The association constant for calcium binding to hydroxybenzoates in aqueous 0.16 M NaCl at 25 °C was found electrochemically to have the value Kass = 280 mol L-1 with ΔHo = -51 kJ mol-1, ΔSo = -122 J mol-1 K-1 for the 2-isomer (salicylate), Kass = 7 mol L-1 with ΔHo = -39 kJ mol-1, ΔSo = -116 J mol-1 K-1 for the 3-isomer, and Kass = 8 mol L-1 with ΔHo = -51 kJ mol-1, ΔSo = -155 J mol-1 K-1 for the 4-isomer. The 3- and 4-isomers were found more efficient as antioxidants than the 2-isomer in decreasing oxygen consumption rate in a peroxidating methyl linoleate emulsion and less sensitive to presence of calcium. All isomers were found prooxidative for iron-catalyzed initiation of oxidation due to enhanced radical formation as shown by electron spin resonance spectroscopy. Calcium salicylate was found to have low solubility with a solubility product Ksp = 4.49·10-6 based on activity with ΔHo = 67 kJ mol-1, ΔSo = 123 J mol-1 K-1 for dissolution in water, when corrected for the strong complex formation. Calcium in food and beverages may thus lower antioxidant activity of plant phenols through complexation or by precipitation.

中文翻译：

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异构羟基苯甲酸酯的抗氧化活性和钙结合

在 25 °C 的 0.16 M NaCl 水溶液中，钙与羟基苯甲酸盐结合的缔合常数通过电化学方法发现，Kass = 280 mol L-1，ΔHo = -51 kJ mol-1，ΔSo = -122 J mol-1 K -1 对于 2-异构体（水杨酸盐），Kass = 7 mol L-1，ΔHo = -39 kJ mol-1，对于 3-异构体，ΔSo = -116 J mol-1 K-1，Kass = 8 mol L-1，ΔHo = -51 kJ mol-1，ΔSo = -155 J mol-1 K-1 为 4-异构体。发现 3-和 4-异构体作为抗氧化剂比 2-异构体在降低过氧化亚油酸甲酯乳液中的耗氧率方面更有效，并且对钙的存在不太敏感。如电子自旋共振光谱所示，由于增强的自由基形成，发现所有异构体对铁催化的氧化起始具有促氧化作用。发现水杨酸钙具有低溶解度，溶解度积 Ksp = 4.49·10-6 基于 ΔHo = 67 kJ mol-1，ΔSo = 123 J mol-1 K-1 溶解在水中的活性，当校正为强复杂的形成。因此，食品和饮料中的钙可能通过络合或沉淀降低植物酚的抗氧化活性。