Abstract
Solubility properties of L-tryptophan in aqueous solution was discussed on the basis of the effects of 3rd component on the optical rotatory dispersion (ORD) and on the adsorption by carbon black. ORD data showed the optical rotation of L-tryptophan around 450 mμ was suitable in analyzing the effect of 3rd component on it. Adsorption data indicated the respective hydrophobicities of the present 3rd components. Alcohols and glycols were classified into three types according to the similarities in hydrophobicity and in structure. Except for urea, formamide and dimethylsulfoxide, there was found a correlation between the ORD and the adsorption data. Alcohols were considered to give effect selectively on the indole group of L-tryptophan, while glycols to give effect also on the moiety other than the indole group. Urea and formamide might give effect on the hydrophilic moiety of L-tryptophan to result in the decrease in optical rotation, but this effect was considered to have no relation to the increase in solubility. Analyzing the relationship between the ORD and the adsorption data, the present 3rd components were classified into three types, corresponding to the previous classification according to solubility studies. Finally, the results verified the concept regarding the contact of 3rd component with L-tryptophan to result in the increase in solubility in aqueous solution.
