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Bioinorganic Chemistry and Applications
Volume 2012, Article ID 672562, 6 pages
Research Article

Computational Study of the Structure of a Sepiolite/Thioindigo Mayan Pigment

1Materials Research and Technology Institute, The University of Texas at El Paso, El Paso, TX 79912, USA
2Department of Metallurgical & Materials Engineering, The University of Texas at El Paso, El Paso, TX 79912, USA

Received 19 June 2012; Accepted 10 August 2012

Academic Editor: Ian Butler

Copyright © 2012 Manuel Alvarado Jr. et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


The interaction of thioindigo and the phyllosilicate clay sepiolite is investigated using density functional theory (DFT) and molecular orbital theory (MO). The best fit to experimental UV/Vis spectra occurs when a single thioindigo molecule attaches via Van der Waals forces to a tetrahedrally coordinated cation with an additional nearby tetrahedrally coordinated also present. The thioindigo molecule distorts from its planar structure, a behavior consistent with a color change. Due to the weak interaction between thioindigo and sepiolite we conclude that the thioindigo molecule must be trapped in a channel, an observation consistent with previous experimental studies. Future computational studies will look at the interaction of indigo with sepiolite.