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

Abstract

The supramolecular recognition of closo,closo- [B 21 H 18 ] À by cyclodextrins (CDs) has been studied in aqueous solution by isothermal titration calorimetry and nuclear magnetic resonance spectroscopy. These solution studies follow up on previous mass-spectrometric measurements and computations, which indicated the formation and stability of CD · B 21 H 18 À complexes in the gas phase. The thermodynamic signature of solutionphase binding is exceptional, the association constant for the γ-CD complex with B 21 H 18 À reaches 1.8 × 10 6 M À 1 , which is on the same order of magnitude as the so far highest observed value for the complex between γ-CD and a metallacarborane. The nature of the intermolecular interaction is also examined by quantum-mechanical computational protocols. These suggest that the desolvation penalty, which is particularly low for the B 21 H 18 À anion, is the decisive factor for its high binding strength. The results further suggest that the elliptical macropolyhedral boron hydride is another example of a CD binder, whose extraordinary binding affinity is driven by the chaotropic effect, which describes the intrinsic affinity of large polarizable and weakly solvated chaotropic anions to hydrophobic cavities and surfaces in aqueous solution.

Two Shared Icosahedral Metallacarboranes through Iron: A Joint Experimental and Theoretical Refinement of Mössbauer Spectrum in [Fe(1,2-C2B9H11)2]Cs

“…An archetype of these systems is obviously a hypothetical [B 23 H 22 ] 2– with a common naked boron atom instead of the metal . Three and four naked boron atoms appear to act as joint vertices in experimentally available B 21 H 18 – and B 20 H 16 . Alternatively, two [ nido -C 2 B 9 H 11 ] (2−) moieties that are similar with the cyclopentadienyl ligand, in particular, in terms of the NICS values assessing aromaticities also in individual fragments of 3D aromatic systems, which confirms isolobal and isoelectronic relation of such open pentagonal belts, both successfully sandwich various metal cations, − with the common labeling MSan, where M is a transition-metal atom with a given oxidation state, and “San” is an abbreviation for “Sandwich”.…”

Mikromolare Affinität und höher: synthetische Wirt‐Gast‐Komplexe mit hoher Stabilität

“…Die Bildung des Wirt-Gast-Komplexes wurde durch den sogenannten chaotropen Effekt erklärt, der die starke Interaktion großer und polarisierbarer Anionen beschreibt, die mit dem hydrophoben Innenraum geeigneter Wirte solvatisiert sind. [98] Petter et al realisierten einen einfachen und eleganten Ansatz, um die Bindungsaffinität auf mikromolarer Ebene zu erhöhen, indem sie zwei β-Cyclodextrineinheiten über eine Disulfidbrücke (S-S-Brücke) nah beieinander platzierten. Auf diese Weise erreichten die Autoren außergewöhnliche Bindungsaffinitäten für die Komplexbildung von Farbstoffen wie Methylorange (MO, K a = 5.8 × 10 5 M À 1 ) und Ethylorange (EO, K a = 2.0 × 10 6 M À 1 ) in einer Wasser/Carbonat-Pufferlösung bei pH 10.5.…”

How areN-methylcarbamates encapsulated by β-cyclodextrin: insight into the binding mechanism

“…[1][2][3] The most frequently used strategy for investigating host-guest systems is to combine experiments with molecular simulations. [1][2][3][4] Recently, there has been a surge in pure theoretical studies that have provided new insights into the binding mode and interaction mechanism of host-guest systems. [5][6][7][8][9][10][11][12][13][14][15][16] b-Cyclodextrin (b-CD) is one of the most common and significant host molecules and is internally hydrophobic and externally hydrophilic, and is often used to encapsulate guest molecules containing a phenyl group.…”

“…1–3 The most frequently used strategy for investigating host–guest systems is to combine experiments with molecular simulations. 1–4 Recently, there has been a surge in pure theoretical studies that have provided new insights into the binding mode and interaction mechanism of host–guest systems. 5–16…”