanes) or light-activated polymers for macroscopic movement. However, single crystals possess many of the properties needed for practical applications of actuators.  The ordered structure of the crystal should allow any induced effect to travel faster which allows faster energy transfer, shorter response times and faster recovery. 

A new highlight article in CrystEngComm recaps some of the recent progress in the field, focusing on the mechanical processes seen in thermo- and photo-responsive crystals. Thermally induced jumping is known as the thermosalient effect and has been reported for many materials. Crystals that exhibit this effect generally fall into three types: crystals which contain hydrogen bonds; crystals without hydrogen bonding groups that form stacked layers; and crystals with no strong intermolecular interactions whatsoever. For the second class, the ability of a layered structure to exhibit hopping depends on the interactions between layers and the thermal motion of the atoms between them. Oxitropium bromide is one such crystalline material, which undergoes a reversible conformational change which has the effect of loading, and then decompressing, a spring. For polar molecules, a compression along the most polar axis can lead to mechanical effects. 

Photo-responsive crystals rely on the photochromic effect, a reversible transformation that occurs on the absorption of electromagnetic radiation. Crystals can respond mechanically to this absorption with a range of mechanical effects. For example, microcrystals of trans-4-aminoazobenzene bend away from UV light. Bending and curling is often seen with cis–trans isomerism, ring opening and closure and cycloaddition reactions. The photosalient effect has also been reported, whereby mechanical strain develops in the crystal due to a photochemical reaction. An example of this is α-santonin, its crystals turn yellow and burst when exposed to sunlight. 

Research into thermal and photo induced mechanical effects is now picking up compared to previous decades after the realisation of their importance in both energy conversion and for developing mechanically responsive materials. 

Read the article now for more details: 

Thermally induced and photoinduced mechanical effects in molecular single crystals—a revival 

N. K. Nath, M. K. Panda, S. C. Sahooa and P. Naumov
CrystEngComm, 2014, DOI: 10.1039/C3CE41313F 

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.

Flufenamic acid (FFA) is a potent non-steroidal anti-inflammatory drug used to treat lower back pain, either orally or topically.  However, it has low solubility and a slow dissolution rate which are problematic.  One way these properties can be improved is by forming a solid solution with polyvinylpyrrolidine or a co-crystal with nicotinamide (NA).  Co-crystals form between the active molecule and a co-former and possess different physicochemical properties from either of the components.

A recent CrystEngComm article reports the formation and X-ray structures of three new co-crystals of FFA, with the co-formers theophylline (TP), 4-pyridone and 4,4’-bipyridine.  Each of the three structures shows the formation of heterosynthons (i.e. interactions between complementary functional groups) e.g. for FFA-TP, interactions between FFA O-H and TP N atoms.   TP is a central nervous system stimulant, found in cocoa beans, and used to treat respiratory diseases such as asthma.  The FFA-TP system is an example of a drug-drug co-crystal, where both components have biological activity and therefore is of particular interest.

The authors found improved solubility and dissolution rate for this system, compared to either pure FFA or the FFA-NA co-crystal.  They also compared the properties to a TP co-crystal with oxalic acid, with the FFA-TP co-crystal proving less hygroscopic.

These results suggest that formation of this co-crystal offers improved properties for both FFA and TP and in addition, offers an opportunity to explore the development of combination drugs by forming drug-drug co-crystals.

For more information see the 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. Currently, she is writing a book on chemicals from plants.

Posted on behalf of Jamie Humphrey, Editor

Crystallography is a core science, underpinning many areas of research, and central to crystal engineering. 2014 marks the centenary of the birth of X-ray crystallography and has been proclaimed the International Year of Crystallography. We are delighted to celebrate this important science in CrystEngComm in a number of ways in 2014.

Our celebrations will take the form of the publication of four themed issues dedicated to the best crystal engineering research from four key geographical regions. Keep an eye out for these issues, which will appear throughout the year, covering India (Guest Editor: Professor Rahul Banerjee, CSIR-National Chemical Laboratory, Pune, India), Europe (Guest Editors: Professor Dario Braga, University of Bologna, Italy and Professor Michaele Hardie, University of Leeds, UK), the Americas (Guest Editors: Professor Christer Aakeröy, Kansas State University, USA and Professor Tomislav Friščić, McGill University, Canada) and Asia-Pacific (Guest Editors: Professor Stuart Batten, Monash University, Australia and Professor Jagadese Vittal, National University of Singapore, Singapore).

We also have a number of excellent topic-themed issues planned for the year, illustrating the breadth of crystal engineering research: Functional co-crystals (Guest Editor: Professor Colin Pulham, University of Edinburgh, UK), Structural macrocyclic supramolecular chemistry (Guest Editors: Professor Len Barbour, University of Stellenbosch, South Africa, Professor Len MacGillivray, University of Iowa, USA and Professor Kari Rissanen, University of Jyväskylä, Finland), Nanoparticle assemblies (Guest Editors: Professor Marie Paule Pileni, UPMC, Paris, France, Professor P. Davide Cozzoli, Università del Salento & National Nanotechnology Laboratory, Italy and Professor Nicola Pinna, Humboldt-Universität zu Berlin, Germany), and Nanocrystal growth via oriented attachment (Guest Editors: Dr R. Lee Penn, University of Minnesota, USA, Dr Hengzhong Zhang, University of California, Berkeley, USA, Dr Zhang Lin, State Key Laboratory of Structural Chemistry, China and Dr Helmut Cölfen, University Konstanz, Germany). These follow the themed issues published in 2013, details of which are in Table 1.

Table 1 2013 themed issues, representing the breadth of crystal engineering

Continuing the International Year of Crystallography celebrations, the Royal Society of Chemistry, in partnership with Calcutta University, Jadavpur University and IISER-Kolkata, will organise a symposium on structural chemistry in November in India. We will also participate in a global experiment for school children involving crystals. Keep an eye out for more information about the symposium and the global experiment as they develop.

In 2013 a number of people joined our Editorial Board, bringing with them expertise and experience of their particular research fields. Joining Editorial Board Chair, Len MacGillivray (University of Iowa, USA), Associate Editors Rahul Banerjee (CSIR-National Chemical Laboratory, India) and Christer Aakeröy (Kansas State University, USA) and Board member Nicola Pinna (Humboldt-Universität zu Berlin, Germany) are Associate Editors Hongjie Zhang (Changchun Institute of Applied Chemistry, China) and Georg Garnweitner (TU Braunschweig, Germany) and Board members Graeme Day (University of Southampton, UK), Tomislav Friščić (McGill University, Canada), Michaele Hardie (University of Leeds, UK), Helmut Cölfen (Universitat Konstanz, Germany) and Pierangelo Metrangolo (Politecnico di Milano, Italy). We very much look forward to our collaborations with them all.

The way we connect with our friends, peers and colleagues is changing, and social media is an important tool for this. CrystEngComm is no different. We have a number of outlets for CrystEngComm via social media, expanding the ways in which people can get involved with the journal. The journal has a Facebook page and Twitter account (why not join our 1000 followers?) and our LinkedIn group is a good way to learn about relevant conferences and other news. Our latest offering is our ‘Crystal Clear’ Pinterest page, illustrating some of the stunning crystal images that are included in the journal.

Fiona McKenzie (Deputy Editor) and I will be attending two conferences in 2014: the Crystal Engineering Gordon Research Conference and the IUCr meeting. An important related meeting is the Faraday Discussion meeting 170 with a focus on Mechanochemistry: From Functional Solids to Single Molecules. The meeting will be in Montreal, Canada in May, and more details are available via www.rsc.org/ConferencesAndEvents/RSCConferences/FD/FD170/index.asp

We were very pleased to support a number of international conferences in 2013 through sponsorship. We also provide support via poster prizes – in 2013, we awarded 10 poster prizes, celebrating the achievements of members of our community in the early years of their academic careers. If you are organising a conference in 2014 and you would like us to sponsor a poster prize, please let us know.

Let us connect you and your work into the world’s leading chemistry community in 2014, the International Year of Crystallography: publish with CrystEngComm!

Have a fantastic 2014!

Download the pdf here

Posted on behalf of Josh Campbell, web writer for CrystEngComm

Stony corals are the main reef builders of the planet and responsible for some of the oceans’ most beautiful architecture. However the processes behind their skeleton mineralisation are of some debate. Skeleton formation occurs at the interface of the coral tissue and the skeleton. This area is rich in proteins that are able to bind to water and has the properties of a highly viscous sol. Also observed at this interface is an amorphous organic membrane, which possibly acts as a colloidal gel matrix. Aragonite (a polymorph of CaCO₃) precipitates out of seawater directly at this interface and is controlled by the organic gel matrix. Ionic concentrations are also believed to play a part, with high concentrations of Mg²⁺ favouring aragonite precipitation.

A recent article in CrystEngComm investigates how the organic matrix and the level of diffusion of Mg²⁺ affects the precipitation of CaCO₃ . The authors of the article extracted two matrices from two different species of coral (differing in their reliance on photosynthetic algae) and placed them in a highly viscous agarose gel/sol. They then transported CaCO₃ through using a counter diffusion system (CDS). Interestingly, they discovered that the different molecular compositions of the matrices resulted in different morphologies and crystallisation conditions which they suggest is due to the symbiotic relationship some corals have with photosynthetic algae (which provide the main energy source for calcification). We now know that the presence of Mg²⁺ has a large effect on the conditions needed for supersaturation in the medium as well as the phase selections of CaCO₃ .

The use of CDS has allowed coral biomineralisation of these two coral species to be studied in vitro for the first time.

Read the article now for more information:

Exploring coral biomineralization in gelling environments by means of a counter diffusion system
M. Sancho-Tomás, S. Fermani, S. Goffredo, Z. Dubinsky, J. M. García-Ruiz, J. Gómez-Morales and G. Falini
CrystEngComm, 2014, DOI: 10.1039/C3CE41894D

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.

Harnessing light from the sun to drive reactions requires the development of photocatalysts which can both absorb light of the required frequency but also absorb enough of this light to meet the energy demands for the reactions.  To solve this latter problem, silver halide catalysts with silver particles adsorbed on the surface (i.e. AgX@Ag) are a possibility, as these utilise the surface plasmon resonance (SPR) effect to enhance the visible light absorbed.  SPR occurs when electrons from the surface Ag atoms oscillate at the same frequency as the visible light. The degree of oscillation  increases and subsequently increases the energy available to facilitate a chemical reaction.  Unfortunately, forming the AgX@Ag particles can require high temperatures and strong light.

A recent CrystEngComm paper reports a facile synthesis of AgCl@Ag under mild conditions, using the biomaterial agar gel as a matrix.  Diffusion of the reactants is mediated by the matrix and on illumination with visible light, Ag atoms are generated on the surface of the AgCl.  The AgCl@Ag particles produced are in the form of concave cubes.  The authors suggest their mild eco-friendly synthesis method could be used to prepare other functional materials at low cost.

For more details, see the paper:

Biomaterial-assisted synthesis of AgCl@Ag concave cubes with efficient visible-light-driven photocatalytic activity
Pei Hu, Xianluo Hu, Chaoji Chen, Dongfang Hou and Yunhui Huang
CrystEngComm, 2014, DOI: 10.1039/C3CE41925H

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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. Currently she is writing a book on chemicals from plants.