Induced circular dichroism active complexes of synthetic gadolinium(III) porphyrinates with chiral amino acids

Synthetic gadolinium(III) meso-tetrakis(3,5-di-tert-butylphenyl)porphyrinat es extracted zwitterionic L-phenylglycine from an aqueous solution to give a 1:1 complex in benzene through synergistic binding of both amino and carb oxylic groups of the amino acids. The resulting highly coordinated complex afforded intense circular dichroism (CD) bands of reversed S-shape type at the Soret region (400-450 nm). In the case of D-phenylglycine, a complete m irror image of the CD spectrum was recorded after extraction. While the int ensity of the induced CD peak was affected by the nature of the organic sol vent, meso-aryl substituent and C-alpha-residue, its sign was well related to the stereochemistry of the bound amino acid. A combination of biphasic e xtraction and CD spectrometry provides a promising method for determination of the absolute configuration of unprotected alpha-amino acids. (C) 2000 E lsevier Science S.A. All rights reserved.