Old Paintings’ Egg White Coatings Unveiled

For hundreds of years, artists coated their paintings with an egg white wash to protect them. Now, scientists have discovered the molecular basis for the coating’s protective properties (Angew. Chem. Int. Ed. 2014, DOI: 10.1002/anie.201400251). Georges Belfort and colleagues at Rensselaer Polytechnic Institute created their own “painting” by using a polytetrafluoroethylene (PTFE) surface, which mimics that of an oil painting. They then soaked the surface in chicken egg white ovalbumin. Infrared spectroscopy investigations show that the ratios of egg white’s α-helix and β-sheet composition changed over time. α-Helix content decreased by 73%, and β-sheet content increased by 44%. These changes make it harder for oxygen to diffuse through the coating, a process that becomes more difficult with each successive coating. By the time the authors had applied four layers of egg white to the PTFE membrane, the oxygen diffusion rate dropped to zero. The authors hypothesize that the increase in stable β-sheet structures allows the protein to stack more tightly and adsorb oxygen, which causes the coating to swell and makes it impenetrable.