Komplexchemische Methode zur relativen Konfigurationsbestimmung der natürlichen α-Aminosäuren.

Cotton Effect in Copper-Proline Complexes in the Visible Region

“…The molecular structure and the corresponding d-state splitting (15,21) absorption at 600 nm (13)(14)(15). As reported first by Pfeiffer (13) and later examined in detail by Yasui (14), and Hawkins and Wong (15), the d-d electronic transitions in the visible region in this complex demonstrate strong optical rotation. The temperature-dependent studies of CD in the visible region revealed the nature of the states involved in the broad absorption at 600 nm.…”

“…A slight puckering of one of the chelate rings contributes into relaxation of the symmetry of the molecule (15). The molecular structure and the corresponding d-state splitting (15,21) absorption at 600 nm (13)(14)(15). As reported first by Pfeiffer (13) and later examined in detail by Yasui (14), and Hawkins and Wong (15), the d-d electronic transitions in the visible region in this complex demonstrate strong optical rotation.…”

“…According to the Cotton effects and the known structural properties (relaxed D 4h symmetry) the broad absorption consists of two underlying spectral features: a transition to a nearly degenerate E g doublet (yz, xz) at 590 nm and a transition to the B 2g state (xy) at 605 nm, while the lowest energy (above 1000 nm) transition to the A 1g state (z 2 ) is magnetically forbidden (15). Since the complex is planar (19,20,22) the observed chirality in this system is solely attributed to the absolute structure of the ligands (13,15) and to the electronic interactions between metal ion and chelated atoms of oxygen and nitrogen (14,16,23). When detected using ORD or CD methods, the metal ion d-d transitions "translate" the information on the stereo-structure of the ligands (typically collected in the near-UV region) into the visible spectral region.…”

“…For example, Cotton effects in CD spectra clearly distinguished and featured the subset of underlying d-d electronic transitions in complexes of copper with different amino acids (14,15). In the case of ORD measurements, reported spectra show a broad positive or negative sum of the Cotton effects depending on the absolute structure of the ligands (5,13). In this article we take advantage of the electronic properties of Cu(II) complex with proline to show the Cotton effect in the visible region.…”

“…Optical activity in transition-metal complexes, observed first by Cotton in 1895 (12), has been the focus of systematic research since its discovery (13)(14)(15)(16). Optical properties in transition-metal chelates (splitting of d states) depend on the symmetry of the complex.…”