Quantifying acidity in heterogeneous systems: Biphasic pKa values

As a result of a recent development in our group, it is now, for the first time, possible to rigorously measure acidity of acids in biphasic systems (aqueous phase at equilibrium with a water-immiscible phase) by using biphasic pKa values (pKaow values). This work has now been published in Analytical Chemistry 2022, 94, 4059–4064.

In this work, the octanol-water biphasic pKaow values have been determined for 35 acids of various structures and chemical properties (carboxylic acids, phenols, diphenylamines, imides, different CH acids) using UV-Vis and NMR (1H, 13C, or 31P) spectrometry.

Biphasic pKa values enable quantifying acid dissociation in biphasic systems in a more realistic and rigorous way than the conventional “mono-phasic” pKa values. The latter completely ignores a large part of the picture – partitioning of the neutrals and the ions between the two phases and ion-pairing in the low-polarity phase. In contrast, pKaow values account for these effects. The ratio of the acid and its conjugate base is measured in the 1-octanol phase, using UV-Vis and/or NMR spectrometric method. The activity of H+ is measured in the aqueous phase with a conventional pH-meter. The pKaow values are obtained at different concentrations and extrapolated to zero concentration.

Biphasic systems are present in many biological and technological systems and processes: cell membranes, solvent extraction, phase-transfer catalysis, sensor membranes, etc. In all such systems, acid-base properties of the participating compounds would be best described using biphasic rather than “mono-phasic” pKa values.

LC-MS Validation online course 6th run has finished!

On February 11, 2022 the on-line course (MOOC) LC-MS Method Validation offered by the University of Tartu finished successfully.

Eventually, altogether 850 people registered from 97 countries. Less than half, 380 participants actually started the course (i.e. tried at least one graded test at least once) and out of them 209 successfully completed the course. The overall completion rate was 25%. The completion rate of participants who started the studies was 55%. These completion rates are lower than we usually have. So, here is some food for thought for us on how we could improve the success 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 200 (!) (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.

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

We plan to repeat this course again in Autumn 2022.

Measurement Uncertainty online course, March 22 – May 3, 2022: Registration is open!

The 2022 edition of the web course (MOOC) Estimation of Measurement Uncertainty in Chemical Analysis will be running from March 22 to May 3, 2022. Registration is now open!

The full course material (as well as the registration link) is accessible from the web page. The course materials include videos, schemes, calculation files, and numerous self-tests (among them also full-fledged measurement uncertainty calculation exercises) and examples. Almost all areas of analytical chemistry are addressed, ranging from simple volumetric operations and titrations to sophisticated instrumental analysis, such as determining pesticide residues by LC-MS. Efforts are made in the course to address also such uncertainty sources encountered in chemical analysis that are difficult to quantify, e.g. uncertainty due to possible interference effects (incomplete selectivity).

In order to pass the course, the registered participants have to take six graded tests and get a higher than 50% score in every graded test. These tests are available to registered participants via the Moodle e-learning platform.

Participants who successfully pass the course will get a certificate from the University of Tartu. A digital certificate of completion is free of charge. A certificate of completion on paper can be requested for a fee of 60 euros.

You are welcome to distribute this message to potentially interested people!

LC-MS Method Validation web course: 854 participants from 97 countries!

On Tuesday, November 23, 2021 the web course LC-MS Method Validation was launched for the sixth time as a MOOC (Massive Online Open Course).

There are 854 registered participants (the largest number ever in this course) from 97 countries. Both numbers are the largest we have had! The countries range from Philippines to Paraguay and from Sweden to Sri Lanka. Image on the left shows the countries where the participants come from.

This is a practice-oriented on-line course on validation of analytical methods, specifically using LC-MS as technique. The course introduces the main concepts and mathematical apparatus of validation, covers the most important method performance parameters and ways of estimating them. The LC-MS validation course is delivered by a team of 8 teachers, each with their own specific area of competence. This way it is expected to offer the best possible knowledge in all the different subtopics of analytical method validation.

The full set of course materials is accessible from the web page https://sisu.ut.ee/lcms_method_validation/. The course materials include videos, schemes, calculation files and numerous self-tests (among them also full-fledged calculation exercises). In order to pass the course the registered participants have to take all tests and get higher than 50% score from each of them. These tests are available to registered participants via the Moodle e-learning platform. Participants who successfully pass the course will get a certificate from the University of Tartu.

The admission for EACH intake 2022 is open

We are glad to announce that the admission for Excellence in Analytical Chemistry (EACH) Erasmus Mundus Joint Master Degree programme intake 2022 is open!

EACH is an international two-year joint master degree programme that educates specialists in analytical chemistry well qualified to work in industry (food, pharmaceutical, materials, energy, etc.), chemical analysis laboratories (environment, food, health, etc.), and research (developing new analysis devices or new analysis methods) worldwide. EACH provides knowledge and practical skills in both fundamental and applied aspects of modern analytical chemistry. Practical internship placement in industry or laboratories is an important part of the training.

The programme is suitable both for students who have finished their bachelor’s studies and want to continue in master’s studies, as well as for working analytical chemistry practitioners wishing to spend a couple of years to bring their knowledge and skills to a new level.

The programme features generous scholarships as detailed on the Scholarships and tuition fees page.

The programme is taught by four universities: University of Tartu (UT, coordinator), Estonia; Uppsala University (UU), Sweden; University Claude Bernard Lyon 1 (UCBL), France; and Åbo Akademi University (AAU), Finland. The language of instruction is English, but students will also learn to communicate in one of the languages of the countries involved.

The online application form, admission requirements, deadlines, list of necessary documents, instructions/explanations, as well as contact data for questions are available from the EACH Admission information page.

We wish you all the success in applying!

The 2021 Nobel Chemistry Prize

 

Selleaastased keemianobelistid Benjamin List ja David MacMillan.

We were very pleased to learn today that the the Nobel Prize in Chemistry 2021 was awarded to Benjamin List (Max-Planck-Institut für Kohlenforschung, Mülheim an der Ruhr, Germany) and David W.C. MacMillan (Princeton University, USA) “for the development of asymmetric organocatalysis”!

The List group is world-famous for developing superacidic organocatalysts, enabling a very wide range of challenging transformations. We are happy that there is also a tiny contribution from our group to prof. List’s research: the acidities (expressed as pKa values in acetonitrile of 1,2-dichloroethane) of some of their acid catalysts (1,1,3,3-Tetratriflylpropene and some chiral superacidic imides) have been measured in our lab. Recently we were happy to host people from the List group in our lab and they learned how to carry out pKa measurements in nonaqueous solutions. The collaboration will continue.

Big congratulations to prof. List and to prof. MacMillan!

(Photo: The Nobel Prize committee)

What did people eat in the region of current Estonia in the distant past?

Researchers’ Night festival 2021. Superheroes of science

In English: Last week, on the 20-24 of September, Reasearchers’ Night festival 2021 took place all over Estonia. Our archaeochemist Dr. Ester Oras gave an interesting audio lecture about the eating habits of people living in the region of current Estonia in the distant past. This topic starts with the first findings related to eating habits from the Mesolithic period and arrives at the Middle Ages. During the whole lecture, she illustrates how chemical analyses can be used for the analysis of archaeological objects. Here is the audio lecture in Estonian, but there’s also a blog post in English on a similar topic. 

Eestikeeles: Eelmisel nädalal (20.-24. septembril) toimus üle Eesti 16. Teadlaste Öö festival. Meie arheokeemia töögrupi juht Dr. Ester Oras andis festivali raames huvitava heliloengu, kus ta rääkis mida inimesed sõid kauges minevikus praeguse Eesti aladel. Ester selgitab inimeste toitumisharjumisi Mesoliitikumi ajajärgust (kust pärinevad esimesed toiduga seotud leiud praeguse Eesti aladel) Keskajani välja. Kogu loengu vältel kirjeldab Ester ka seda, kuidas keemilised analüüsid aitavad mõista arheoloogilisi leide. Mainitud eestikeelse heliloengu leiab siit, kuid samal teemal on olemas ka ingliskeelne blogipostitus.

Derivatization-targeted analysis of amino compounds in plant extracts by LC-MS/MS

In the recently published paper including the members of our Analytical Chemistry Chair, a method was developed to detect amino compounds with diethyl ethoxymethylenemalonate (DEEMM) derivatization in neutral loss scan mode by liquid chromatography-tandem mass spectrometry (LC-MS/MS). Amino compounds react with DEEMM, and the derivatives lose a neutral ethanol molecule [M+H-46]+ from the parent ion upon collision-induced dissociation (CID) fragmentation. Therefore, it is possible to employ neutral loss scan (NLS) mode of the triple quadrupole mass analyzer.

The first part of the work was dedicated to the development of the method, such as testing different solvents and quenching reagents in order to obtain a cleaner chromatographic profile. Hydroxylamine was chosen as the quenching reagent, considering the retention time of its DEEMM-derivative and its solubility in the solvent employed (0.1 M HCl in 30% methanol).

Finally, the developed method was applied to an extract from the plant species Carduus nutans subsp. macrocephalus (Desf.) Nyman, in which 18 amino acids and 3 biogenic amines were identified for the first time in this plant species. The method can be applied to different matrices for the detection of known and unknown amino compounds.

Here you can find the 50-day free access to the article.

Design of Novel Uncharged Organic Superbases: Merging Basicity and Functionality

Emerging organosuperbase families
Examples of emerging organosuperbase families

In a recent account Design of Novel Uncharged Organic Superbases: Merging Basicity and Functionality. Acc. Chem. Res. 2021, 54, 3108-3123 four groups doing research at the forefront of superbase chemistry – IOCB (Czech Republic), Rudjer Boskovic Institute (Croatia), Philipps-Universität Marburg (Germany) and our group at University of Tartu – have joined forces in charting the direction for further developments of the whole organosuperbases area. What synthetic chemists need, are “non-ionic, metal-free superbases as chemically stable neutral organic compounds of moderate molecular weight, with intrinsically high thermodynamic basicity, adaptable kinetic basicity, and weak or tunable nucleophilicity at their basicity centres”. Such superbases would be are useful, being able to catalyze a number of reactions that are impossible otherwise.

The account demonstrates that just trying to achieve ever higher basicity is not the main challenge. Very high basicities have been demonstrated, both computationally and experimentally. Instead, the combination of high basicity with moderate molecular weight, ease of synthesis and stability is the key issue.

The account starts with the state of the art of neutral organic superbase research, theirs synthesis and basicity measurements, as well as computations and thereafter presents several examples of emerging organosuperbase families (see the Figure on the left) and discusses their synthesis, basicity and demonstrated, as well as potential applications.

Dr. Merit Oss, PhD thesis on the ionization efficiency in ESI

On the 24th of August, 2021, Merit Oss successfully defended her PhD thesis titled “Ionization efficiency in electrospray ionization source and its relations to compounds’ physico-chemical properties” 

The thesis by Merit revolves around ionization efficiency in electrospray ionization (ESI) MS. The main aim was to gain a better understanding of the relations between different molecular properties of compounds and the signal intensities of their ions in ESI-MS. During this study, a large number of ionization efficiency values were obtained. Eleven molecular parameters were taken into account for estimating their importance for evaluating the compound’s ionization efficiency in ESI. It was concluded that in the studied solvent system, a compound’s ionization in the ESI source is determined by its basicity, molecular size, and hydrophobicity/lipophilicity. The results showed that the obtained models for estimating compounds’ ionization efficiency can be used for approximate prediction. 

Congratulations, Merit! We wish you all the best for your future.