CrystEngComm Blog

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.