Pfeiffer effect on configurationally labile dyes within ternary complexes with metal ions and enantiopure macrocycles.

A configurationally-labile helical dye, 2,4,5,7-tetranitrofluorenone oximate, is used to probe complexes made of enantiopure macrocycles and mono/divalent metal ions. Induced electronic circular dichroism (ECD) and 1 H NMR responses are amplified at room temperature only in the presence of K + and Na + ions despite larger binding efficiency with alkaline earth metal ions.