Helix–coil transition of poly‐γ‐N‐carbobenzoxy‐L‐α,γ‐diaminobutyrate and poly‐δ‐N‐carbobenzoxy‐L‐ornithine

The helix–coil transition of poly‐γ‐ N ‐carbobenzoxy‐ L ‐α,γ‐diaminobutyrate (PCLB) and poly‐δ‐ N ‐carbobenzoxy‐ L ‐ornithine (PCLO) in chloroform–dichloroacetic acid mixtures was followed by optical rotatory dispersion. PCLB displays a “normal” temperature‐induced transition, but PCLO an “inverse” one. The thermodynamic parameters for helix formation of the two polymers were determined using the Zimm‐Bragg theory. The enthalpy for adding an amide residue to a helical region, Δ H , and the initiation factor σ were Δ H = −180 cal/mole and σ = 9.2 × 10 −5 for PCLB and Δ H = +490 cal/mole and σ = 1.9 × 10 −5 for PCLO.