Chemical Modification of Biomarkers through Accelerated Degradation: Implications for Ancient Plant Identification in Archaeo-Organic Residues
Abstract
:1. Introduction
Activation energy: | Refers to the minimal quantity of energy required for the reactants to start a chemical reaction. |
Aromatization: | A chemical reaction in which an aromatic system is formed from a single nonaromatic precursor. Typically, aromatization is achieved by dehydrogenation of existing cyclic compounds. |
Catalyst: | A substance that increases the rate of a reaction because it lowers the activation energy of the reactants. Catalytic specificity refers to the particular ability of a substance or closely related group of substances to catalyze a given type of chemical transformation. |
Functional group: | A structural unit of an atom or group of atoms within an organic compound that has its own characteristic property, regardless of the other atoms in the molecule. |
Redox: | A chemical reaction where oxidation and reduction occur simultaneously. An atom is oxidized when it loses electrons and reduced when it gains electrons. Rust is the classic example of oxidation where the reduced iron metal (oxidation state 0) is oxidized to brown iron (oxidation state III) and oxides in the presence of catalysts, such as water, air, or an acid. |
Temperature: | An increase in temperature will raise the average kinetic energy of the reactant molecules. As more molecules move faster, the number of molecules moving fast enough to react increases, which results in faster formation of products. |
2. Experimental Design
3. Results and Discussion
3.1. GC-MS Results and Multivariate Analyses
3.2. Compound Identification
4. Materials and Methods
4.1. Materials
4.2. Sample Preparation, Extraction and Analysis
4.3. Data Pretreatment and Statistical Analysis
5. Conclusions
- G1 compounds disappeared or were decreased after seven days of incubation. If such stark declines were evident after only seven days, albeit under conditions that accelerate degradation, it can be assumed that they are very unlikely to remain in ancient residues, deposited for centuries or millennia. These compounds should, therefore, not be considered as diagnostic biomarkers for ancient plants and plant products under most conditions. Perhaps as importantly, their absence in archaeological samples cannot be considered as useful evidence for the absence of certain plants or for the identification of certain plants over other possible candidates.
- G2 compounds remained relatively stable or increased over time, particularly oxidized and dehydrogenated compounds that have lost even numbers of hydrogen atoms to form double bonds, which generally makes them more stable and conceivably likely to remain in archaeological samples. These compounds might therefore be considered as more valid biomarkers aiding in the identification of archaeological residues.
- G3 compounds were not present in fresh cedar oil but formed during specific experiments and are indicative of certain catalysts/storage materials. These compounds could, therefore, also be possible biomarkers for identifying plant materials in archaeological samples provided that these compounds can be identified. In our study, we were only able to securely identify one of the 42 G3 compounds. However, unknown compounds can still provide information regarding the processes involved in the preparation of plant-based products in the past. For example, compound #76 was relatively high in RT treatments in combination with Cu, Fe, and Br, showing that a high abundance of this compound could be indicative for the contact of cedar residues with metal vessels. Concomitantly, compound #79 appeared in high abundance in both reduction treatments, indicating a reduction process.
Supplementary Materials
Author Contributions
Funding
Institutional Review Board Statement
Informed Consent Statement
Data Availability Statement
Acknowledgments
Conflicts of Interest
References
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Catalyst | Simulated Archaeological Material or Natural Reactions | Sample Code for Room RT and HT Treatments |
---|---|---|
Montmorillonite KSF clay (SiO2, Al2O3, H2SO, Fe2O3, CaO, MgO) | Clay | ClayRT, ClayHT |
Calcium sulfate dihydrate (CaSO4 2H2O) | Gypsum (alabaster) | GypsRT, GypsHT |
Bronze powder (Cu:Sn, 90:10) | Bronze | BrRT, BrHT |
Copper powder (Cu, 106 μm) | Copper | CuRT, CuHT |
Iron powder (Fe, <212 μm) | Iron | FeRT, FeHT |
Sodium borohydride (NaBH4) | Reduction | RedRT, RedHT |
Flushing with N2 | Non-oxidizing atmosphere | N2RT, N2HT |
Ammoniumperoxodisulfat ((NH4)2S2O8) | Oxidation | OxRT, OxHT |
Air | Oxidation | AirRT, AirHT |
ID | tr | Compound Identification |
---|---|---|
#01 | 8.28 | 4-Acetyl-1-methylcyclohexene |
#02 | 8.46 | 3-Cyclohexene-1-methanol, α,4-dimethyl- |
#03 | 8.94 | Ethanone, 1-(4-methylphenyl)- |
#04 | 8.99 | α-Terpineol |
#07 | 11.48 | α-Longipinene |
#10 | 11.90 | Isolongifolene, 4,5-dehydro- |
#17 | 12.52 | Longifolene |
#20 | 12.80 | Vestitenone |
#23 | 13.07 | Himachala-2,4-diene |
#24 | 13.24 | α-Himachalene |
#29 | 13.70 | γ-Himachalene |
#30 | 13.77 | Himachala-1,4-diene |
#32 | 14.09 | β-Himachalene |
#33 | 14.25 | α-Dehydro-ar-himachalene |
#34 | 14.31 | δ-Cadinene |
#35 | 14.39 | Calamene (cis/trans?) |
#37 | 14.49 | α-Bisabolene |
#38 | 14.58 | γ-Dehydro-ar-himachalene |
#39 | 14.72 | ar-Himachalene |
#40 | 14.80 | Calacorene (α/β?) |
#47 | 15.47 | Oxidohimachalene |
#55 | 16.32 | β-Himachalene oxide |
#57 | 16.51 | Epicubenol |
#63 | 17.03 | Himachalol |
#66 | 17.26 | Allohimachalol |
#70 | 17.48 | γ-Atlantone (E/Z?) |
#73 | 17.70 | 2,2,6-Trimethyl-6-(4-methylcyclohex-3-en-1-yl)dihydro-2H-pyran-4(3H)-one |
#74 | 17.80 | α-Atlantone |
#87 | 18.79 | Atlantone |
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Huber, B.; Vassão, D.G.; Roberts, P.; Wang, Y.V.; Larsen, T. Chemical Modification of Biomarkers through Accelerated Degradation: Implications for Ancient Plant Identification in Archaeo-Organic Residues. Molecules 2022, 27, 3331. https://doi.org/10.3390/molecules27103331
Huber B, Vassão DG, Roberts P, Wang YV, Larsen T. Chemical Modification of Biomarkers through Accelerated Degradation: Implications for Ancient Plant Identification in Archaeo-Organic Residues. Molecules. 2022; 27(10):3331. https://doi.org/10.3390/molecules27103331
Chicago/Turabian StyleHuber, Barbara, Daniel Giddings Vassão, Patrick Roberts, Yiming V. Wang, and Thomas Larsen. 2022. "Chemical Modification of Biomarkers through Accelerated Degradation: Implications for Ancient Plant Identification in Archaeo-Organic Residues" Molecules 27, no. 10: 3331. https://doi.org/10.3390/molecules27103331