Micellar fibres with crystalline surfaces and their co-crystallization

Abstract

Amphiphiles with an amide bond between the head group and the hydrophobic chain show strong binding interactions between the members of micellar fibres. The surface of such fibres has high curvature and becomes crystalline. This is shown, for example, by very regular helicities, sharp melting points at which dissolution of the fibres occur, the amide I infrared band at 1650 cm⁻¹, and solid state NMR spectra. Furthermore, diastereomeric glyconamides (glucon, gulon, talon) form crystals with very different sheet arrangements (head to tail or tail to tail) and hydrogen bond patterns (homodromic or other cycles). The same diastereomers also form molecular assemblies of extremely different curvatures (bimolecular rods, ribbons, scrolls, tubules and sheets). There are strong correlations between interactions in crystals and molecular assemblies. The micellar structures with crystalline surfaces should not be stable. They should quickly rearrange to three-dimensional crystals with much smaller surface energies. Effects which impede in such a rearrangement are discussed (e.g. chiral bilayer effect, dissolution of crystallization nuclei). Guest molecules can only be included into the micellar fibres by co-crystallization processes. The fibres thus obtain the character of covalent polyamides or proteins with selective uptake of functional molecules such as porphyrins. The crystalline micellar fibres are thus sharply differentiated from the usual micellar aggregates. Hydration and steric forces lead to head group repulsion and the viscous liquid character of the much less organized molecular assemblies.