Synthesis and characterization of tailor-made zwitterionic lignin for resistance to protein adsorption

Tailor-made zwitterionic lignin with protein resistance was synthesized by a two-step grafting reaction. Lignin was modified using 3-Dimethylamino-1-propyl chloride hydrochloride and 1,3-Propanesultone by a continuous grafting reaction to provide sulfobetaine structures. Structural analyses from Fourier-transform infrared (FT-IR) spectroscopy, X-ray photoelectron spectroscopy (XPS), and proton nuclear magnetic resonance spectroscopy (¹H NMR) confirmed the successful introduction of zwitterionic sulfobetaine structures into lignin. A higher dosage of 1,3-Propanesultone resulted in a higher density of zwitterionic sulfobetaine structures in lignin. A negative zeta potential, improved hydrophilicity, and slightly decreased thermal stability were observed after zwitterionication. Additionally, the protein (bovine serum albumin, BSA) adsorption of zwitterionic lignin (ZL2) was 27.0 ± 0.9 μg⋅ cm⁻², which represented a significant decrease compared to the 114.3 ± 8.1 μg⋅ cm⁻² measured for unmodified lignin. Moreover, ZL2 maintained comparable antioxidant activity to the commercial antioxidant butylated hydroxytoluene (BHT). Therefore, zwitterionic lignin with excellent protein resistance and antioxidant activity presents a promising prospect.