The effect of biothiol on UV irradiated alpha-lipoic acid.

alpha-Lipoic acid (LA) and its reduced form dihydrolipoic acid (DHLA) are well known as strong antioxidants. LA has the characteristic distorted five membered 1,2-dithiolane ring, which is quite vulnerable to UV irradiation. The UV induced decomposition of LA and the effect of the following addition of biothiols to the photoirradiated solution of LA were investigated by UV-vis spectrometry and (1)H NMR spectral analysis. The mechanism of UV irradiated LA decomposition was proposed based on the results obtained from NMR and GPC measurements.