Host–Guest Binding Hierarchy within Redox‐ and Luminescence‐Responsive Supramolecular Self‐Assembly Based on Chalcogenide Clusters and γ‐Cyclodextrin

Abstract

Water-soluble salts of anionic [Re Q (CN) ] (Q=S, Se, Te) chalcogenide octahedral rhenium clusters react with γ-cyclodextrin (γ-CD) producing a new type of inclusion compounds. Crystal structures determined through single-crystal X-ray diffraction analysis revealed supramolecular host-guest assemblies resulting from close encapsulations of the octahedral cluster within two γ-CDs. Interestingly, nature of the inner Q ligands influences strongly the host-guest conformation. The cluster [Re S (CN) ] interacts preferentially with the primary faces of the γ-CD while the bulkier clusters [Re Se (CN) ] and [Re Te (CN) ] exhibit specific interactions with the secondary faces of the cyclic host. Furthermore, analysis of the crystal packing reveals additional supramolecular interactions that lead to 2D infinite arrangements with [Re S (CN) ] or to 1D "bamboo-like" columns with [Re Se (CN) ] and [Re Te (CN) ] species. Solution studies, using multinuclear NMR methods, ESI-MS and Isothermal titration calorimetry (ITC) corroborates nicely the solid-state investigations showing that supramolecular pre-organization is retained in aqueous solution even in diluted conditions. Furthermore, ITC analysis showed that host-guest stability increases significantly ongoing from S to Te. At last, we report herein that deep inclusion alters significantly the intrinsic physical-chemical properties of the octahedral clusters, allowing redox tuning and near IR luminescence enhancement.

The Chaotropic Effect as an Assembly Motif in Chemistry

“…Te and the entropy-enthalpy correlation resembled that of other superchaotropic anions,n amely B 12 X 12 2À . [27] TheB 12 H 11 SH 2À ion has recently shown potential as an inorganic capping ligand to stabilize gold nanoparticles. [21,153] This allows for the creation of hierarchical supramolecular architectures on the surface of gold nanoparticles through strong host-guest complexation between the dodecaborate anions and an amphiphilic calixarene (Figure 5a).…”

“…[3,19,20] Thee ffect becomes particularly pronounced for superchaotropic ions that reach beyond the classical Hofmeister scale. [10,18] Thechaotropic effect extends to molecular recognition events with macrocyclic hosts, [10,12,[21][22][23][24][25][26][27] biologically relevant interactions with proteins and peptides, [13,[28][29][30][31][32] association to small organic molecules, [10,33] binding to membranes, [17,[34][35][36][37][38] polymers, [39] as well as colloids, [15,18,40] and it manifests itself in solid-state structures between superchaotropic ions and organic components. [10,12,26,41,42] Thet erms "chaotropic effect" and "superchaotropic ions" have been readily absorbed by the chemical literature in different contexts.…”

Face‐Fusion of Icosahedral Boron Hydride Increases Affinity to γ‐Cyclodextrin: closo,closo‐[B21H18]− as an Anion with Very Low Free Energy of Dehydration

“…The ITC data showed that the complexation is enthalpically driven. The large Δ H values are compensated by large entropic penalties, which are jointly in line with the thermochemical fingerprint of the chaotropic effect …”

“…The complexation of closo ‐B 12 X 12 2− to the hydrophobic inner cavity of CDs appears counterintuitive at first glance, due to the doubly negative charge of these clusters and their high water solubility (hydrophilicity). The high affinity of such large anionic clusters, not only borate clusters but also others such as polyoxometalates or octahedral metal clusters, to hydrophobic cavities as well as to neutral surfaces, membranes, and proteins has been described as the chaotropic effect that presents a topic of considerable current interest. Accordingly, the propensity of anionic clusters to associate to hydrophobic cavities has been attributed to ( i ) the comparative ease of desolvation of the large clusters in combination with ( ii ) the stabilization of the resulting assemblies by dispersion interactions, promoted by the high polarizability of these large anions.…”

Encapsulation of Chaotropic closo‐Decahydrodecaborate Clusters Within Cyclodextrins: Synthesis, Solution Studies, and DFT Calculations

“…On their side, α‐, β‐ and γ‐Cyclodextrins (CDs) are natural macrocyclic oligosaccharides comprised of 6, 7 and 8 linked d ‐glucopyranose units respectively. The interest in CD research mainly arises from their ability to act as robust hosts to a wide variety of organic or inorganic guest species, as a consequence of their hydrophobic annuli being able to form host‐guest complexes in aqueous solution. This property makes them very useful for drug delivery in living systems.…”