Synthesis and Study of Copper(II) Complexes with Aspartic Acid, Serine, and Valine

Abstract

Binary and ternary copper(II) complexes with aspartic acid (H 2 Asp), serine (HSer), and valine (HVal) were prepared by electrochemical and chemical procedures. The purity of the compounds was confirmed by elemental and thermogravimetric analyses. According to the IR spectra, all the complexes contain a five-membered chelate ring in which the Cu(II) atom is bonded with the oxygen atom of the carboxy group and nitrogen atom of the amino group. This is also confirmed by the ESR spectra.Complexation of natural amino acids as components of proteins is of undoubted interest [1]. It is particularly urgent to study mixed-ligand complexes, since real biological systems simultaneously contain several substances capable of complexation with a metal ion. For example, it is known [2] that mixedligand complexes involving two amino acids play an important role in metal transport.Copper is an essential trace element in a human body [3]; the majority of Cu(II) ions in blood plasma are in the form of mixed complexes with amino acids, peptides, and other biomolecules [4]. A series of mixed-ligand Cu(II) complexes with amino acids in solution were studied by polarography [5], UV spectroscopy [6], circular dichroism spectroscopy [7], ESR [8], potentiometry [6, 9311], and voltammetry [12]; their stability constants were determined, and their structure in solution was discussed.Examination of properties of solid mixed-ligand complexes can reveal relationships between the bioactivity of a compound and its composition and structure. Despite numerous papers concerning complexation of Cu(II) ions with amino acids, the structure and properties of solid binary and ternary compounds are studied insufficiently. This may be caused, in particular, by the fact that it is difficult to prepare and isolate these compounds pure. Previously [13,14] we suggested a procedure for anodic synthesis of binary compounds of d elements with various organic ligands, showing advantages as compared to common chemical synthesis of these compounds. We determined the range of potential difference between the electrodes of the electrochemical cell, at which the compounds could be prepared in high yields (90 3 95%) without side anodic processes.The goal of this study was to examine the possibility of electrochemical synthesis of mixed-ligand complexes in various media, to compare the results with those yielded by chemical synthesis, and to determine the physicochemical properties of the complexes.We found that pure organic solvents (acetonitrile, ethanol, dioxane, dimethylformamide, dimethyl sulfoxide) are unsuitable for electrochemical synthesis, because amino acids are poorly soluble in them.Evaluation of the solubility of 1 : 1 amino acid mixtures (H 2 Asp3HVal, H 2 Asp3HSer) in aqueousorganic solvents showed that acceptable solubility (~0.05 M) is provided by water3ethanol (60 390% alcohol) and water3dioxane (80 390% dioxane) mixtures. When amino acids are taken in a 1 : 1 ratio, the relative content of the CuLL`species in the nearelectrode space is several times...

Synthesis and Characterization of Mixed Ligand Complexes of Cu(II)-Oxalate-Amino Acids (Aspartic acid and Cysteine)

“…The important IR spectral bands for the ligands and their copper complexes are given in Table-2. The IR frequencies for ligands are in good agreement with those reported in the literature 12,13 . The mixed ligand complexes exhibit strong characteristic vibrations for the carbonyl groups of the oxalate ligand.…”

A combined experimental and quantum mechanical investigation on some selected metal complexes of l-serine with first row transition metal cations

“…The DTA curves of the metal complexes also show similar behavior that corresponds to the TGA curves; the small peaks at the range of 265-342°C which could be attributed to melting of the complexes. Thermal analyses results of this study are in good agreement with those of the [Cu(Ser) 2 ]Á2H 2 O complex prepared in the solution phase [43].…”

“…It is evident from the experimental IR assignments that no free ligand molecules were present after the grinding procedure. The appearance of m(OAH) stretching mode at 3342-3447 cm À1 for L-Ser and all of its metal chelates bears clear evidence of the presence of an associated AOH group in their molecular geometries, besides indicating that L-Ser does not interact with the metal ions via its sidechain AOH group [6,43]. The experimental infra-red spectral data on the asymmetric and symmetric m(NAH) stretching frequencies of L-Ser and its metal complexes suggest that the m as (NAH) and m s (NAH) frequency values of L-Ser (observed at 3215 and 3096 cm À1 respectively) are blue-shifted in all the three metal complexes (3271-3344 and 3176-3258 cm À1 respectively).…”

Self-Organization of Bolaamphiphile Bearing Biphenyl Mesogen and Aspartic-Acid Headgroups

“…However, the band at 1724 cm -1 does not disappear but obviously decreases, which indicates that not all carboxyl groups of aspartic acid headgroups are involved in the coordination. This is because that aspartic acid and copper ion can coordinate into a five-membered chelate ring, with the copper ion bonded to the oxygen atom of the carboxyl group and nitrogen atom of the amino group . Therefore, the hydrogen bonding between the carboxyl groups without being coordinated with Cu 2+ ion is not strong enough to form fiber-like structure, but is strong enough to form uniform-sized spherical structures.…”