Praseodymium Metallacrown-Based NMR Probe for Enantioselective Discrimination of Mandelate Anions in Water
Мarina A. Katkova, Galina S. Zabrodina, Roman V. Rumyantcev, Grigory Zhigulin, Maria S. Muravyeva, Andrey S. Shavyrin, Dmitriy G. Sheven, Sergey Yu. Ketkov
Abstract
Recently, the enhanced interest in water-soluble aminohydroximate Ln(III)–Cu(II) metallacrowns (MC) is largely due to their fascinating structural chemistry, diverse properties and ease of synthesis. We examined the water-soluble praseodymium(III) alaninehydroximate complex Pr(H 2 O) 4 [15-MC Cu(II)Alaha -5]·3Cl ( 1 ) as a highly effective chiral lanthanide shift reagent for NMR analysis of the biologically relevant (R/S)-mandelate (MA) anions in aqueous media. The R-MA and S-MA enantiomers can be easily discriminated in the presence of small (1.2–6.2 mol %) amounts of MC 1 by the 1 H NMR signals of multiple protons exhibiting an enantiomeric shift difference (ΔΔδ) of 0.06 ppm up to 0.31 ppm. Additionally, a possibility of coordination of MA to the metallacrown was investigated by the ESI-MS technique and a Density Functional Theory modeling of the molecular electrostatic potential and noncovalent interactions.