Comparison of Cu Cu and Cu clusters as potential antioxidants: A theoretical quest.

Context: Herein, we compare and contrast the dual roles of Cu 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 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 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 radical complexes than in ROH⋅⋅⋅Cu. Therefore, the interactions of Cu clusters with RO radicals (antioxidant) are more pronounced than their interactions with ROH non-radicals (pro-oxidant).

Methods: 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 and ROH⋅⋅⋅Cu, binding energy (E), and bond dissociation energy (BDE).