New breed of supermolecule ‘hunts down’ harmful drugs and removes them from water

A University of Surrey academic is leading research that has found an effective, environmentally friendly way to monitor and remove pharmaceuticals from water.  

The research involves the detection and removal of pharmaceuticals in or from water, as contamination from pharmaceuticals can enter the aquatic environment as a result of their use for the treatment of humans and animals. This contamination can be excreted unchanged, as metabolites, as unused discharge or by drug manufacturers.

The research has found that a new type of ‘supermolecule’, calix[4], actively seeks certain pharmaceuticals and removes them from water.  

Contamination of water is a serious concern for environmental scientists around the world, as substances include hormones from the contraceptive pill, and pesticides and herbicides from allotments. Contamination can also include toxic metals such as mercury, arsenic, or cadmium, which was previously used in paint, or substances that endanger vital species such as bees. 

Professor Danil de Namor, University of Surrey Emeritus Professor and leader of the research, said: “Preliminary extraction data are encouraging as far as the use of this receptor for the selective removal of these drugs from water and the possibility of constructing a calix[4]-based sensing devices. 

“From here, we can design receptors so that they can bind selectively with pollutants in the water so the pollutants can be effectively removed. This research will allow us to know exactly what is in the water, and from here it will be tested in industrial water supplies, so there will be cleaner water for everyone.  

“The research also creates the possibility of using these materials for on-site monitoring of water, without having to transport samples to the laboratory.”

Dr. Brendan Howlin, University of Surrey co-investigator, said: “This study allows us to visualise the specific receptor-drug interactions leading to the selective behaviour of the receptor. As well as the health benefits of this research, molecular simulation is a powerful technique that is applicable to a wide range of materials. 

“We were very proud that the work was carried out with PhD students and a final year project student, and research activities are already taking place with the Department of Chemical and Processing Engineering (CPI) and the Advanced Technology Institute (ATI).

“We are also very pleased to see that as soon as the paper was published online by the European Journal of Pharmaceutical Sciences, we received invitations to give keynote lectures at two international conferences on pharmaceuticals in Europe later this year.” 

Supramolecular materials are a class of materials that exploit the weak forces occurring between ionic and molecular species. 

Three commonly used drugs have been investigated in this study. The first is Diclofenac, a non-steroidal anti-inflammatory drug currently used to treat painful conditions resulting from arthritis, sprains and strains, gout, migraine, and other illnesses. Clofibric acid is known as the active metabolite of a number of drugs, currently used to reduce the levels of cholesterol in blood.  The third drug, aspirin, is one of the most frequently-used drugs, as it is an analgesic with pain relief and anti-inflammatory properties.

The hosting ability of the receptor was found to be greater for clofibric acid and diclofenac given that two protons are taken up per unit of receptor. For aspirin only one proton is transferred to the receptor. 

The calix[4]arene amine receptor is able to recognise selectively clofibric acid, diclofenac and aspirin and discriminates against other drugs containing carboxylic functional groups (cyprofloxacin, nalidixic acid and ibuprofen). The interaction occurs via a hydrogen transfer mechanism and it is controlled by the dissociation constants of the carboxylic groups of the drug. 

Molecular simulation studies suggest that for the latter drug, one of the amino functionalities is protonated while the remaining one enters hydrogen bond formation with the carbonyl oxygen of the ester group of aspirin.

Thermodynamics provides a quantitative assessment of the strength of interaction through the stability constant. The availability of enthalpy and entropy data allows to assess whether the process is enthalpy or entropically controlled.

For more information on the paper, please visit: 

http://www.sciencedirect.com/science/article/pii/S092809871630567X.