7, 8-Dimethyl-10-[(2R, 3R, 4S)-2, 3, 4, 5-Tetrahydroxypentyl] benzo[g]pteridine-2, 4-Dione or Riboflavin (RF) was tested as inhibitor of copper corrosion in 1M HNO3, using mass loss technique at 308-328K and theoretical studies based on quantum chemistry methods. RF showed an inhibition efficiency of 86% at the concentration of 5.3×10-4M. The inhibition efficiency was found to be concentration and temperature dependent. The standard thermodynamic adsorption parameters (Δ , Δ , Δ ) were determined. They revealed a spontaneous adsorption and a strong interaction between the molecule and the surface of copper. Adsorption isotherms including Langmuir, Temkin and El-Awady were tested. It was found that RF adsorbs on copper according to the modified Langmuir adsorption isotherm. Furthermore, the Dubinin-Radushkevich model was used to distinguish between chemisorption and physisorption. Thermodynamic activation parameters ( , Δ ∗ , Δ ∗ ) were also determined and discussed. On the other hand, quantum chemical parameters were calculated using DFT at B3LYP level with 6-31G (d) and LanL2DZ basis sets. The descriptors in concern are EHOMO (the highest occupied molecular orbital), ELUMO (the lowest unoccupied molecular orbital), the HOMO-LUMO energy gap Δ , the dipole moment and the descriptors derived from the first ones mentioned, such as electronegativity (), hardness (), softness (S), fraction of electrons transferred () and electrophilicity index (). Local reactivity has been analyzed through the condensed Fukui function and local softness. The theoretical results were consistent with the experimental data.
