Selenium Substitution-Induced Hydration Changes of Crown Ethers As Tools for Probing Water Interactions with Supramolecular Macrocycles in Aqueous Solutions

Abstract

Understanding of aqueous solutions is of significance to a wide range of fields. Crown macrocycles emerge as a new generation of model hosts for studying the chemistry of water and aqueous supramolecular chemistry. Herein, we present the oxacrown ether cyanobenzo-21-crown-7 ether (C7CN), and its selenium-containing counterpart selencrown ether C7SeCN possess only one chalcogen atom diverse in structure but exhibits dramatic difference in shape, solvation (e.g., hydration), and consequent thermodynamics of guest binding experimentally. The hydrogen bond strength of Se···H is similar to that of O···H, but theoretical calculations pointed out that there is a prominent electrostatic potential change for the entire molecule caused by Se substitution, which leads to the decrease of the interactions between water clusters and crown macrocycles thermodynamically and kinetically. Results established that C7CN and C7SeCN provide an easy-to-access model pair to exclusively probe water–solute interaction and host pocket wettability change caused by one atom substitution.

The aqueous supramolecular chemistry of crown ethers

“…Interestingly, C7COOH exhibits upper critical solution temperature (UCST) behavior followed by LCST phase behavior, implying that the benzo-group functionalization is instrumental in modulating the thermo-responsiveness of the CEs. Substituting the O atom opposite the benzo-moiety on the CE with an Se atom transformed the C7CN from hydrophilic to strongly hydrophobic, and the aqueous solubility of C7SeCN decreased to 1 mM (Figure 1) (Jin et al, 2019). Using detailed computer modeling, the solvation free energies (ΔG θ s ) of C7CN and C7SeCN were calculated to be −104.21 and −81.82 kJ/mol, respectively, which are in accordance with the experimentally determined solubility trend.…”

The Prodigious Hydrogen Bonds with Sulfur and Selenium in Molecular Assemblies, Structural Biology, and Functional Materials

“…54 Various attributes of S/SeCHBs can be harnessed in manipulation of ensembles of molecular units for targeting specific functionalities. 52,53 A unique example is the molecular design and effective supramolecular folding of phenoselenazine molecules, as seen from Figure 6B, that yields two conformers exhibiting dual characteristics of room temperature phosphorescence (RTP) and thermally activated delayed fluorescence. An enhancement was noted in phosphorescence radiative decay with the use of selenium instead of sulfur.…”

“…An enhancement was noted in phosphorescence radiative decay with the use of selenium instead of sulfur. Such H-bonds were also demonstrated to be useful in changing solvation and guest-binding ability and solvation in host macrocycles like cyanobenzo-21-crown-7 ether 53 (more examples are provided in Supporting Information).…”

“…The unique directionality of these S/SeCHBs is often exploited in engineering diverse supramolecular architectures. ,− Effective H-bond donor–acceptor interactions can dictate the packing patterns (as depicted in Figure A) within the crystal structures and can also be responsible for assisting in their stereoselective synthesis . Various attributes of S/SeCHBs can be harnessed in manipulation of ensembles of molecular units for targeting specific functionalities. , A unique example is the molecular design and effective supramolecular folding of phenoselenazine molecules, as seen from Figure B, that yields two conformers exhibiting dual characteristics of room temperature phosphorescence (RTP) and thermally activated delayed fluorescence. An enhancement was noted in phosphorescence radiative decay with the use of selenium instead of sulfur.…”