The Interactions of the Corn Protein Zein and Ionic Liquids
The solubility and secondary structure of the hydrophobic corn protein zein in ionic liquids was studied as a function of temperature and solvent properties. The solubility of zein was measured gravimetrically from 30°C to 60°C. The secondary structure of zein as a function of temperature and solvent was examined via curve fitting of infrared spectroscopic data. Two-dimensional correlation infrared spectroscopy was employed to monitor changes in the secondary structure of the zein as a function of temperature. These data clearly illustrate changes in the temperature dependent behavior between different solvents.
Most of the ionic liquids investigated change zein's secondary structure. Large solvent molecules increase the amount of β-turn secondary structure through non-polar interactions between the aromatic imidazolium cations (with alkyl substitutions) and the non-polar portions of the zein. Strong hydrogen bond accepting molecules increase the amount of β-turn secondary structure.
Solubility - solvent property relationships were explored to better understand the solvent properties of importance and how to design an ionic liquid to better dissolve a hydrophobic protein. It is found that a good solvent for zein has a small molecular volume, has a low polarity, and is a poor hydrogen bond acceptor. This combination of properties will enhance zein's solubility and limit secondary structure changes that can harm protein properties.
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