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Biometic Molecularly Imprinted Polymer Research
Molecularly imprinted polymers are a class of material, designed to have a high affinity for a specific molecule. Molecular imprinting leaves cavities in the ordinary structure of the polymer – usually, this is done by initiating polymerization of the polymer molecule while the imprint molecule is present. When it’s subsequently removed, the cavity remains, and the polymer is very likely to bind to that original molecule again.
This has clear applications – for example, molecularly imprinted polymers can catalyze reactions by bringing appropriate molecules together in a similar way to biological enzymes. This can also be used in chemically separating molecular bonds, or even as chemical sensors for the specific molecules you’re looking for.
Amylase Enzyme - carries out the hydrolysis of starch into sugars. (Image Credit: molekuul_be/Shutterstock)
Nature has its own way of performing these kinds of chemical tasks, using enzymes. Enzymes have adapted over millions of years of evolution to be particularly good at molecular transport and catalyzing reactions. Amongst other properties, natural enzymes can catalyze reactions in a highly specific way, as well as exhibiting high regioselectivity – the preference to react with a particular bond – and stereoselectivity – the possibility of favorably forming a single isomer when many different pathways might be available.
However, there are issues with using natural enzymes - they are optimized for biological conditions at relatively standard temperatures and pH, and they will denature under extreme reaction conditions. In organic solvents, many enzymes will dissolve. Additionally, isolating and purifying enzymes for chemical use can be costly.
For this reason, scientists hope to create biomimetic imprinted polymers – catalysts for the same kind of natural chemical reactions, without the disadvantages of trying to use natural enzymes. It may then be possible to engineer systems that are both more robust and more selective, or that perform reactions humans would find useful, but nature doesn’t.
In many ways, the applications and fundamental research into biomimetic molecularly imprinted polymers can be divided into two parts. One side is attempting to find enzyme-like behaviour for reactions where no enzyme exists; for example, the Diels-Alder reaction. The reaction has been described as one of the most useful synthetic reactions, and won the 1950 Nobel Prize in Chemistry when it was discovered.
The other side is attempting to improve on nature by producing polymers that are more robust, more efficient, or more selective.
Example applications for biomimetic catalyst systems include forming C-C bonds, elimination reactions (which can manipulate molecules like hydrocarbons) and hydrolysis (the breaking down of chemical bonds with water, which is used in the biological setting to break down complex proteins and sugars). This allows for synthetic alternatives to enzyme biotechnology, which is used across a range of detergents, textiles, biodegradable plastics, and biofuels; as well as in food and beverage creation (e.g. artificial sweeteners).
When biomimicry researchers add an additional feature that closely resembles one in nature, they usually find that the result is an improvement on previous performance. An example of this is the development of thermally sensitive polymers, which change their structure across the range of temperatures in which enzymes usually operate. This change in structure can result in a change in catalytic activity.
These “thermoreactive” polymers could develop further by mimicking biological systems even more closely, and hence allow for fine-tuned catalysts that work across specific temperature ranges, and respond to their environment – perhaps ceasing catalyzing a reaction once a certain temperature is reached.
The binding sites associated with enzymes are also associated with antibodies produced by our own immune systems. It has been suggested that someday, imprinted polymers could become synthetic antibodies – bolstering our immune systems, finding use as reagents in protein capture or as protein inhibitors.
Replicating the behaviour of natural enzymes is not the only potential application that has been suggested for imprinted polymers. in a particularly striking piece of research back in 2010, it was reported that biomimetic surfaces based on the eyes of the blowfly – which collect solar radiation from a range of different angles – could make solar cells.
Image Credit: Sarin Kunthong/Shutterstock
The optical properties of butterfly wings, which create color without pigmentation through their physical structure, has also been a considerable area of research leading to several patented devices – imprinted polymers could produce similarly complex surfaces.
It seems certain that the growing collaboration between chemistry and biology will produce a number of applications and technologies. Mimicking nature on all scales gives you access to the results of an optimization process that has been ongoing for millions of years, so there are sure to be secrets still to unlock.