Interaction between thiamine hydrochloride and lipoic acid.

An interaction between thiamine hydrochloride and DL-alpha-lipoic acid in aqueous solution was depicted. Evidence is presented through spectrophotometric as well as vapour pressure measurements to show that thiamine hydrochloride and DL-alpha-lipoic acid form a single 1:1 complex. The stability constant and the molar extinction coefficient of the complex (at 244 nm) were determined at 25 degrees C and found to be 3.1-10(4) and 970, respectively. Vapour pressure measurements at 60 degrees C reveal that more or less complete dissociation of the complete takes place at this temperature.