Structure of poly( l-glutamate) with n-fluoroalkyl side chains in the solid state as studied by high-resolution 13C NMR spectroscopy

Abstract

13C CP/MAS and PST/MAS NMR experiments are carried out on poly( l-glutamate) with n-fluoroalkyl side chains over a range of temperatures from 30 to 100°C to elucidate structural features in the solid state in addition to the experimental findings on poly(γ- n-alkyl l-glutamate) reported previously. From these experimental results it was found that the conformation of the main chain depends on the carbon number of the n-fluoroalkyl side chains. The main chain of poly(γ-trifluoroethyl l-glutamate) with short n-fluoroalkyl side chains takes the helix form and that of poly(γ- n-2-(perfluorodecyl)ethyl l-glutamate) with long n-alkyl side chains takes the β-sheet form. These conformational behaviors of poly(L-glutamate) with n-fluoroalkyl side-chains in the solid state are different from those of poly(γ-n-alkyl L-glutamate).