Toxic contaminates have profound consequences on both health and the environment. Consequently, effective approaches for addressing the effects of these toxicants are paramount. Here, we review recent progress in developing polymeric sequestrants for biological toxins, heavy metals and organic micropollutants. Polymers have several advantages as sequestration materials, including relatively low cost and high affinity for target compounds. As a result a number of polymer-based toxin-mitigation applications have been investigated. Naturally occurring toxins may be neutralized with polymers capable of binding and eliminating them from the body. Heavy metal contamination from mining operations, energy and industrial sources may also be mitigated with appropriate chelating polymers, both for environmental remediation and in chelation therapy for metal poisoning. Micropollutants such as pesticides from agriculture and polycyclic aromatic hydrocarbons from combustion processes may also be isolated using polymeric materials. Each of these applications illustrates the capabilities of polymers for eliminating toxic contaminants, thereby facilitating greater health and sustainability.

Site-specific modification is a great challenge for polysaccharide scientists. Chemo- and regioselective modification of polysaccharide chains can provide many useful natural-based materials and help us illuminate fundamental structure–property relationships of polysaccharide derivatives. The hemiacetal reducing end of a polysaccharide is in equilibrium with its ring-opened aldehyde form, making it the most uniquely reactive site on the polysaccharide molecule, ideal for regioselective decoration such as imine formation. However, all natural polysaccharides, whether they are branched or not, have only one reducing end per chain, which means that only one aldehyde-reactive substituent can be added. We introduce a new approach to selective functionalization of polysaccharides as an entrée to useful materials, appending multiple reducing ends to each polysaccharide molecule. Herein, we reduce the approach to practice using amide formation. Amine groups on monosaccharides such as glucosamine or galactosamine can react with carboxyl groups of polysaccharides, whether natural uronic acids like alginates, or derivatives with carboxyl-containing substituents such as carboxymethyl cellulose (CMC) or carboxymethyl dextran (CMD). Amide formation is assisted using the coupling agent 4-(4,6-dimethoxy-1,3,5-triazin-2-yl)-4-methylmorpholinium chloride (DMTMM). By linking the C2 amines of monosaccharides to polysaccharides in this way, a new class of polysaccharide derivatives possessing many reducing ends can be obtained. We refer to this class of derivatives as multi-reducing-end polysaccharides (MREPs). This new family of derivatives creates the potential for designing polysaccharide-based materials with many potential applications, including in hydrogels, block copolymers, prodrugs, and as reactive intermediates for other derivatives.

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The cover image is based on the Research Article Polymer Sequestrants for Biological and Environmental Applications by William R Archer et al. DOI: https://doi.org/10.1002/pi.5774.