(253g) 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.