Binary twinned-icosahedral [B₂₁H₁₈]⁻ interacts with cyclodextrins as a precedent for its complexation with other organic motifs

Abstract

The weakly coordinating binary macropolyhedral anion closo,closo- [B 21 H 18 ]À (B21; D 3h symmetry) has been synthesized using a simplified strategy compared to that in the literature. While gas-phase complexes of B21 with b-and c-cyclodextrin (CD) were detected using ESI FT-ICR spectrometric measurements, a-CD did not bind to the B21 guest. This spectroscopic evidence has been interpreted using quantum-chemical

The Chaotropic Effect as an Assembly Motif in Chemistry

“…Understanding the driving forces between ions and concave binding sites is therefore of prime importance for the supramolecular design of synthetic receptors with defined affinity and selectivity.A ccordingly,t he unexpectedly high binding affinities of superchaotropic anions and the chaotropic effect as ag eneric driving force have recently found their entry into the important area of anion recognition. [44,65,117,[131][132][133][134][135][136][137][138][139][140][141][142][143] In follow-up studies with inclusion complexes,the affinity of dodecaborate clusters to cyclodextrins (CDs) has been extended to the larger CD homologues (Figure 3) [23] as well as other borate clusters, [14,144] both in solution and in the gas phase. [14,23,24] Theb inding propensity of borate clusters has also been demonstrated for calixarenes [21] and at etrathiafulvalene host [24] as an alternative macrocyclic host (Figure 3).…”

“…[1][2][3][4][5][6] Specific-ion solvation has additionally been related, since Hofmeister, to the kosmotropic (water-structure-forming) and chaotropic (water-structure-breaking) properties of ions. [7][8][9] Following up on scattered reports on the unusual behavior of large anions, [10][11][12][13][14][15][16][17][18] the propensity of these anions to associate with hydrophobic and neutral polar phases has recently been generalized and named the chaotropic effect, contrasting the hydrophobic effect as ad istinct assembly motif in chemistry. [3,19,20] Thee ffect becomes particularly pronounced for superchaotropic ions that reach beyond the classical Hofmeister scale.…”

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

“…[2] B21 exhibits a low chemical reactivity, which resists most reaction conditions except for fluorination. [3] However, complexation of the potassium salt of B21 with β‐ and γ‐cyclodextrin (CDs, naturally occurring macrocycles that are water‐soluble and formed by oligomerization of seven or eight glucopyranoside units, respectively) has already been observed in the gas phase . Quantum‐chemical computations in the gas phase suggested dihydrogen bonds between the B−H vertices and the polar hydroxyl groups of CDs .…”

“…[3] However, complexation of the potassium salt of B21 with β‐ and γ‐cyclodextrin (CDs, naturally occurring macrocycles that are water‐soluble and formed by oligomerization of seven or eight glucopyranoside units, respectively) has already been observed in the gas phase . Quantum‐chemical computations in the gas phase suggested dihydrogen bonds between the B−H vertices and the polar hydroxyl groups of CDs . Since the interaction of boron clusters with CDs in the aqueous solution phase might open novel avenues towards interactions with other water‐soluble biomolecules, we now extended our studies of B21 to the solution phase …”

Predicted Gas‐Phase and Liquid‐Phase Acidities of Carborane Carboxylic and Dicarboxylic Acids

“…Given the polyhedral nature of heteroborane molecules – in this work carborane mono‐ and dicarboxylic acids respectively – from a chemical reactivity point of view, transferability is more difficult to define for these compounds . Therefore, tabulation of acid/base properties of (di)acids derived from heteroboranes may give more insight into the prediction of reaction mechanisms with other organic molecules, such as amino acids, proteins and biomolecules in general . We should also emphasize that heteroboranes are not found in Nature.…”