Human-derived glutathione S-transferase mu 1 mediated hydrolysis of nitrocellulose: reaction mechanisms and thermal decomposition behavior

This study proposes the innovative application of human-derived glutathione S-transferase mu 1 (GSTM1) for biocatalytic denitration of nitrocellulose (NC), designed to achieve nitrate ester hydrolysis under mild conditions while effectively reducing NC's hazardous properties. The experimental results showed that GSTM1 protein was expressed heterologously in engineered Escherichia coli (E. coli). After 48 h of treatment with purified enzyme GSTM1, the nitrogen content of NC significantly decreased from 12.97 % to 8.4 %. Fourier transform infrared spectroscopic analysis combined with cellulase enzymatic hydrolysis experiments of substances insoluble in ethyl acetate demonstrated GSTM1-mediated conversion of nitrate ester groups to hydroxyl groups in NC, accompanied by hydrogen bond formation and subsequent regeneration of cellulose. Gel permeation chromatography revealed that GSTM1 treatment significantly reduced the relative molecular weight of NC while broadening its molecular weight distribution. Moreover, scanning electron microscopy images revealed increased crack density and surface roughness on NC fiber. The TG-DSC and DSC experiments confirmed decreased combustion heat and reduced activation energy (E_a) from 195.92 kJ·mol⁻¹ to 168.47 kJ·mol⁻¹ post-treatment of NC. The thermal decomposition process of NC before and after the reaction was thoroughly analyzed using the model-free Friedman method. Through systematic optimization, the ideal enzymatic reaction parameters were established as 3.2 g·L⁻¹ NC substrate concentration with 1.0 g·L⁻¹ GSTM1 at 37 °C for 8 h. This novel technique safely and environmentally friendly treats waste military compounds while offering new insights for developing multi-enzyme synergistic systems for NC-based waste treatment.