Fibrils, self-assembly

Dinca and colleagues (2008) have combined fibril self-assembly, lithographic features, and covalent and noncovalent binding to create three-dimensional patterned fibrillar structures that could be used in electronics or tissue engineering. Images of these structures, which are described as fibril bridges, are shown in Figure 15. 

Fibrils self-assemble in the extracellular space, as desaibed in Section 9.03.2.1. Only later, this stmcture is stabilized and mechanically reinforced by chemical cross-links between the molecules. For a recent review on cross-linking in collagen, see Avery and Bailey. There are different types of cross-links that... 

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... 

For instance, Pn-2 forms ribbons at concentrations >0.1 mM in water. At 0.6 mM, these ribbons self-assemble into fibrils and at higher concentrations into fibres. Conversely, glutamine-rich Pn-1 (Ac-QQRQQQQQEQQ-Am) forms ribbons at 1 mM and does not form fibrils, even at concentrations as high as 25 mM. Association of Pn-2 into ribbons is much more favourable due to it having hydrophobic aromatic residues arranged such that there is a large disparity between the hydrophobicity of each of its tape faces. 

For technological applications it is highly desirable to be able to design self-assembling systems to have particular physico-chemical properties under a given set of experimental conditions. Using computer simulation, it is possible to construct an atomistic model of tapes, ribbons and fibrils to study all of the interatomic interactions within the system in a quantitative manner. Figure 13 shows atomistic... 

Self-assembly is not restricted to merely a mixture of functionalised and non-functionalised, but otherwise identical, sequences. It is possible to use distinct sequences in mixtures and combine functionality. The formation of modified fibrils... 

Mixtures of three peptides were also screened for their ability to form fibrils containing all three. Rather than testing all possibilities, carefully selected mixtures were used. Peptides in the equimolar mixtures were charged, but the overall sum of the peptide charges was zero, to build in chain-chain electrostatic attractions. If individual peptides or a peptide pair in a mixture formed fibrils, the mixture was not studied. Application of these criteria led to six possible mixtures these were mixed at 4 pM each at pH 7.4 and left for several days at room temperature to self-assemble. 

Lamm MS, Rajagopal K, Schneider JP et al (2005) Laminated morphology of nontwisting beta-sheet fibrils constructed via peptide self-assembly. J Am Chem Soc 127 16692-16700... 

Meegan JE, Aggeli A, Boden N et al (2004) Designed self-assembled beta-sheet peptide fibrils as templates for silica nanotubes. Adv Fund Mater 14 31-37... 

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.

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