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The Photochemistry of Lipoic Acid: Photoionization and Observation of a Triplet Excited State of a Disulfide
Author(s) -
Bucher Götz,
Lu Changyuan,
Sander Wolfram
Publication year - 2005
Publication title -
chemphyschem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.016
H-Index - 140
eISSN - 1439-7641
pISSN - 1439-4235
DOI - 10.1002/cphc.200500211
Subject(s) - photoionization , excited state , photochemistry , triplet state , chemistry , ionization , atomic physics , organic chemistry , ion , physics
Under short‐wavelength UV irradiation, lipoic acid (LipSS) and its reduced form, dihydrolipoic acid (DHLA), undergo photoionization processes through a bi‐ or monophotonic pathway. After ionization, the LipSS radical cation (LipSS . + ) and radical anion (LipSS . − ) are generated. LipSS . − can be converted to equimolar amounts of LipSS and DHLA through second‐order decay. Triplet acetone can be quenched by LipSS and DHLA with a rate close to the diffusion‐controlled limit. The mechanism was further confirmed by continuous irradiation experiments. When LipSS is directly irradiated with UVA light, the first excited triplet state of LipSS is observed, with a lifetime τ =75 ns. Characteristic reactions include triplet energy transfer to oxygen and β‐carotene and addition to isoprene. The lifetime of triplet LipSS is also shortened by addition of water and methanol.