Circular Dichroism and UV Resonance Raman Study of the Impact of Salts and Alcohols on the Gibbs Free Energy Landscape of an α‐helical Peptide

KAN XIONG; ELIANA K. ASCIUTTO; JEFFRY D. MADURA; SANFORD A. ASHER

Conferencia; XXII INTERNATIONAL CONFERENCE ON RAMAN SPECTROSCOPY; 2010

We used CD and UV resonance Raman spectroscopy to study the impact of salts on the conformational equilibria and relative Gibbs free energy landscapes along the Ramanchandran Ψ-coordinate of a mainly poly-ala peptide, AP of sequence AAAAA(AAARA) 3 A. NaClO4 stabilizes α-helix-like conformations more than does NaCl, which stabilizes more than Na2SO4 at identical ionic strengths. This α-helix stabilization ordering is the reverse of the Hofmeister series of anions in their ability to disorder water hydrogen bonding. Much of the NaClO α-helix stabilization results from ClO4- association with the AP terminal -NH 3+ groups and arg side chains .ClO 4- stabilizes 3 10 -helix conformations but destabilizes turn conformations. The decreased Cl- and SO42- AP alpha helix stabilization probably results from a decreased association with the Arg side chains and the terminal -NH3+ groups. Cl- is expected to have a smaller binding affinity and thus will stabilize alpha helical conformations intermediately between NaClO4 and Na2SO4. Electrostatic screening stabilizes pi-bulge conformations.