Reaction of Pb(II) and Zn(II) with Ethyl Linoleate To Form Structured Hybrid Inorganic-Organic Complexes: A Model for Degradation in Historic Paint Films

Margaret G MacDonald; Michael R Palmer; Matthew R Suchomel; Barbara H Berrie

doi:10.1021/acsomega.6b00075

Reaction of Pb(II) and Zn(II) with Ethyl Linoleate To Form Structured Hybrid Inorganic-Organic Complexes: A Model for Degradation in Historic Paint Films

ACS Omega. 2016 Sep 7;1(3):344-350. doi: 10.1021/acsomega.6b00075. eCollection 2016 Sep 30.

Authors

Margaret G MacDonald¹, Michael R Palmer¹, Matthew R Suchomel², Barbara H Berrie¹

Affiliations

¹ Scientific Research Department, Conservation Division, National Gallery of Art, 2000B South Club Drive, Landover, Maryland 20785, United States.
² CNRS, University of Bordeaux, ICMCB, 87 Avenue du Docteur A. Schweitzer, UPR 9048, 33608 Pessac Cedex, France.

Abstract

To investigate soap formation in drying oils in historic paints, the reaction between metal acetates (K⁺, Zn²⁺, Pb²⁺) and ethyl linoleate (EL) was studied using optical microscopy, X-ray powder diffraction, and electron microscopy. Pb(II) and Zn(II) react rapidly with EL to form highly structured, spherulitic, luminescent crystallites that aggregate. Evidence from Fourier transform infrared (FTIR) and scanning electron microscopy/energy dispersive X-ray analysis and high-resolution synchrotron powder X-ray diffraction indicates that these are organic-inorganic hybrid complexes or coordination polymers. FTIR absorbance peaks at ca. 1540 cm^-1 for Pb(II) and ca. 1580 cm^-1 for Zn(II) are consistent with the formation of carboxylate complexes. The complexes formed offer insight into the degradation processes observed in oil paint films, suggesting that soap formation is rapid when metal ions are solubilized and can occur with unsaturated fatty acids that are present in fresh oils. These complexes may account for the atypical luminescence observed in lead-containing cured oil paint films.