Helix–coil stability constants for the naturally occurring amino acids in water. XXI. Glutamine parameters from random poly(hydroxypropylglutamine‐co‐ L ‐glutamine) and poly(hydroxybutylglutamine‐co‐ L ‐glutamine)

Water‐soluble, random copolymers containing L ‐glutamine and either N 5 ‐(3‐hydroxypropyl)‐ L ‐glutamine or N 5 ‐(4‐hydroxybutyl)‐ L ‐glutamine were synthesized, fractionated, and characterized. The thermally induced helix–coil transitions of these copolymers were studied in water. A short‐range interaction theory was used to deduce the Zimm‐Bragg parameters σ and s for the helix–coil transition in poly( L ‐glutamine) in water from an analysis of the melting curves of the copolymers in the manner described in earlier papers. The computed values of s indicate that L ‐glutamine is helix‐indifferent at low temperature and a helix‐destabilizing residue at high temperature in water. At all temperatures in the range of 0–70°C, the glutamine residue promotes helix–coil boundaries since the computed value of σ is large.