Lanthanide extraction isolates valuable chitin derivative

A team of chemists has reported a practical approach to isolating Chromogen I, an elusive but potentially high-value compound that can be derived from waste biomass such as shrimp shells (Inorg. Chem. 2016, DOI: 10.1021/acs.inorgchem.6b02589). Chromogen I is a derivative of N-acetyl-d-glucosamine (GlcNAc), the chemical building block of the structural biopolymer chitin—Earth’s most abundant type of nitrogen-containing biomass—that is found in fungi, insects, and shrimp. The commercial fishing industry already sells shrimp and crab shells to processors that depolymerize chitin by acid or enzymatic hydrolysis to make GlcNAc, which is used in cosmetics and dietary supplements. Repurposing GlcNAc into higher-value chemicals is on the industry’s to-do list but has been hampered by poor yields and the need for catalytic processing at high temperature and pressure and chromatographic separations. Researchers led by La-Sheng Long and Xiang-Jian Kong of Xiamen University and Zhiping Zheng of the University of Arizona found that adding a solution of gadolinium or dysprosium ions to treated GlcNAc under mild conditions leads to formation of clusters of nine metal atoms and four Chromogen I ligands, with six of these clusters self-assembling via hydrogen bonding into a cagelike assembly. Further treating the solution results in precipitation of a lanthanide salt, leaving behind pure Chromogen I that can be recrystallized.