Chiral head group

It is apparent that the solubilization of amphiphilic molecules with chiral head groups produces aggregates such as braided fibers, helices, ribbons, rods, or tubules. When these organizations are sufficiently extended, they start to get entangled and develop the ability to entrap solvent molecules in the resulting reticulum. Many such instances eventually lead to the formation of gels. This phe-... 

Amphiphiles with chiral head groups play an important role in the investigation of recognition processes in monolayers and in the construction of helical fibres. Amino acid, hydroxy acid and carbohydrate head groups were usually selected... 

In natural membranes bolaform amphi-philes have chiral head groups, which are dif-... 

Heterodimers and heterotrimers are formed in water if planar cations and anions are mixed and if polymerization is impeded by ethyl groups or larger alkyl substituents (Fig. 1.5.4). Other possibilities are the isolation of hydrophobic C-G or A-T pairs in small micelles (Fig. 2.5.4), formation of racemates (Figs. 4.2.7, 8.6.1, and 9.5.3), and formation of pseudo-racemates (Fig. 4.5.10) between enantiomeric amphiphiles with chiral head groups and the same or similar hydrophobic skeletons. 

The intermediacy of diastereomeric host-guest complexes, held together by polar forces, hydrogen bonds, etc., as postulated by Prof. Schwyzer in his mechanism for the effects observed in bilayers with chiral head groups, has been widely accepted to in explaining chromatographic separations of enantiomers on chiral phases. 

Addition of 5% ganglioside Gmi into the L-Glu-Bis-3 resulted in the appearance of vesicles along with twisted ribbons, while addition of nonchiral 10,12-docosadiynedioic acid caused the formation of platelets.97 These results affirm the importance of packing geometry, along with head group chirality, for the formation of helical structures. 

Scheme 4.19 Self-sorting in dendritic peptide gels based on head group size or chirality.

The observed structures were explained by a chiral bilayer effect mechanism proposing that only the enantiomerically pure compounds can lead to the formation of helical fibers which in turn slowly rearrange to enantiopolar crystal layers (Scheme 7.1). Within the micellar fibers, the polar head groups are oriented toward the aqueous environment and must therefore go through an energetically unfavourable -slow- dehydration followed by a 180 ° to form the enantiopolar crystals. 

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