Two new biomolecular studies of early farming by the Archemy group

Our Archemy group has recently published two major collaborative articles about the arrival and spread of early farming in NE Baltic.

Based on pottery lipid residue and dietary stable isotope analysis combined with zooarchaeological data and archaeobotanical studies, it was shown that farming arrived in the NE Baltic with migrating Corded Ware cultures in the early 3rd millennium cal BCE, but here this new subsistence strategy relied on stockbreeding rather than crop cultivation.

Early farmers in the NE Baltic were exploiting both domesticated and wild species, whilst the introduction of domesticates had little if any impact on local hunter-fisher-gatherer communities who remained true to their forager lifeways. There was no clear transition from foraging to farming in the 3rd millennium cal BCE NE Baltic, instead we see separated communities and parallel worlds of local foragers and incoming early farmers practicing mixed economy. However, the lipid residue data in the wider Baltic context shows several regional variations in the arrival and spread of early farming practices.

Read full articles here:

Oras, E., Tõrv, M., Johanson, K, Rannamäe, E.  et al. 2023. Parallel worlds and mixed economies: multi-proxy analysis reveals complex subsistence systems at the dawn of early farming in the northeast Baltic. R. Soc. open sci. 10230880230880. http://doi.org/10.1098/rsos.230880

Lucquin, A., Robson, H. Oras, E. et al. 2023. The impact of farming on prehistoric culinary practices throughout Northern Europe. PNAS. 120 (43) e2310138120. https://doi.org/10.1073/pnas.2310138120

Tris(benzophenoneimino)phosphane and Related compounds

Our group recently published a new article titled “Tris(benzophenoneimino)phosphane and Related Compounds” led by Marta and Agnes.

Marta working in glovebox

In this work, a new group of bases with benzophenoneiminyl (bpi) moiety was synthesized and characterized. A convenient one-pot approach was employed to synthesize the starting compound tris(benzophenoneimino)phosphane (P(bpi)3): benzophenone imine was deprotonated using MeMgCl, followed by its reaction with PBr3 in diglyme. This method offers an alternative for preparing other (amino)phosphanes as well when lithio-intermediates and/or protonated phosphanes are not viable options. P(bpi)3 was subsequently utilized to synthesize a variety of related phosphonium cations and phosphazenes.

Crystals from synthesis

The stability of the resulting phosphonium ylides was assessed through their deprotonation. In certain cases, the bulky substances demonstrated the ability to form P-N heterocycles with adjacent P and N atoms and P=C double bonds which are quite rare and only some representatives of this type of heterocycles have been reported before. The basicities of benzophenone imine, P(bpi)3, phosphonium ylides, and phosphazenes were evaluated experimentally (in MeCN) or computationally (in MeCN, THF, and gas-phase). Additionally, representative X-ray crystallography (XRD) structures were presented and discussed. Although the bpi-compounds are not as strong as many existing bases, they still exhibit considerable basicity and could be employed as reagents to overcome common challenges such as solubility, ion-pairing, lack of UV-Vis properties, and other issues.

 

Non-invasive analysis of natural textile dyes using fluorescence excitation-emission matrices

Elsa Vanker
Sigrid Selberg

Our group recently published a new article Non-invasive analysis of natural textile dyes using fluorescence excitation-emission matrices, Talanta, 2022, 123805 led by Sigrid Selberg and Elsa Vanker.

In this study, multidimensional front-face fluorescence spectroscopy measured from surfaces using a fiber optic probe was assessed as a non-invasive and non-destructive method for the analysis of components in natural textile dyes. Multidimensional fluorescence data was acquired for a collection of wool yarns dyed with natural dyes (31 dyed wool yarn samples that were self-dyed with 18 different natural dyes) that were used as references in a case study of two historical textiles for which liquid chromatography-mass spectrometry was used as a confirmatory technique.

Self-dyed reference yarns
Selection of characteristic EEMs of self-dyed reference samples

Natural dyes are multicomponent mixtures and can originate from different sources (e.g., plants, insects, and fungi). Due to their complex chemical composition and the inherent lability (photooxidative fading and bleaching), the analysis of natural dyes can be quite challenging and in order to analyze dyes on textiles, it is often best to combine different analytical methods.  However, for the analysis of dyes, common and often the most informative methods, like chromatographic separations coupled with different detectors, are all invasive/destructive. The aim of this work was to explore the potential and limitations of fluorescence spectroscopy in analyzing natural dyes from dyed wool yarns using EEMs (excitation-emission matrices), measured directly from the surface of the objects, non-destructively and without any sample preparation.

To demonstrate the utility of the fluorescence method, analysis was conducted on two case study samples – fibers from historical artifacts. Comparing the EEMs of the reference yarns with our unknown case study samples, we were able to identify that dye from a plant of the Rubiaceae family (bedstraws and madders) was used for dyeing the case study samples. 

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

One of the case study objects; Tapestry “Solomon is receiving a bride. Solomon Court” (year of production 1547); Textile sample was obtained from the Conservation and Digitization Centre Kanut (Estonia).

Solid-State Composite reference electrodes

Recently, a collaborative study on the Solid-State Composite reference electrodes was published in the journal of Membranes 2022, 12, 569. Slim Blidi, EACH alumnus and the first author of this publication, provides here a short overview of this novel research.

Potentiometric measurements using conventional electrodes do have some drawbacks when used. This is especially true for the conventional liquid-filled reference electrodes. They are non-robust in use and are maintenance-intensive due to the necessity of refilling the inner solution and keeping the liquid junction clog-free.

By eliminating the liquid component from the electrode structure, Solid-State Composite (SSC) reference electrodes are a viable alternative to conventional reference electrodes. Prepared by either injection molding or chemical polymerization, they are based on a silver/silver chloride reference element enclosed in a polymeric matrix (e.g. polyvinyl acetate) mixed with an inorganic salt (potassium chloride). The composite is the inorganic salt storage material while being in contact with the sample solution.

In this study, a set of the SSC reference electrodes was prepared and their performance was tested in different synthetic solutions to assess the possible influence of pH, solution composition, as well as the concentration and mobility of ions. Using potentiometry and electrochemical impedance spectroscopy methods over a period of several months, stability tests were also performed to evaluate the suitability of the studied SSC reference electrodes for continuous, prolonged, and intensive usage. Concentrations of K+, Na+, Ca2+, and Cl– ions and pH values were measured in river water samples at different temperatures using the SSC reference electrodes.

better than commercial liquid-filled reference electrodes in terms of calibration range and actual measurements. It is safe to say that SSC reference electrodes represent the future of potentiometric measurements applied to environmental samples as they are cheap to manufacture and easy to maintain.

I am extremely grateful to my supervisors at Åbo Akademi: Dr. Kim Granholm, Dr. Zekra Moussavi, and Dr. Tomasz Sokalski for their valuable guidance and moral support during the experimental work as well as to the EACH programme for this life-changing experience.

 

Slim Blidi

 

 

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.

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.

New publication: Classification of archaeological adhesives

Our group recently published a new article: Classification of archaeological adhesives from Eastern Europe and Urals by ATR-FT-IR spectroscopy and chemometric analysis. Archaeometry, 2021, 1–18. 

In this study, 100 adhesive samples, collected from hafting tools and ceramic containers as well as some adhesive lumps were analyzed using ATR-FT-IR in combination with PCA-based DA classification. The aim of this study was to discover the capabilities of ATR-FT-IR-DA classification as a potential screening method for the identification and grouping of different archaeological adhesive samples, and subsequently reduce the use of laborious GC-MS analysis.

100 archaeological adhesives were classified into 3 groups: birch bark tar without major additives (72), birch bark tar with additives (13) and minor/non birch bark tar samples (15). Birch bark tar containing adhesives were separated from minor/non birch bark tar samples. Samples identified as birch bark tar without major additives were further classified possibly by their location, age or cultural specific manufacturing practices. The classification results were confirmed by GC-MS analysis of 9 archaeological samples selected from three compositional groups.

The study proves that ATR-FT-IR-DA classification is a non-destructive, rapid and reliable pre-scanning method for analyzing archaeological adhesives, especially suitable for small samples. Based on the results of ATR-FT-IR spectroscopic analysis, DA classification can help further distinguish samples with different backgrounds such as sample age, initial production, environmental conditions and site-specific preservation. GC-MS analysis could be used as a supplementary/confirmatory method to investigate samples with complex components and provide archaeological DA references for future research.

The full text can be found here.

New Open Access publication: GC-MS analysis of aged oil paints

Our group recently published a new Open Access research article – Quantitative GC-MS Analysis of Artificially Aged Paints with Variable Pigment and Linseed Oil Ratios, Molecules 2021, 26 (8), 2218. 

In this freely accessible publication, seven sets of artificially aged paints prepared from a pigment (chrome oxide green, natural cinnabar, Prussian blue, red ochre, hematite + kaolinite, zinc white, or yellow ochre) and linseed oil were analysed with GC-MS. One of the main aims was to study if the pigment concentration in the paint samples affects the drying of the linseed oil. 

The palmitic acid to stearic acid ratio (P/S), azelaic acid to palmitic acid (A/P), and the relative content of dicarboxylic acids (∑D) showed, that besides the type of the pigment, also the concentration of the pigment can influence these values that are commonly used to identify the type of the oil or to characterize how dried is the sample. 

The absolute quantification of stearic acid (see figure on the right) showed that the drying of all paint sets (except for zinc white) were influenced by the pigment concentration. Therefore, this is another factor that needs to be taken into account when studying aged oil paints. 

 

 

Aminoacridines as matrix materials for the analysis of complex samples in MALDI(-)-MS

A highly interdisciplinary study ranging from computational chemistry to cultural heritage has now been published – Experimental and Computational Study of Aminoacridines as MALDI(-)-MS Matrix Materials for the Analysis of Complex Samples, J. Am. Soc. Mass Spectrom. 2021.  

9-aminoacridine (9-AA) is a well-known matrix material used for the MALD(-)-MS analysis. Among the other monoaminoacridines (AAs), only 3-AA has been tested once (in our cultural heritage workgroup) but the suitability of the other AAs was unknown.

To fill this gap, the capabilities of all five AAs were studied by analysing different materials (stearic acid, colophony resin, dyer’s madder, and a resinous sample from a 16th-century shipwreck). Also, a vast range of properties for these aminoacridines were experimentally or computationally characterized (including UV-Vis absorption and fluorescence spectra, proton transfer reactions, crystallization). 

The results demonstrated, that all the AAs are suitable for the MALDI(-)-MS analysis of these materials. Interestingly, 3-AA and 4-AA outperformed the other AAs (including the best-known 9-AA) and were the preferred matrices for the analysis of samples studied in this work.   

 

 

Acidity scale in acetonitrile: 231 pKa values spanning 30 orders of magnitude

The equilibrium acidity scale (pKa scale) in acetonitrile (MeCN) has been supplemented by numerous new compounds and new ΔpKa measurements and has been published in Eur. J. Org. Chem. 2021, 1407–1419 (Open access). The pKa scale now contains altogether 231 acids – over twice more than published previously – linked by 566 ΔpKa measurements and spans between the pKa values of hydrogen iodide (2.8) and indole (32.57), covering close to 30 orders of magnitude. The acids have wide structural variety, ranging from common families – phenols (e.g. picric acid, alizarin, polyhalogenophenols), carboxylic acids (e.g. acetic, benzoic, retinoic and sorbic acid), sulfonic acids, hydrogen halides) to highly special molecules (chiral BINOL catalysts, bis(benzoxazole-2-yl)methanes, polyfluorinated compounds) and superacids (fluorinated sulfonimides, cyanoform, tetracyanopropenes).

Measurement results acquired over the last 15 years were added to the scale and new least squares treatment was carried out. The treatment yielded revised pKa values for the compounds published previously, with the root mean square difference between revised and previous values 0.04, demonstrating very good stability of the scale.

Correlation equations were developed for estimating pKa values for the studied types of compounds in water, DMSO, DMF and 1,2-dichloroethane on the basis of pKa values in acetonitrile. These equations enable predicting pKa values with an average error around or less than 1 pKa unit, which is a sufficient accuracy for many applications.

The scale is expected to be a useful tool for the widest possible research areas in organic chemistry, electrochemical power sources, catalysis, etc.