Molecular modeling characterization of cellulose and chitosan metal oxide hybrid interfaces

Abstract

The interfacial electronic structure of biopolymer–metal oxide hybrids determine their stability, yet this structure is still not well understood. Here, we report a density functional theory study of 10 model systems consisting of cellulose and chitosan functionalized with ZnO and V2O5 separately and in ternary combination at the B3LYP/SDD level. According to frontier molecular orbital analysis, hybridization reduces the energy gap in the ternary composites from 7.106 eV for cellulose and 6.908 eV for chitosan to 3.559 eV and 3.496 eV, while the dipole moment increases from 0.536 D to 26.697 D in cellulose-ZnO-V2O5. Systematic changes in reactivity descriptors include increased chemical softness (0.141 to 0.281 eV-1) and electrophilicity (0.890 to 5.418 eV). Topological research using the Quantum Theory of Atoms in Molecules (QTAIM) shows a progression from pristine polymers (73–76 bond critical points [BCPs]; 149–155 total CPs) to complex hybrids with up to 95 BCPs and 193 total CPs. New interfacial metal–oxygen (M-O) BCPs, which reach 11 in ternary complexes (3 Zn-O and 8 V-O), confirm heterojunction development. In cellulose-ZnO-V2O5, ring critical points rise from 9 to 22 along with new cage critical points that indicate cyclic patterns at the organic-inorganic border. Secondary hydrogen bonds and van der Waals contacts surrounding these M-O anchors are resolved by non-covalent interaction analysis. This dual covalent-non-covalent anchoring mechanism identifies the M-O interface as the crucial location for bioconjugation and surface functionalization in biomedical, sensing, and protective-coating applications and offers a quantum-chemical explanation for hybrid structural stability.