Metallo-polyelectrolytes as a class of ionic macromolecules for functional materials

Abstract

The fields of soft polymers and macromolecular sciences have enjoyed a unique combination of metals and organic frameworks in the name of metallopolymers or organometallic polymers. When metallopolymers carry charged groups, they form a class of metal-containing polyelectrolytes or metallo-polyelectrolytes. This review identifies the unique properties and functions of metallo-polyelectrolytes compared with conventional organo-polyelectrolytes, in the hope of shedding light on the formation of functional materials with intriguing applications and potential benefits. It concludes with a critical perspective on the challenges and hurdles for metallo-polyelectrolytes, especially experimental quantitative analysis and theoretical modeling of ionic binding.

Fig. 1

Diverse topologies of metallo-polyelectrolytes. a metal ions attached to the side chain of organic polyelectrolytes through electrostatic interaction; b neutral metal complexes at the side chain of polyelectrolytes; c charged metal complexes at the side chain by covalent bonding; d charged metal complexes at the side chain through coordination; e main chain metallo-polyelectrolytes formed by coordination; f main chain metallo-polyelectrolytes formed by covalent bonding

Fig. 2

An overarching summary to illustrate a few key functions of metallo-polyelectrolytes. a most common transition metals for building metallo-polyelectrolytes; b a few properties of metallo-polyelectrolytes including electrostatic binding, redox and physiochemical stability; c applications in the areas of polyelectrolyte multilayers, antimicrobials, gene delivery and ion exchange for transport

Fig. 3

Metallo-polyelectrolyte interactions with oppositely charged molecular substrates at three different levels. a small molecules, b macromolecules, and c membranes or crosslinked networks

Fig. 4

Controlled disassembly and controlled swelling of metallo-polyelectrolyte based PEMs. a reduction-induced disassembly of cobaltocenium-based PEMs, adapted from ref. with permission from The Royal Society of Chemistry; b a strategy used in controlled swelling of PEMs, adapted from ref. with permission, Copyright©2014, Elsevier

Fig. 5

Structural units of antimicrobial metallo-polyelectrolytes. a polypyridylruthenium(II) complex polymer;^– b copper-terpyridine carboxymethyl cellulose polymer; c η⁶-arene-η⁵-cyclopentadienyliron(II) complex polymer;^– d cobaltocenium polymer; e Fenton chemistry involving redox of ferrocene

Fig. 6

Proposed interactions between metallo-polyelectrolytes and bacterial cells. It involves the following steps: electrostatic interactions between cationic metallo-polyelectrolytes and anionic membranes; surface binding on membranes, membrane insertion and eventual membrane disruption. Metallo-polyelectrolytes could also interact with lipoteichoic acid in the outer leaflet of Gram-positive bacteria

Fig. 7

Proposed dene delivery of non-viral metallo-polyelectrolytes. The delivery requires the formation of polyplexes between metallo-polyelectrolytes and nucleic acids. It involves endocytosis, endo/lysosome escape and release of nucleic acids

Fig. 8

Metallo-polyelectrolytes for ion transport. Synthesis of metallo-polyelectrolytes by ROMP with metal complexes at the side-chain: a heteroleptic bis(terpyridine) Ru(II) complex; b nickel-containing complex; c cobaltocenium cation. Metallo-polyelectrolytes by polycondensation: d permethyl cobaltocenium-containing polysulfone; e cobaltocenium-containing polybenzimidazole; f illustration of single ion site migration inside alkaline anion-exchange membranes; g A highly preferred phase separated morphology containing continuous hydrophilic ion transport channels and a hydrophobic matrix, adapted with permission from ref.. Copyright © 2017, American Chemical Society