Modeling of bovine Type-I collagen fibrils: Interaction with pickling and retanning agents

Bovine Type I collagen was investigated, building on a large scale computer model of a collagen fibril in water, and focusing on two stages of the leather manufacturing process. The effects of different salts (NaCl, CaCl2, and Na2SO4) on the swelling behavior of collagen at low pH (the pickling process) were studied. The salts suppress the swelling of the fibrils at low pH and we find specific stabilizing influences for CaCl2 and Na2SO4, due to weak Ca2+/Cl- and strong SO42-/lysine/arginine interactions, respectively. Using state-of-the-art sampling techniques, such as the metadynamics algorithm, to allow an efficient exploration of configuration space, we were able to investigate the effect of polyacrylate and poly(methyl acrylate) - two polymeric retanning agents - on the fibril. Both polymers interact with the ammonium groups on the surface, but polyacrylate shows significantly stronger interactions. We suggest that it is this stronger interaction that contributes to the reduced suitability of PAA as a tanning agent.