Helix-coil transitions nucleation parameter

The helix-coil transition has occupied polypeptide chemists as models for such structural transformations in proteins (Poland and Scheraga, 1970). Both theoretical and experimental approaches have been taken in such studies (Scheraga, 1978) in order to obtain quantitative measures of the tendency of each of the 20 naturally occurring amino acids to adopt the helix vs. the coil (i.e. all other, non-helical) conformations. These tendencies are expressed in terms of the Zimm-Bragg (1959) nucleation and growth parameters, O and s, respectively. The values of a and s may be used directly to predict the locations of a-helices in proteins. The values of a and s have been obtained from experimental studies of thermally-induced helix-coil transitions in host-guest random copolymers... 

If any intermediate differing in enthalpy from N and D is significantly populated, then the inequality holds. A typical example is provided by the helix coil transition which gives very different values of and AH the Zimm-Bragg nucleation parameter h is related to the enthalpies Ai/, and AHvh t y the relation... 

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