小分子有机酸和温度对木质素自组装制备纳米颗粒的影响OA

Lignin nanoparticles(LNP),known for their excellent biocompatibility and oxidation resistance,are widely utilized in biomedicine,agriculture,and related fields,with their structure and properties directly determine performance.During lignin extraction,the reaction liquor typically contains various small organic acids generated from hemicellulose and cellulose degradation.These acids can form hydrogen bonds with lignin oligomers,thereby influencing their self-assembly behavior and ultimately affecting the quality of resulting LNP.In this work,organosolv lignin was extracted from red cedar using solvothermal extraction in an H2O-γ-valerolactone co-solvent,followed by isolation and purification to obtain high-purity lignin.The purified organosolv lignin was subsequently dissolved in the same H2 O-γ-valerolactone co-solvent,after which several representative small organic acids(formic acid,acetic acid,and levulinic acid)derived from polysaccharides degradation were individually introduced.With H2O as antisolvent,LNP were prepared via solvent shifting method at 30℃.The structural features of the organosolv lignin and the morphology of the prepared LNP were comprehensively characterized by gel permeation chromatography(GPC),2D HSQC nuclear magnetic resonance(NMR),and scanning electron microscope(SEM),meanwhile molecular dynamic simulation and quantum chemistry calculation were employed to analyze the interaction forces between lignin and lignin/small organic acids.It was found that the above three acids could form hydrogen bond with lignin,impeding the self-assembly of lignin driven by hydrogen bonding.Noticeably,among the different organic acids,formic acid showed the strongest π-π interaction with lignin.It was because the dissociation of formic acid inhibited the ionization of the phenolic hydroxyls of lignin,reducing electrostatic repulsion of lignin molecules,ultimately promoting lignin molecules self-assembling into big LNP(0.46 μm).Conversely,acetic acid and levulinic acid with the larger aliphatic sidechains presented hindered approaching to lignin molecules,causing the decrease of self-assembly driving force and consequently generating smaller LNP(0.23 and 0.16 μm,respectively).In addition,since the sonication elevates the temperature of lignin solutions during the preparation process of LNP,the temperature effect on the self-assembly of lignin was also studied.In lignin-formic acid system,the Gibbs free energy rose from 10.16 to 10.85 kJ/mol with the temperature increasing from 5 to 55℃,which was ascribed to the reduction of hydrogen bonds of lignin-formic acid and the enhancement of non-bonding interaction between lignin molecules at higher temperature,destabilizing the lignin clusters and generating LNPs with larger diameter and smooth surface.This work reveals the influence of small organic acids and temperature on the production process of LNP,providing the theoretical basis for the controlled preparation of LNP,facilitating scalable application of LNP in various fields.