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Cleaning Up with Crystal Engineering
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Crystal engineering, a relatively new field of chemistry, has been rapidly expanding since it was first introduced in 1971. Crystal engineering is a cross-disciplinary field that uses aspects of supramolecular chemistry (the study of how molecules interact with each other) and X-ray crystallography (a technique for determining the position of atoms in crystals) to develop the protocols for predicting and controlling the structure and functional properties of solids. This field encompasses all aspects of design in the solid state and has no boundaries in terms of the chemical type of moieties involved or which intermolecular/ionic forces can be exploited. Dr. Mike Zaworotko of Saint Mary’s University, Halifax, Nova Scotia, is a crystal engineer involved in developing two types of new compounds that are functionally and structurally similar to well-known minerals such as clays and zeolites but are chemically very different. Dr. Zaworotko has focused primarily on using organic molecules or metal cations for the assembly of 2-dimensional networks. The organic molecules are multifunctional carboxylic acids such as trimesic acid and pyromellitic acid and they can form either salts or cocrystals.
Zeolites are naturally occurring or synthetic aluminosilicate compounds with a framework structure enclosing cavities occupied by large ions and water molecules. Natural zeolites are used in kitty litter to absorb ammonia and control odours, and in the "cracking" of crude oil. In this case the large molecules of crude oil are "cracked" into smaller ones thereby altering the petroleum product. The new clays and zeolites that Dr. Zaworotko is developing are mainly organic in nature and can have many possible applications. Some of these new applications involve the clean-up of pollutants, drug delivery (matrix for oral delivery of otherwise unstable drugs), crop remediation (slow release of pheromones), and new industrial catalysts.
One of the compounds that Dr. Zaworotko’s research group has created is a sponge-like zeolite compound that is capable of "soaking up" PCB’s and polyaromatics which makes it ideal for hazardous waste clean-up. The tiny zeolite crystals form a molecular mesh that has a hydrophobic interior surface that preferentially adsorb organic molecules. This characteristic makes it ideal for cleaning polluted water as the sponge-like zeolite can be used as a filter. The research has been supported over the past few years by NSERC (National Science and Engineering Research Council) and the Environmental Science and Technology Alliance of Canada.
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