ENVIRONMENTALLY FRIENDLY PROCESSES AND NEW APPLICATIONS FOR ANIMAL HIDES AND LEATHER
Location: Biobased and Other Animal Co-Products
Title: Molecular modeling approach to vegetable tanning: preliminary results for gallotannin interactions with the collagen microfibril
Submitted to: Journal of American Leather Chemists Association
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 1, 2010
Publication Date: May 1, 2011
Citation: Brown, E.M., Shelly, D.C. 2011. Molecular modeling approach to vegetable tanning: preliminary results for gallotannin interactions with the collagen microfibril. Journal of American Leather Chemists Association. 106(5):145-152.
Interpretive Summary: Tanning of animal hides produces leather, the highest value coproduct of the meat industry. Tanning stabilizes the protein structure of the hide and imparts heat stability, enhanced tensile properties, and resistance to microbial degradation. Currently most high quality leather is "chrome-tanned," produced by treatment of the hide with salts of the mineral chromium. Because of environmental considerations, and customer preference, there is interest in developing new chrome-free tannages. The art of tanning with chromium salts, vegetable tannins or synthetic organic materials is highly developed, but the mechanisms are poorly understood. This study uses our previously reported computerized model of the collagen, the supermolecular protein component of hides and skins, to explore the interactions of gallotannin, a component of vegetable tannins, with collagen. Models of the gallotannin molecule were inserted into the collagen microfibril model and subjected to molecular dynamics simulation to mimic heating of the molecular complex that permits the tannin molecules to migrate into more optimal positions. Comparison of the environments of initial and final gallotannin positions provided new information concerning possible vegetable tanning mechanisms. This information will be valuable in designing more focused mechanistic studies leading to new tanning agents.
Tanning of animal hides produces leather, a durable, flexible material that is stabilized against putrefaction. Chrome-tanned wet blue, aldehyde crosslinked wet white, and vegetable tanned hides are major contributors to current leather production. Although the chemistries involved are significantly different, the product in each case is leather. Vegetable tanning, the oldest of these technologies is, from a mechanistic perspective, the least well understood. To explore possible vegetable tanning mechanisms, we have applied molecular modeling techniques to the study of interactions of gallotannin, a component of chestnut tannins, with the collagen microfibril. A model gallotannin molecule was constructed and energy minimized. This model was docked into several energetically favorable positions on a fragment of the ERRC collagen microfibril model, generally with a good fit at a proline or hydroxyproline residue. The alpha carbon backbone of collagen was kept immobile during molecular dynamics simulations at 400 - 800K with and without an added layer of water for solvation to identify possibly more favorable interactions sites for the gallotannin molecules. Both inter and intra chain interactions were possible, and several potential sites for hydrogen bonding via arginine residues or hydrophobic interactions with alanine or isoleucine residues were identified. The information gained from this model study is an early step in the development of a vegetable-tanning model.