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!

During recent years, we have been engaged in extensive investigations of the unified pH (pH_abs) values of reversed-phase liquid chromatography (RPLC) mobile phases. The pH_abs scale has the advantage over the conventional pH scale because pH_abs values express acidity in terms of the thermodynamic activity of the solvated proton. Therefore, pH_abs values are directly comparable between solvents/media of different compositions. At the same time, pH_abs is convenient to use, as pH_abs values of aqueous solutions are equal to the respective conventional pH values.

This comparability is especially useful in RPLC, as mobile phases are mixtures of water with organic solvents in different ratios. Thus, it can be said that pH_abs is the best way of expressing pH if a rigorous comparison of pH between solutions in different solvents is needed.

As a result of our work, we have carefully measured the pH_abs values of 78 mobile phases commonly used in RPLC, using around 300 individual ΔpH_abs measurements between different mobile phases (see the “ladder” scheme below). This is, to the best of our knowledge, the most comprehensive collection of rigorous pH_abs values of RPLC mobile phases and has now been published as A. Heering, M. Lahe, M. Vilbaste, J. Saame, J. P. Samin, I. Leito. Improved pH measurement of mobile phases in reversed-phase liquid chromatography. Analyst 2024.

The ΔpH_abs values were measured by differential potentiometry, using potential differences in a symmetric cell with two glass electrode half-cells (see figure above) and almost ideal ionic liquid triethylamylammonium bis((trifluoromethyl)sulfonyl)imide [N₂₂₂₅][NTf₂] salt bridge with multiple overlapping measurements. The system of altogether 300 ΔpH values, pictured in the “ladder” scheme below, was anchored to the pH value of standard pH 7.00 aqueous buffer solution.

In addition, a simpler measurement method that uses double junction reference or double junction combined electrodes was tested and was found suitable for routine laboratories. The results show that the design of the junction is an important factor in deciding if the electrode can be used for unified acidity measurements. This is the first successful use of double junction combined electrodes filled with ionic liquid for the measurement of pH_abs values.

The article is featured in the themed collection Analyst HOT Articles 2024.

On February 8, 2024 the on-line course (MOOC) LC-MS Method Validation offered by the University of Tartu finished successfully.

Eventually, altogether 1014 people registered from 109 countries. Around half of them, 508 participants actually started the course (i.e. tried at least one graded test at least once) and out of them 311 successfully completed the course. The overall completion rate was 31%. The completion rate of participants who started the studies was 61%. The completion rates of active participants (i.e. who started the course) seems to have stabilized at around 60%, which can be considered good. In addition, the overall completion rate is starting to increase again. In any case, there is some food for thought for us on how we could improve the overall completion rate…

At the same time, those participants who actually took part in the course, were very active and asked lots of questions. The questions were often very much to the point and addressed things that are really important to analysts in their everyday work. The course has several forums (general and by topic) and during the course period the overall number of forum posts was above 400 (!) (overall number of posts, both from participants and from teachers) and the forums are still active and posts are still coming in.

This active participation made teaching of this MOOC a great experience also for us, the teachers. The discussion threads gave a lot of added value to the course and some of them triggered making important modifications to the course materials, even during the course. Importantly, thanks to active participants, several mistakes were found and corrected in the course materials. As a result, the overall quality of the course improved.

We want to thank all participants for helping to make this course a success!

We plan to repeat this course again in Autumn 2024.

The Institute of Chemistry received an award for its consistent and systematic efforts over the past three years to improve the quality of education.

One of the main goals was to develop students’ skills in specific subjects by changing teaching methods and involving students more actively in learning. For that, seminars were organized together with the teachers, which led to the realization that also the subjects of the lectures needed to be adjusted and coordinated with each other. Student feedback was used to improve courses, and the online learning platforms were updated. In parallel, the entire curriculum was revised.

According to the Vice-Rector Aune Valk, the award recognized the Institute’s systematic and integrative approach to improving the quality of education. She emphasized the importance of consistent work for keeping the students engaged by active learning and motivating the students by making education more interactive and relevant to future careers. She also highlighted that there has already been a positive response from the students who appreciated the improvements.

In the University of Tartu, the award for improving the quality of education acknowledges a university institute, college, or department for their successful planning and implementation of activities that enhance the quality of learning. It is important that these initiatives include the collaboration between the faculty and students. Here is the original post in Estonian.