Self-assembling fiber

Kato T, Mizoshita N, Moriyama M, Kitamura T (2005) Gelation of Liquid Crystals with Self-Assembled Fibers. 256 219-236 Kaul M, see Pilch DS (2005) 253 179-204... 

Figure 9.12 (a) AFM image of spin-cast 15d 16d from benzene showing cylindrical nanodomains from the microphase separation of the supramolecular block copolymer and (b) AFM image of spin-cast 15b 16b from benzene showing self-assembled fibers. 

The surface stability of other self-assembling fiber systems such as EAK16-II have been extensively characterized (Yang et al., 2007). These fibers are stable on HOPG under both acidic and basic conditions, most... 

Other applications use self-assembling fibers to coat materials. For example, preassembled peptide amphiphiles have been covalently immobilized on titanium implant surfaces via a silane layer (Sargeant et al., 2008). Primary bovine artery endothelial cells or mouse calvarial preosteoblastic cells spread on these coated surface and proliferated to a far greater extent than on samples where the peptide amphiphiles had been drop cast onto the metal surface. This study therefore suggests that covalent attachment is required in order to prevent fibers lifting from the coated surface and to encourage maximal cell growth. 

Wolffs M, George SJ, Tomovic Z et al (2007) Macroscopic origin of CD-effects by alignment of self-assembled fibers in solution. Angew Chem Int Ed Engl 46 8203-8205... 

Spada GP (2008) Alignment by the convective and vortex flow of achiral self-assembled fibers induces strong circular dichroism effects. Angew Chem Int Ed Engl 47 636-638... 

Fig. 21. Top schematic representation of the subsequent aggregation and gelation processes with the Pt(II) complex. Middle fluorescence microscopy images of the aggregates, and (right) of the gel. Bottom (left and center) SEM micrographs of the self-assembled fibers and TEM micrograph (bottom, right) of the self-assembled gel. Reproduced with the permission of Wiley-VCH (217).

Komatsu, T., Yanagimoto, T., Furubayashi, Y., Wu, J. and Tsuchida, E. (1999) Self-assembled fibers made of lipidporphyrinato-zinc(II) and -iron(II) complexes with an intramolecular coordinated axial imidazole, Langmuir, 15, 4427M433. 

Woolfson et al. reported the design of a self-assembling fiber (SAP) system [73] that comprises two complementary de novo designed leucine zipper peptides. Due to complementary interactions in the core and flanking ion pairs, the two peptides combine rapidly to form partly helical staggered heterodimers. These heterodimers have sticky ends to promote their lateral noncovalent association into extended coiled-coil fibers. 

V. Duzhko, K.D. Singer, Self-assembled fibers of a discotic phthalocyanine derivative internal structure, tailoring of geometry and alignment by a direct current electric field. J. Phys. Chem. C 111, 27-31 (2007)... 

Methods for Probing Chirality in Self-assembled Fibers. 194... 

Chirality seems to be intimately associated with the growth and stabdity of self-assembled fibrillar networks of small organic molecules and with the most common macroscopic property of these networks, which is the ther-moreversible gelation of the solvent. The importance of chirality is apparent both at the molecular scale and at the scale of the self-assembled fibers, which typically ranges from nanometers to micrometers. This chapter attempts to review literature data about both these aspects. 

On the other hand, molecular chirahty is sometimes expressed at a much larger scale in the morphology of self-assembled fibers. Elongated, fibrous objects such as rods, tapes, or tubes may be helically twisted, coiled, or wound around one another, and therefore exist in a left-handed or a right-handed form. These intriguing shapes can often be simply visualized by microscopic techniques and have fascinated both chemists and physicists. The third section of this chapter aims to illustrate the structural variety of these objects and the extent to which their formation can be altered and their shapes tuned upon changing the experimental conditions. It also gives a perspective of the... 

The fourth section of the chapter focuses on the various approaches to experimentally address chirality in self-assembled fibers. The unique chi-roptical properties of chiral molecules can be studied by circular dichro-ism and give access to valuable information about the conformations and relative positions of the molecules in the fibers. This section also gives an overview of the techniques that have been used to observe and assign fiber handedness. 

One of the reasons why gels and self-assembled fibers affracf so much attention is their very high potential for applications. The last section of this chapter addresses applications which specifically make use of chirality, such as those based on enantioselective molecular recognition, or those based on the use of chiral fibers as templates for the generation of helical arrays of proteins or of chiral inorganic materials. 

Fig. 2 Electron micrograph of AT-octyl-D-gluconamide self-assembled fibers and 3D model of four entwined ribbons [71,72]. Image kindly provided by Dr. BOttcher...

The various relations that can be established between molecular chirality and fiber handedness are worth a detailed presentation. The general rule is that the handedness of a chiral self-assembled fiber is controlled by the stereochemistry of the molecule. One enantiomer gives a right-handed fiber and the other enantiomer a left-handed fiber. However, there are some rare cases where a pure enantiomer of a chiral molecule assembles into a mixture of right- and left-handed helices. This is the case for the phosphonate analogues of diacetylenic lipid 22 (Fig. 8) [98-100], for cholesteryl anthryloxy-butanoate [83], or for a mixture of a bile salt, a phosphatidylcholine, and cholesterol (Fig. 9) [101]. In the latter case, in addition to the fact that both right- and left-handed helical ribbons are observed, two or three different and well-defined helical pitches coexist (Fig. 9) [101]. 

Various tools may be used to probe intramolecular and intermolecular interactions and to study molecular packing in self-assembled fibers infrared or UV/Vis absorption spectroscopy fluorescence spectroscopy NMR spectroscopy X-ray diffraction and X-ray scattering etc. In this section we focus on the techniques that may provide information related to chirality. 

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... 

Gelation of Liquid Crystals with Self-Assembled Fibers... 

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