Formation of Chiral Aggregates of Acylamino Acids in Solutions

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Abstract
An alcoholic solution of optically active acylamino acid (AAA) was found to show a circular dichroism (CD) band at 212 nm. The CD band should be inherent to the solution system, since AAA and alcohol per se have no absorption band at this wavelength. The CD band intensity decreased on addition of urea and rise in temperature. This is attributed to the formation of chiral aggregate through hydrogen bonds among AAA molecules. Hydrophobic interaction seems to be of minor importance for the formation of the chiral aggregate in alcoholic solution, since the variation of the chain length in the acyl group or addition of myristic acid did not affect the magnitude of profile of the CD band. In aqueous solutions, salts of optically active AAA formed micelles with hydrophobic interactions among the molecules, and only in the case of optically active monosodium salt of N-acylglutamic acid (AGS) showed a CD band at 220 nm resulting from the formation of chiral hydrogen bonds at concentrations above the critical micelle concentration (CMC). This type of chiral aggregation may be caused by the existence of free carboxyl group in the optically active AGS molecule.

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