The new method can be used to construct copolymers comprising different metal species, which have potential uses in catalysis and drug discovery

From plastics to clothing to DNA, polymers are everywhere. Polymers are very versatile materials made up of long chains of repeating units called monomers. Polymers containing metal complexes on their side chains have enormous potential as hybrid materials in a variety of fields. This potential only increases with the inclusion of more metal species in polymers. But conventional methods of making polymers with metal complexes are not suitable for building multimetallic polymers, because controlling the composition of metal species in the resulting polymer is complex.

Recently, a research team, led by Assistant Professor Shigehito Osawa and Professor Hidenori Otsuka from Tokyo University of Science, proposed a new polymerization method that can overcome this limitation. Dr. Osawa explains: “The usual method of preparing such complexes is to engineer a polymer with ligands (molecular ‘skeletons’ that bind other chemical species together) and then add the metal species to form complexes on it. But each metal has a different binding affinity to the ligand, which complicates the control of the resulting structure.By considering polymerizable monomers with complexes of different metal species, we can effectively control the composition of the resulting copolymer.The study was uploaded April 1, 2022 and published in Volume 58, Issue 34 of Chemical Communications on April 30, 2022.

When the monomers that make up a polymer are themselves polymers, the polymer is called a copolymer. For their study, the scientists designed a dipicolylamine acrylate (DPAac) monomer. DPA was chosen because it is an excellent metal ligand and has been used in various biochemical applications. They then polymerized DPAAc with zinc (Zn) and platinum (Pt) to form two polymer chains with metal complexes — DPAZn(II)Ac and DPAPt(II)Ac. They then copolymerized the two monomers. They discovered that they could not only successfully create a copolymer, but they could also control its metal composition by varying the feed composition of the monomers.

Next, they applied this copolymer as a building block to make nanoparticles using plasmid deoxyribonucleic acid (DNA) as a template. Plasmid DNA was chosen as the template because the two constituent monomers are known to bind to it. The formation of the resulting nanoparticle polymer complexes with DNA (polyplexes) was confirmed using high-resolution scanning electron microscopy and energy dispersive X-ray spectroscopy.

This technique – now a patent-pending technology – can be extended to a new method of manufacturing intermetallic nanomaterials. “Intermetallic catalytic nanomaterials are known to have significant advantages over nanomaterials containing only a single metal species,” says Dr. Osawa.

The polyplexes formed in the study are DNA-binding molecules, indicating that they could be used to develop cancer drugs and gene carriers. The proposed manufacturing method will also lead to advances in catalysis that move away from precious metals like platinum. “These multimetallic copolymers can serve as building blocks for future macromolecular metal complexes of many varieties,” Dr. Osawa concludes.

The results of this study will certainly have considerable consequences in the field of polymer chemistry.

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