Molecular monolayers of poly-∈-benzyloxycarbonyl-l-lysine were studied at the air/water interface. Deuterium-exchange measurements and the surface area of the monolayer are consistent with a structure consisting of condensed ordered arrays of α-helices. Collapsed films removed from the surface and air-dried were examined by polarized infrared spectroscopy and electron diffraction and found to consist of molecules in the α-helical conformation. There is no indication of a conformational change during compression of the monolayer, and a series of transitions found in the force–area curve are interpreted as the consecutive formation of additional layers of molecules. Some of the factors that influence this almost perfect plastic behaviour are discussed.
