Comparison of Cu3, Cu5, and Cu7 clusters as potential antioxidants: A theoretical quest

CONTEXT

Herein, we compare and contrast the dual roles of Cun 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 Cun 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 Cun 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•⋅⋅⋅•Cun radical complexes than in ROH⋅⋅⋅•Cun. Therefore, the interactions of Cun 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•⋅⋅⋅•Cun and ROH⋅⋅⋅•Cun, binding energy (Eb), and bond dissociation energy (BDE).

Novel triplet germylenes in focus: normal vs. abnormal triplet exocyclic tetrazol-5-vinylidene germylenes at DFT

Substituent effects on stability (assumed as the singlet and triplet energy gaps, ΔΕ_S-T) of novel 1,4-disubstituted-tetrazole-5-vinylidene germylenes (normal, 1_R) and their corresponding 1,3-disubstituted-tetrazole-5-vinylidene germylenes (abnormal, 2_R) are computed and compared, at B3LYP/6-311++G** and M06/6-311++G**, where R = H, CN, CF₃, F, SH, C₆H₆, OMe, and OH. Interestingly, every triplet vinylidene germylene shows more stability than its corresponding singlet. Also, every triplet abnormal isomer (2_R) emerges to be more stable than its corresponding normal (1_R). All abnormal 2_R isomers show broader band gaps (ΔE_HOMO-LUMO) and higher nucleophilicity (N), but less electrophilicity (ω) than their corresponding normal 1_R isomers. The NICS (nuclear-independent chemical shift) results indicate that every 1_R (except singlet 2_Ph) emerges more aromatic than its corresponding 2_R. Our Hammet studies indicate that 1_R is more sensitive to the electronic effects of substituents, R, than 2_R. Electron-donating species increase N in both 1_R and 2_R, while electron-withdrawing groups increase stability.

Zinc and cadmium complexes based on bis-(1H-tetrazol-5-ylmethyl/ylethyl)-amine ligands: structures and photoluminescence properties

Nine zinc and cadmium coordination compounds with bis-(1H-tetrazol-5-ylmethyl/ylethyl)-amine were synthesized and structurally characterized, and the fluorescent emission and fluorescence lifetime of complexes 1–9 have been investigated and discussed.