Neutralization of orotic acid (OrH2) by lithium or magnesium hydroxide in aqueous medium yields the crystalline metal orotate hydrates Li(OrH). H2O (1) and Mg(OrH)2. (H2O)6 (2). By single‐crystal X‐ray diffraction studies it has been shown that 1 (space group P1) forms a layer structure, with lithium in a tetrahedral environment of oxygen atoms from three different orotate( ‐ I) anions (one carboxylate and two uracil oxygen atoms) and the water molecule. 2 (space group P21/c) has been shown to feature a hexaquo complex of magnesium, the Mg(H2O)26 cations being associated with two hydrated OrH⊖ ions only through hydrogen bonds. The anions are also engaged in “base‐pairing” hydrogen bonds between the planar uracil ring systems of different units. The results are relevant for applications of magnesium orotates in magnesium therapy.

Crystalline magnesium, strontium, and barium L‐glutamate complexes containing the dianion L‐Glu2− have been prepared as the tetrahydrate (Mg) and hexahydrates (Sr, Ba), respectively. Their aqueous solutions have pH values of 10.45, 11.05, and 10.93, respectively. The solid state structures of the Mg and Sr complexes have been determined by single crystal X‐ray methods, and the structure of the Ba analogue inferred through its isomorphism with the Sr analogue. The crystals are orthorhombic, space group P212121. The magnesium atoms were found to be hexacoordinated with the L‐glutamate functioning as a chelating N,Oα‐donor. Four water molecules complete the first coordination sphere. The γ‐carboxylate group is only engaged in hydrogen bonding. Strontium and barium are nine‐coordinated. The α‐carboxylate group of the L‐Glu2− ligand is O,O‐chelating to one metal and forming oxygen bridges to two further metal atoms. The γ‐carboxylate group is also chelating a neighbouring strontium atom, but the nitrogen function is not engaged in metal coordination. By MOM bridging double strings of metal‐oxygen chains are formed, which are interlinked by the amino acids to give a layered structure. Three water molecules are also part of the first coordination sphere of each metal, while three others are interlayer hydrogen‐bonded components. The amino groups are also involved in this hydrogen bonding.

Magnesium hydrogen L-aspartate hydrogen Baspartate tetrahydrate M~(D-As~H)(L-As~H) . 4 H20 crystallizes on cooling from the reaction mixture obtained from equivalent quantities of racemic aspartic acid and magnesium hydroxide in water under reflux conditions. The same product is also formed by slow racemization in analogous experiments carried out with pure as aspartic acid. -The compound crystallizes in the monoclinic space group P2,/c with centrosymmetric complex units, in which magnesium is in an octahedral environment of four water oxygen atoms in the equatorial plane and two f3-carboxylate oxygen atoms in axial positions. The NH: and cr-CO1 functions form a hydrogen-bonded system integrating the individual molecules into a three-dimensional network. While the monoanionic hydrogen L-aspartate ligand LAspH is typical for the system at pH < 7, the L-aspartate dianion L-A@ is the predominant ligand in basic medium. Accordingly, a product of the composition Mg(L-Asp) .(H20), is isolated from aqueous solution at pH 9.85.In an attempt to contribute to the understanding of the biological activity of these complexes through a systematic study of their structure, we have demonstrated that the LAsp2-dianion functions as a tridentate ligand to magnesium with both carboxylate groups and the amino group as the donor centers3), whereas the L -A s~H -monoanion (with its protonated amino function) is only bidentate2! For related complexes of calcium 5), strontium, and barium4', as well as of lithium and potassium6', however, other structural features are emerging. -Der Komplex kristallisiert in der monoklinen Raumgruppe P2& mit zentrosymrnetrischen Komplexmolekiilen, in denen das Magnesium oktaedrisch von vier aquatorial gebundenen Wassermolekiilen und zwei axial koordinierten p-Carboxylat-Sauerstoffatomen umgeben ist. Die NH: -und a-CO, -Funktionen bilden ein System von Wasserstoflbriickenbindungen, das die individuellen Komplexmolekiile zu einem dreidimensional verkniipften Netzwerk zusammenfiigt.Obviously optical purity is another important aspect in the application of metal aminodicarboxylates, and, therefore, we became also interested in the racemization of the L-amino acid anions in the presence of magnesium ions in aqueous medium under certain conditions of pH and temperature. A literature survey shows that racemization of an aqueous solution of L-aspartic acid is slow even at temperatures above 100°C and in strong acid orIn the presence of various metal ions or on the surface or in cavities of certain inorganic and organic polymers, the racemization rate is enhanced quite significantly"."'.We describe here details of preparation') and the molecular structure of the racemic magnesium bis(hydrogen aspartate), which could be isolated as the crystalline tetrahydrate Mg(L-AspH)@-AspH) . 4 H 2 0 . This product was obtained from racemic aspartic acid as well as by racemization of magnesium L-hydrogen aspartate. ResultsWhen a slurry of magnesium hydroxide and racemic aspartic acid in the molar ratio 1:2 in water is heated un...

Crystalline calcium(II) L‐aspartate dihydrate, Ca(LAsp) · 2H2O (2), has been obtained in a three‐step procedure from CaCO3 and L‐aspartic acid L‐AspH2 via calcium bis(L‐hydrogenaspartate) Ca(L‐AspH)2 and calcium hydrogen L‐aspartate chloride dihydrate Ca(L‐AspH)Cl · 2H2O. The crystals of 2 are orthorhombic, space group P212121. The structure is a coordination polymer with the metal atoms arranged in double chains interconnected by aspartate dianions. Each Asp2− ligand is coordinated to the metal ion as a N,Oα,Oβ tripod. In addition, two water molecules and three β‐carboxylate oxygen atoms from neighbouring units are also coordinated to each metal atom, giving a coordination number of eight for each calcium. The β‐carboxylate oxygen atoms form also a bridge between metals of a parallel chain of metal atoms. – A crystalline tetrahydrate (monoclinic, space group C2) Ca(L‐Asp) · 4H2O (1) has been prepared from L‐AspH2 and Ca(OH)2. The structure contains two molecules in the asymmetric unit. Each calcium atom is seven‐coordinate and surrounded by an N,Oα‐chelating L‐Asp2− ligand, four water molecules, and one oxygen atom of the β‐carboxylate group of a neighbouring molecule. Due to this interaction, the monomeric units are linked to give a one‐dimensional coordination polymer chain. – In both structures the double stands and chains, respectively, are crosslinked by a network of hydrogen bonds.

Strontium L-glutamate hexahydrate / Barium L-glutamate hexahydrate Crystalline magnesium, strontium, and barium L-glutamate complexes containing the dianion L-GIu'-have been prepared as the tetrahydrate (Mg) and hexahydrates (Sr, Ba), respectively. Their aqueous solutions have pH values of 10.45, 11.05, and 10.93, respectively. The solid state structures of the'Mg and Sr complexes have been determined by single crystal X-ray methods, and the structure of the Ba analogue inferred through its isomorphism with the Sr analogue. The crystals are orthorhombic, space group P2,2,2,. The magnesium atoms were found to be hexacoordinated with the L-glutamate functioning as a chelating N,Oa-donor. Four water molecules complete the first coordination sphere. The ycarboxylate group is only engaged in hydrogen bonding. Strontium and barium are nine-coordinated. The a-carboxylate group of the t-GluZ-ligand is U,O-chelating to one metal and forming oxygen bridges to two further metal atoms. The y-carboxylate group is also chelating a neighbouring strontium atom, but the nitrogen function is not engaged in metal coordination. By M -0 -M bridging double strings of metal-oxygen chains are formed, which are interlinked by the amino acids to give a layered structure. Three water molecules are also part of the first coordination sphere of each metal, while three others are interlayer hydrogen-bonded components. The amino groups are also involved in this hydrogen bondi Complexation by amino aciLs and proteins of several of the alkaline earth metals, mainly magnesium and calcium, plays an important role in many biological processes' -3). Evidence suggests that glutamate and aspartate units are among the principal mediators in most calcium-and magnesium-protein interaction^^-^). These amino acids have been found, e.g., at the metal binding sites of several crystalline proteins'-'''. In solution the amino acid complexes with magnesium and calcium have only limited stability"). This characteristic is very important, however, for metal transport and release in biological systems. Magnesium and calcium therapy with aspartates and glutamates are examples for the application of these well-documented observations12). Complex formation constants with the alkaline earth metals in aqueous solution are higher for amino acids than for hydroxy carboxylic acids and the related nonsubstituted carboxylic acids, which suggests a participation of the amino group in the coordination. The differences in association constants for the various ligands become smaller, however, as the radius of the metal increases, and hence for strontium and barium complex stability is also strongly reduced 'I). It appears that with the heavy group-I1 metals the amino function in both aspartic and glutamic acid is much less significant for metal complexation, probably due to the unfavourable chelation of large metals in five-or six-membered rings.As part of a current study on the bioinorganic chemistry of magnesium and its homologues oriented towards, for exChem.