Supramolecular chemistry with ureido-benzoic acids

Abstract

The controlled self-assembly of multiple molecules into predefined architectures requires highly directional and controllable non-covalent interactions with a high association constant. Here, we introduce the self-complementary ureido-benzoic acid (UBA) quadruple hydrogen-bonding motif. The dimerization constant is of the order of 10⁹ M⁻¹ in chloroform, which makes it an excellent candidate for supramolecular chemistry in dilute conditions. The self-complementary quadruple hydrogen bonding was confirmed in the solid state by a crystal structure. The applicability of the motif in supramolecular polymers was evaluated by bis-UBA telechelic poly(ethylene-butylene) polymers, which showed a dramatic increase in mechanical properties upon functionalization. The potential of the UBA motif in supramolecular chemistry was further evaluated in solution. One of the synthesized UBA molecules revealed hydrogen bonding to NaPy at high concentrations in chloroform. However, upon dilution, the UBA:NaPy hydrogen bonding is disrupted and UBA homodimers are obtained. This shows the potential of NaPy as a supramolecular protective group for the UBA molecule, which can be deprotected upon dilution. Furthermore, the dimerization of the UBA motif was reversibly switched between the ‘off’ and ‘on’ states using base and acid, demonstrating an alternative method of influencing the UBA dimerization. Switching of a UBA molecule in the presence of UPy revealed that UBA dimerization can be selectively switched ‘off’ and ‘on’ in the presence of UPy dimers. These results show the applicability and great potential of the self-complementary quadruple hydrogen-bonding UBA motif for supramolecular chemistry.