On the analyses of graphene oxide/polypyrrole/zinc oxide nanocomposites

Graphene oxide/Polypyrrole/Zinc oxide GrO/PPy/ZnO nanocomposite was investigated for possible interaction with alanine using B3LYP/LANL2DZ model. Results indicated that GrO/PPy/ZnO exhibited notable electronic accessibility with a total dipole moment (TDM) of 5.62 Debye and HOMO-LUMO energy gap of 1.64 eV, which was significantly modulated upon alanine binding. COOH functionalization induced the greatest reduction in ionization potential (from 3.03 eV to 2.56 eV) alongside increased electron affinity (4.68 to 4.77 eV), while NH₂ functionalization showed moderate improvements (ionization potential to 2.67 eV, electron affinity to 4.75 eV). Quantum Theory of Atoms in Molecules (QTAIM) analysis revealed distinct binding characteristics: NH₂-bound systems formed multiple Zn-N and Zn-O coordination bonds with flexible interaction networks, while COOH-bound systems exhibited fewer but stronger, more localized coordination and hydrogen bonds. Molecular electrostatic potential (MESP) demonstrated enhanced positive potential near NH₂ binding sites and pronounced dipolar features around COOH regions. Non-covalent interaction (NCI) and reduced density gradient (RDG) analyses revealed that COOH functionalization produced more concentrated blue domains, indicating stronger interactions and enhanced selectivity. Density of states (DOS) showed notable band gap reduction after composite formation and functionalization, with GrO/PPy/ZnO exhibiting the most favorable electronic structure for charge transport. Alanine binding lowered system polarity (TDM: 2.81 Debye for COOH and 2.77 D for NH₂) while preserving structural stability, as shown by slight changes in chemical hardness. Overall, COOH-functionalized GrO/PPy/ZnO shows the best balance of reactivity, stability, and selective binding, with favorable electrostatics and strong interactions, highlighting its promise as an efficient amino acid sensor.