Investigation of antioxidant synergisms and antagonisms among thymol, carvacrol, thymoquinone and p-cymene in a model system using the Briggs-Rauscher oscillating reaction

Auto-oxidation of lipids has been recognised as a major deterioration process affecting both the sensory and nutritional quality of foods; the application of antioxidants is one of the technically simplest ways of reducing this process. Previous reports showed that these compounds were found in selected aromatic plants and that thymol, carvacrol, thymoquinone and p-cymene as constituents of different essential oils possess substantial antioxidant activity. In the present study their antioxidant capacities were evaluated using the Briggs-Rauscher oscillating reaction method.Our results indicate that the majority of the antioxidant mixtures demonstrated some level of discrepancy in antioxidant capacity when compared to individual values of their constituents. The strong antagonistic effect was found only when thymoquinone was paired with p-cymene. All other combinations of two antioxidants clearly showed some degree of synergistic effect. The mixtures of three antioxidants showed a decrease in antioxidant capacity when compared to their individual values. The results obtained for more complex mixtures of four antioxidants showed a decrease in antioxidant capacity, indicating and confirming that the antagonistic effect between thymoquinone and p-cymene overrides the synergistic effect of other pairs.     

Influence of the phenophase on the phenolic profile and antioxidant properties of Dalmatian sage

This study aimed to research the influence of phenophase on the phenolic profile (phenolic acids, flavonoids and stilbenes) and related antioxidant properties of sage, one of the most characteristic plants of Dalmatian karst. The total phenol and flavonoid contents in sage leaves were determined spectrophotometrically, while the principal phenolics were determined using HPLC-RP-DAD. Antioxidant properties of this well known medicinal plant were determined as free radical scavenging activity (DPPH), ferric reducing/antioxidant power (FRAP) and by Briggs-Rauscher oscillating reaction (BR). The results strongly indicate that Dalmatian sage leaves are rich source of valuable phenolics, mainly phenolic acids, with extremely good antioxidant properties. The presence of resveratrol or its derivatives was confirmed in all extracts. The best results for total phenols and flavonoids, as well as the best antioxidant properties were obtained for May sage, while the highest amounts of catechin monomers and compounds from group of stilbenes were found in February extract.     

利用四氮杂大环镍配合物催化Briggs-Rauscher振荡反应测定2,6-二叔丁基4-甲基苯酚的新方法

报道了一种利用四氮杂大环配合物催化Briggs-Rauscher(BR)振荡反应测定2,6-二叔丁基-4-甲基苯酚(BHT)的方法,所涉及的体系为H2SO4-KIO3-[NiL](ClO4)2-MA-H2O2(其中L为四氮杂大环5,7,7,12,14,14-六甲基-1,4,8,11-四氮环杂十四4,11-二烯,MA表示丙二酸).通过研究发现,在该体系中加入一定浓度的BHT,会使得振荡体系的周期、振幅等都发生改变,同时体系会产生抑制时间.当BHT浓度在1.95×10-7 ～6.25×10-6 mol/L范围内,抑制时间与加入的BHT浓度呈很好的二次函数关系;当BHT浓度在6.25×10-6 ～ 1.56×10-5 mol/L范围内,抑制时间与加入的BHT浓度呈很好的一次线性关系.为了达到更好的定量检测效果,对各组分的浓度进行了优化,使得检测效果达到最佳,最后对反应机理进行了探讨.