Synthetic Anion Receptors, Sensors and Related Topics







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Eur. J. Org. Chem. 2017, 52315237.
Exploring Selectivity of 22 Acyclic
Urea-, Carbazole- and Indolocarbazole-Based Receptors
towards 11 Monocarboxylates

Synthetic molecular receptors (derivatives of indolocarbazole, urea, thiourea, etc)


measured with formate, acetate, anions of propionic acid derivatives (ibuprofen, ketoprofen, naproxen, pivalic acid and lactic acid), hexanoate, sorbate, benzoate

and glucuronate

DMSO with 0.5% of water


22 acyclic synthetic receptors with different numbers and geometric arrangements of hydrogen-bond donors (HBD) and hydrophobic moieties have been applied to experimentally study selective binding of 11 carboxylate anions of widely differing basicity, hydrophobicity and steric demand, which resulted in 242 accurately determined binding constants. It was found that besides the basicity of the anions, structural and steric factors of anions and receptors influence the binding. Several interesting cases are pinpointed and analysed. The ability of selected receptors to discriminate between anions according to structural features (hydrophilicity, substitution at α-carbon, etc.) is demonstrated.


pKa values in water and DMSO for formic acid, acetic acid, pivalic acid, lactic acid, Naproxen, Ibuprofen, Ketoprofen Glucuronic acid, hexanoic acid, sorbic acid and benzoic acid (pKa in H2O and DMSO).

Scheme 1. Investigated anions X‑COO together with pKa values of X‑COOH in water (experimental) and DMSO. (PDF)


Scheme 2. Binding-structure relationship comparing the binding affinity changes of all anions under study. (PDF)

Chem. Eur. J. 2015, 21, 5145 5160. Towards the Discrimination of Carboxylates by Hydrogen-Bond Donor Anion Receptors

Synthetic molecular receptors (derivatives of indolocarbazole, urea, thiourea, etc)


measured with lactate, benzoate, acetate and trimethylacetate (pivalate)

DMSO with 0.5% of water


The binding constants (logKass) of small synthetic

receptor molecules based on indolocarbazole, carbazole, indole, urea and some others, as well as their combinations were measured for small carboxylate anions of different basicity, hydrophilicity and steric demands, that is, trimethylacetate (pivalate), acetate, benzoate and lactate, in 0.5% H2O/[D6]DMSO by using the relative NMR-based measurement method. Four separate binding affinity scales (ladders) including thirty-eight receptors were obtained. The results indicate that the binding strength is largely, but not fully, determined by the strength of the primary hydrogen-bonding interaction. The latter in turn is largely determined by the basicity of the anion. The higher is the basicity of the anion the stronger in general is the binding, leading to the approximate order of increasing binding strength, lactate < benzoate < acetatetrimethylacetate, which holds with all investigated receptors. Nevertheless, there are a number of occasions when the binding order changes with changing of the carboxylate anion, sometimes quite substantially. Principal component analysis (PCA) reveals that this is primarily connected to preferential binding of trimethylacetate, supposedly caused by an additional hydrophobic/solvophobic interaction. These findings enable making better predictions, which receptor framework or cavity is best suited for carboxylate anions in receptor design.

Scheme showing the trends in binding affinity of acetate lactate benzoate and trimethylacetate (pivalate) to different molecular receptors (PDF)

J. Org. Chem. 2014, 79, 2501−2513. NMR Method for Simultaneous Host−Guest Binding Constant Measurement

Synthetic molecular receptors (derivatives of indolocarbazole, urea, thiourea, etc)


measured with acetate

DMSO-H2O (99.5%:0.5% m/m)

NMR, UV-Vis spectrophotometry

An NMR-based relative binding affinity measurement method has been developed in which differences in the

binding affinities of different hosts toward a particular guest (ΔlogKass values) are measured in the same solution. As an advancement, the method allows the simultaneous determination of several ΔlogKass values in a single run. As a result, a binding affinity scale containing 33 receptors and spanning 2.32 log units with excellent self-consistency (consistency standard deviation = 0.01 log unit) was created in DMSO-d6/H2O (99.5%:0.5% m/m). Together with the very good agreement of the results with those obtained by UV−vis spectrophotometry, this demonstrates the high accuracy of the method and the fact that the NMR and UV−vis techniques can be used interchangeably (in spite of the very different concentrations used in these techniques).


J. Org. Chem. 2013, 78, 7796−7808. Accurate Method To Quantify Binding in Supramolecular Chemistry

Synthetic molecular receptors (derivatives of indolocarbazole, urea, thiourea, etc)

Acetonitrile with 0.5% of water

UV-Vis spectrophotometry

An accurate measurement method of host−guest binding affinities (binding constants) is introduced whereby differences in binding strength (ΔlogKass values) are measured between two host molecules toward a particular guest under identical solvent conditions. This method was applied to the measurement of the binding strength of 28 synthetic anion receptors (indolocarbazoles, ureas, thioureas) toward acetate in acetonitrile containing 0.5% water. A self-consistent (consistency standard deviation 0.04 log units) binding affinity scale ranging for around 2.7 log units was constructed from the results. This new approach of ligand receptor binding measurement is expected to find use in accurate quantification of a wide range of binding processes relevant to supramolecular chemistry.

Ligand-receptor Binding constant measurement data, structures of the receptor molecules, absolute association constants pKa values of the more acidic receptor molecules (PDF)

Chem. Comm. 2012, 48, 10490-10492. Unusual para-substituent effects on the intramolecular hydrogen-bond in hydrazone-based switches

Hydrazone-based molecular switches


UV-Vis spectrophotometry, NMR,

The switching of the described molecular switches is sensitive towards acidity of the medium. The two H-bond fragments HNNQCCQN and HNNQCCQO in a series of hydrazone-based switches adopt two distinct H-bonding motifs. The HNNQCCQN fragment cannot take advantage of RAHB enhancement, because that will diminish the aromatic character of the pyridyl group. On the other hand, the HNNQCCQO fragment follows RAHB theory. By measuring the pKa values of the pyridyl ring and dissecting its components, we were able to show that both electron donating and withdrawing p-substituents strengthen the H-bond in the HNNQCCQN fragment by inversely modulating the acidity and basicity of the NH and pyridyl nitrogens, respectively.


Sensors 2010, 10, 4430-4455 Measurement Uncertainty Estimation in Amperometric Sensors: A Tutorial Review

No limits

No limits

Electrochemical amperometric sensors

This tutorial focuses on measurement uncertainty estimation in amperometric sensors. The main uncertainty sources are reviewed and their contributions are discussed with relation to the principles of operation of the sensors, measurement conditions and properties of the measured samples. The discussion is illustrated by dissolved oxygen (DO) measurement case studies based on the two major approaches for uncertainty evaluation: the ISO GUM modeling approach and the Nordtest approach.

Graphical representation of the paper


Figure 2. Expanded uncertainties for all conditions using two estimation approaches

Meas. Sci. Technol 2007, 18, 1877. Model-based measurement uncertainty estimation in amperometric dissolved oxygen concentration measurement

Dissolved oxygen, DO, (O2)

Water (H2O)

Electrochemical amperometric sensors

Uncertainty sources in amperometric dissolved oxygen (DO) concentration measurement are explored and an ISO GUM uncertainty estimation procedure based on a detailed measurement model is presented. The procedure is applied to two different commercial amperometric DO measurement instruments of galvanic type differing in cathode and membrane area and membrane thickness. The complete uncertainty budgets of several typical measurement processes of the two instruments are discussed. The high importance of the cathode and membrane area, membrane material and membrane thickness on the uncertainty is demonstrated. Based on these results, a set of recommendations for the DO sensor design is formulated.

Table 1. Measurement conditions and uncertainty budgets of the results obtained by instruments I and II corresponding to the cases 15

using calibration in water


Figure 3. The relative uncertainties of DO concentrations measured with instruments I and II calibrated in air and in water. The points have

been connected for better readability


Excel spreadsheet of uncertainty calculation examples for Instrument I

Accreditation and Quality Assurance 2004, 9, 340-348. Estimation of uncertainty in electrochemical amperometric measurement of dissolved oxygen concentration

Dissolved oxygen, DO, (O2)

Water (H2O)

Electrochemical amperometric sensors

A procedure for the estimation of measurement uncertainty of dissolved oxygen (DO) concentration measurement based on the ISO approach is presented. It is based on a mathematical model that involves 14 input parameters. The uncertainty of DO concentration strongly depends on changes in experimental details (temperature difference between calibration and measurement, the time interval between calibration and measurement, etc.).

Fig. 1 Schematic presentation of a galvanic dissolved oxygen (DO)



Table 1 The uncertainty budgets at DO concentration 7.0 mg/l various measurement conditions



Should you have any questions regarding the data, the used experimental, data treatment or computational methods, etc, please do not hesitate to contact Ivo Leito (e-mail:!     Proposals for collaboration are also most welcome!

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See also other research topics at UT Chair of Analytical chemistry


University of Tartu



Last edited:  Friday, 26-Jan-2018 18:50:07 EET