Abstract
Much attention has recently focused on helical structures that can change their helicity in response to external stimuli. The requirements for the invertible helical structures are a dynamic feature and well-defined structures. In this context, helical metal complexes with a labile coordination sphere have a great advantage. There are several types of dynamic helicity controls, including the responsive helicity inversion. In this review article, dynamic helical structures based on oligo(salamo) metal complexes are described as one of the possible designs. The introduction of chiral carboxylate ions into Zn3La tetranuclear structures as an additive is effective to control the P/M ratio of the helix. The dynamic helicity inversion can be achieved by chemical modification, such as protonation/deprotonation or desilylation with fluoride ion. When (S)-2-hydroxypropyl groups are introduced into the oligo(salamo) ligand, the helicity of the resultant complexes is sensitively influenced by the metal ions. The replacement of the metal ions based on the affinity trend resulted in a sequential multistep helicity inversion. Chiral salen derivatives are also effective to bias the helicity; by incorporating the gauche/anti transformation of a 1,2-disubstituted ethylene unit, a fully predictable helicity inversion system was achieved, in which the helicity can be controlled by the molecular lengths of the diammonium guests.
Highlights
One of the ubiquitously found higher-order structures in biomolecules is the helical structure, such as α-helix of proteins and complementary double helix in nucleic acids. These helical structures could have a dynamic feature because they are spontaneously formed from flexible molecules via reversible processes and maintained by non-covalent interactions
Chemistry of helical structures based structures based on metal coordination has been initiated from the self‐assembled double helicates that are obtained by complexation of oligobipyridine ligands with metal ions
If the chiral group is relatively small compared with the the helix, shift equilibrium while keeping theP Pand andMMhelices helicesas as the the approximate approximate mirror helix, we we cancan shift thethe equilibrium while keeping the image of each other. This is the basic concept of the dynamic helicity control, which has been used to obtain various dynamic helical structures such such as metal helicates and helical obtainone-handed one‐handedforms formsof of various dynamic helical structures as metal helicates and polymers
Summary
Non-covalent interactions are effectively utilized for obtaining thermodynamically-favored self-assembled structures thanks to reversible processes [1,2]. One of the ubiquitously found higher-order structures in biomolecules is the helical structure, such as α-helix of proteins and complementary double helix in nucleic acids These helical structures could have a dynamic feature because they are spontaneously formed from flexible molecules via reversible processes and maintained by non-covalent interactions. Chemistry of helical structures based structures based on metal coordination has been initiated from the self‐assembled double helicates that are obtained by complexation of oligobipyridine ligands with metal ions [12]. Various on metal coordination has been initiated from the self-assembled double helicates that are obtained that are obtained by complexation of oligobipyridine ligands with metal ions [12]. From the appropriate and linkers [13,14]
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