Design, synthesis and application of carbazole macrocycles in anion sensors

Our supramolecular analytical chemistry team has published an article (Beilstein J. Org. Chem. 2020, 16, 1901-1914) about developing carboxylate sensor prototypes that use macrocyclic carbazole receptors as ionophores.

Usually, reported research concludes with the demonstration of binding abilities of receptors and only suggests possible applications at a theoretical level. This work stands out from most publications by incorporating the entire workflow from receptor design to the characterisation of working sensor prototypes.

By involving this additional step, the team demonstrated the shortcoming of evaluating binding with just the receptor and analyte in solution. The predictions of selectivity can change considerably when measuring binding in an actual sensor membrane. This does not mean that such binding measurements would be obsolete, as the issue of binding anions selectively remains relevant in supramolecular chemistry.

The work was published in collaboration with the group of prof. Johan Bobacka at Åbo Akademi. The open access article was published in the Beilstein Journal of Chemistry thematic issue “Molecular Recognition” (in memory of Prof. Carsten Schmuck).

Synthesis and characterization of novel phosphazene-based indicator molecules

On August 22, 2019 Sigrid Selberg successfully defended her PhD thesis titled Synthesis and properties of lipophilic phosphazene-based indicator molecules.

The dissertation presented by Sigrid Selberg is focused on the design and synthesis of a family of highly lipophilic phosphazene based indicators. 16 new phosphazene based indicators where phosphazene structure is extended with an azo group or with 4- (trifluoromethyl)coumarin backbone were synthesized and characterized, indicators are active in both visible absorption and fluorescence. These compounds are highly lipophilic in both neutral and protonated form, therefore, the synthesized compounds have all the desired and suitable properties to employ them in the design of an optical pH sensor. For the first time, alkyl and aryl phosphazenes are used for this purpose.

In addition, the original approach for quantifying acidity/basicity of lipophilic molecules in water-immiscible media that is at equilibrium with aqueous phase is developed and applied in the determination of biphasic pKa values of some of the synthesized compounds.

Congratulations to you, Sigrid!

UT Analytical chemistry at Suprachem 2019: From receptor synthesis to ion-selective electrode

During 24-26.02.2019 the Suprachem 2019 conference took place at University of Würzburg (Germany). The UT Analytical chemistry chair was represented by two posters: Optimization of the reaction pathway for the synthesis of substituted 1,3-bis(carbazolyl)urea anion receptors by Alo Rüütel and Mihkel Ilisson and From receptor-anion binding ladder to ion-selective electrode by Kerli Martin, Sandip A. Kadam, Ulriika Mattinen, Johan Bobacka and Ivo Leito.

Synthesis of 1,3-bis(carbazolyl)urea based anion receptors

The presentation from Alo and Mihkel focused on optimization of the synthesis route of anion receptors (ionophores) based on the 1,3-bis(carbazolyl)urea building block, augmented with additional amide functionalities (see the poster). The developed synthesis route is very valuable for the synthesis of a wide variety of analogous receptors (ionophores) that have previously been demonstrated to bind carboxylates with high affinity (see K. Martin et al, Eur. J. Org. chem. 2017, 5231-5237).

First solid contact acetate electrodes using receptor molecules

Kerli Martin et al present the first practical application of such receptors: a solid-contact acetate-selective electrodes. For acetate anion the electrodes show linearity over the activity range of 10-4.50 – 10-1.10 with a sub-Nernstian slope of -51.3 mV per decade and a detection limit of 10-5.00. The anion-selectivity pattern of these electrodes deviates markedly from the pattern found in DMSO solution and from the Hofmeister pattern. The selectivity coefficients of SCN–, I–, NO3– and Br– decrease by 3-5 orders of magnitude when adding the studied ionophore to the membrane. The selectivity coefficients of hydrophilic anions such as Cl–, F–, HPO42–, and SO42– are significantly lower than in case of the ionophore-free control membrane. All in all, it is clear that a lot of work is still needed for improving the selectivity of the electrode.
This work has been accepted for publication: K. Martin et al Electroanalysis 2019 (the link will work soon).

The combined contributions from our group stood out from the majority (the conference altogether had 27 oral and 111 poster presentations) by a clear line of development from fundamental research (receptor design) to highly practical application (ion-selective electrode).

(Photos: above left: Mihkel Ilisson explaining his work to Dr Diane Smith from Wiley; right: Poster by Kerli Martin et al)

 

From high-resolution mass spectrometry in art to measurement of receptor-anion binding

Anu_Teearu_Kristjan_HaavThis is the range of topics addressed on Aug 16, 2017 as PhD dissertations addressing these topics were defended at UT Institute of Chemistry.

 

Anu_Teearu_presenting_her_PhD_ThesisAnu Teearu (left on the photo) in her thesis titled Development of MALDI-FT-ICR-MS methodology for the analysis of resinous materials addressed the analysis of resinous materials in order to obtain the maximum amount of high-accuracy data from these complex materials. Several important methodological developments (novel calibrants, novel matrix materials, etc) were introduced to MALDI-FT-ICR-MS and its capabilities were assessed during the analysis of three case study samples originating from different types of cultural heritage objects.

 

Kristja_Haav_presenting_his_PhD_ThesisThe central aim of the thesis of Kristjan Haav Quantitative relative equilibrium constants measurements in supramolecular chemistry was development of highly accurate binding constant measurement methods. The key development was measuring relative equilibrium constants instead of absolute ones, which enables eliminating or strongly reducing the influence on several error sources. Kristjan tested the applicability of this approach on two instrumental techniques: UV-vis spectrophotometry and nuclear magnetic resonance spectrometry (NMR). Comparison of the two – completely independent – techniques showed good agreement between the obtained results and thus supports the reliability of both of them.

Kristjan Haav is an alumnus of the Applied Measurement Science programme – the predecessor programme of EACH.