Induced circular dichroism by complexation of gadolinium(III) porphyrinates with chiral amino acids and dipeptides: effects of axial β-diketonate ligands on chirality sensing and recognition

Synthetic gadolinium(III)porphyrins with various achiral β-diketonates as axial ligands in benzene solutions extracted chiral α-amino acids and dipeptides from aqueous phases to give intense induced CD peaks in the Soret region via 1:1 supercomplexation. Their CD spectral shapes were dependent on the stereochemistry at the α-positions of amino acids and of the C-terminal components of dipeptides: a reverse S-shape for the l-form and an S-shape for the d-form. When chiral 3-acetylcamphorate was introduced as an axial ligand, Gd(III)porphyrins showed CD spectral changes by supercomplexation with chiral alanylalanine; (+)-acetylcamphorate ligating Gd(III)porphyrin offered larger CD signal with the ll- or dl-form than the corresponding (−)-type Gd(III)porphyrin did, while the former afforded smaller CD peaks by supercomplexation with the dd- or ld-form than the latter Gd(III)porphyrin.