Photodegradation of folate sensitized by riboflavin

TY - JOUR

T1 - Photodegradation of folate sensitized by riboflavin

AU - Scurachio, Regina S.

AU - Skibsted, Leif Horsfelt

AU - Metzker, Gustavo

AU - Cardoso, Daniel R.

PY - 2011/7

Y1 - 2011/7

N2 - Folate is shown to react with singlet-excited state of riboflavin in a diffusion controlled reaction and with triplet-excited state of riboflavin in a somewhat slower reaction with 3kq = 4.8 × 10 8 L mol-1 s-1 in aqueous phosphate buffer at pH 7.4, ionic strength of 0.2 mol L-1, and 25°C. Singlet quenching is assigned as photo-induced reductive electron transfer from ground state folate to singlet-excited riboflavin, while triplet quenching is assigned as one-electron transfer rather than hydrogen atom transfer from folate to triplet-excited riboflavin, as the reaction quantum yield, φ = 0.32, is hardly influenced by solvent change from water to deuterium oxide, φ = 0.37. Cyclic voltammetry showed an irreversible two-electron anodic process for folate, E = 1.14 V versus NHE at a scan-rate of 50 mV s-1, which appears to be kinetically controlled by the heterogeneous electron transfer from the substrates to the electrode. Main products of folate photooxidation sensitized by riboflavin were pterin-6-carboxylic acid and p-aminobenzoyl-l- glutamic acid as shown by liquid chromatographic ion-trap mass spectrometry (LC-IT-MS). Folate reacts with triplet-excited riboflavin with 3kq = 4.8 × 108 L mol-1 s -1 in aqueous solution by one-electron transfer from folate to triplet-excited riboflavin. The reaction quantum yield of φ = 0.32 confirms an efficient photodecomposition of folate sensitized by riboflavin producing mainly pterin-6-carboxylic acid, p-aminobenzoyl-l-glutamic and an oxaziridine derived from folate.

AB - Folate is shown to react with singlet-excited state of riboflavin in a diffusion controlled reaction and with triplet-excited state of riboflavin in a somewhat slower reaction with 3kq = 4.8 × 10 8 L mol-1 s-1 in aqueous phosphate buffer at pH 7.4, ionic strength of 0.2 mol L-1, and 25°C. Singlet quenching is assigned as photo-induced reductive electron transfer from ground state folate to singlet-excited riboflavin, while triplet quenching is assigned as one-electron transfer rather than hydrogen atom transfer from folate to triplet-excited riboflavin, as the reaction quantum yield, φ = 0.32, is hardly influenced by solvent change from water to deuterium oxide, φ = 0.37. Cyclic voltammetry showed an irreversible two-electron anodic process for folate, E = 1.14 V versus NHE at a scan-rate of 50 mV s-1, which appears to be kinetically controlled by the heterogeneous electron transfer from the substrates to the electrode. Main products of folate photooxidation sensitized by riboflavin were pterin-6-carboxylic acid and p-aminobenzoyl-l- glutamic acid as shown by liquid chromatographic ion-trap mass spectrometry (LC-IT-MS). Folate reacts with triplet-excited riboflavin with 3kq = 4.8 × 108 L mol-1 s -1 in aqueous solution by one-electron transfer from folate to triplet-excited riboflavin. The reaction quantum yield of φ = 0.32 confirms an efficient photodecomposition of folate sensitized by riboflavin producing mainly pterin-6-carboxylic acid, p-aminobenzoyl-l-glutamic and an oxaziridine derived from folate.

U2 - 10.1111/j.1751-1097.2011.00916.x

DO - 10.1111/j.1751-1097.2011.00916.x

M3 - Journal article

C2 - 21375537

SN - 0031-8655

VL - 87

SP - 840

EP - 845

JO - Photochemistry and Photobiology

JF - Photochemistry and Photobiology

IS - 4

ER -