Helix–coil transition model

Helix-coil transition models are formalized techniques in statistical mechanics developed to describe conformations of linear polymers in solution. The models are usually but not exclusively applied to polypeptides as a measure of the relative fraction of the molecule in an alpha helix conformation versus turn or random coil. Most models contain parameters for the likelihood of helix nucleation from a coil region, and helix propagation along the sequence once nucleated; because polypeptides are directional and have distinct N-terminal and C-terminal ends, propagation parameters may differ in each direction.

Common transition models include the Zimm-Bragg model and the Lifson-Roig model, and their extensions and variations.

Energy of host poly-alanine helix in the aqueous solution:

$\Delta G_{folding}=(m-2)\Delta H_{\alpha }-mT\Delta S,where''m''-isnumberofresiduesinthehelix$