K. Burger

A novel polynuclear iron(III) mixed ligand complex for use in parenteral iron therapy

A novel, water soluble, electrically neutral polynuclear iron(III) mixed ligand complex has been prepared for use in parenteral iron therapy. The composition of the new compound has been determined by preparative and analytical methods. Osmomotic pressure measurements have shown its polymeric nature. The complex molecule has a composition of Fe8L2D2AcO(OH)19 where L denotes the lactiobionate ion, D stands for one glucopyranose unit of dextrane and Ac is the acetate ion. Iron(III) acetate is the starting material in the preparation of the complex. The acetate neutralises the protons liberated in the interaction of iron(III) and the ligands and the acetic acid formed in this reaction is removed by steam distillation. An aqueous solution of 1.8 mol dm−3 iron concentration was prepared which has an osmotic pressure below 300 mosmol.

Formation microequilibria of proton, calcium and magnesium complexes of the γ-carboxyglutamate ion and related compounds

The formation microequilibria of the proton, calcium and magnesium complexes of γ-carboxyglutamic acid (GLA) and some related compounds were studied via pH-metric titration. The inductive effects of differently protonated or protected donor groups are discussed. The distribution curves of the differently protonated microspecies and the probabilities of the different protonation pathways are presented. The formation constants of differently protonated metal complexes are given. The calcium ion binding constants for N-acetyl-γ-carboxyglutamic acid α-methylamide (which functionally models a single GLA in polypeptide chains) was found to be greater than that for GLA, but much smaller than that for the natural GLA-containing polypeptides.

Calcium, magnesium and zinc ion coordination equilibria of vincristine

The zinc ion coordination of vincristine was studied by polarography; the analogous calcium ion coordination process was studied potentiometrically by a calcium ion selective electrode. In both cases, complexes of 1:1 composition were formed. The formation constant of the calcium complex was found to be 1g K = 3.27 ± 0.1. On the basis of the substitution of zinc in its vincristine complex by calcium and magnesium ions respectively, the ratio of the corresponding stability constants could be estimated as KZn:KCa (and KZn:KMg) ∼ 105−3 × 104. The complex formation processes proved to be pH-independent in the pH range 3.4–5.5, indicating that the metal ions are coordinated by the unprotonated oxygen donor atoms of vincristine.

Coordination-chemical study of polypeptides, III protonation-deprotonation equilibrium study of synthetic αH-corticotropin1–32. Data on the pH-dependent conformation of corticotropin

By potentiometric equilibrium measurements and the computer evaluation of experimental data, the protonation equilibrium constants of four fragments of corticotropin (ACTH), ACTH1-32. ACTH1-28, ACTH1-14 and ACTH1-4, were determined and assigned to the corresponding functional groups. From the dependence of the protonation constants on the length of the peptide chain, it was established which functional groups participate in the formation of intramolecular hydrogen-bonds in aqueous solutions at various pH. These results indicated a pH-dependent conformation of the molecule.

The effects of cations on the calcium ion coordination of herapin

Abstract The calcium complex formation equilibria of heparin were investigated by potentiometry, using a new calcium ion selective electrode. The measurements were performed in aqueous solutions adjusted to 0.3 constant ionic strength by lithium, sodium, potassium and magnesium chlorides, respectively. The data reflect the effect of the latter cations on the calcium ion coordination of heparin resulting not only in the change of the equilibrium constants, but also in that of the composition of the dominating species in the solution.

Coordination chemical studies of polypeptides. I. polarographic investigation of the zinc complex of synthetic αh-corticotropine [1–32]

Abstract Through the polarographic study of the interaction between zinc ions and ACTH it was established that there are two different zinc complexes in solutions at pH between 6 and 8 depending on the Zn : ACTH ratio. On the basis of the data obtained their likely composition could be also given. The formation of the zinc complexes of ACTH results in the apperance of the catalytic hydrogen discharge at lower negative potentials. This effect can be attributed to the coordination of zinc ions to the nitrogens of the heterocycle of hystidine in ACTH.

Mössbauer spectroscopic study of the reductive decomposition of iron(III) complexes

Iron injections containing high spin iron(III) complexes may undergo a reductive decomposition during preparation or storage. This process was investigated by the Mössbauer spectroscopy of ice samples prepared by quick-freezing of the injection. The comparison of three model compounds and the correlation between the osmotic pressure of the solutions and their iron(II) concentration formed in the decomposition process and determined by Mössbauer measurements revealed the reason and mechanism of the decomposition.

Coordination-chemical study of polypeptides—II: Equilibrium study of the zinc complex formation of synthetic αH-corticotropin1−32

Abstract Separation, with the aid of a dialysis membrane, of the measuring electrode from the solution to be studied, enabled a zinc amalgam electrode system to be developed which is suitable for determination of zinc ion activity, even in the presence of macromolecules which poison the electrode. Equilibrium measurements with this apparatus and computer evaluation of the experimental results allowed determination of the compositions of the complexes formed between the zinc ion and ACTH1−32, a 32 aminoacid-containing fragment of corticotropin (ACTH), in aqueous solution, and also their conditional stability constants in a system of pH 5.9. On the basis of earlier independent deprotonation and polarographic equilibrium investigations, proposals have been put forward as to which of the large number of donor groups of the polypeptide take part in the formation of the individual complexes.

Zinc ion coordination equilibria of thymopoietin fragments and of an angiotensin antagonist octapeptide

Etude polarographique de la coordination de Zn a 3 peptides: Arg-Lys-Asp-Val-Tyr, Sar-Arg-Val-Tyr-Ile-Pro-Lac et Ary-Lys-Asp-Val