Anion‐Assisted Supramolecular Polymerization: From Achiral AB‐Type Monomers to Chiral Assemblies

Abstract

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 recog-nition 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 mo...

Supramolecular Polymers: Historical Development, Preparation, Characterization, and Functions

“…The looser the ion-pairing interactions, the higher the DP. Furthermore, Gattuso et al demonstrated an elegant strategy to significantly enhance the DP by synthesizing a heteroditopic monomer, 40 , a calix[5]­aren derivative with an ancillary anion-binding site on the upper rim (Figure b) …”

“…DOSY is becoming a popular method for characterization of supramolecular polymers. ,, The diffusion coefficient is inversely proportional to the size of supramolecular polymers. Furthermore, the size of supramolecular polymers can be qualitatively estimated according to the Stokes–Einstein equation.…”

31-Benzyloxy-5,11,17,23,29-penta-tert-butylcalix[5]arene-32,33,34,35-tetraol

“…For the synthesis of the title compound, see: Stewart et al (1995). For calix [5]arene molecules derived from the title compound, see: Garozzo et al (2005); Capici et al (2011); Pappalardo et al (2012). For the structures of calix [5]arene/ alkylammonium complexes, see: Gattuso et al (2012).…”

Influence of H-bond competitors on the solvent-dependent structures of an octaurea-calix[4]tube

“…19 Our work conrmed the crucial role played by the encapsulation of potassium ion within the cryptand-like binding site of this calix [4]tube derivative in the noncovalent synthesis of discrete porphyrin-calixarene nanostructures. 19 Inspired by the self-assembly motif 3,20-24 of tetraurea-calix [4] arenes, and in alignment with our focus on designing linear supramolecular polymers, [25][26][27][28][29][30][31] we decided to shi our attention towards investigating the supramolecular properties of ureacontaining calix [4]tubes.…”