1-Butyl-3-Methylimidazolium Acetate as an Alternative Solvent for Type I Collagen

Abstract

Low solubility and undesirable denaturation in conventional solvents continue to represent a significant challenge for efficient extraction, accurate characterization and versatile processing of collagen. In the present study, a room temperature ionic liquid (IL), 1-butyl-3-methylimidazolium acetate ([BMIM]Ac), was synthesized, and then evaluated as an alternative solvent for type I collagen. Real-time polarizing optical microscope observation indicated complete disintegration of hierarchical structure of collagen aggregates as solubilized in [BMIM]Ac at 25 oC. The solubility reached up to approximately 8.0 wt.% at 25 oC, more than ten times higher than that in conventional dilute acetic acid. In comparison with dilute acetic acid and recently reported chloridion ILs, high solubility of collagen in [BMIM]Ac at room temperature was ascribed to loose binding between [BMIM]+ and acetate, as well as stronger proton-accepting ability of [BMIM]Ac, which enabled rupture of those intermolecular hydrogen bonds and ionic bonds that stabilized collagen aggregates. However, such bond-rupturing effect was found selective at room temperature. As demonstrated by Fourier transform infrared, circular dichroism, atomic force microscope, and ultrasensitive differential scanning calorimetry analysis, [BMIM]Ac did not destroy the special triple-helical structure of tropocollagen molecules that had been identified as being of importance for the functional and bioactive properties of collagen. According to these results, the discovery of [BMIM]Ac as an ideal solvent for collagen may open up new possibilities for the chemistry and engineering of collagen, which has long been established as a readily accessible and renewable resource with many unique properties.