STRUCTURAL AND REACTIVITY INSIGHTS INTO SULFATED α-1 LINKED LIGNIN DERIVATIVES: A DFT-BASED COMPARATIVE ANALYSIS

This work aims to study the structure, charge distribution, and vibrational characteristics of α-1 lignin and α-1 lignin sulfate molecules based on density functional theory (DFT) at the B3LYP/6-31G(d,p) level of theory. The addition of a sulfur group to the α-1 molecule resulted in the formation of the α-1 lignin sulfate molecule, and the geometry of the O-H bond changed. Based on the APT (Atomic Polar Tensor) and Mulliken charge distribution, the charge of the α-1 lignin sulfate molecule was significantly different from that of α-1 lignin, indicating that it had a larger polarization, which was important in intermolecular interactions. In addition, the molecular electropotential (MEP) map showed that the α-1 lignin sulfate molecule has a large number of nucleophilic and electrophilic sites that are active in hydrogen (H)-bonding. The α-1 molecule is highly reactive, as indicated by the small HOMO-LUMO energy gap. Based on the global reactivity properties, the α-1 molecule is more nucleophilic than α-1 lignin sulfate, which indicates its chemical stability. The presence of vibrations of the O-H, C-H, N-H, C=C, and S-O functional groups in these molecules was theoretically calculated, which was in agreement with the experimental results (scaled at 0.9608). In general, the α-1 lignin sulfate molecule has strong polarizability, structure, and reactivity, which may be used in materials science and biological sensors in the future.