Issue 2, 2020

A pH-responsive graftable supramolecular polymer with tailorable surface functionality by orthogonal halogen bonding and hydrogen bonding

Abstract

Inspired by nature, the field of supramolecular assembly is largely dominated by hydrogen (H)-bonding interactions. However, the scope of H-bonding driven assembly is limited in aqueous medium due to competing solvent interactions. This makes solvent-resistant halogen (X)-bonding an alternative emergent tool for molecular recognition in aqueous milieu. A unique supramolecular strategy based on two orthogonal directional interactions, hydrogen bonding and halogen bonding, has been described to constitute a graftable supramolecular polymer in water. The backbone of the supramolecular polymer is composed of a benzene-1,3,5-tricarboxamide (BTA) core with three pyridyl motifs on the periphery that can participate as both X- and H-bond acceptors. While threefold H-bonding and concomitant π-stacking within the hydrophobic core trigger the formation of the precursor supramolecular polymer, the pendant reactive pyridyl acceptors regulate the outer surface functionality by means of X-bonding with complementary X-bond donating iodotetrafluorophenyl based moieties. By employing this design principle, both X-bond donating polyethyleneglycol (mol wt = 2000 Da) and short triethyleneglycol chains were grafted to the polymer backbone that triggers the formation of spherical micelles and 1D fibers, respectively, in water. pH responsive denaturing of X-bonds leads to reversible switching from the graft copolymer to the precursor BTA polymer in acidic pH as evident from reversible morphology transition from micelles to nanofibers. Contrastingly, control PEG-OH lacking an X-bond donating unit at the chain end could not be grafted to the supramolecular polymer, as bulk water competes for H-bonding with the hydroxyl group on the outer surface of the supramolecular polymer. The present study demonstrates X-bonding as a more attractive tool for non-covalent surface functionalization in water, where hydrophobic shielding is a prerequisite for the performance of ubiquitous H-bonding. The present design offers new insight into the development of multi-component pH responsive complex molecular assemblies.

Graphical abstract: A pH-responsive graftable supramolecular polymer with tailorable surface functionality by orthogonal halogen bonding and hydrogen bonding

Supplementary files

Article information

Article type
Paper
Submitted
27 jun 2019
Accepted
16 aug 2019
First published
16 aug 2019

Polym. Chem., 2020,11, 385-392

A pH-responsive graftable supramolecular polymer with tailorable surface functionality by orthogonal halogen bonding and hydrogen bonding

A. Jamadar and A. Das, Polym. Chem., 2020, 11, 385 DOI: 10.1039/C9PY00944B

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