A Helicate‐Based Three‐State Molecular Switch

Abstract

The control of structural transformations triggered by external signals is important for the development of novel functional devices. In the present study, it is demonstrated that helicates can be designed to structurally respond to the presence of different counterions and to adopt either a compressed or an expanded structure. Reversible switching is not only possible between those two states, furthermore, the twist of the aggregate also can be controlled. Thus, three out of four possible states of a helicate (expanded/left-handed, expanded/right-handed, compressed/left-handed) based on an enantiomerically pure ester bridged dicatecholate ligand are specifically addressed by introduction, exchange, or removal of countercations. This approach is used to reversibly switch between the different states or to successively address them.

From Hierarchical Helicates to Functional Supramolecular Devices

“…Therefore, two triscatecholate titanium(IV) complex moieties must be connected. In this case, the lithium‐dependent monomer–dimer equilibrium, as described before, would not lead to separate species but in the presence of lithium cations would result in a compressed form [Li 3 ( 14 ) 3 Ti 2 ] − , which expands in the absence of lithium cations to form [( 14 ) 3 Ti 2 ] 4− (Scheme ) …”

“…In this case,t he lithium-dependentm onomer-dimere quilibrium,a sd escribed before,w ould notl eadt o separate speciesb ut in thep resenceo fl ithium cationsw ould result in ac ompressedf orm[ Li 3 (14) 3 Ti 2 ] À ,w hich expandsi nt he absenceo flithium cationstoform[(14) 3 Ti 2 ] 4À (Scheme4). [28] This can be demonstrated by connecting two catechole ster units to long-chain diols and preparing the complexes. For example,t he decyl bridged diester leads in ac oordination study with titanium(IV) ions in the presence of lithium carbonate to the dinuclear helicate that internally binds three lithium cations [Li 3 (14 a) 3 Ti 2 ] À .T he obtained coordination compound represents the compressed form of the "spring".…”

Positive Allosteric Control of Guests Encapsulation by Metal Binding to Covalent Porphyrin Cages

“…Many more complex multidomain regulatory proteins and biological machines that integrate multiple signaling events and long‐range coupled conformational modifications through homotropic or heterotropic binding events have shown to proceed also through allosteric mechanisms . Although the design of 3D hollow structures has led to selective receptors for guest encapsulation and promising molecular nanoreactors, their development as biomimetic allosteric receptors able to control guest complexation through large conformational changes remains a significant challenge . Such a control implies to integrate in the framework of the structure several components with defined regulation and guest binding functions.…”

“…[2,3] Althought he design of 3D hollow structures has led to selective receptors for guest encapsulation and promising molecular nanoreactors, their development as biomimetic allosteric receptors able to control guest complexation through large conformational changes remains as ignificant challenge. [25][26][27][28][29][30][31][32] Such ac ontrol implies to integrate in the framework of the structures everalc omponents with defined regulation and guest binding functions. Moreover,t he structure must ensure the preorganizationo ft he active components, the flexibility for conformational rearrangementsa nd should prevent direct interactions between the recognition and regulation sites.…”

Molecular Springs: Integration of Complex Dynamic Architectures into Functional Devices

“…In addition to the anion‐dependent regulation, supramolecular springs can also be triggered by metal cations such as sodium, potassium, and lithium . In 2010, Yashima et al .…”