Preferential Enrichment of Enantiomer from Amino Acid Schiff Bases by Coordination Interaction and Crystallization

Abstract

In this paper, preferential enrichment (PE) is described for three pairs of novel amino acid Schiff base Cu(II)/Cu(I) complexes. Single crystal X-ray diffraction indicated that 1-S/R are one-dimensional coordination polymers (CPs) with helical structures, and 2-S/R and 3-S/R are one-dimensional CPs with auxiliary ligands. By tuning the pH, the solvent and second ligands, the 1-S/R, 3-S/R underwent polymorphic transitions, resulting in enantioselective liberation of excess enantiomers into solution, until the deposited crystals were slightly enriched with the opposite enantiomer, thereby successfully exhibiting PE. However, under the effects of Cu(II), the solvent and low pH, 2-S/R did not exhibit PE and resulted in enrichment of racemic compounds, which was attributed to amino acid Schiff base chiral complex mechanisms of PE. The three pairs of Cu complex structures were characterized by UV-vis, MS and X-ray photoelectron spectroscopy (XPS). All chiral properties were studied by circular dichroism (CD) in the solid and liquid.

Recent Advances in Chiral Schiff Base Compounds in 2023

“…As a method for introducing optical activity, there is a preferential enrichment of enantiomers through racemic crystallization. A new example from the amino acid Schiff base was shown [5]. Reports of new cases of rare phenomena are expected to play a role in deepening new understanding of their mechanisms and principles.…”

Exploring enantioselective recognition of dTMP-Co-bpe coordination polymer for natural amino acids using molecular simulations and circular dichroism

“…It is necessary to investigate the stereochemical configurations of amino acids, which exist in two enantiomeric configurations. 2 Typically, amino acids occur in the L form in organisms and the natural world. Conversely, the presence of the D-form in the human body often indicates pathological conditions, aging, and other concerning health indicators.…”