The reaction energetics of the multiple free radical scavenging mechanisms of ellagic acid and its derivatives were studied by DFT method. Ellagic acid and its derivatives that bear catechol or guaiacyl moieties can proceed multiple free radical scavenging processes. Intramolecular hydrogen-bonds were found in the most stable geometries of the investigated compounds and can influence the antioxidant activity of the related groups and hydrogen atom/proton loss sequence. The stronger hydrogen-bond, the weaker antioxidant activity of the hydrogen atom/proton-donating group. The preferred mechanisms vary among different phases. All of the investigated compounds prefer to trap free radicals by multiple HAT mechanisms in gas and benzene phases. The second HAT reaction preferably occurs in the same catechol or guaiacyl unit of the first HAT group with the formation of stable quinone or benzodioxole. The catechol and guaiacyl moieties not only retain high free radical scavenging ability of the parent compounds but even show increased potency for the second and fourth H+/e‒ reactions. In water phase, ellagic acid and its derivatives would proceed consecutively PL reactions from the OH groups. The formed di/tri/tetra-anion would proceed one/four electron transfers following with single/double SPLET mechanism and electron donation reactions until forming the stable quinone or benzodioxole.

中文翻译：

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鞣花酸及其衍生物在多种 H+/e- 过程中的自由基清除能力

采用DFT方法研究了鞣花酸及其衍生物多种自由基清除机制的反应能量学。带有儿茶酚或愈创木酰基部分的鞣花酸及其衍生物可以进行多种自由基清除过程。在所研究化合物的最稳定几何结构中发现了分子内氢键，并且可以影响相关基团的抗氧化活性和氢原子/质子损失序列。氢键越强，氢原子/供质子基团的抗氧化活性越弱。优选的机制因不同阶段而异。所有研究的化合物更喜欢通过多种 HAT 机制在气相和苯相中捕获自由基。第二次HAT反应优选发生在与形成稳定的醌或苯并二氧杂环戊烯的第一HAT基团的相同儿茶酚或愈创木酰基单元中。儿茶酚和愈创木酚基部分不仅保留了母体化合物的高自由基清除能力，而且甚至显示出对第二和第四 H+/e- 反应的增强效力。在水相中，鞣花酸及其衍生物会从 OH 基团连续进行 PL 反应。形成的二/三/四-阴离子将进行一/四电子转移，遵循单/双 SPLET 机制和给电子反应，直到形成稳定的醌或苯并二氧杂环戊烯。儿茶酚和愈创木酰基部分不仅保留了母体化合物的高自由基清除能力，而且甚至显示出对第二和第四 H+/e- 反应的效力增加。在水相中，鞣花酸及其衍生物会从 OH 基团连续进行 PL 反应。形成的二/三/四-阴离子将进行一/四电子转移，遵循单/双 SPLET 机制和给电子反应，直到形成稳定的醌或苯并二氧杂环戊烯。儿茶酚和愈创木酰基部分不仅保留了母体化合物的高自由基清除能力，而且甚至显示出对第二和第四 H+/e- 反应的效力增加。在水相中，鞣花酸及其衍生物会从 OH 基团连续进行 PL 反应。形成的二/三/四阴离子将进行单/双 SPLET 机制和给电子反应的一/四电子转移，直到形成稳定的醌或苯并二氧杂环戊烯。