Selective Host–Guest Binding of Anions without Auxiliary Hydrogen Bonds: Entropy as an Aid to Design

Abstract

Entropy matters! In contrast to classic host–guest design, which employs dedicated enthalpic interactions of the binding partners, the novel electroneutral host 1 binds its anionic guests by virtue of an overwhelmingly positive entropy of association. The prime driving force is guest desolvation. Despite the total omission of hydrogen bonding, host 1 is one of the best electroneutral receptors known for binding anions in polar solution.

Different and Often Opposing Forces Drive the Encapsulation and Multiple Exterior Binding of Charged Guests to a M4L6 Supramolecular Vessel in Water

“…Encapsulation of the investigated guests into the cavity of 1 is always an entropy‐driven process . Desolvation of the cationic guests and the release of water molecules from the interior of the empty (solvent filled) host to the bulk of the solvent explain the large entropic gain observed .…”

“…[35] Desolvationo ft he cationic guests and the release of water molecules from the interior of the empty (solvent filled) host to the bulk of the solvent explain the large entropic gain observed. [35] Desolvationo ft he cationic guests and the release of water molecules from the interior of the empty (solvent filled) host to the bulk of the solvent explain the large entropic gain observed.…”

“…Encapsulation of the investigated guests into the cavity of 1 is always an entropy-driven process. [35] Desolvationo ft he cationic guests and the release of water molecules from the interior of the empty (solvent filled) host to the bulk of the solvent explain the large entropic gain observed. [36][37][38][39][40] The encapsulation process is also favored by enthalpy in all cases;t his slightly favorable enthalpy of encapsulation is not the sole result of attractive host-guest interactions but also ac onsequence of the releaseo f" high-energy water" molecules from the host cavity to the bulk upon guest inclusion.…”

Aqueous Sulfate Separation by Sequestration of [(SO4)2(H2O)4]4− Clusters within Highly Insoluble Imine‐Linked Bis‐Guanidinium Crystals

“…Thus, this example of selective sulfate crystallization as sulfate–water clusters represents a complex recognition phenomenon that extends far beyond the simple lock‐and‐key principle commonly invoked in supramolecular chemistry . It involves a multitude of factors, including the mutual recognition of molecular and ionic components, a fine interplay of enthalpy and entropy, and a series of binding, self‐assembly, and solvent exchange events that lead in the end to the nucleation and growth of highly insoluble crystals. Understanding and ultimately controlling all these factors through systematic crystal engineering and structure–solubility relationship studies offer prospects for predictive design of advanced separation systems for sulfate and other environmentally and energy relevant anions.…”

Relevance of the Entropy Factor in Stereoselectivity Control of Asymmetric Photoreactions

“…It is clear that the enthalpy term for the enantioselection process is compensated to some degree by the entropy factor, to eventually determine the observed enantiomeric excess at a given temperature. In the presence of (R)- [10]paracyclophane-12-carboxylate as the sensitizer, (Z)-cyclooctene T. Mori Account Syn lett (7) and (Z,Z)-1,5-cyclooctadiene (8) were photochemically isomerized into the corresponding chiral (E)-and (E,Z)-isomers in up to 44% and 87% enantiomeric excess, respectively, through effective planar-to-planar chirality transfer. 25 Again, the differential enthalpies were compensated by the differential entropy to considerable degrees, and the interplay of both parameters controls the observed enantioselectivity.…”