Helix compactness and stability

Structure, stability, cooperativity and molecular packing of two major backbone forms: 3-10-helix and
b-strand are investigated. Long models HCO-(Xxx)n-NH2 Xxx = Gly and (L-)Ala, n < 34, are studied at
two levels of theory including the effect of dispersion forces. Structure and folding preferences are
established, the length modulated cooperativity and side-chain determined fold compactness is quantified.
By monitoring DG(b->a) rather than the electronic energy, DE(b->a), it appears that Ala is a much better
helix forming residue than Gly. The achiral Gly forms a more compact 310-helix than any chiral amino
acid residue probed here for L-Ala.