Helix promotion in polypeptides by polyols

The helix content of [L-Lys(Me3)]n.ClO4 and [L-Lys(Me3)50,L-Ala50]n.ClO4 in water is markedly increased by the presence of sucrose and glycerol. For [L-Lys(Me3)]n.ClO4 the ellipticity at 222 nm changes from +2 x 10(3) deg cm2 dmole-1 in water to -44 x 10(3) in 50% glycerol. Sucrose does not promote helix formation in melittin at pH 7.2, but glycerol does. At pH 5.5 sucrose and, more so, glycerol, induce helix in melittin. Glycerol induces some helix in methylated melittin, but less than in melittin. The results are discussed in relation to excluded volume effects, delta G of transfer of peptide and hydrophobic groups from water to mixed solvents, electrostatic effects, and preferential hydration.