Sources of optical activity in complexes of copper(II) with amino acids (proline, hydroxyproline, and allohydroxyproline)
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The vicinal effect of the asymmetric nitrogen is not the dominant contribution to the optical activity of the complexes and scarcely exceeds the vicinal effect of the asymmetricγ-carbon.
The presence or absence of ligands in the axial positions of the complex markedly affects only the position of the weak2B1g→2A1g transition.
The sign and amplitude of the dominant Cotton effect, which seems to represent the2B1g→2B2g transition, is mainly determined by the chirality of the nonplanar chelate rings, whose conformations depend on the presence of substituents on the nitrogen andα-carbon of the ligand and on their interaction with the adjacent ligand and with solvent molecules coordinated in the axial positions.
The conformation of the chelate rings in the allohydroxyproline complexes is locked by the location of theγ-hydroxyl group close to the axial position of the copper.
KeywordsNitrogen Copper Proline Solvent Molecule Hydroxyproline
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