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From Chiral Counterions to Twisted Membranes
journal contribution
posted on 2002-10-22, 00:00 authored by Damien Berthier, Thierry Buffeteau, Jean-Michel Léger, Reiko Oda, Ivan HucIn membranes, the chirality of the amphiphile constituents is sometimes expressed at a
supramolecular scale of nanometers or micrometers. We have recently reported that membranes of nonchiral
dicationic n−2−n amphiphiles can also be chirally twisted upon interacting with chiral tartrate counterions.
Here, we demonstrate that the mechanism of the chiral induction by counterions involves specific anion−cation recognition and the induction of conformationally labile chirality in the cations. Single-crystal X-ray
diffraction shows that the amphiphilic cations exist as a mixture of chiral conformers. 1H NMR data establish
a specific recognition between tartrate and n−2−n cations and show that chiral conformers also exist in
solution. Circular dichroism (CD) in the UV−vis shows a sharp conformational change of tartrate ions from
anti to gauche when bound to the chiral cationic membranes. This is confirmed by CD in the infrared region
which also shows concomitant induced CD bands in the vibrations of the n−2−n amphiphiles. These results
represent the first example of the so-called Pfeiffer effect in a membrane. They provide a general framework
for designing new tunable membrane systems. Our work also includes the first application of vibrational
circular dichroism in the study of chiral conformations of amphiphiles in membranes and demonstrates the
very high potential of this technique.