Protein aggregation and partial globular state in aqueous 1-alkyl-3-methylimidazolium nitrate solutions

We have investigated the relationship between protein size and the structural modification in concentrated aqueous solutions of ionic liquids (ILs) 1-alkyl-3-methylimidazolium nitrate ([Cnmim][NO3] (n = 2, 4)). Proteins with the radii of gyration (Rg) above ∼20 Å form amorphous aggregates in an aqueous [C4mim][NO3] solution at X (mol% IL) = 20, whereas those with Rg values below ∼20 Å assume partial globular states. Remarkably, a decrease in the alkyl-chain length causes an increase in the protein size at which protein aggregation occurs. Concentrated [Cnmim][NO3] (n = 2, 4) solutions might control a boundary between the protein aggregation and partial globular states.