Micromorphological and chemical elucidation ofthe degradation mechanisms of birch barkarchaeological artefacts

Introduction: Since ancient times, the unique properties of birch barks (Betula genus) have made them a material of choice for producing both everyday-life and artistic objects. Yet archaeological birch bark artefacts are rare, and little is known about the chemical transformations undergone by bark (chemically composed mainly of suberin and triterpenes) in archaeological contexts. Understanding the chemical modifications induced by ageing is essential for selecting suitable preservation and conservation approaches. Thus, the main aim of this research is to assess the preservation and state of degradation of archaeological findings made of birch bark: a Neolithic bow case recovered from a melting ice patch in the Bernese Alps (Switzerland) and a waterlogged birch bark vessel discovered at Moossee Lake (Canton of Bern, Switzerland). Scanning electron microscopy (SEM) and gas chromatography/mass spectrometry (GC/MS) were used to obtain information at micro-morphological and molecular levels on the state of degradation of the birch bark findings. GC/MS analysis followed two different sample preparations, alkaline hydrolysis and solvent extraction, in order to investigate respectively the hydrolysable and soluble constituents, and to test whether part of the suberin structure was depolymerised by the long period of burial. Results and conclusions: SEM investigations on archaeological birch bark samples have shown that the extent of degradation of the microstructure is much higher in waterlogged birch bark than in birch bark preserved in ice. GC/MS analysis revealed that at a molecular level, the birch bark was quite well preserved. In both the archaeological environments, ice patch and lake water, various reactions had taken place leading to the depletion of reactive and sensitive compounds such as unsaturated acids and epoxy-compounds. In addition, archaeological birch bark had undergone depolymerization and oxidation reactions leading to the appearance of free suberin monomers and of oxidised triterpenes (betulone and lupenone). GC/MS data also seems to suggest that the birch bark preserved in the waterlogged site had a more pronounced degradation both in terms of oxidation and depolymerisation

Thermal degradation chemistry of archaeological pine pitch containing beeswax as an additive

Thermo analytical techniques and gas chromatography/mass spectrometry (GC/MS) were used to evaluate the presence of chemical-physical interactions between pine pitch and beeswax used as additive The mixtures found in several archaeological objects demonstrate that by modifying the physical and chemical properties of pitch and tar, our ancestors were able to add a variety of organic materials, such as waxes or animal fats.Westudied pine pitch replicas from Pinus sylvestris prepared following a test from the field of experimental archaeology. Varying proportions of beeswax were added and then the resulting pitches were studied by a multi-analytical approach comprising the use of thermo analytical techniques (DSC, TG and TG-FTIR) and GC/MS, which provides molecular information. The same approach was also used to study a mixture of pitch from Pinus sylvestris L. and beeswax ("Zopissa"), whose relative proportions were unknown, and two archaeological adhesives collected from glass opus sectile fragments found in the northern necropolis of Antinoopolis (Egypt, 4th-5th century AD). Our thermo-analytical techniques managed to determine the relative proportion of pine pitch and additives, such as beeswax, in unknown archeological mixtures, and to evaluate the presence of interactions between pitch and additive

Measuring arrangement and size distributions of flowing droplets in microchannels through deep learning

In microfluidic systems, droplets undergo intricate deformations as they traverse flow-focusing junctions, posing a challenging task for accurate measurement, especially during short transit times. This study investigates the physical behavior of droplets within dense emulsions in diverse microchannel geometries, specifically focusing on the impact of varying opening angles within the primary channel and injection rates of fluid components. Employing a sophisticated droplet tracking tool based on deep-learning techniques, we analyze multiple frames from flow-focusing experiments to quantitatively characterize droplet deformation in terms of ratio between maximum width and height and propensity to form liquid with hexagonal crystalline order. Our findings reveal the existence of an optimal opening angle where shape deformations are minimal and crystal-like arrangement is maximal. Variations of fluid injection rates are also found to affect size and packing fraction of the emulsion in the exit channel. This paper offers insights into deformations, size and structure of fluid emulsions relative to microchannel geometry and other flow-related parameters captured through machine learning, with potential implications for the design of microchips utilized in cellular transport and tissue engineering applications.Comment: 10 pages, 6 figure

Degraded proteins from paintings, polychromies and archaeological objects

Proteins are the building blocks of cells in all living species, and they carry the information necessary for life, replication, defence and reproduction. It has recently been proven that proteins are much longer preserved than DNA, as they have been found in paleontological findings dating back to the Pleistocene. Proteins are also important components of archaeological findings, including bones, textiles and residue of ceramic and vessels, and they are the ingredients of cosmetics thanks to their ability to protect the first layer of the skin from the harsh effects of aging and environment (such as UV rays, pollution and free radicals). Proteins are also fundamental constituents of works-of-art, used as paint binders, as adhesives and varnishes in painting, polychromies and to decorative objects. The study of proteins in artistic, archaeological and paleontological objects provides significant information to understand the evolution of life through the ages, to improve our knowledge of our history, to understand technological developments and artistic manufacture, and to bring essential information to art-historians and conservators. This PhD thesis aims at studying structural and molecular changes undergone by proteins and proteinaceous materials commonly used in paintings, polychromes and archaeological objects, as an effect of manufacture and ageing. This information is fundamental to design reliable analytical techniques, approaches, methods and models for data analysis, to successfully characterise and indentify proteins in art and archaeological objects. Many analytical methods for the identification and characterization of proteins from artistic, archaeological and paleontological objects have been proposed . Although, procedures optimized for protein denaturation and extraction from ancient materials and artworks were recently developed, the analysis of these samples present several drawbacks and the identification of protein is often a difficult task. As an effect of the long term exposure to the changeable and sometimes harsh environments where the object is displayed or stored, degradation phenomena take place. Besides some information are available on the degradation of certain acids -deamidation, hydroxylation, oxidation and carbonylation - very little is known on the degradation of proteins in art and archaeological objects. The main observation relates to the loss of solubility of aged proteins, which has been suggested to be related to aggregation, crosslinking and complexation phenomena with pigments. If these hypothesis prove to be true, then they might account for several drawbacks that are encountered in the analysis of proteins in degraded samples. Aggregation, crosslinking and complexation with pigment may make the protein binding site unavailable for the stain, may control the degree of flexibility of the polypeptides chains, and may form deleterious changes of the protein conformation, compromising the antigen/antibody interaction, cause loss of solubility, making the protein extraction necessary for chromatographic and mass spectrometric techniques a difficult task and may affect the degree of access of cleavage enzymes in proteomics experiments

Analytical pyrolysis to gain insights into the protein structure. The case of ovalbumin

We report a novel study based on analytical pyrolysis coupled with mass spectrometry to investigate, at the molecular level, the formation of aggregates and cross-linked structures in ovalbumin (OVA). For this scope, OVA was dissolved in water at different concentrations and temperatures (up to 80 °C), and was added with 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDC). The formation of β-sheets and intermolecular aggregates, which are stabilized by weak hydrophobic and hydrogen bonds, is favoured in OVA by higher protein concentration and temperatures. The cross-linker (EDC) gives the formation of covalent bonds randomly distributed in the protein, inducing significant portions of random coil structures in OVA. FTIR-ATR spectroscopy was employed to study the protein conformation. Evolved gas analysis coupled with mass spectrometry (EGA-MS) and pyrolysis coupled with gas chromatography mass spectrometry (Py-GC–MS) were used to characterise the gaseous compounds evolved during pyrolysis at the different temperatures. Aggregation and cross-linking increase the thermal stability of OVA and significantly affect its pyrolytic profile. The study reveals that analytical pyrolysis coupled to mass spectrometry can be used to gain insights into the protein structure

Analytical pyrolysis of proteins in samples from artistic and archaeological objects

The paper presents a study of proteins found in artistic and archaeological objects based on analytical pyrolysis. Proteins (mainly egg yolk and/or egg white, casein, animal glue and collagen) have been extensively used as paint binders, adhesives and varnishes in mural and easel paintings, and they can be found in archaeological findings, such as bones and skin tissues. In order to overcome limitations of wet chemical methods arising from the reduced solubility of aged proteins in samples of cultural heritage, a combination of analytical pyrolysis techniques was used to characterise reference materials, paint reconstructions and samples from different historical periods (2nd century BC-20th century AD) and geographical origins, which were collected from paintings and archaeological findings. In particular evolved gas analysis mass spectrometry (EGA/MS), pyrolysis coupled with gas chromatography/mass spectrometry (Py/GC/MS) and double shot pyrolysis/gas chromatography/mass spectrometry (DSP/GC/MS) were used. This analytical approach allowed us to characterise and differentiate the proteinaceous media, investigate their thermal behaviour and evidence changes occurring with ageing. Data clearly indicate that egg, casein and animal glue can be identified and distinguished in a sample of unknown composition using each of the analytical pyrolysis techniques used. With time though differences tend to disappear to the extent that extremely degraded samples present pyrolytic profiles extremely similar to each other, irrespective of the nature of the proteins present. The data also indicate that proteins tend to become more thermally stable with ageing, suggesting that extensive intramolecular and intermolecular aggregation, and/or covalent cross-linking occur with time

Analytical pyrolysis of ovalbumin

In this study the thermal degradation of ovalbumin (OVA) under nitrogen atmosphere was investigated. For this scope, a multi instrumental approach based on thermogravimetry (TG), thermogravimetry coupled with infrared spectroscopy (TG/FTIR) and pyrolysis coupled with mass spectrometric detection, i.e. flash pyrolysis-coupled with gas chromatography-mass spectrometry (Py/GC/MS), evolved gas analysis coupled with mass spectrometry (EGA/MS) and double shot pyrolysis-coupled with gas chromatography-mass spectrometry (DSP/GC/MS), was used. The pyrolysis of a protein involves a combination of several complex mechanisms resulting in a very high number of products. The study highlighted that pyrolysis of OVA produces low-molecular weight gasses, such as CO2, H2O, HCNO, NH3and CO, as main compounds. In addition, a series of organic compounds containing heteroatoms and unsaturations were also identified, whose formation occurred at different temperatures over the pyrolytic process. Among these, cyclic pyrolysis products were identified: dialkyl substituted 2,5-diketopiperazines (DKPs) and, for the first time, unsaturated-DKPs (un-DKPs), 3,5-alkyl-3,4-dihydro-2H-pyrrole-2,4-diones (ADPDs) and 3-alkenyl-5-alkyl-pyrrolidine-2,4-diones (AAPDs). These compounds are formed below 350° and are produced by cyclisation reactions of two neighbouring amino acids. Pyroglutamic acid was also found among the main pyrolysis products of OVA, obtained as pyrolytic product of Glu, which is the most abundant amino acid in OVA. Aromatic compounds, such as pyridine, pyrrole, toluene, alkyl-benzenes and alkyl-pyrroles, phenol and alkyl-phenols, benzeneacetonitrile, benzenepropanenitrile, indole and alkyl-indoles, were detected, produced over a wide range of temperatures. This study highlighted for the first time that aromatic compounds produced below 320 °C are associated to the pyrolysis of specific amino acid side chains, while at higher temperatures, they are the pyrolysis products of the residual material remaining after condensation reactions, pyrolytic scissions and cyclization reactions

Bitumen residue on a Late Ceramic Age three-pointer from Marie-Galante, Guadeloupe: Chemical characterization and ligature evidence

International audienc

Py-GC/MS, GC/MS and FTIR investigations on late Roman-Egyptian adhesives from opus sectile: new insights into ancient recipes and technologies

L'articolo prende in esame gli adesivi utilizzati per fissare elementi vitrei e marmorei di opus sectile rinvenuti nel corso degli scavi ad Antinoe (Egitto)

Circularly polarized luminescence reveals interaction between commercial stains and protein matrices used in paintings

Chemistry is at the front line of preservation of work of arts. Reliable but simple protocols for localizing proteins in art samples are necessary to guide conservators in their work. In this article, we investigated the interaction between some commonly used fluorescent stains and protein-based paint binders. Beside fluorescence, we used for the first time circularly polarized luminescence (CPL) as a tool to reveal interactions in complex matrices relevant for the field of cultural heritage. We show that, in such cases, CPL provides unique information compared to more common techniques such as fluorescence and circular dichroism. These findings will contribute to provide a rational base to empirical observations in staining procedures, even in arduous and complex cases