Chiral phosphorescent probes for amino acids: hybrids of iridium(III) complexes with synthetic saponite
An attempt of developing a chiral luminescent probe for amino acids was described. Two types of chiral iridium(III) complexes were synthesized: [Ir(dfppy)2(R-pep-bpy)]+ (dfppyH = 2-(2′,4′-difluorophenyl)pyridine); R-pep-bpy = 4,4′-bis((R-1,2-dimethylpropyl)aminocarbonyl-2,2′-bipyridine) and [Ir(piq)2(R-pep-bpy)]+ (piqH = 1-phenyisoquinoline). In both complexes, amido groups (R-pep-) were attached to 2,2′-bipyridine with an intension of increasing the affinity for an amino acid. The complexes were optically resolved on a chiral column. When the complexes were adsorbed by the colloidal particles of synthetic saponite, they were highly emissive even in a medium containing water. The remarkable quenching of emission was observed for the combination of [Ir(dfppy)2(R-pep-bpy)]+ and tryptophan methyl ester. By the use of the enantiomeric complexes, the possibility of enantioselective quenching was examined for various amino acid derivatives.