Experimental characterization of poly(hydroxyalkyl‐L‐glutamine) conformations in aqueous calcium chloride and sodium perchlorate solutions

Abstract

AbstractPoly(hydroxyalkyl‐L‐glutamine) (alkyl = ethyl, propyl, butyl) solutions have been studied by CD as functions of temperature and activity of calcium chloride and sodium perchlorate. Helical content is altered by changes in salt activity and temperature. The helicity of poly(hydroxybutyl‐L‐glutamine) and poly(hydroxypropyl‐L‐glutamine) falls to zero in a monotonic fashion with increasing calcium chloride activity. A nonzero helicity reappears at activities in excess of 5–50 mol kg−1. Poly(hydroxypropyl‐L‐glutamine) is much more sensitive to calcium chloride than is poly(hydroxybutyl‐L‐glutamine), and both polypeptides are more sensitive to calcium chloride than are typical proteins. Markedly different behavior is observed with sodium perchlorate. This salt acts as a helix stabilizer at low activities but becomes a destabilizer at activities higher than 0.3–1.0 mol kg−1. In this respect the effect of sodium perchlorate on nonionic poly(hydroxyalkyl‐L‐glutamines) resembles that seen with cationic poly(L‐lysine) and poly(L‐arginine). Helix stabilization at low sodium perchlorate activity is moderate for poly(hydroxybutyl‐L‐glutamine) and large for poly(hydroxypropyl‐L‐glutamine) and poly(hydroxyethyl‐L‐glutamine).