Solvent-Stabilized Molecular Capsules

Abstract

Pyrrogallolarenes 2 were prepared by acid-catalyzed condensation of pyrrogallol with aldehydes. Compound 2a crystallizes from a methanol solution of quinuclidine hydrochloride to give a dimeric molecular capsule surrounding one disordered quinuclidinium cation. The molecules of 2a are connected by direct hydrogen bonds and by bridging methanol and water molecules. The chloride anion is positioned outside the capsule and is hydrogen bonded to the hydroxy groups of 2a. The shortest distance between the cation and anion was found to be 6.7 A. Crystallization of 2b from aqueous acetonitrile resulted in a dimeric capsule linked by a polar belt of 16 hydrogen bonding water molecules. Four acetonitrile molecules occupy the cavity of this dimeric capsule and assume two binding sites that differ in hydrogen bonding and electronic environment. Compounds 2 also form hydrogen-bonded dimeric molecular capsules in alcohols and aqueous acetonitrile solutions. These assemblies readily encapsulate tetramethylammonium, tetramethylphosphonium, quinuclidinium, and tropylium cations to give complexes stable on the NMR time scale at 233 K.

Metallo-supramolecular capsules

“…19) [121]. The two PgC 3 molecules in the metal-organic capsule are arranged asymmetrically, and the pyrogallol [4]arene arrangement bears resemblance to a hydrogen-bonded analogue reported by Rebek and co-workers [122]. This metal-organic capsule can therefore be considered as another example of how hydrogen-bonded templates are useful precursors for the formation of such analogues under specific conditions.…”

Aromatische Ringe in chemischer und biologischer Erkennung: Energien und Strukturen

“…[229] Wegen ihrer elektronenreichen Natur komplexieren Pyrogallol [4]arene größere Kationen, wie Tetramethylphosphonium, sogar stärker als die entsprechenden Resorcin [4]aren-Wirte. [230] ITC-Studien in Ethanol-Lösung (T = 298 K) zeigten, dass der Pyrogallol [4]aren-Wirt 22 (Abbildung 26 a) l-Carnitin (K a = (18 000 AE 1000) m À1 ) mit viel hö-herer Affinität als Betain (K a = (3200 AE 100)…”

Head-to-tail Aggregates of Sulfonatomethylated Calix[4]resorcinarene in Aqueous Solutions

“…Thus amphiphilic calixarenes are promising building blocks for the development of nano-scale aggregates, able to recognize molecules [7 -10] and ions [11 -15]. Non-covalent multiple interactions, hydrogen bonding in particular, are a well known approach for the construction of capsule-like dimers and hexamers [1,2,[11][12][13][14][15]. Most of these systems, however, are restricted to nonpolar solvents, though there are some interesting X-ray structures of crystals grown from aqueous methanol solutions, which bring to light hydrogen bonded resorcinarene capsules with tetra-alkyl ammonium cations inside [15].…”