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NMR’s got sole
PIERRE ALAIN BAYLE
The researchers used two types of signalsOno tannins or lubricant reGarbage is like gold to an archaeologist. solid-state 13C-NMR techniques: crossmained. “That was a moment that was For example, in Lyon, France, near the very surprising,” says Bardet. “Probably Saoˆne River, an excavation is under way polarization transfer magic-angle spinthe tannins have been leached out of the on a giant, 800-year-old trash dump ning (CP-MAS) and single-pulse excitamaterial because of the wa(discovered during the conter.” struction of a parking garage) where people used to discard So why were the soles so all manner of waste. In a rewell preserved if their typical cent paper published in AC leather-preserving agents had (DOI 10.1021/ac802052a), been washed away? Luckily, Michel Bardet and colleagues Bardet and colleagues almost of the Commissariat a` l’E´neralways subject their samples to gie Atomique (France) report EPR analysis to look for parafindings from NMR and elecmagnetic compounds. “It’s tron paramagnetic resonance important to check for their (EPR) studies on the leather presence in the sample besoles of shoes found in this cause it’s important for interA leather sole recovered from an archaeological trash dump in Lyon, trash heap. preting the NMR spectra,” France. The new analyses, accordsays Bardet. “For instance, if ing to Bardet, will help archaeyou have a high concentration tion magic-angle spinning (SP-MAS). ologists understand the preservation of of metallic impurities, it can lead to an MAS is a solid-state NMR technique in leather in anaerobic, wet environments enlargement of the NMR peaks and lose which the sample is tilted to the “magic and will assist in the restoration of those the resolution in your spectra.” artifacts. “We looked at the research and angle” of 54.74° with respect to the exIn this case, EPR analysis of the soles ternal magnetic field and spun at a high found that very little had been done in showed that they had accumulated large rate. This sharpens the signals and makes amounts of iron oxidesOcompounds this field,” says Bardet, an NMR specthe spectra much more useful. CP-MAS troscopist. The archaeologists “found not found in the modern leather takes advantage of the strong dipolar these soles dating from the 13th samples. The presence of iron cominteractions between 13C and protons through the 18th century. It was very pounds may explain the surprisingly and is good for looking at the relatively interesting to have all these sets of good condition of the artifacts. “We rigid domains of collagen and tannin samples available.” think that iron more or less took the Bardet and his group usually work on moieties. SP-MAS instead directly explace [of the tannins] and acted as a cites 13C and is used to observe the archaeological wood samples, so analyzpost-tannin effect,” says Bardet. The more “mobile” part of the materialOfor ing leather was new to them. “One iron likely leached from the environment instance, the lubricants used to soften thing that was interesting for us...is that where the soles were found. the leather. both [wood and leather] are what we Bardet says that their work continues. “You can only observe mobile molcall ‘waterlogged’ materials. It’s organic They plan to look at “historical leather ecules with direct excitation,” explains matter full of water,” he says. “Generdated from the same periods but not Bardet. “That’s the case if you have lually, when we are working on wood preserved in water surroundings in order bricant in your sampleOfor example, oil found in similar conditions, the wood is to check and to look at the tannins,” he or wax. You can see them very easily in very poor condition.... Most of the says. “We also continue the work on with direct excitation. By doing both cellulose has been destroyed. In the case archaeological wood.” experiments, you are sure to see all types of leather, the material seems to be in —Jennifer Griffiths of carbons that you have in your better preservation.” samples.” Leather is made up of collagen, a roThe investigators subjected both bust protein that can survive hundreds modern leathers and archaeological soles of thousands of yearsOmaybe even tens to the NMR analysis. The modern of millionsOunder the correct condileather showed clear signals for tannins tions. But the wet environment where and lubricants, as well as for collagen. these samples were found isn’t ideal for The soles generated only collagen preservation. 10.1021/AC9000223 2009 AMERICAN CHEMICAL SOCIETY
Published on Web 01/21/2009
MARCH 1, 2009 / ANALYTICAL CHEMISTRY
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