Simultaneous Determination of Concentration and Enantiomeric Composition of Amino Acids in Aqueous Solution by Using a Tetrabromobinaphthyl Dialdehyde Probe

3,3 '-Diformyl-1,1 '-bi-2-naphthol or its methoxymethyl-protected derivative is found to undergo a highly selective reaction with excess bromine in CH2Cl2 at reflux to give the novel 5,5 ',6,6 '-tetrabrominated product (S)- or (R)-2. The observed electrophilic substitution at the 5,5 '-positons of an optically active binaphthyl compound is unprecedented. Unlike unbrominated 3,3 '-diformyl-1,1 '-bi-2-naphthol, which is not suitable for fluorescent recognition in water, compound (S)-2, in combination with Zn2+, exhibits a highly enantioselective fluorescent response toward amino acids in aqueous solution (HEPES buffer, pH 7.4). It is further found that the condensation product of (R)-2 with tryptophan, (R)-3, shows dual-responsive emissions toward amino acids; the short wavelength (lambda(1)=350 nm) emission is sensitive to the concentration of the substrate regardless of the chiral configuration and the long wavelength (lambda(2)>500 nm) emission is highly enantioselective. Thus, the use of (R)-3 allows the simultaneous determination of the concentration and enantiomeric composition of an amino acid sample from one fluorescence measurement.