Unraveling the structural and electronic reorganization of oxidized cellulose: a density functional theory perspective on carboxyl-induced modifications

Abstract

Controlled oxidation of cellulose introduces carboxyl functionalities at the C6 position, significantly modifying its hydrogen-bonding network, crystalline structure, and electronic properties. In this work, density functional theory (DFT) is employed to investigate pristine cellulose Iβ and an oxidized model where the C6 hydroxymethyl group (–CH₂OH) is converted into a carboxyl group (–COOH), mimicking dichromate-induced oxidation. Structural optimization reveals anisotropic lattice distortion, including contraction along the a-axis, slight expansion along the b-axis, and increased lattice angles, indicating rearrangement of interchain packing. Hydrogen-bond analysis shows that oxidation increases the total number of hydrogen bonds from 18 to 24 while shortening the shortest H•••O distance from 1.78 Å to 1.70 Å, reflecting stronger intermolecular interactions. Bader charge analysis indicates significant electron depletion at the oxidized C6 sites, consistent with the electron-withdrawing nature of carboxyl groups. Electronic structure calculations reveal a reduction in the band gap and a downward shift of the chemical potential, suggesting enhanced electron-accepting behavior. Optical absorption spectra demonstrate increased intensity and pronounced anisotropy in the oxidized system. These findings provide atomistic insight into oxidation-induced transformations and establish a theoretical basis for designing functionalized cellulose materials with tailored properties.