AN INFINITE CHIRAL SINGLE-HELICAL STRUCTURE FORMED IN CU(II)-L- D-GLUTAMIC ACID SYSTEM/

Reaction of Cu(ClO4)(2). 6H(2)O 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 po sitions complete a distorted octahedron. The [Cu(L-glu) (H2O)] units l inked by coordination of the side-chain carboxylate group form an infi nite left-handed single helix; the use of D-glu in place of L-glu give s a right-handed helix, indicating that the glu enantiomerism determin es the helicity. Thermogravimetric and differential thermal analyses o f the complex showed reversible, desorption of just two water molecule s at 95-130 degrees C, whose behavior was examined by ESR and circular dichroism spectral and powder X-ray diffraction methods in solid stat e. The crystals obtained from the reaction of Cu(II) ion with DL-glu s howed spontaneous resolution. (C) 1998 Elsevier Science S.A. All right s reserved.