On 7th of August, 2024, Kerli Martin successfully defended her PhD dissertation titled Recognition of carboxylates by synthetic receptors – from structure-affinity studies to solid-contact anion-selective electrode prototyping.
This dissertation begins with the observation that while polymer membrane ion-selective electrodes (ISEs) have been well known and widely used for decades to detect small cations, determining organic anions with ISEs remains a challenge, essentially without a solution. The dissertation presents a journey starting with the study of the interactions between small monocarboxylates and numerous anion receptors – potential new ionophores.
By measuring the binding constants of eight carboxylates (formate, acetate, pivalate, lactate, ibuprofen, ketoprofen, glucuronate, and benzoate) to 44 synthetic receptor molecules using nuclear magnetic resonance, Kerli constructed eight binding affinity scales where all the binding affinities are comparable. These results were then assembled into a large overall map of the receptor-anion binding constants (Figure on the right). The results revealed that the selected synthetic hydrogen-bond donor receptors can distinguish between carboxylates with different structures.
As a result of this binding study, a 1,3-bis(carbazolyl)urea derivative (receptor 13 in the Figure on the right) was selected as the hydrogen-bonding ionophore to create prototypes of ion-selective electrodes that can detect acetate. The electrodes built by Kerli displayed a unique selectivity pattern for different anions. The addition of this ionophore to the electrode membrane significantly (by up to several orders of magnitude) reduced the interference from other common ions such as chloride, bromide and nitrate. Kerli’s work is an important step forward in designing ionophores that can specifically bind carboxylates and building sensitive and selective ion-selective electrodes for different anions.
The defence procedure itself was quite a battle for Kerli! It started with the detailed questioning by the opponent prof. Claudia Caltagirone (University of Cagliari, Italy) on all the aspects of the thesis. Particularly interesting and difficult were some of her highly technical questions regarding the fluorescence measurement of binding affinities. Then there was a long string of questions from the defence committee members. The topics of Kerli’s thesis ranged from receptor-anion binding to computational chemistry and from materials science to hard-core electrochemistry. Thus, most committee members found something familiar and worth asking about. Kerli managed nicely with all the questions and left a very good impression on everybody in the room!
Please accept our warm congratulations, Kerli!