Comparison of Cu_3, Cu_5, and Cu₇ clusters as potential antioxidants: A theoretical quest

Herein, we compare and contrast the dual roles of Cu_n clusters (n = 3, 5, and 7 atoms) in scavenging or generating RO^• free radicals from ROH at the theoretical levels (where R = H, methyl, ethyl, n-propyl, i-propyl, n-butyl, t-butyl, and phenyl). This investigation is performed in water media to mimic the actual environment in the biological system. In the presence of the Cu_n clusters, bond dissociation energy (BDE) of RO-H and R-OH is reduced. This is clear evidence for the increased possibility of both the RO-H and R-OH bonds breakage and scavenging of RO^• radicals. The nature of anchoring bonds responsible for the interaction of Cu_n clusters with ROH and RO^• are interpreted using the quantum theory of atoms in molecules (QTAIM) and the natural bond orbital (NBO) analysis. The DFT results indicate that the O^•⋅⋅⋅^•Cu bond is stronger and has more covalent character in RO^•⋅⋅⋅^•Cu_n radical complexes than in ROH⋅⋅⋅^•Cu_n. Therefore, the interactions of Cu_n clusters with RO^• radicals (antioxidant) are more pronounced than their interactions with ROH non-radicals (pro-oxidant).

The GAMESS software package was utilized in this paper. The B3LYP and M06 functions with the 6-311 +  + G(d,p), and LANL2DZ/SDD basis sets was used to perform the important geometrical parameters of RO^•⋅⋅⋅^•Cu_n and ROH⋅⋅⋅^•Cu_n, binding energy (E_b), and bond dissociation energy (BDE).