Allow me to take you on a trip down memory lane — back to your first ever chemistry class. Remember learning about atoms? Your teacher probably explained how molecules are made up of atoms, each of which contains the electrons used to form the bonds within molecules. Of course, things started to get complicated: with just a couple too many or a couple too few electrons, these molecules can pick up a charge, turning them into ions. With time, I’m sure the confusion over Lewis dot diagrams and cations versus anions subsided as you began to know these molecules better on paper. I wonder, though — how well did any of us know them in real life? Back then, if you had picked up a solution with a number of unknown anions and walked into a lab, would you have known how to determine which anions it contained? I know I wouldn’t have. Luckily, researchers at the University of Huddersfield have discovered a way to make this part of life in lab easier.

A molecule that self-assembled with nitrate ions.

University of Huddersfield

If you approach this problem using the analytical chemistry tools at your disposal, there are many ways to proceed: you could try gathering boiling point data, creating a precipitate, or initiating reactions. These attempts could get you some information — or they could not. Even then, there’s not always a quick and easy way to distinguish between similar results. Professor Craig Rice of Huddersfield recently discovered a new compound that has a leg up on these difficulties: when exposed to a spectrum of different ions, it undergoes a colorimetric response. The intensity of this color can be used to determine the concentration of the anion in solution, providing some valuable information about the solution’s composition. More notably, this compound creates a different color for each anion that it is exposed to. This means that researchers can use it to reliably distinguish between anions, not just recognize if one is present or not.

How is this possible? The fascinating new compound does a remarkable thing: when it senses an anion in solution, it spontaneously self-assembles into a new sensor, unique for that anion. For example, in the presence of phosphate, the compound creates a complex consisting of six organic molecules and six copper ions that binds exclusively to phosphate ions. This means that the one compound can be used as a reliable indicator for a huge number of anions, minimizing the need for the trial-and-error testing that might be required otherwise.

This discovery has broad implications for research in the lab. Whenever anions must be analyzed in the course of developing an experiment, researchers now have an incredibly valuable new tool at their disposal. However, the benefits don’t stop there. This compound will let us study the operations of the human body in more depth. Ion flow, concentration, and transport are vital to the functioning of the human body, and understanding how ion concentrations balance and change over time can tell us more about, say, the progression of a disease through the body. Although a certain set of ions is essential inside the body, other ions are incredibly harmful. Detecting pollutants with this compound could also help keep ecosystems safe from these dangerous toxins. New applications for this promising new discovery are sure to be found, but it will certainly help us better understand anions not just on paper, but also in practice.


Robert A. Faulkner, Lindsay P. Harding, Joshua Higginson, Craig R. Rice, Christopher Slater. Formation of a Dimer of Trinuclear Helicates which Encapsulates an Array of Six Hydrogen-Bonded Anions. Angewandte Chemie International Edition, 2014; 53 (49)

University of Huddersfield. “Chemistry professor discovers color sensor compound for anions.” ScienceDaily. ScienceDaily, 27 August 2015. <>.

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