Resorcarenes: Hollow Building Blocks for the Host-Guest Chemistry

Abstract

The continuous search for new qualities and the desirability of controlling the size, shape and the chemical features had led to the successful synthesis of various molecular containers and their complexes starting from resorcarene skeleton. The rigidified cavitands have been extended to capture in their round hug bigger and bigger molecules. By covalent synthesis many kinds of new hosts have been built, that maintain guests in their prison for more and more long time. Self assembly, driven by metal-ligand interaction, van der Waals forces, hydrophobicity and, mainly, hydrogen bonds, is at the base of capsules, a novel type of compounds with a peculiar inner phase, stereochemistry and reactivity. The amazing variety of hollow buildings with a resorcarene-based framework and often unique properties is reviewed. OH HO 1168 Current Organic Chemistry, 2005 Botta et al. RESORCARENES AS CONTAINER 2.1 Resorcarenes and Cations or Charged MoleculesAlso resorcarenes form stable complexes with alkali metal cations (Li I , Na I , K I , Rb I , Cs I ) [14]. The interaction of simple resorcarenes with metal cations and ammonium ions has been extensively studied. The conformational change of the host resorcarene, the most favourable binding locations and the relative binding energies have been investigated by ab initio methods [15]. The same group studied the interaction with cations of resorcarene 3a, (Chart 2) in comparison with its permethylated derivative 3b, by Electrospray Ionization Fourier Transform Ion Cyclotron Resonance Mass Spectrometry (ESI-FT-ICR-MS) and ab initio calculations [16]. The significance of intramolecular hydrogen bonding for the cone conformation and the presence of intramolecular flip-flop hydrogen bonding in 3a were confirmed by calculations and ND 3 -exchange experiments. Regard to the complexation, the following items were established: i) all the above alkali metal cations formed host-guest complexes by docking inside the cavity of the host; ii) the complexation with larger cations, especially Cs + , was favoured; iii) all the cations formed stable dimer resorcarene capsules. Chart 2. Resorcarenes octol (3a) and octamethyl ether (3b).Conversely, Cu II cations were shown to interact with cyano-4a (Chart 3) and amino-resorcarenes 4b, forming in the latter case a complex with octahedrical geometry, as evidenced by the EPR spectrum; accordingly, the computercalculated structure suggested a three-molecular complex between Cu II and two molecules of 4b, in which the ligands use three of their functionalities at the lower rim to fix the ion with a distorted octahedral coordination [17]. Chart 3. Resorcarenes interacting with metal cations.The interaction of resorc[4]arenes octamethyl ethers such as 4c with Fe III in organic media was analysed by 1 H NMR studies, carried out using Ga III instead of Fe III . As a result, resorcarenes bearing carboalkyloxy groups in the side chains were shown to have two active sites of interaction, the first located at the aromatic upper rim and the other in the vicinity ...

Stereochemical Preference of 2'‐Deoxycytidine for Chiral Bis(diamido)‐bridged Basket Resorcin[4]arenes

“…Their complexing properties and solubility characteristics can be predetermined in a truly and distinctly targeted rational approach. Calix[4]arenes and resorcin[4]arenes have had enormous impact in the field of supramolecular chemistry by virtue of their multireceptorial character and high level of structural preorganization. The presence of rationally designed functional groups on their rims offers the opportunity of preselecting their complexing properties also by means of a fine tuning of the conformational features, making them very attractive as artificial receptors for biologically relevant molecules.…”

Size‐ and Structure‐Selective Noncovalent Recognition of Saccharides by Tetraethyl and Tetraphenyl Resorcinarenes in the Gas Phase

“…[4] Over the past decade, resorcinarene structures have turned out to be a versatile basis for molecular recognition. [5] Various resorcinarenes have reportedly formed noncovalent and mainly hydrogen-bonded complexes, especially with small polar organic molecules containing nitrogen or oxygen atoms. [6][7][8] The saccharide and alkyl glycoside complexation of upper-rim unsubstituted resorcinarenes were earlier studied by Aoyama et al [9,10] They detected sugar complexes mainly from apolar organic solutions by using circular dichroism (CD) and 1 H NMR spectroscopic techniques.…”

Bringing a Molecular Plus One: Synergistic Binding Creates Guest-Mediated Three-Component Complexes

“…22 Making of ternary complexes requires control of the noncovalent interactions in the solution, particularly in protic polar solvents where hydrogen bonding is ubiquitous. 23 Control is rendered even more complicated as the co-operative binding interactions involved, although derived from the nature of the individual components, are true emergent properties of the complex itself.…”

“…Defined ternary complex formation is the result of the interplay between a number of factors that determine the overall thermodynamics and structure: p K a value of acidic protons, electronic effects, electrostatics, polarization, resonance-assistance, and dipole–dipole interactions . Making of ternary complexes requires control of the noncovalent interactions in the solution, particularly in protic polar solvents where hydrogen bonding is ubiquitous . Control is rendered even more complicated as the co-operative binding interactions involved, although derived from the nature of the individual components, are true emergent properties of the complex itself.…”