Photoelectron spectroscopy of gramicidin polyanions: Competition between delayed and direct emission

Abstract

We present the first photoelectron (PE) spectra of polypeptide polyanions. Combining PE spectroscopy and mass spectrometry provides a direct measurement of the stability of the polyanions with respect to electron detachment and of the repulsive energy between excess charges. The second electron affinity of gramicidin was found to amount to 2.35 ± 0.15 eV, and the value of the repulsive Coulomb barrier was estimated to be 0.5 ± 0.15 eV. The spectra are interpreted as resulting from a competition between delayed and direct emission. © 2008 American Chemical Society.