Sheets/tapes

Aggeli A, Bell M, Boden N et al (1997) Responsive gels formed by the spontaneous self-assembly of peptides into polymeric beta-sheet tapes. Nature 386 259-262... 

Aggeli, A., Bell, M., Boden, N., Keen, J. N., Knowles, P. F., McLeish, T. C., Pitkeathly, M., and Radford, S. E. (1997). Responsive gels formed by the spontaneous self-assembly of peptides into polymeric beta-sheet tapes. Nature 386, 259-262. 

Other self-reinforced polymers are being developed. For example, PURE is based on highly oriented co-extruded tapes of polypropylene and a consolidation binder. Properties vary according to the form (see Table 6.27) - sheets, tapes or fabrics. 

PE, being a commodity polymer, is used in its different physical forms viz. fibres, sheets, membranes, moulds with different backbone chemical configurations (LPE, LLDPE, LDPE, HDPE, UHMWPE, UHSPE etc). Each of these forms of PE requires surface modification at some stage of application. The surfaces of PE fibres are often modified to make them compatible in the composites, whereas PE sheets/tapes are modified to achieve adhesion. Moulds are frequently surface-modified for probability and membranes for selective permeation. In the same way, different chemical configurations of PE, by the virtue of their properties, are used for different applications after surface modification. 

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. 

Robert P.W. Davies, Amalia Aggeli, Neville Boden, Tom C.B. McLeish, Irena A. Nyrkova, and Alexander N. Semenov, Mechanisms and Principles of 1 D Self-Assembly of Peptides into ft-Sheet Tapes... 

Figure 4.9 Model for the hierarchical selforganization of A-l. (a) E forms tapes comprising two covalently linked single parallel P-sheet domains with opposite orientation, (b) F-l aggregate into more flexible and less stable single antiparallel P-sheet tapes, (c) Tapes obtained by parallel P-sheet formation from A-D are polar...

The use of self-assembling peptides is also explored beyond the medical, pharmaceutical, or cosmetics industry. Areas of interest are among others functional foods, electronics, functional coatings, and catalysis (but different from enzyme research). As an example, peptides can be designed to switch from a random coil-like primary structure organization into an a-helix or [3-sheet secondary structure with unique properties. Short peptides align to form [3-sheet tapes with different functionalities, for example, hydrophilic and hydrophobic on either side of the tape to form monolayer coatings (Boden et al., 1996). 

Figure 16 In situ AFM images of single P-sheet tapes grown on mica from 5 (XM Pu-2 in 10% H20 in 2-propanol. The tapes are aligned with the hexagonal symmetry of the underlying mica lattice (Whitehouse et al., 2005).

Carrick, L.M., Aggeli, A., Boden, N., Fisher, J., Ingham, E., and Waigh, T.A. "Effect of ionic strength on the self-assembly, morphology and gelation of pH responsive beta-sheet tape-forming peptides". Tetrahedron 63(31), 7457-7467 (2007). 

Aggeli, A., Nyrkova, I.A., Bell, M., Harding, R., Carrick, L., McLeish, T.C.M., Semenov, A.N., and Boden, N. "Hierarchical self-assembly of chiral rod-like molecules as a model for peptide-sheet tapes, ribbons, bris and bers". Proc. Nat. Acad. Sci. U.S.A. 98,11857-11862 (2001). Attri, A.K., Lewis, M.S., and Korn, E.D. "The formation of actin oligomers studied by analytical ultracentrifugation". ]. Biol. Chem. 266, 6815-6824 (1991). 

Fig. 12 Schematic representation of the self-assembly of a growing antiparallel 8-sheet tape...

Small-strain oscillatory shear experiments show that the /1-sheet tapes form elastic gels over the whole frequency window (10 -10 rads ), implying that the relaxation time of the network is very long [48]. 

In the case of oligopeptides which form dynamic antiparallel /1-sheet tapes (Sect. 2.1.5), chirality of the amino-acids is directly responsible for the twisting of the tapes [142,143]. Moreover, the lateral aggregation of the tapes can lead to the formation of fibrils of discrete thickness, and is in fact controlled by the twisting of the tapes [144-146]. 

As an illustration of the second approach to biosynthesis, the work of Boden et al. will be taken as an example. Again the first step is to identify an interesting motif to be incorporated in a molecule. The motif that they have focussed on is the P-sheet. By incorporating a sequence which facilitates the formation of this structure it becomes possible to form a peptide which spontaneously self-assembles into P-sheet tapes. In appropriate solvents these peptides can form gels whose rheological properties can then be controlled by external parameters such as pH. Thus, what they have termed rational design coupled with the peptide synthesiser may yield macromolecules with a specific set of controlled properties. 

---