Nondestructive Analysis of Mummification Balms in Ancient Egypt Based on EPR of Vanadyl and Organic Radical Markers of Bitumen

Abstract

The black matter employed in funeral context by ancient Egyptian is a complex mixture of plant-based compounds with variable amounts of bitumen. Asphaltene, the most resistant component of bitumen, contain Vanadyl porphyrins and carbonaceous radicals which can be used as paramagnetic probes to investigate embalming materials without sample preparation. Electron Paramagnetic Resonance (EPR) at X-band, combining in-phase and out-of-phase detection schemes, provides new information in a non-destructive way about the presence, the origin, and the evolution of bitumen in these complex materials. It is found that the relative EPR intensity of radicals and vanadyl porphyrins is sensitive to the origin of the bitumen. The presence of non-porphyrinic vanadyl complexes in historical samples is likely due to the complexation of VO2+ ions by carboxylic functions at the interface between bitumen and other biological components of the embalming matter. The absence of such oxygenated vanadyl complex in natural bitumen and in one case of historical human mummy acquired by a museum in the 19th century reveals a possible, non-documented, ancient restoration of this mummy by pure bitumen. The linear correlation between in-phase and out-of phase EPR intensities of radicals and vanadyl porphyrins in balms and in natural bitumen, reveals a nanostructuration of radicals and vanadyl porphyrin complexes, which was not affected by the preparation of the balm. This points to the remarkable chemical stability of paramagnetic probes in historical bitumen in ancient Egypt. File list (2) download file view on ChemRxiv BackMatter_EPR.pdf (1.68 MiB) download file view on ChemRxiv Supporting Information.pdf (1.32 MiB)Non-destructive analysis of mummification balms in Ancient Egypt, based on EPR of vanadyl and organic radical markers of bitumen.

Insight into the structure of black coatings of ancient Egyptian mummies by advanced EPR spectroscopy of vanadyl complexes.

“…S3) and, to a lesser extent An 2, show a broad baseline distortion due to a ferromagnetic resonance (FMR) signal of iron oxide microparticles. 28 This FMR signal, which does not give electron spin echo, can be eliminated by recording the echo-detected EPR spectrum (ED-EPR), as clearly shown for An 2 and Hum 3 at X-band (Fig. 2a).…”

“…28 In addition to VO-P, the latter contain also non-porphyrinic VO 2+ complexes (hereafter referred to as VO-nP), with four oxygen ligands in nearly square planar configuration. 28 These VO-nP complexes are absent in Dead Sea bitumen used by Egyptians, and present in black coatings containing natural substances in addition to bitumen. We hypothesized that these VO-nP could result from the demetallation of VO-P of bitumen followed by the complexation of VO 2+ by oxygenated functions of other components of the black matters.…”

“…27 Recently, we showed that EPR analysis of VO-P complexes and C 0 radicals is a simple and nondestructive way (no sample preparation) to reveal the presence of bitumen in black coatings of Egyptian mummies, even in small amount. 28 In addition to VO-P, the latter contain also non-porphyrinic VO 2+ complexes (hereafter referred to as VO-nP), with four oxygen ligands in nearly square planar configuration. 28 These VO-nP complexes are absent in Dead Sea bitumen used by Egyptians, and present in black coatings containing natural substances in addition to bitumen.…”

Insight into the structure of black coatings of ancient Egyptian mummies by advanced Electron magnetic resonance of vanadyl complexes

“…S3) and, to a lesser extent An 2, show a broad baseline distortion due to a ferromagnetic resonance (FMR) signal of iron oxide microparticles. 28 This FMR signal, which does not give electron spin echo, can be eliminated by recording the echo-detected EPR spectrum (ED-EPR), as clearly shown for An 2…”

“…S2 and S3) characterized by g// = 1.925±0.003, g Ʇ = 1.978±0.003, A// = 176(±3)×10 -4 cm -1 and A Ʇ = 70±(3)×10 -4 cm -1 and attributed to non-porphyrinic vanadyl complexes with oxygenated ligands (referred to as VO-nP complexes). 28 These complexes are thought to result from the interaction of bitumen with oxygenated molecules of other bioorganic substances (resins, wax, fat …) in the black matters. The only exception is Hum 3 sample (the human mummy from the Boulogne museum, Fig.…”