Nuclear magnetic resonance spectra and 207pb chemical-shift tensors of lead carboxylates relevant to soap formation in oil paintings

Jaclyn Catalano, Yao Yao, Anna Murphy, Nicholas Zumbulyadis, Silvia A. Centeno, Cecil Dybowski

Research output: Contribution to journalArticle

17 Citations (Scopus)

Abstract

Soap formation in traditional oil paintings occurs when heavymetal- containing pigments, such as lead white, 2PbCO3·Pb(OH) 2, and lead tin yellow type I, Pb2SnO4, react with fatty acids in the binding medium. These soaps may form aggregates that can be 100-200 lm in diameter, which swell and protrude through the paint surface, resulting in the degradation of the paint film and damage to the integrity of the artwork. The factors that trigger soap formation and the mechanism(s) of the process are not yet well understood. To elucidate these issues, chemical and structural information is necessary, which can be obtained using solid-state 207Pb and 13C nuclear magnetic resonance (NMR). In this article, we report 207Pb and 13C solid-state NMR spectra and 207Pb chemical-shift tensors of lead carboxylates implicated in soap formation: lead stearate, lead palmitate, and lead azelate, in addition to lead oleate and lead heptanoate for comparison. The 13C cross polarization with magicangle spinning (MAS) spectra of these lead carboxylates show resonance doubling for the carbons closest to the lead, indicating two different conformations of the fatty acid chains in the asymmetric unit. The 207Pb NMR spectra, from which tensors were determined, were obtained with direct excitation and spin-temperature alternation, with and without MAS, and with the wide band uniform rate smooth truncation Carr-Purcell-Meiboom-Gill pulse sequence. The results of these experiments show that the local coordination environment of lead azelate is different from lead palmitate and lead stearate and could thus be distinguished from these in a paint film displaying soap formation. In addition, comparing the 207Pb NMR chemical-shift tensors of the lead carboxylates studied shows that crystal packing of the acyl chains may be a factor in determining the coordination environment around the lead.

Original languageEnglish
Pages (from-to)280-286
Number of pages7
JournalApplied Spectroscopy
Volume68
Issue number3
DOIs
StatePublished - 1 Mar 2014

Fingerprint

soaps
Soaps (detergents)
Chemical shift
Painting
carboxylates
Tensors
chemical equilibrium
Oils
Lead
oils
Nuclear magnetic resonance
tensors
nuclear magnetic resonance
paints
Paint
Stearates
stearates
Palmitates
fatty acids
Fatty acids

Keywords

  • Heavy-metal carboxylates
  • Lead soap
  • Oil paintings
  • Pb NMR
  • Solid-state NMR

Cite this

Catalano, Jaclyn ; Yao, Yao ; Murphy, Anna ; Zumbulyadis, Nicholas ; Centeno, Silvia A. ; Dybowski, Cecil. / Nuclear magnetic resonance spectra and 207pb chemical-shift tensors of lead carboxylates relevant to soap formation in oil paintings. In: Applied Spectroscopy. 2014 ; Vol. 68, No. 3. pp. 280-286.
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abstract = "Soap formation in traditional oil paintings occurs when heavymetal- containing pigments, such as lead white, 2PbCO3·Pb(OH) 2, and lead tin yellow type I, Pb2SnO4, react with fatty acids in the binding medium. These soaps may form aggregates that can be 100-200 lm in diameter, which swell and protrude through the paint surface, resulting in the degradation of the paint film and damage to the integrity of the artwork. The factors that trigger soap formation and the mechanism(s) of the process are not yet well understood. To elucidate these issues, chemical and structural information is necessary, which can be obtained using solid-state 207Pb and 13C nuclear magnetic resonance (NMR). In this article, we report 207Pb and 13C solid-state NMR spectra and 207Pb chemical-shift tensors of lead carboxylates implicated in soap formation: lead stearate, lead palmitate, and lead azelate, in addition to lead oleate and lead heptanoate for comparison. The 13C cross polarization with magicangle spinning (MAS) spectra of these lead carboxylates show resonance doubling for the carbons closest to the lead, indicating two different conformations of the fatty acid chains in the asymmetric unit. The 207Pb NMR spectra, from which tensors were determined, were obtained with direct excitation and spin-temperature alternation, with and without MAS, and with the wide band uniform rate smooth truncation Carr-Purcell-Meiboom-Gill pulse sequence. The results of these experiments show that the local coordination environment of lead azelate is different from lead palmitate and lead stearate and could thus be distinguished from these in a paint film displaying soap formation. In addition, comparing the 207Pb NMR chemical-shift tensors of the lead carboxylates studied shows that crystal packing of the acyl chains may be a factor in determining the coordination environment around the lead.",
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Nuclear magnetic resonance spectra and 207pb chemical-shift tensors of lead carboxylates relevant to soap formation in oil paintings. / Catalano, Jaclyn; Yao, Yao; Murphy, Anna; Zumbulyadis, Nicholas; Centeno, Silvia A.; Dybowski, Cecil.

In: Applied Spectroscopy, Vol. 68, No. 3, 01.03.2014, p. 280-286.

Research output: Contribution to journalArticle

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T1 - Nuclear magnetic resonance spectra and 207pb chemical-shift tensors of lead carboxylates relevant to soap formation in oil paintings

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AU - Yao, Yao

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AB - Soap formation in traditional oil paintings occurs when heavymetal- containing pigments, such as lead white, 2PbCO3·Pb(OH) 2, and lead tin yellow type I, Pb2SnO4, react with fatty acids in the binding medium. These soaps may form aggregates that can be 100-200 lm in diameter, which swell and protrude through the paint surface, resulting in the degradation of the paint film and damage to the integrity of the artwork. The factors that trigger soap formation and the mechanism(s) of the process are not yet well understood. To elucidate these issues, chemical and structural information is necessary, which can be obtained using solid-state 207Pb and 13C nuclear magnetic resonance (NMR). In this article, we report 207Pb and 13C solid-state NMR spectra and 207Pb chemical-shift tensors of lead carboxylates implicated in soap formation: lead stearate, lead palmitate, and lead azelate, in addition to lead oleate and lead heptanoate for comparison. The 13C cross polarization with magicangle spinning (MAS) spectra of these lead carboxylates show resonance doubling for the carbons closest to the lead, indicating two different conformations of the fatty acid chains in the asymmetric unit. The 207Pb NMR spectra, from which tensors were determined, were obtained with direct excitation and spin-temperature alternation, with and without MAS, and with the wide band uniform rate smooth truncation Carr-Purcell-Meiboom-Gill pulse sequence. The results of these experiments show that the local coordination environment of lead azelate is different from lead palmitate and lead stearate and could thus be distinguished from these in a paint film displaying soap formation. In addition, comparing the 207Pb NMR chemical-shift tensors of the lead carboxylates studied shows that crystal packing of the acyl chains may be a factor in determining the coordination environment around the lead.

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