Tuning the chaotropic effect as an assembly motif through one-electron transfer in a rhenium cluster

Anton Ivanov (1) , Clement Falaise (2) , David Landy (3) , Mohamed Haouas (2) , Yuri V Mironov , Michael A Shestopalov , Emmanuel Cadot (2)

1 JPL - Jet Propulsion Laboratory
2 ILV - Institut Lavoisier de Versailles
3 UCEIV - Unité de Chimie Environnementale et Interactions sur le Vivant

We report how only one electron transfer from the hydrophilic reduced cluster [{Re 6 Se 8 }(CN) 6 ] 4-induces both a dramatic increase of the host-guest affinity with γ−cyclodextrin and a drastic alteration of the supramolecular dynamics. This striking behaviour, underlined by its thermochemical fingerprint, evidences the self-assembly process is driven by chaotropic effect. Supramolecular approach for designing smart materials are of considerable interest on account of wide range of newfound potential applications which can be imparted in diverse fields such as medicine, energy conversion, information storage, and green catalysis. Mimicking the "lock and key" systems functioning in biological machinery such as receptor-effector recognition in proteins, 1 this conceptual approach targets to develop molecular devices built from complex self-assembled structures, 2 as tools for electronic and biological interfacing 3 or synthetic self-replicating systems. 4 Cyclodextrins (CDs) are cyclic oligosaccharides built from glucopyranose units, which have already shown to behave as effective host to encapsulate different hydrophobic entities to form biomedical drugs. 5 Recently, inorganic species such as dodecaborates, 6,7 polyoxometalates 8-11 or metal cluster complexes 12-14 were found to form inclusion complexes with one or two CDs existing both in water solution and solid-state. Solvent effects arising from these ionic species have been identified as the main contributor to the host-guest self-assembly processes in these systems. 15 More precisely, their water structure-breaking ability, namely the chaotropic effect favours creation of host-guest interface through desolvation process, resulting from the water structure reconstruction, pointed as the main contributor of the supramolecular recognition. Furthermore, the extremely large magnitude of this effect featured by highly stable supramolecular adducts allowed considering such fascinating phenomenon as an effective assembly motif in supramolecular chemistry, opening new avenues for designing multifunctional soft materials. 15 In context, special attention is given to octahedral rhenium cluster complexes [{Re 6 Q 8 }L 6 ] n due to their redox and photoluminescence properties, and high radiodensity, 16 which in combination with solubility increase in aqueous CD media are promising for numerous applications ranging from photodynamic therapy 17 or computed tomography 18 to photocatalysis. 19 Previous reports have shown the host-guest affinity depends on both inner and apical ligands of the octahedral cluster and also on the size of cyclodextrins (Fig. 1), demonstrating that several contributors operate within the host-guest recognition process. 12-14 Figure 1 Structural representations of molecular components used as guest and host units. The [{Re6Se8}(CN)6] 3-/4-cluster contains six rhenium ions (green sphere) disposed on the octahedron corners while the selenium atoms (inner ligand) are located on the eight faces of the octahedron and the terminal cyano groups (outer ligands) complete the coordination sphere of the rhenium atoms. The γ-cyclodextrin macrocycle C48H80O40 results from the condensation of eight glucopyranose units {C6H10O5} and delimits a large inner cavity of about 10 Å in diameter. Herein, we report how a single-electron transfer leading to the oxidized species [{Re 6 Se 8 }(CN) 6 ] 3-from the reduced one [{Re 6 Se 8 }(CN) 6 ] 4-affects drastically the host-guest stability in solution. While keeping constant the cluster composition and

Domaines: Chimie

Anton Ivanov, Clement Falaise, David Landy, Mohamed Haouas, Yuri V Mironov, et al.. Tuning the chaotropic effect as an assembly motif through one-electron transfer in a rhenium cluster. Chemical Communications, 2019, 55 (67), pp.9951-9954. ⟨10.1039/c9cc05136h⟩. ⟨hal-02335733⟩