The Color of Cation-π Interactions: Subtleties of Amine-Tryptophan Interaction Energetics Allow for Radical-like Visible Absorbance and Fluorescence.

ABSTRACT: Several peptides and a protein with an inter- or intramolecular cation-π interaction between tryptophan (Trp) and an amine cation are shown to absorb and fluoresce in the visible region of the spectrum. Titration of indole with sodium hydroxide or ammonium hydroxide yields an increasing visible fluorescence as well. Visible absorption and multipeaked fluorescence excitation spectra correlate with experimental absorption spectra and the vibrational modes of calculated absorption spectra for the neutral Trp radical. The radical character of the cation-indole interaction is predicted to stem from the electrostatic dislocation of indole highest occupied molecular orbital (HOMO) charge density toward the cation with a subsequent electronic transition from the HOMO-2 to the HOMO. Because this is

SUBMITTER: Juszczak LJ 

PROVIDER: S-EPMC5683389 | biostudies-literature | 2017 Jun

REPOSITORIES: biostudies-literature