Robert D. Bereman

Identification of ferrihydrite in polysaccharide iron complex by mossbauer spectroscopy and x-ray diffraction

A polysaccharide-iron complex (PIC), synthesized by the neutralization of an FeCl3−carbohydrate solution, is marketed as an oral hematimic (“Niferex”). The iron component was examined using Mossbauer Spectroscopy (12.8-295 K) and X-ray diffraction. From the Mossbauer spectra (a) the iron is high-spin Fe3+; (b) there is a continuous distribution of hyperfine fields at low T with a maximum field approaching 500 k0e as T approaches 0 K; (c) low-temperature spectra have small quadrupole interaction (2ϵ ≅ —0.08 mm/sec); (d) at T ⩾ 77 K the spectrum collapses to a broadened doublet; (e) high-temperature spectra require ⩾ 3 doublets for a good fit. Except for (a) all the above points are inconsistent with akageneite (even though the syntheses are similar) and are consistent with ferrihydrite. The X-ray diffraction spectrum has peaks at 1.48, 2.25, and 2.52 A (broad) and is consistent with ferrihydrite. No akaganeite peaks are present. Except for a slightly larger particle size (evidenced by smaller doublet component above 20 K), PIC resembles ferritin in all of the above characteristics. It may therefore serve as a useful model for the iron core of ferritin.

The recharacterization of a polysaccharide iron complex (Niferex)

An oral hematinic marketed as Niferex, the active component of which is a polysaccharide-iron complex (PIC), has recently been recharacterized. PIC is synthesized by the neutralization of an FeCl3 carbohydrate solution. Original characterization of this complex by Mössbauer spectroscopy and X-ray powder diffraction suggested that the iron-rich core was similar in structure to the mineral ferrihydrite. Higher precision X-ray powder diffraction now indicates that the core has a long-range order more similar to the mineral akaganéite, beta-FeOOH, than to ferrihydrite. This structure has been found for other similar ferric iron-carbohydrate polymers, especially those synthesized by the hydrolysis of FeCl3. Also discussed are the variable temperature (24-295 K) Mössbauer spectroscopic data for PIC. The first example of EXAFS data for polysaccharide iron complexes confirms that the iron is in an octahedral environment, coordinated to oxygen, with a short-range order similar to that for ferritin. The second iron shells in the PIC samples are less ordered than the second shell in ferritin. The size of the PIC core was found to be approximately 5 nm by X-ray powder diffraction, and is of the same order of magnitude as the ferritin core.

A study of an iron dextran complex by Mössbauer spectroscopy and x-ray diffraction

Abstract An injectable iron dextran complex used as a hematinic has been studied using Mossbauer spectroscopy (18–295 K) and x-ray powder diffraction. The iron is 100% high-spin Fe 3+ as determined by Mossbauer spectroscopy. While different samples of the complex showed different magnetic ordering temperatures, all the spectra can be adequately fitted to a distribution of doublets at room temperature and to a distribution of sextets at low temperatures. The sextet distribution is broad and asymmetric due to the relatively large distribution of particle sizes. There is a range of temperatures over which both sextet and doublet coexist. The x-ray diffraction patterns of the different samples gave similar patterns with broad, weak peaks at 5.07, 3.24, 2.51, 2.28, 1.94, 1.63, and 1.49 A. These values are consistent with cell contracted akaganeite, s-FeOOH. In one sample, the peaks are slightly shifted and are consistent with “normal” akaganeite.

Synthesis and characterization of square planar and pseudo-tetrahedral M(II)N2S2

Abstract Copper(II), nickel(II) and zinc(II) complexes of methyl-2-amino-1-cyclopentenedithiocarboxylate and N,N′ -pentamethylene-bis(methyl-2-amino-1-cyclopentenedithiocarboxylate) have been prepared and characterized in order to provide a basis for comparison of neutral molecules involved in planar and pseudo-tetrahedral coordination geometries with similar N 2 S 2 ligand donor sets. Methyl-2-amino-1- cyclopentenedithiocarboxylate chelates as a bidentate ligand through a thioketonate sulfur and an imine nitrogen, forming planar complexes with the divalent ions of copper(II), nickel(II) and zinc(II). The Cu(II) complex exhibits EPR spin Hamiltonian parameters typical of an axial system with g ∥=2.139 and A ∥=175x10 −4 . N,N′ -pentamethylene-bis(methyl-2-amino-1-cyclopentenedithiocarboxylate) coordinates as a tetradentate ligand, where the pentamethylene bridge between the nitrogens introduces steric strain forcing distortion of the inner coordination sphere. Spectral data support pseudo-tetrahedral coordination geometries for both Cu(II) and Ni(II). The EPR spectrum of this Cu(II) complex is characteristic of a large tetrahedral distortion with g ∥=2.146 and A ∥=133x10 −4 cm −1 , while 1 H NMR studies on the Ni(II) analogue indicate paramagnetic contact shifts of resonances, also indicative of tetrahedral distortion. The complexes are examined as possible spectral models of N 2 S 2 coordination environments at the active sites of metalloproteins such as in the type I blue copper(II) and nickel hydrogenase proteins.

MOLECULES OF COPPER(II) l-SPARTEINE DINITRATE ARE MIXED FOUR- AND FIVE-COORDINATE IN ONE CRYSTALLINE PHASE AND ONLY FOUR-COORDINATE IN ANOTHER

Abstract A neutral complex of Cu(II) with the chiral bidentate nitrogen-chelating alkaloid (−)-sparteine, with nitrate groups occupying the remaining coordination sites, has been prepared and characterized. Solution conductivity measurements indicate that both nitrate groups are coordinated to copper to give a neutral molecule. Optical and electron-spin-resonance spectra in toluene/CHCl3, did not show a clear picture of the coordination geometry. A frozen-glass ESR spectrum showed the same evidence for mixed species, with the predominant species characterized by a very low A11 value of 118 G. Crystals 1 and 2 of Cu(C15H26N2)(NO3)2 were grown by two methods: 1 at 25°C from saturated acetonitrile, and 2 at 5°C from ethanol/dichloromethane under CCl4 vapor. Their structures were determined by X-ray crystallography. Crystals 1 were monoclinic, space group P21, with a = 7.851(6), b = 14.408(10), c = 16.079(10) A, β = 97.93(6)°, V = 1801(2) A and Z = 4. Crystals 2 were orthorhombic, space group P212121, with a ...

Synthesis and characterization of the nickel and copper complexes of the new dithiolene, 1,3-propanediyldithioethylene-1,2-dithiolate (PDDT)

Abstract Nickel and copper complexes in the formal oxidation state three of the new 1,2-dithiolene ligand, 1,3-propanediyldithioethylene-1,2-dithiolate, were prepared and characterized. Electrochemical, ESR and IR characterizations indicate that the electronic structures are different for the 1,2-ethane analog. X-ray structures for the tetraethylammonium salts of both complexes were obtained. Both belong to the monoclinic space group P 2 1 / c . Each complex is planar through the tetrathioethylene portion of each ligand with the propane moiety forming a chair configuration. Packing diagrams reveal an unusual double layer array. Details of the molecular structures and packing are discussed.

Structural Characterization of bis(arylimino)isoindoline Complexes of Dimolybdenum

Abstract The complexes [Mo2(OAc)3(BAII)], where BAII is either bis(pyridylimino) isoindoline or bis(4,6-dimethylpyridylimino)isoindoline, have been synthesized. A detailed interpretation of their 1H NMR spectra has been made. The structure of the bis(pyridylimino)isoindoline derivative has been determined by X-ray analysis to facilitate the assignment of the resonance lines in the NMR spectra. The complex is triclinic belonging to the space group P1 with a = 8.241(3), b = 12.274(4), c = 15.390(6) A, V = 1490.1(9) A3 and Dcalc = 1.66 g cm−3. The final R value was 0.058. The structure consists of a quadruply bonded dimolybdenum unit which is bound to three bridging acetates and one bridging BAII ligand. The BAII ligand is bound to one molybdenum by an imino nitrogen and to the other molybdenum by the isoindoline nitrogen and a pyridyl nitrogen. The pyridyl nitrogen is bound in a position approximately co-axial with the metal-metal bond. The Moue5f8Mo bond distance is 2.109(1) A.

Synthesis and electrochemical properties of Pt(II) 5,7,12,14-tetramethyldibenzo[b,i][1,4,8,11]tetraaza[14]annulene: factors affecting the electropolymerization rates

Abstract The Pt complex of platinum dibenzotetraaza[14]annulene has been prepared from the reaction of the free base ligand with bis(dimethylsulfoxide)platinum(II) chloride. This represents one of the first 14 membered tetraazaannulene macrocyclic complexes reported. The electrochemical properties of platinum 5,7,12,14-tetramethyldibenzo[b,i][1,4,8,11]tetraaza[14]annulene were characterized by cyclic voltammetry. The platinum tetraazaannulene as well as a Pd(II) analog, have been found to form films on electrode surfaces during cyclic voltammetry. These films form either by constant potential electrolysis at +1.4 V, by cycling from 0.0 to +1.4 V, or by cycling from +1.4 to −2.0 V ( versus SCE). Films can be made to form on several electrode surfaces as well as in various solvents and with a variety of tetraalkylammonium salts as electrolytes. The amount of film grown depends on the method of deposition, the solvent and the rate of cycling. As part of the study, a quantitative analyses of the effects of solvents, scan rate, electrode, scan range and electrolytes or the amount of film actually formed on the electrode was carried out.

Crystal and molecular structure of [N, N′-ethylenebis(methyl-2-amino-1-cyclopentenedithiocarboxylato)]copper(II): A quantitative relationship between tetrahedral distortion and redox potentials in copper N2S2 compounds and the relevance to type I copper(II) centers ☆

The crystal and molecular structure of the copper(II) complex of the N2S2 tetradentate ligand, ethylenebis(methyl-2-amino-1-cyclopentenedithiocarboxylate), was solved at room temperature by a single crystal x-ray diffraction study. The complex crystallizes in the orthorhombic space group P212121 with a = 7.739(1) A, b = 13.893(2) A, c = 17.096(3) A, V = 1838(1) A3, ϱobserved = 1.56 g cm−3 and ϱcalculated = 1.57 g cm−3 for a molecular weight of 434.2, and Z = 4. Diffraction data were collected with a Syntex P diffractometer using graphite-monochromatized Cu (λ = 1.5418 A) radiation. The heavy atoms were located from a Patterson synthesis; all other nonhydrogen atoms were located using difference Fourier techniques, and hydrogen atoms were placed in calculated positions. Final refinement resulted in discrepancy indices of R = 0.067 and goodness of fit of 2.92 for all 995 reflections (5° < 2θ < 100°) greater than three times their standard deviation. The molecules are monomeric and well separated. Bond distances in the two ”halvesldquo; of the ligand are sufficiently different to suggest that different resonance structures exist in each portion. This agrees with the rhombic symmetry displayed by the frozen glass esr spectrum of the compound (xx ≠ gyy). The dihedral angle between the planes defined by the CuN2 and CuS2 planes is 20.0°, indicating a rather distorted inner coordination sphere. The copper(II)-copper(I) reduction potentials found for this compound and the trimethylene and tetramethylene analogs were determined to be −1.01, −0.79, and −0.64 V respectively. A quantitative relationship between tetrahedral distortion and redox potentials is obtained, and these results are discussed in terms of ”blueldquo; copper(II) sites in proteins. Trends in Cuue5f8S and Cuue5f8N bonding patterns in the same three compounds are discussed with regard to the short Cuue5f8S (cys) bond distance in plastocyani Finally, a brief discussion of the optical spectra of these three compounds, their variation, and their significance with respect to tetrahedral symmetry in copper(II) protein sites is presented.

Syntheses and characterization on nickel group complexes of two new 1,2-dithiolenes containing the tetrathioethylene unit☆

Abstract The synthesis of the 1,2-dithiolene dianion, (bis(methylthio)-1,2-dithiolate: MTDT2−) along with bis complexes with Ni(III). Pd(III) and Pt(III) are reported. In addition, the syntheses of the Pt(III) and Pd(III) complexes of a second 1,2-dithiolene (5,6-dihydro-1,4-dithiin-2,3-dithiolate: DDDT2−) which also contains the tetrathioethylene unit are reported. The reduced, M(II), complexes can also be isolated in an air free environment. Cyclic voltammetric data for each complex were typical of ‘dithiolenes’. These data allowed the authors to determine a stability order for 1,2-dithiolene complexes for both M(II) and M(III) oxidation states. ESR data were obtained for all new M(III) complexes. A rhombic symmetry was evident from the presence of three well defined g values in frozen glass spectra. We were able to utilize the Maki approach to determine the ground state electronic configurations for the Ni(III) and Pd(III) complexes. Those results support a dyz HOMO for both Ni(III)L22− and Pd(III)L2−. Comparison of the Pt(III) data with that for other Pt(III) dithiolenes suggest a 2B2g ground state.