Optical activity of d-d transitions in copper(II) complexes of dipeptides and dipeptide amides. Molecular orbital model

Abstract

The chiroptical properties associated with the d-d and low-lying charge-transfer transitions in a series of four-coordinate and six-coordinate Cu(II)-dipeptide and Cu(II)-dipeptide amide complexes are calculated on a semiempirical molecular orbital model. Electronic rotatory strengths are calculated directly using wave functions of the entire complex generated from the molecular orbital model. Excited states are constructed in the virtual orbital approximation and electric and magnetic dipole transition integrals are computed including all one-, two-, and three-center contributions. The results are compared to those obtained using other theoretical models of molecular optical activity, to semiempirically derived spectra-structure relationships and rules formulated for pseudotetragonal metal complexes, and to empirical data.

Interactions of Nickel(II) with Histones. Stability and Solution Structure of Complexes with CH3CO-Cys-Ala-Ile-His-NH2, a Putative Metal Binding Sequence of Histone H3

“…The geometry of these complexes is distorted from regular square due to sterical crowding between the thiol and the imidazole ring, a phenomenon similar to those observed previously for other complexes with His-containing peptides (37,40,41). The d-d bands of this species would be expected to have a very weak CD due to the existence of only the large macrochelate loop and the resulting conformational nonrigidity (42). In such a situation, the asymmetric effects of the electronic density localized on chirality centers of the peptide molecule effectively cancel out.…”