Stiffening the Helix

In principle, stable, regular polyisocyanides can be formed by polymerization reactions that are under (i) thermodynamic control (driving force AGab) or (ii) kinetic control (driving force AGBz AGAz) (Fig. 12.8). The different possibilities are depicted in Fig. 12.8, for a polymerization of monomer M to a polymer with monomer units in conformations P-MA and P-MB, which might correspond to structures that differ in helicity, backbone (s-cis)-(s-trans) isomerism or imine syn-anti isomerism (only...

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Distribution of Physicochemical Properties 8.2.2.1 Antimicrobial Peptoids Antimicrobial amphiphilic peptides such as magainin-II and defensins are a widely distributed component of eukaryotic and prokaryotic host immune systems 152-154 . Although magainin-II forms an a-helix and defensins form b-sheets, both are amphiphilic and display a facial distribution of cationic and hy-drophobic groups on the folded structures 152-154 . While the mechanism of action remains to be fully understood, it is...

Hindered Polymer and Oligomer Backbones

Attractive interactions play a major role in determining conformation and are easily identified in the structures as they result in a close proximity between the groups involved. Repulsive interactions are no less important. However, since repulsive interactions often result in some distance between the groups that repel each other, they are sometimes overlooked, and definitely less commonly used in design. Steric effects represent one very large class of repulsive interactions. As shown in the...