Studies On The Capacity Of Antioxidants Containing Hydroxyl And Amine

In recent years, the investigation of antioxidants is one of the hot spots in physical organic chemistry, the investigation of antioxidants focuses on aspects of natural antioxidants. A lot of research work focused on the type of antioxidants, while rarely focused on the methods to evaluate the activity of antioxidants.The current methods to evaluate the activity of antioxidants could be defined as two types: chemical systems and chemical simulation biological systems. The former methods can evaluate the activity of antioxidants in the chemical systems fast and quantitative, but the antioxidants which have good activity in the chemical systems are often not have well capacity in the biological systems, thus affecting the application of antioxidants; Simulation of biological systems did not have a quantitative criteria, could not be used to evaluate the activity of antioxidants quantificational. So, in order to carry out new research on antioxidants, the development of accurate and efficient evaluation system is imperative.In this thesis, the kinetic equation was introduced into chemical simulate of biological systems, which can be used in biological system to evaluate the activity of antioxidant quantificational.1,16 types of Schiff bases with different substituent were designed and synthesized, which antioxidant properties were also investigated in different systems.Firstly, the reactions between 8 Schiff bases and 2,2′-diphenyl-1-picrylhydrazyl (DPPH) or 2,2′-azinobis(3-ethylbenzothiazoline-6-sulfonate) radical cation (ABTS+?) were carried out, their capacities to scavenge ABTS+? are better than their capacities to scavenge DPPH, which are also associated with the location and electronic effects of substituent. Secondly, chemical kinetic equation was introduced into the AAPH-induced hemolysis to investigate the antioxidant activities of these Schiff bases. The results revealed that the radical-scavenging activity of the–OH attached to the para position of methylene in Schiff base was much lower than that attached to the ortho position of the N atom. The large conjugate system and low steric hindrance in the framework of Schiff base benefit the Schiff base to trap radicals. Meanwhile, since a Schiff base, even without any substituent, can also play an antioxidative role in this experimental system. Finally, six Schiff bases were used together with four familiar antioxidants, such as 6-hydroxyl-2,5,7,8-tetramethyl chroman-2-carboxylic acid (Trolox),L-ascorbic acid (VC),α-tocopherol (VE) and L-ascorbyl-6-laurate (VC-12) in AAPH-induced hemolysis of erythrocytes. It was found that, except for benzylidene aniline (BAN)+VC-12,2-(phenyliminomethyl)phenol (BAH)+VC-12,2-benzimidoylphenol (OBH)+VC-12,4-benzimidoylphenol (PBH)+VE,2-((o-hydroxylphenylimino) methyl)phenol (OSAP) + VC-12,2-((p-hydroxylphenylimino) methyl)phenol (PSAP) + Trolox,PSAP + VE,PSAP + VC-12, all the other combinations protected erythrocytes more perfectly than when used individually.2,The AAPH-induced DNA oxidative damage system was developed, and was used to investigate the antioxidant ability of the natural product chlorogenic acid (CGA) as well as several other different systems.Firstly, the reaction between CGA and ABTS+? or DPPH revealed that CGA was able to trap radicals by reducing radicals more than by donating its hydrogen atoms to radicals. Secondly, in the case of hemin-induced hemolysis of erythrocytes CGA is proved to be a membranestabilizer. Then, it was found that the n of CGA to protect erythrocytes was 0.77, which the n indicates the number of radical-propagation chains terminated by CGA in AAPH-induced hemolysis; furthermore, CGA facilitated a mutual protective effect with VE and VC on AAPH-induced hemolysis by increasing n of VE and VC. Finally, AAPH-induced oxidation of DNA was developed, after introduce the chemical kinetic into this system, the DNA oxidative damage could be tested quantificationally through the formation of thiobarbituric acid reactive substance(TBARS). CGA was found to be a radical scavenger to protect DNA against AAPH-induced oxidation of DNA, it could capture n=6.01 radicals in this system, this fact revealed that CGA served as an efficient antioxidant to protect DNA more than to protect erythrocytes.3,Two anti-inflammatory drugs, diclofenac (DaNH) and its sodium salt (DaNaH), were selected to investigate their antioxidant activity in different systems.Firstly, the reaction between these two drugs and ABTS+? or DPPH were investigated, they could able to effectively restore the ABTS+., in which DaNaH with a strong reduction. It was very difficult for them to scavenge DPPH, which indicated that DaNH was very difficult to give hydrogen atom from its N-H bond. Secondly, phosphate-buffered saline (PBS) and dimethylsulfoxide (DMSO) were used to investigate these two drugs'protection against the hemin-induced hemolysis. The result revealed that these two drugs'protection to red blood cell in this system was not only associated with their structure, but also associated with the solvents which dissolved these drugs. In addition, AAPH-induced hemolysis system was used to study the antioxidant activity of these two drugs, it was found that DaNH(4.95) could scavenge more radicals than DaNaH(3.60). The synergistic effects between DaNH and VE,DaNH and VC-12,DaNaH and Trolox,DaNaH and VC were also investigated, it was found that DaNH could repair these four familiar antioxidants'radical. Finally, the number of peroxyl radicals trapped by DaNH and DaNaH in AAPH-induced DNA oxidative damage were nDaNH = 3.86 (±0.54) and nDaNaH = 3.56 (±0.54) respectively.4,Five tricyclic amines'antioxidant activities were investigated in different systems.Firstly, mechanisms of the reactions between tricyclic amines and ABTS+. or DPPH were studied through change the pH of the reaction system, the addition of acetic acid accelerated the reaction rate of Ar2NH to scavenge DPPH, suggesting that a sequential proton loss electron transfer (SPLET) mechanism occurred with amine-type antioxidants during the trapping of DPPH. In contrast, the addition of acetic acid or pyridine reduced the reaction rate of Ar2NH to scavenge ABTS+., suggesting that the hydrogen atom transfer (HAT) mechanism is the basis for the reaction that is occurring. Secondly, these 5 tricyclic amines were applied to protect human erythrocytes against AAPH-induced hemolysis in vitro, all of them function as efficient antioxidants in protecting human erythrocytes against AAPH-induced hemolysis, in which the activity sequence is phenoxazine (PozNH) > diphenylamine (DpaNH) > carbazole (CazNH) > iminostilbene (IsbNH) > phenothiazine (PtzNH); Moreover, they exhibit higher activities when it was used together with Trolox,VE,VC and VC-12 in this experimental system. Finally, these 5 tricyclic amines'protection against DNA were investigated in the AAPH-induced oxidation of DNA system, all of them were found to be radical scavengers to protect DNA against AAPH-induced oxidation of DNA, and they had different mechanisms protect DNA. PozNH,IsbNH and DpaNH could produce inhibition period while CazNH and PtzNH could not produce inhibition period when they protect DNA in this system.