Co-solvent effects on biomolecules and water structure:

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Recently, room temperature ionic liquids (ILs) have been shown to counteract the deleterious effect of urea on proteins. Using atomistic molecular dynamics we show that a ternary mix- ture containing a particular 20 ammonium-based IL, triethylammonium acetate (TEAA), and urea (in The folding/unfolding equilibrium of proteins in an aqueous medium can be altered by adding small organic molecules generally termed as co-solvents. Denaturants such as urea are instrumental in the unfolding of proteins while protecting osmolytes favor the folded ensemble (1 : 5 molar ratio) helps a small 15- residue S-peptide analog regain most of its native structure, whereas a binary aqueous mixture containing a large amount of urea alone completely distorts it. Our simulations show that the denaturant urea directly interacts with the peptide backbone in the binary mixture while for the ternary mixture both urea as well as the IL are preferentially excluded from the peptide surface. Similar observation for Choline chloride and we have analyzed the phenomenon in detailed, focusing on the hydrogen bond and rotational dynamics of choline chloride.