From Chiral Counterions to Twisted Membranes

Abstract

In 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. (1)H 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.

Concise theory of chiral lipid membranes

“…τ m is the geodesic torsion along the unit vector m at some point. Here m represents the projected direction of the lipid molecules in the experiments [2,3,4,5,6,7,8] and chiral tartrate counterions in the experiment [9,10] on the membrane surface, respectively. If we take a righthanded orthonormal frame {e 1 , e 2 , e 3 } with e 3 being the normal vector of the membrane as shown in Fig.…”

“…Since tubules were fabricated successfully from chiral lipid molecules, chiral lipid structures have attracted much experimental attention [1,2,3,4,5,6,7,8,9,10]. Most of chiral structures in experiments are self-assembled from DC 8,9 P C which is a typical chiral molecule.…”

“…Cholesterol is another kind of chiral molecules used in the experiments where helical stripes with pitch angles 11 • and 54 • are usually observed [7,8]. Additionally, Oda et al have reported twisted ribbons of achiral cationic amphiphiles interacting with chiral tartrate counterions [9,10]. It is found that the twisted ribbons can be tuned by the introduction of opposite-handed chiral counterions in various proportions [9].…”

Synthesis and characterization of nanoarchitectures from fatty acid derivatives of 2,6-diaminopyridine and 2-aminopyridine

“…Hence, unsaturated oleic moiety appears to be critical in nanotube formation. The literature survey [29][30][31][32][33] reveals that tube-forming self-assembled molecular species requires unsaturation in the lipophilic moiety although, the evidence is limited. A recent study [34,35] of cardanol-based glycolipid also shows that glycolipid with unsaturated chain self-assembled into coiled or tubular structures by non-parallel chiral packing due to kink into alky chain's structure expressed by the cisdouble bond of the monoene, while the saturated analogue self-assembled into twisted fibers through parallel chiral packing.…”

Preparation of dicholesteryl-derivatives: The effect of spatial configuration upon gelation

“…chirality, on assembled systems can be profound. It has been reported that chirality plays critical roles in assembling processes taking place on surfaces and interfaces, in liquid crystalline phase, and in the formation of supramolecular polymers and gels [38,39]. Shinkai and coworkers synthesized nineteen cholesteryl derivatives containing a variety of azobenzene moieties coupled to (S)-and (R)-C-3 of a steroidal moiety through an ester linkage.…”