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Maldi-Tof Used to Examine Renaissance Art

Photonics Spectra
Apr 2006
Hank Hogan

Whereas others may look at a work of fine art and see a painting, Cécile Cren-Olivé, a research assistant professor in analytical chemistry at the Université des Sciences et Technologies de Lille 1 in Villeneuve d’Ascq, France, sees proteins. Specifically, she sees those proteins that bind pigments.

For art historians, knowing what is in the binding can reveal clues as to when, where and how a piece was painted. To identify the binding, it must be extracted and analyzed, a difficult undertaking.

“The whole analysis depends on this preliminary step,” Cren-Olivé said. “And this step is a real challenge due to the necessity to work with very tiny samples.”

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Modified proteomic techniques identify the proteins used as a binder in artwork. The approach revealed that Benedetto Bonfigli employed an unusual combination of binders in this triptych that depicts, from left, St. John the Baptist, The Virgin and Child, and St. Sebastian. It represents the Italian School of painting from the 15th century and is located in the Musée du Petit Palais in Avignon, France. ©Centre de Recherche et de Restauration des Musées de France.

As part of a study undertaken by the university and the Centre de Recherche et de Restauration des Musées de France in Paris, Cren-Olivé and her colleagues have developed a way to successfully extract and analyze the binding proteins. They evaluated the various extraction methods that had been proposed in the literature, many of which involve some form of the chemical separation technique of chromatography.

They also tried the techniques used in proteomics to analyze proteins, such as enzymatic hydrolysis, peptide purification, tandem mass spectrometry analysis and protein databank interrogation, optimizing and adapting these methods for use with the 10 µg or so of material with which they typically had to work.

In the end, the investigators succeeded in developing their own approach that borrows from proteomics and from the more traditional extraction procedures.

“A combination of these two worlds leads to the best results,” Cren-Olivé declared.

As they developed the extraction process, the researchers also needed a way to verify that it was working. She noted that the first objective in their proteomics approach was to obtain peptide mass fingerprints. That would, in turn, enable them to identify proteins during database searching. Therefore, they needed to come up with a way to analyze these biological macromolecules.

For this, they used a matrix-assisted laser desorption/ionization time-of-flight (Maldi-Tof) system from PerSeptive Biosystems Inc., part of Applied Biosystems of Foster City, Calif. By firing a laser at a matrix containing the sample to be measured, a Maldi-Tof system desorbs and ionizes biological macromolecules such as proteins or peptides so they can be analyzed b y a mass spectrometer. This is done without fragmenting the molecules. In the case of the work by the team in France, the system used a 337-nm nitrogen laser.

Once the methodology was developed, the researchers studied two Renaissance paintings that were chosen because of an interest in the paintings by the Musée du Louvre in Paris, a collaborating institution in the research. Some of the results were unexpected. They found, for example, that Benedetto Bonfigli's 15th-century triptych features a complex binder called tempera grassa that enabled the artist to achieve bright, shimmering effects.

The new proteomics approach also could have applications in archaeology. Cren-Olivé said that the group is using the method to analyze milk proteins in ancient pottery shards to see what types od domesticated animals — cows, goats or sheep — people kept in that region. The method, she explained, could enable investigators to study the human diet through time and to understand the orgin of dietary habits.

Contact: Cécile Cren-Olivé, Université des Sciences et Technologies de Lille 1, Villeneuve d’Ascq, France; +33 3 2033 5954; e-mail: cecile.cren@univlille1.fr.



GLOSSARY
chromatography
The chemical method of separating compounds dissolved in one phase (usually mobile) through its equilibration with a second phase (usually stationary). The mechanism of separation may involve partition, adsorption, permeation or exclusion, or ion exchange.
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