On the unusual stability of Maya blue paint: molecular dynamics simulations

Classical molecular dynamics simulations of the indigo-containing clay palygorskite (Maya blue) have been carried out at different temperatures in order to get insight into the high stability of this paint. After several tens of picoseconds the molecules set into stable sites along the channels of the clay, where they remain for relatively long times even at high temperature (573 K). The hydrogen bonds between indigo carbonyl and structural water are seemingly the most important guest-host interactions, however, there is some evidence that they are not essential in keeping the organic dye trapped in the stable sites. Therefore, van der Waals interactions are expected to be crucial in stabilizing Maya blue, allowing to fit the bulky indigo molecules into the palygorskite channels. Furthermore, we successfully tested the possibility that a direct interaction between indigo and clay octahedral cations (not mediated by structural water) could also play an important role in trapping the indigo molecules. (C) 2002 Elsevier Science Inc. All rights reserved.