Mechanochemical conversion of chitin to high-bioactivity oligomers of N-acetyl-D-glucosamine

Organonitrogen chemicals are crucial in pharmaceutical production and material synthesis. However, the current overreliance on the energy-intensive and highly polluting Haber-Bosch synthesis process necessitates an urgent need to explore more sustainable and environmentally friendly methods for producing these chemicals. Herein, we report an effective method for the selective conversion of chitin into its oligomers in deionized water. A systematic investigation was conducted on the pretreatment of chitin using various physical methods, such as microwave, ultrasonic, and ball milling while keeping the power consumption constant. A series of techniques were used to investigate the molecular structure, surface morphology, and depolymerization degree of the pretreated chitin. Results demonstrate that ball milling is the most effective pretreatment method which achieves a significant reduction in the crystallinity and viscosity average molar mass of chitin. These changes are advantageous for the subsequent chitin selective depolymerization reactions. Ball milling chitin with solid acid Fe₃O₄@C-SO₃H could improve the physical contact between chitin and the catalyst, leading to a substantial advancement in the subsequent selective depolymerization of chitin to its oligomers. 37.9 % yield of N-acetyl-D-glucosamine and chitin oligosaccharides with polymerization of 2-4 could be obtained from ball-milled chitin when they were depolymerized in deionized water at a low temperature of 140 °C, and the yield of desired products is 23 times greater than that obtained from untreated chitin. The products obtained exhibited notable antioxidant and antifungal activities and could be directly used as biological pesticides. This strategy enables the efficient production of high-value organonitrogen chemicals from inexpensive bioresources in an environmentally friendly way.