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Abstract
Each of reduction-polarograms of vitamin A-alcohol, -palmitate and β-carotene showed three steps in 60 vol% benzene-acetonitrile mixture containing 0.1 M-tetrabutylammonium iodide. The first half-wave potentials were determined at -1.41 V vs. Hg-pool for the alcohol, -1.23 V for the palmitate and -1.02 V for β-carotene. The second half-wave potentials were determined at -1.65 V identically for first two vitamins and -1.67 V for β-carotene. The third waves were raised at ca. -2.0 V but were quite ill-defined. All of the first and the second waves were controlled by diffusion and those wave-heights were proportional to concentrations of the vitamins and β-carotene in the range from 5×10-5M (ca. 50 IUA•ml-1) to 10-3 M (ca. 1000 IUA•ml-1).
Calculations with Ilkovic Eqn. and Perrin Eqn. gave n≈4 for the first and the second waves of β-carotene, and n≈2 for those of vitamin A and its palmitate.
A preliminary study on vitamin A-acetate was also made under the same experimental conditions. The first and the second half-wave potentials of vitamin A-acetate were -1.26 V and -1.66 V vs. Hg, respectively, and the proportionalities between wave-heights and concentration were held in the same concentration range as above.
Abstract
Polarographic and spectrophotometric examinations on reduction-products obtained by electrolyses at controlled potentials led to the following interpretations in electrode-reductions of vitamin A and its related compounds in acetonitrile-benzene mixture. Each of vitamin A-aicohol and -palmitate is reduced to a structure of conjugated four double-bond system at the first step, and then, at the second step to a conjugated three double-bond system. The first reduction-products of β-carotene are not uniform and their structures cannot be clarified, but the second reduction-products show absorption spectra of conjugated three double-bond system, consequently, products by the third reduction-step would have a structure of conjugated two double-bond.