Solution- and solid-state evidence for alkali metal cation-pi interactions with indole, the side chain of tryptophan

Research was conducted to examine solution- and solid-state evidence for alkali metal cation-pi interactions with indole, the side chain of tryptophan. The solid-state data confirm parallel results derived for the same complexes in solution. Results demonstrate that in all three cases, ppyrrolo, rather than benzo, proves to be the pi-donor. Solution experiments confirm the structure of one of these complexes which reinforces the conclusion that indole is an excellent pi-donor for Na+ and K+ cations.