Pseudoenantiomeric Fluorescent Sensors in a Chiral Assay

Two enantioselective fluorescent sensors, namely, the 1,1'-binaphthol (BINOL)-amino alcohol (S)-1 and the H(8)BINOL-amino alcohol (R)-2, have been prepared as a pseudoenantiomeric pair. These two compounds have the opposite chiral configuration at both the axially chiral biaryl centers and the amino alcohol units. In methylene chloride solution, (R)-mandelic acid greatly enhances the emission of (S)-1 at λ(1) = 374 nm and (S)-mandelic acid greatly enhances the emission of (R)-2 at λ(2) = 330 nm. A 1:1 mixture of (S)-1 and (R)-2 was used to interact with mandelic acid at a variety of concentrations with various enantiomeric compositions. It was found that both the concentration of mandelic acid and its enantiomeric composition can be directly determined by measuring the sum and difference of the fluorescence intensities at λ(1) and λ(2).