Study On The Antioxidant Activity Of Hydroxyl-substituent Schiff Bases And Diclofenac Acid

This paper firstly aimed to explore the relationship between hydroxyl- substituent Schiff bases′structure and their free-radical-scavenging ability. We synthesized eight hydroxyl-substituent Schiff bases, i. e., 2-(4-(dimethylamino) benzylideneamino)phenol, 4-(4-(dimethylamino)benzylideneamino)phenol, 2-(4- ((2-hydroxyphenylimino)methyl)benzylideneamino)phenol, 4-(4-((4-hydroxylph- enylimino)methyl)benzylideneamino)phenol, 4-(furan-2-ylmethylleneamino) phenol, 2-(naphthalenen-1-ylimino)methyl)phenol, 2-(Phenylimino)methyl) phenol, 4-((4-hydroxylphenylimino)methyl)-2-methoxyphenol. All the compoun- ds were characterized by elemental analysis, IR, UV and NMR. Then determined their IC50 by reaction with tworadical species, that is, 2, 2′-azinobis(3-ethyl benzothialozinesulfonic acid) radical cations (ABTS·+) and 2, 2- diphenyl-1- picrylhydrazyl radicals (DPPH.). Furthermore, the mechanism and rule how the chemical structure factors influence the antioxidant activity of Schiff bases are analyzed in detail. This illustrates that the free radical reaction mechanism of phenolic compound in antioxidant reactions. 2, 2′-[1, 4-pheny-lenebis- (benzylidene amino)] bis-phenol has the smallest IC50, this indicates that it has the strongest antioxidant activity both in ABTS·+ and DPPH·test. It is found that the -OH attached to the ortho-position of the N atom has the most contribution to a Schiff bases′ability to scavenge radicals. The results also reveal that electron withdraw group reduces the antioxidant activity while electron donor group increases it. Secondly, an in vitro experimental method, 2, 2′-azobis(2- amidinopropane hydrochloride) (AAPH) induced haemolysis of human erythrocytes can be applied to assess the free-radical-scavenging activity of diclofenac acid (DaH) and diclofenac sodium (DaNaH). It has been found that DaH and DaNaH protect human erythrocytes against AAPH-induced haemolysis dose-dependently. Moreover, the free-radical-scavenging activity of lipophilic antioxidants (DaH, VC-12 and VE) is higher than the corresponding water- soluble specie (DaNaH, VC and Trolox). A mutual antioxidant (DaH+VC-12, DaH+VE, VC+DaNaH, Trolox+DaNaH) effect prolongs the lifespan of VC-12, VE, VC and Trolox, respectively. Tests showed that all of them had antibacterial activities.