Crystal Structures of Mixed Ligand Copper(II) Complexes Containing l-Amino Acids. I. l-Asparaginato-l-histidinato-copper(II) and Its Hydrate

Abstract

Two copper complexes containing l-histidine and l-asparagine crystallize from aqueous solution at pH 7.0. Both crystals are monoclinic, space group P21. l-Asparaginato-l-histidinatocopper(II): a=10.913(3), b=12.911(4), c=10.206(3) Å, β=113.83(2)°, Z=4. l-Asparaginato-l-histidinatoaquacopper(II) trihydrate: a=12.654(4), b=11.623(4), c=5.931(2) Å, β=100.47(3)°, Z=2. In both structures, four coordinating atoms in an approximately planar arrangement around copper are the α-amino and imidazole δ-nitrogen atoms of l-histidine and α-amino nitrogen and α-carboxyl oxygen of l-asparagine. The fifth coordination site is occupied by the α-carboxyl oxygen of l-histidine. Difference between the two complex crystals is found at the sixth coordination site; a water molecule is coordinated in the hydrated crystal to complete a distorted octahedral environment, while in the anhydrous crystal this site is unoccupied so that the geometry of the complex is square-pyramidal.

Conformational Analyses of Physiological Binary and Ternary Copper(II) Complexes with l‐Asparagine and l‐Histidine; Study of Tridentate Binding of Copper(II) in Aqueous Solution

“…Generally, in the experimental studies in solutions, the tridentate nature of l ‐His was exclusively supposed to be in the H mode with an axially placed O in the ternary copper(II) amino acid complexes . Such an l ‐His coordination was observed in the X‐ray crystal structures of Cu( l ‐His) 2 , Cu( l ‐His)( l ‐Thr), and Cu( l ‐His)( l ‐Asn) . However, as l ‐His has three donor groups which may be placed in a unique axial position, two more tridentate binding modes can exist as follows: with apical N im in the GN and GNp conformers, and apical N am in the IN conformers (Table ).…”

“…The solid‐state copper(II)‐ l ‐Asn complexes were characterized by the IR spectra [Cu( l ‐Asn) 2 , Cu( l ‐His)( l ‐Asn)], a Raman spectrum of Cu( l ‐Asn) 2 , the electron paramagnetic resonance (EPR) spectra of Cu( l ‐Asn) 2 , and by the X‐ray single crystal structural analysis . Cu( l ‐Asn) 2 crystallized as an anhydrous trans compound .…”

“…Cu( l ‐Asn) 2 crystallized as an anhydrous trans compound . The X‐ray crystal and molecular structures of an anhydrous Cu( l ‐His)( l ‐Asn) complex and an aqua trihydrate [Cu( l ‐His)( l ‐Asn)(H 2 O)⋅3H 2 O] modification were determined …”

Investigation of the reactions of hexanitrocobaltate(III) with amino acids. XIII. The structure and absolute configuration of (–)589-ab-(histidinato-N,N')-cdf-(histidinato-O,N,N')-e-nitrocobalt(III) monohydrate

“…In the crystal structure of [Cd(L-his) 2] (Fuess & Bartunik, 1976), the Co-O bond length is 0.2,4, longer than the Co-N bond lengths. Metal-oxygen distances are even longer in complexes [Zn(D-his)(L-his)]- (Harding & Cole, 1963), [Zn(D-his) 2] (Kretsinger, Cotton & Bryan, 1963) and [Cu(L-his)(L-asn)] (Ono, Shimanouchi, Sasada, Sakurai, Yamauchi & Nakahara, 1979); the principal coordination sites of histidine in these compounds are imidazole and amino N atoms, with a close approach of carboxylato O atoms. In the structures of (-)-[CoNO2(L-hiS)E].H20 and [Cu(Lhis)(D-his)(H202)].…”

A speciation model of essential trace metal ions in phloem

“…5B. Crystal structures have also been determined for the mixed-ligand complexes Cu(His)(Thr) [102] and Cu(His)(Asn) [103], and both complexes have essentially the same mode of bonding. The His ligand is tridentate, while the Thr and Asn ligands are bidentate, with their side chains oriented in the direction of the axial carboxylate group of the histidine.…”