Rapid enantiomeric excess and concentration determination using simple racemic metal complexes

Abstract

Racemic-metal complexes were used to determine identity, enantiomeric excess, and concentration of chiral diamines using metal-to-ligand charge transfer bands in circular dichroism spectroscopy. It takes under just 2 min per sample to determine [G]t and %R with tolerable errors (19% and 4%, respectively). The simplicity of the achiral receptors employed confers to this technique great potential for high-throughput screening.

Figure 1

(A) Diamines employed: 1,2-phenylethylenediamine (PD), 1,2-diaminocyclohexane (DC), 1,2-diaminopropane (DP), bis-(4-methoxyphenyl)-1,2-diaminoethane (MD). (B) Racemic-metal complexes employed.

Figure 2

CD spectra of receptors [0.4 mM] with the guests [0.8 mM]: (A) (Rac)-1 and (B) (Rac)-2.

Figure 3

LDA plots obtained with the: (A) receptor 1, (B) receptor 2.

Figure 4

Linear discriminate analysis for a combination of all receptors.

Figure 5

(A) Titration of receptor 2 [0.4 mM] with enantiomers of DP at 381 nm. (B) PCA plot of DP with four ee training sets at four different [G]_t values: 0.2, 0.4, 0.8, 1.4 mM.