Doctoral defence: Kerli Martin "Recognition of carboxylates by synthetic receptors - from structure-affinity studies to solid-contact anion-selective electrode prototyping"

On 7. August at 10:15, Kerli Martin will defend her thesis "Recognition of carboxylates by synthetic receptors - from structure-affinity studies to solid-contact anion-selective electrode prototyping".

Supervisor: 
Professor Ivo Leito, University of Tartu

Opponent: 
Professor Claudia Caltagirone, PhD University of Cagliari, Italy

Summary:
To address the need for precise anion detection in various production processes, remote locations, and even wearable devices, the development of simple and portable devices is essential. Ion-selective electrodes (ISEs) are well-suited for this purpose due to their favorable characteristics: simplicity, affordability, speed, miniaturization, and direct placement in the measured solution without extensive sample preparation or laboratory handling. While polymer membrane ISEs have been effective for detecting small cations for over four decades, the challenge lies in determining more complex ions, such as organic anions. Finding suitable ionophores to prepare electrode membranes for these anions has proven difficult.

This dissertation studies the interactions between small monocarboxylates and potential new ionophores. By measuring the binding constants of eight carboxylates to 44 synthetic receptor molecules using nuclear magnetic resonance, eight binding affinity scales where constructed where all the binding affinities are comparable. Planar tetradentate receptors were identified as particularly effective for binding carboxylate anions. Additionally, it is explored how non-polar substituents, steric effects, additional interactions, and solvophobic effects impact the binding of specific carboxylates. The results revealed that the selected synthetic hydrogen-bond donor receptors can distinguish carboxylates with different structures.

As a result of this binding study, a 1,3-bis(carbazolyl)urea derivative was utilized as a hydrogen-bonding ionophore to create test versions of electrodes that can detect acetate. These electrodes showed a unique pattern in how they selected different ions, preferring smaller carboxylates like acetate and formate, as well as bicarbonate, over chloride. The addition of this ionophore to the electrode's membrane also reduced the interference from other common ions like SCN^-, I^-, NO₃^-, and Br^-. This discovery is an important step forward in making ionophores that can specifically bind to carboxylates.