SALT-DEPENDENT CONFORMATIONAL DIVERSITY OF ALTERNATING POLY(GLU-LEU)

Alternating poly(Glu-Leu) was synthesized by the condensation of the c orresponding dipeptide p-nitrophenyl ester at high concentration. It e xhibits a random coil structure in pure water at neutral pH. Addition of monovalent cations, such as NH4+ to a final 0.1 M solution, induces a transition to a water soluble beta-structure. The salt effect is qu ite selective since no transition was observed with Li+, Na+ or Cs+ io ns. Addition of 0.5 equiv. of calcium, cobalt or manganese chlorides p er glutamyl residue induces similar coil to beta-sheet transitions. No polymer precipitation was observed at these very low salt concentrati ons. Addition of 0.5 equiv. of Cu2+ or 0.15 equiv. of Fe3+ induces a c oil to alpha-helix transition. Molecular modeling has been used to und erstand tentatively the main factors controlling the different conform ations observed with the various metal ions. (C) Munksgaard 1997.