Structural characterization of archaeomaterials by mass spectrometry: lipidomic, proteomic and method development

The biomaterials from Heritage – related to art works or archaeological remains – are clearly witnesses of past civilizations. Their chemical characterization could deliver both some cultural, social, historical, economic or environmental information. At the interface between archeology, history, chemistry of natural products and analytical chemistry, their precise structural study is a real challenge due to the complexity of the materials, their human or natural degradation and the preciousness of the samples. This theme of biomolecular archaeometry has benefited from advances in mass spectrometry in recent decades, a technique that has become a tool of choice and that is now the object of specific development. The characterization of bioarchaeomaterials is based on structural identification of molecular markers not only to determine the biological and geographical origins, but also to understand the weathering and ageing processes. If the study of low molecular weight lipids using techniques such as gas chromatography coupled with mass spectrometry (GC / MS) or high performance liquid chromatography coupled with mass spectrometry (LC / MS) remains valid, our current research is moving towards a new range of biomolecules (soluble or membrane proteins for example) and high molecular weight lipids. The techniques used are those of proteomics with equipment such as MALDI-TOF or Q-TOF-nanoLC. Protocols should however be adapted to this particular context.

Methodological development: the example of TLC-MALDI-TOF

The coupling between thin layer chromatography (TLC) and mass spectrometry began in the 1980s. It was carried out indirectly, requiring often the recovery of the analytes by various complex methods prior to mass spectrometric analysis. Direct coupling TLC-MALDI was developed in the 1990s for analysis of peptides (800-1300 Da) and small proteins (3000-19000 Da). The analytical challenge of this research is to apply this coupling with complex systems including different structure, polarity or molecular weight. The limits of this technique in terms of amount of sample are also tested. This approach is completely different from those described so far since they were based on compounds of similar nature. The development is made specifically for two types of complex systems for which there is a real questioning and a significant need for structural characterization by mass spectrometry. The first is related to organic archaeomaterials. This type of samples has indeed a very complex chemical composition, which has changed over the centuries or millennia by human or environmental alteration. For a better characterization of these systems, it is necessary to reach a structural and molecular identification as accurate as possible, while using a minimum of material to maintain the integrity of the studied materials and artifacts. The second question is directly linked with cell biology. Some membrane proteins show activity when they are in association with lipids (membrane lipids - phospholipids, glycolipids -). The aim is to characterize both these lipids and related proteins only available in lesser amounts.

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