胆钙化醇通过能量转移的异构化作为一种针对黄素敏化光氧化的保护机制。
Isomerization of Cholecalciferol through Energy Transfer as a Protective Mechanism Against Flavin-Sensitized Photooxidation.
机构信息
†Instituto de Química de São Carlos, Universidade de São Paulo, Avenida Trabalhador São Carlense 400, CP 780, 13560-470 São Carlos, Brazil.
‡Food Chemistry, Department of Food Science, University of Copenhagen, Rolighedsvej 30, DK-1958 Frederiksberg C, Denmark.
出版信息
J Agric Food Chem. 2015 May 13;63(18):4629-37. doi: 10.1021/jf505958c. Epub 2015 Apr 29.
Cholecalciferol, vitamin D3, was found to isomerize to 5,6-trans-vitamin-D3 with a quantum yield of 0.15 ± 0.01 in air-saturated 7/3 tert-butyl alcohol/water (v/v) at 25 °C, increasing to 0.32 ± 0.02 in the absence of oxygen, through quenching of triplet excited state flavin mononucleotide, FMN, rather than becoming oxidized. The quenching was found by laser flash photolysis to have a rate constant of 1.4 × 10(8) L mol(-1) s(-1) in 7/3 tert-butyl alcohol/water (v/v) at 25 °C, assigned to energy transfer from (3)FMN* to form a reactive vit.D3 diradical. vit.D3 forms a 1/1 precomplex with FMN by hydrophobic stacking with ΔH° = -36 ± 7 kJ mol(-1) and ΔS° = -4 ± 3 J mol(-1) K(-1), as shown by single photon counting fluorescence spectroscopy and steady-state fluorescence spectroscopy. Both ground-state precomplex formation and excited-state energy transfer seem important for vit.D3 protection against flavin-sensitized photooxidation of nutrients in food and biological systems.
胆钙化醇，维生素 D3，在 25°C 的空气饱和 7/3 叔丁醇/水（v/v）中，量子产率为 0.15±0.01 异构化为 5,6-顺式维生素 D3，在没有氧气的情况下增加到 0.32±0.02，通过猝灭三线态激发态黄素单核苷酸（FMN），而不是被氧化。通过激光闪光光解发现，在 25°C 的 7/3 叔丁醇/水（v/v）中，猝灭的速率常数为 1.4×10(8)Lmol(-1)s(-1)，归因于 FMN*的能量转移，形成活性维生素 D3 二自由基。维生素 D3 通过疏水性堆积与 FMN 形成 1/1 预复合物，ΔH°=-36±7kJmol(-1)和ΔS°=-4±3Jmol(-1)K(-1)，如单光子计数荧光光谱和稳态荧光光谱所示。看来，基态预复合物形成和激发态能量转移对于维生素 D3 防止食物和生物系统中黄素敏化的营养物光氧化都很重要。
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