An infinite chiral single-helical structure formed in Cu(II)-L-/D-glutamic acid system

Article abstract of DOI:10.1016/S0020-1693(98)00224-2

Reaction of Cu(ClO₄)₂·6H₂O with L-glutamic acid (L-glu) in 1:1 or 1:2 molar ratio at pH 5 gave only the complex [Cu(L-glu)-(H₂O)]·H₂O, whose crystal structure revealed that the copper atom was coordinated in square-planar geometry, with the amino nitrogen and the carboxylate oxygen of L-glu, the side-chain carboxylate oxygen of a neighboring L-glu, and the oxygen of a water molecule in the equatorial positions. Weak coordination of two additional glutamate oxygens to both axial positions complete a distorted octahedron. The [Cu(L-glu) (H₂O)] units linked by coordination of the side-chain carboxylate group form an infinite left-handed single helix; the use of D-glu in place of L-glu gives a right-handed helix, indicating that the glu enantiomerism determines the helicity. Thermogravimetric and differential thermal analyses of the complex showed reversible desorption of just two water molecules at 95-130°C, whose behavior was examined by ESR and circular dichroism spectral and powder X-ray diffraction methods in solid state. The crystals obtained from the reaction of Cu(II) ion with DL-glu showed spontaneous resolution.