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Fig. 8.14 Major repeat of heparin and a heparin binding aryl amide. Backbone rigidifying H-bonds are shown as dashed lines. inhibitory effect on cholesterol uptake in either model. On the other hand, while none of the previously tested a-peptide inhibitors induced effects in whole CaCO-2 cells, a b-peptide nonamer decreased the absorption rate of radiolabeled cholesterol to background levels (indicated by an increase in T1 2 of cholesterol absorption rate from 102 min to 2.6 h). This suggested...

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The ability to construct relatively rigid helical peptide modules can be used to advantage in the creation of larger designed structures, in which distinct helical segments are connected by a non-helical linking loop. The orientation of two helical modules will then be determined by the conformational properties of the linking segment. Several attempts have been reported to design antiparallel helix-helix motifs using an Aib-rich helical module. In these cases, Gly, Pro and d-amino acids...

Helical Structures Formed upon Adsorption

Tween Detergent

Adsorption of unfolded structures at interfaces can also induce the formation of helical conformations. Hydrophobins are among the best biosurfactants and Fig. 13.9 Self-assembly and conformational equilibria of hydrophobin SC3 in different environments and at different interfaces (Tween detergent poly(ethylene glycol) sorbitan monolaurate with n 20) 22 . (Adapted from ref. 22 .) Fig. 13.9 Self-assembly and conformational equilibria of hydrophobin SC3 in different environments and at different...

Foldamers Based on Solvophobic Effects

Solvophobic effects are responsible for the association of poorly-solvated molecular surfaces and are one of the most important noncovalent forces used by nature in biofoldamers. Unlike specific interactions such as hydrogen bonds, solvophobic effects rely on collective interactions among solvents and solutes instead of specific functional groups for operation. To use solvophobic effects for foldamer design, one must create solvophobic sites or patches along the primary sequence to collapse an...

Adsorbed Sheet Structures at Interfaces

Another important class of secondary structures is the sheet motif. b-Sheet structures are abundant peptide and protein secondary structures, and similar secondary sheet structures are also found in a variety of artificial backbones (see Chapter 4). In most sheet structures, the individual foldamer chains are stretched and intermolecular interactions between different strands lead to the formation of two-dimensional ribbons or sheets via dimerization and further aggregation. A few examples of...

Inversion of Macromolecular Helicity

Right Handed Helix

Another interesting and unique feature of dynamic helical polymers is the reversible helix inversion helix-helix PM transition between right- and left-handed helical conformations regulated by external stimuli, such as a change in temperature, solvent or by irradiation with light. Because the extremely high sensitivity of dynamic helices to a chiral environment arising from a high cooperativity, the formation of an excess of the preferred helical sense can be altered, resulting in the inversion...