PDF(Pubmed)
Abstract：
Since the deep cause for the anti-oxidation of carnosic acid (CA) against oleic acid (OA) remains unclear, we focused on exploring the CA inhibition mechanism via a combined experimental and computational study. Atomic charge, total molecular energy, phenolic hydroxyl bond dissociation enthalpy (BDE), the highest occupied molecular orbital (HOMO), and the lowest unoccupied orbital (LUMO) energy were first discussed by the B3LYP/6-31G (d,p) level, a density functional method. A one-step hydrogen atom transfer (HAT) was proposed for the anti-oxidation of CA towards OA, and the Rancimat method was carried out for analyzing the thermal oxidation stability. The results indicate that the two phenolic hydroxyl groups located at C7(O15) and C8(O18) of CA exert the highest activity, and the chemical reaction heat is minimal when HAT occurs. Consequently, the activity of C7(O15) (303.27 kJ/mol) is slightly lower than that of C8(O18) (295.63 kJ/mol), while the dissociation enthalpy of phenol hydroxyl groups is much lower than those of α-CH2 bond of OA (C8, 353.92 kJ/mol; C11, 353.72 kJ/mol). Rancimat method and non-isothermal differential scanning calorimetry (DSC) demonstrate that CA outcompetes tertiary butylhydroquinone (TBHQ), a synthetic food grade antioxidant, both in prolonging the oxidation induction period and reducing the reaction rate of OA. The Ea (apparent activation energies of reaction) of OA, TBHQ + OA, and CA + OA were 50.59, 57.32 and 66.29 kJ/mol, revealing that CA could improve the Ea and thermal oxidation stability of OA.
摘要：
由于鼠尾草酸（CA）对油酸（OA）的抗氧化作用的深层原因尚不清楚，我们通过实验和计算相结合的研究来探索CA抑制机制。原子电荷,总分子能量，酚羟基键解离焓（BDE），最高占据分子轨道（HOMO），B3LYP/6-31G首先讨论了最低的未占用轨道（LUMO）能量（d，p)水平，密度泛函方法。提出了一步氢原子转移（HAT）用于CA对OA的抗氧化。并进行了Rancimat方法的热氧化稳定性分析。结果表明，位于CA的C7（O15）和C8（O18）上的两个酚羟基具有最高的活性，和化学反应的热量是最小的，当帽子发生。因此,C7(O15)(303.27kJ/mol)的活性略低于C8(O18)(295.63kJ/mol),而酚羟基的解离焓远低于OA的α-CH2键的解离焓（C8，353.92kJ/mol；C11，353.72kJ/mol）。Rancimat方法和非等温差示扫描量热法（DSC）表明，CA胜过叔丁基对苯二酚（TBHQ），一种合成的食品级抗氧化剂，既延长了氧化诱导期，又降低了OA的反应速率。OA的Ea(表观反应活化能),TBHQ+OA,CA+OA分别为50.59、57.32和66.29kJ/mol，表明CA可以提高OA的Ea和热氧化稳定性。
