Lead Ion-Driven Assembly and Reinforcement of Chitin: From Single-Molecule Origin to Macroscale Architecture

Heavy metal ions are widely recognized for their strong affinity and disruptive effects on biomacromolecules, such as polysaccharides. However, the underlying mechanism of their interactions remains unclear, hindering a comprehensive understanding that bridges molecular and macroscale properties. Herein, we investigate the interaction between the natural polysaccharide chitin and lead ion (Pb²⁺) using a combination of experimental and theoretical approaches from single-molecule to macroscale. We find that Pb²⁺ forms specific chelation with chitin, inducing distinct conformational changes and enhancing the mechanics of individual chains. Beyond isolated chains, Pb²⁺ can also stably chelate multiple chains and induce significant aggregation of chitin, accompanied by ordered molecular alignment and organization. As a result, the macroscale structures display markedly improved mechanical performance, characterized by an increase in both tensile strength and modulus. In contrast, light metal ions like Na⁺ do not exhibit specific interactions or induce notable impacts. These findings demonstrate a unified mechanism underlying the interaction between chitin and Pb²⁺, which offers mechanistic insights into the structure and behavior of polysaccharides in heavy metal environments.