Chiroptical rhythmicity, part 2. Evidence for signal transduction by stereoselective ion pair formation at the membrane/water interface

The initiation mechanism of chiroptical rhythmicity, a novel chiroptical ph enomenon (Ghebremariam and Matile preceding contribution), was investigated by exploring the functionality of five structural analogs of the inducing L-His ligand. Disappearance of chiroptical rhythmicity with L-His methyl es ters as well as with D-His implied that stereoselective ion Fair formation between carboxylate anion of L-His bound at the membrane/water interface an d ammonium cations of phosphatidylcholine is essential for signal transduct ion to the hydrophobic core of the membrane. It was further shown that "H" aggregation of the asymmetric septi(p-phenylene) chromophore induced by mul tivalent L-His (i.e., poly-L-His) exceeds the extent required for chiroptic al rhythmicity by far and ultimately results in the formation of achiral he rringbone lattices.