Abstract

Previous research demonstrated the dependence of the optical properties of aqueous L-methionine solutions on the concentration of zinc cations. Given that this phenomenon may offer a potential method for controlling the metabolism of active pharmaceutical ingredients, this article presents a detailed study of the optical activity of zinc complexes with L- and D-amino acids (AAs). In this study, we used automated polarimetry with automatic temperature correction via a Peltier system, dynamic laser light scattering, X-ray diffraction analysis, and biotesting on a cellular biosensor. Our results showed a dramatic difference in the dependence of optical activity on pH value for the aqueous solution of a zinc-chelate compound with L-aspartate compared to the free AA. X-ray diffraction analysis of tridentate dicarboxylic AA with Zn2+ revealed the formation of a crystallized polymer compound at pH values higher than 5.6. Zn2+ affects the chirality of aqueous solutions of bidentate monocarboxylic L- and D-AA: the rotation angle of the solutions increases for D-Val and decreases for L-Val ranging from –0.2 to +0.2 degrees, respectively. For tridentate tricarboxylic L- and D-AA, the effect of zinc on the chirality of the aqueous solution is just the opposite. The cellular biosensor of Spirostomum ambiguum is not sensitive to free AA but responds significantly to zinc complexes with L- and D-Asp. We hypothesize that chelation of L- and D-AA with zinc at pH 5.5–6.0 leads to the formation of complexes with a specific optical activity, which aligns well with the theory of predetermined chirality.

Key words: predetermined chirality; metal toxicity; zinc chelates, Spirotox, α-amino acids.