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Preferential interactions of guanidinium ions with aromatic groups over aliphatic groups

Research output: Contribution to journalArticle

Original languageEnglish
Pages (from-to)16689 - 16696
Number of pages8
JournalJournal of the American Chemical Society
Volume131
Issue number46
DOIs
DatePublished - Nov 2009

Abstract

Small angle neutron scattering (SANS) and molecular dynamics (MD) simulations were used to characterize the long-range structuring (aggregation) of aqueous solutions of isopropanol (IPA) and pyridine and the effect on structuring of guanidinium chloride (GdmCl). These solutes serve as highly soluble analogs of the nonpolar aliphatic (IPA) and aromatic (pyridine) side chains of proteins. SANS data showed that isopropanol and pyridine both form clusters in water resulting from interaction between nonpolar groups of the solutes, with pyridine aggregation producing longer-range structuring than isopropanol in 3 m solutions. Addition of GdmCl at 3 m concentration considerably reduced pyridine aggregation but had no effect on isopropanol aggregation. MD simulations of these solutions support the conclusion that long-range structuring involves hydrophobic solute interactions and that Gdm+ interacts with the planar pyridine group to suppress pyridine−pyridine interactions in solution. Hydrophobic interactions involving the aliphatic groups of isopropanol were unaffected by GdmCl, indicating that the planar and weakly hydrated Gdm+ cation cannot make productive interactions with the highly curved or “lumpy” aliphatic groups of this solute. These observations support the conclusion that the effects of Gdm+ ions on protein-stabilizing interactions involving aromatic amino acid side chains make significant contributions to the denaturant activity of GdmCl, whereas interactions with the “lumpy” aliphatic side chains are likely to be less important.

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