Coordination of Biologically Important α-Amino Acids to Calcium(II) at High pH: Insights from Crystal Structures of Calcium α-Aminocarboxylates
| العنوان: | Coordination of Biologically Important α-Amino Acids to Calcium(II) at High pH: Insights from Crystal Structures of Calcium α-Aminocarboxylates |
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| المؤلفون: | Walter Barklage, Henry Strasdeit, Insa Büsching, Stefan Fox |
| المصدر: | Inorganic Chemistry. 46:818-824 |
| بيانات النشر: | American Chemical Society (ACS), 2007. |
| سنة النشر: | 2007 |
| مصطلحات موضوعية: | Magnetic Resonance Spectroscopy, Stereochemistry, chemistry.chemical_element, Crystal structure, Calcium, Crystallography, X-Ray, Ligands, Inorganic Chemistry, chemistry.chemical_compound, Organometallic Compounds, Carboxylate, Amino Acids, Physical and Theoretical Chemistry, Solubility, Tetramethylammonium, Aqueous solution, Molecular Structure, Ligand, Water, Nuclear magnetic resonance spectroscopy, Hydrogen-Ion Concentration, Crystallography, chemistry, Crystallization |
| الوصف: | A series of calcium alpha-aminocarboxylates was prepared by refluxing aqueous solutions/suspensions of calcium hydroxide and the respective alpha-amino acid. The colorless, crystalline hydrates Ca(gly)2.H2O (1), Ca(ala)2.3H2O (2), Ca(val)2.H2O (3), Ca(leu)2.3H2O (4), Ca(met)2.nH2O (5, n approximately 2), and Ca(pro)2.H2O (6) have been isolated in yields between 29 and 67% (gly- = glycinate, ala- = rac-alaninate, val- = rac-valinate, leu- = rac-leucinate, met- = rac-methioninate, pro- = rac-prolinate). The compounds 1-6 are readily soluble in water. The 0.10 M solutions have ca. pH 10-11 which is consistent with a noticeable degree of dissociation. The 13C NMR spectra of 1-6 in D2O were measured, and their comparison with those of the corresponding tetramethylammonium alpha-aminocarboxylates point to carboxylate coordination in solution, but no indication of nitrogen coordination was found. Infrared spectra of 1-6 gave similar results for the solid state. Complete single-crystal X-ray structure analyses of 1-4 and preliminary ones of 5 and 6, however, revealed that all aminocarboxylate ligands are N,O-chelating. Crystals of 2 consist of mononuclear complexes, while the other five compounds form three different types of one-dimensional coordination polymers. Structural diversity is also observed with the binding modes of the aminocarboxylate ligands and the calcium environment. Besides terminal aminocarboxylate coordination, there are three different types of aminocarboxylate bridges. The calcium ions are seven- or eight-coordinate in N2O5 and N2O6 coordination environments, respectively; one or three water molecules are part of the first ligand sphere of each metal ion. The crystal structures support conjectures about the existence of the yet undetected solution species [Cax(aa)2x(H2O)n] (aa- = alpha-aminocarboxylate). For example, x = 1 is realized in crystalline [Ca(ala)2(H2O)3] (2), and in 4 [Ca2(leu)4(H2O)4] complexes (x = 2) are linked to infinite chains by bridging aqua ligands. |
| تدمد: | 1520-510X 0020-1669 |
| URL الوصول: | https://explore.openaire.eu/search/publication?articleId=doi_dedup___::0a5d8b97a4fb49afaf8af69839abba0e https://doi.org/10.1021/ic061838b |
| رقم الأكسشن: | edsair.doi.dedup.....0a5d8b97a4fb49afaf8af69839abba0e |
| قاعدة البيانات: | OpenAIRE |
Find this issue from the American Chemical Society | تدمد: | 1520510X 00201669 |
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