Fibrillization chiral self-assembly

To illustrate the diversity of chiral inorganic objects that can be obtained by transcription of chiral self-assembled fibers as organic templates, even double-helical silica has been produced. Gels of a mix of sugar-based gela-tors produce double-helical silica nanotubes by transcription (Fig. 26) [180]. In addition, gels of gemini smfactant 23 (Scheme 4) produce double-helical fibrils of silica [181]. In the latter case, the continuous variation of the pitch... 

Fig. 10 (a-f) Hierarchical self-assembly model for chiral rod-like units A curly tape (c ), a twisted ribbon (d ), a fibril (e ) and a fibre (f). Adapted from Aggeli et al. [20], Copyright 2001 National Academy of Sciences, USA... 

Figure 5.24 Model of hierarchical self-assembly of chiral rodlike monomers.109 (a) Local arrangements (c-f) and corresponding global equilibrium conformations (c -f) for hierarchical selfassembling structures formed in solutions of chiral molecules (a), which have complementary donor and acceptor groups, shown by arrows, via which they interact and align to form tapes (c). Black and the white surfaces of rod (a) are reflected in sides of helical tape (c), which is chosen to curl toward black side (c ). (b) Phase diagram of solution of twisted ribbons that form fibrils. Scaled variables relative helix pitch of isolated ribbons h hh /a. relative side-by-side attraction energy between fibrils eaur/e. Reprinted with permission from Ref. 109. Copyright 2001 by the National Academy of Sciences, U.S.A.

Aggeli, A., Nyrkova, I. A., Bell, M., etal., Hierarchical self-assembly of chiral rod-like molecules as amodel for peptide beta-sheet tapes, ribbons, fibrils, and fibers. Proc. Natl. Acad. Sci. U. S. A. 2001,98, 11857-11862. 

Peptides composed of various coded and noncoded amino acid residues self-assemble to form various types of supramolecular architectures, including supramolecular helices and sheets, nanotubes, nanorods, nanovesicles, and nanofibers. The higher-order self-assembly of supramolecular (3-sheets or supramolecular helices composed of short synthetic acyclic peptides leads to the formation of amyloid-like fibrils. Synthetic cyclic peptides were used in supramolecular chemistry as molecular scaffolding for artificial receptors, so as to host various chiral and achiral ions and other small neutral substrates. Cyclic peptides also self-assemble like their acyclic counterparts to form supramolecular structures, including hollow nanotubes. Self-assembling cyclic peptides can be served as artificial ion channels, and some of them exhibit potential antimicrobial activities against drug-resistant bacteria. 

Recently, aerogels based on peptides were synthesized [41] as well. Self-assembling of the fibril network was observed and chiral, nanostructured low-density aerogels out of the resulting gel. This product can be used for sensing, tissue engineering, and drug release. 

In some cases, nanoscale chirality can be observed by using electron microscopy methods, for example, in the form of self-assembled helical fibrils/fibers. It has been reported that using opposite enantiomers as gelators can give rise to fibers with opposite heUcities (Figure 1). In this way, chirality on the molecular scale is directly translated into chirahty on the nanoscale. 

The systems described above formed linearly extended, fibrous self-assemblies, although the morphological structures depended on amphiphiles. The molecular arrangement in fibers were maintained by the formation of concentric multilamellar bilayer, besides hydrophobic interaction and hydrogen bonding, except C Asp fibers with chiral character. The assemblies underwent temperature-dependent fibril-vesicle transition. The fibril-vesicle transition resulted from the rearrangement of bilayers. Generally, multilamellar layers were diminished in ves-... 

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