Specific effects of urea and anions on the optical rotatory properties of aqueous amino acid solutions

Changes in the optical rotatory properties of amino acids are induced by 6 m urea, which cannot be ascribed to systematic changes in the ionization state of the amino acid, nor to refractive index changes. Extremes of acidity or alkalinity generally cancel the effect. The effects of common salts at 0.1 m concentration are generally small, and additive to the urea effect. Below pH 4.5, NaF at 0.1 m has an effect as strong as urea. This effect has been correlated with changes in the circular dichroism. A fluoride effect is noted for lactic acid also.