Self-assembly of a calix[5]arene bearing a 12-aminododecyl pendant group on the lower rim into supramolecular oligomers through intermolecular iterative inclusion events is readily triggered by contact with acid solutions and is reversed to the amino monomer precursor by treatment with a base. 1H NMR data are consistent with the formation of head-to-tail assemblies derived from endo-cavity inclusion of the alkylammonium moiety. Diffusion NMR and light-scattering studies provide evidence for the presence of oligomers in solution and show that different counterions and concentrations result in different oligomer sizes, whereas ESI-MS and SEM investigations, respectively, indicate that self-assembly also takes place in the gas phase and in the solid state. The growth of these supramolecular oligomers is concentration-dependent; however, as a consequence of the saline nature of the monomer, it also shows a distinct counterion-dependence owing to ion-pairing/solvation effects.

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Control over the self-assembly process of monomeric species by functional group modulation is highly desirable in the context of supramolecular polymer design. These materials, unlike covalently linked polymers, consist of monomeric arrays held together by reversible and highly directional noncovalent bonds.[1] Owing to the dynamic and reversible nature of noncovalent interactions, supramolecular polymers display unique topologies and unconventional properties (such as stimuli responsiveness [2] and self-healing [3] ) and are thus becoming cutting-edge species in modern materials science. Multiple hydrogen bonds, metal-ligand coordination, and p-p stacking are, by far, the most common weak forces used for engineering supramolecular polymers.[4] Recently, however, oligomeric and polymeric architectures based on host-guest inclusion complexes have started to become more and more popular. [5] Within this research frame, we have recently described a pH-responsive aminododecyloxy-calix[5]arene derivative (C5-NH 2 ) that, upon exposure to a variety of acids, selfassembles into linear oligomers.[6] Protonation activates the two latent self-complementary binding sites of this heteroditopic monomer precursor (i.e. a preorganized cone-shaped p-rich calix[5]arene cavity and a linear alkylamine pendant chain) and, according to a well-established host-guest recognition pattern, [7] which involves a concerted set of weak interactions (NH···O, CH-p, cation-p), [8] supramolecular oligomer formation readily occurs. However, because of the intrinsically saline nature of the monomers used, the growth of these supramolecular assemblies was found to be aniondependent. More specifically, the looser the ion-pairing interactions between the ammonium monomer and its counterion, the higher the degree of polymerization observed. [9] Although ion-pairing effects have been analyzed extensively in relation to simple one-to-one host-guest systems, [10] to the best of our knowledge they have not yet been examined in the context of supramolecular polymers derived from charged monomers. Elegant examples of polymeric species derived from crown ethers, [11] cryptands, [12] cyclodextrins, [13] cucurbiturils, [14] calixarenes, [15,16] and resorcinarenes [17] have been described, but in none of these instances-neither ABtype (self-complementary heteroditopic) [11a,b,d,e, 12a,b, 13a, 17a] nor AA/BB-type (complementary homoditopic) [11c, 12c, 14, 15, 17b] systems-has the role of the counterion in the growth of the polymer or the tuning of the supramolecular properties been addressed.Drawing on our earlier investigations on the simultaneous complexation of cations and anions [8,18] and on the design of heteroditopic [19] and heterotetratopic receptors [20] in an attempt to override the drawback of ion-pairing effects in AB-type salt monomers, we have now incorporated an ancillary anion-binding site (namely a ureido moiety) [21] into calix[5]arene C5-NH 2 with the aim of facilitating salt dissociation and ultimately making polymer formation more ef...

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After more than a century of research on resorcin[4]arenes (1) it is clear that such systems form spontaneously [1(6)(H(2)O)(8)]-type hexameric capsules in wet, non-polar, organic solvents. However, the interactions of these hexameric capsules with alcohols are far from being solved. Here we provide the results of an extensive study on the interaction of different alcohols with the hexameric capsules of resorcin[4]arene 1a by focusing on the exchange of magnetization manifested in diffusion NMR measurements of such capsular systems. We found that some alcohols such as 2-octyl-1-dodecanol and 1-octadecanol do not interact with the hexamers of 1a, whereas other alcohols such as 3-ethyl-3-pentanol, 2-ethyl-1-butanol and more act as simple guests and are simply encapsulated in the hexamers. Others alcohols such as 3-pentanol, 2-methyl-1-butanol and others, are part of the hexameric structure where they can exchange magnetization with alcohols in the bulk. The bulkier alcohols, due to an increase of the chain length or in branching, have a higher tendency to be encapsulated rather than being part of the hexameric capsule superstructure. This study demonstrate the unique information that diffusion NMR spectroscopy can provide on supramolecular systems in solution and on the precaution that should be exercised when analyzing diffusion NMR data of such dynamic supramolecular capsules.