†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.
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。
