FT-IR STUDY OF THE NATURE OF THE PROTON AND LI-A AND GRAMICIDIN-C( MOTIONS IN GRAMICIDIN)

Gramicidin A and C as well as their proton and Li+ complexes were stud ied by FT-IR spectroscopy. With an increasing number of hydrated and p rotonated channels, infrared continuous absorption is observed. It pro ves large proton polarizability due to very fast collective fluctuatio ns and shifts of the excess proton in hydrogen-bonded single file wate r chains in the gramicidin channels. The infrared spectrum of the hydr ated Li+ cation in the channels shows a continuum in the far-infrared region. This continuum is explained in terms of Li+ ion fluctuations a nd shifts between the electron lone pairs of two water molecules and a t least three carbonyl O atoms of the backbone. The continuum indicate s large Li+ polarizability of these channels. If the Lif-bonded system is polarized by an external electrical field, the diffusion of the Li +-water complex in field direction is favored.