Synthesis, crystal structure and antioxidant activity of butylphenol Schiff bases: Experimental and DFT study

Abstract

Schiff bases are chemical compounds formed from the condensation reaction of aldehydes or ketones with amines. In medicinal chemistry, these compounds have received widespread attention due to significant biological activities, including antioxidant, antibacterial, antifungal, antiviral, antitumor, and anti-inflammatory. Herein, three Schiff base compounds, namely 2-(3, 5-di‑tert‑butyl‑2-hydroxybenzylideneamino)-4‑tert-butylphenol (1), 2-(4-(diethylamino)-2-hydroxybenzylideneamino)-4‑tert-butylphenol (2) and (1E)-1-((5‑tert‑butyl‑2-hydroxyphenylamino)methylene)naphthalen-2(1H)-one (3) were synthesized and characterized by NMR,IR,HRMS and UV–vis. Moreover, the structures of compounds 1 and 3 were determined by single crystal X-ray diffraction techniques. The theoretically simulated NMR, IR and the UV-visible absorption spectra have been compared with the experimental datas. Based on the absorbed UV spectra and TD-DFT calculations, assignment of the absorption bands are carried out. The antioxidant capacity of three butylphenol derivatives was evaluated by 2, 2-diphenyl-1-picrylhydrazyl (DPPH) free radical scavenging experiments using Vitamin C as a standard drug. The scavenging rates of compounds 1 (92.62%) and 2 (91.05%) were comparable to that of Vitamin C (98.31%) at the concentration of 1.0 mg/mL. In order to investigate the DPPH free radical scavenging mechanism, a theoretical study based on density functional theory (DFT) was performed. The results show that ET-PT mechanism is favored which is in agreement with the experimental results.