Studies on Fe complexes produced by yeast. V. Role of the ligand in Fe absorption from an Fe(II)-oligosaccharide complex

The role of the ligand (oligosaccharide) of an Fe(II) complex (B1-c) produced in wine by Saccharomyces cerevisiae in gastrointestinal Fe absorption was examined. B1-c was found to consist of Fe(II) and an oligosaccharide having the composition of Ara: Xyl: Man: Glc: GalUA (1:1:1:5:1), and the sequence of these constituent monosaccharides was presumed by means of partial hydrolysis of B1-c with glycosidases and a diluted acid. The physicochemical comparison of the partially hydrolyzed, Fe(II)-containing products (Fe-containing fragments) obtained by glycosidase treatment indicated that the Man and GalUA residues of the ligand should be essential for stabilization of the complex form at the physiological pH in the digestive tract. The intestinal Fe absorption in vivo showed marked differences among the Fe-containing fragments having different ligands (sugar chains). Furthermore, the inhibitory effects of the Fe-containing fragments on B1-c uptake by brush border membrane vesicles of the small intestine varied with the ligand, probably being related to the composition of the sugar chain. These results suggest that the sugar chain of the ligand of B1-c may be involved, through its coordination with Fe(II), in (i) high stability and Fe solubility of B1-c at the physiological pH in the digestive tract and (ii) recognition of B1-c molecules in its transport system on the intestinal brush border membrane and, thereby, may contribute to excellent intestinal Fe absorption from B1-c.     

Air-stable,electron-deficient Fe(II) catalytic porphyrins. Characterization and molecular structures of rare high spin Fe(II) hexacoordinated porphyrins

The synthesis, characterization, and molecular structures of the first air-stable, hexacoordinated high spin Fe(II) porphyrins (1) with axial alcohols are reported (1 = Fe(II) meso-tetrakis(o-dichlorophenyl)-beta-octanitroporphyrin). The structure of 1 with two axial waters is also presented. The very different conformations and metrics observed with the two types of ligands illustrate the acute interplay between ligands, conformations, and spin states in Fe porphyrins.     

Zeolite included Fe(II)Phthalocyanine

The title compound was prepared by treating iron(0) or pentacarbonyl-iron(0) containing Y zeolite with the appropriate complexant. Because of steric hindrance, the phthalocyanine guest molecule, turns out to be encapsulated within the zeolite cavity.     

Olefin cis-dihydroxylation with bio-inspired iron catalysts. evidence for an Fe(II)/Fe(IV) catalytic cycle

Iron(II) complexes of a series of N-acylated dipyridin-2-ylmethylamine ligands (R-DPAH) have been investigated as catalysts for the cis-dihydroxylation of olefins to model the action of Rieske dioxygenases that catalyze arene cis-dihydroxylation. The Rieske dioxygenases have a mononuclear iron active site coordinated to a 2-histidine-1-carboxylate facial triad motif. The R-DPAH ligands are designed to provide a facial N,N,O-ligand set that mimics the enzyme active site. The iron(II) complexes of the R-DPAH ligands activate H(2)O(2) to effect the oxidation of olefin substrates into cis-diol products. As much as 90% of the H(2)O(2) oxidant is converted into cis-diol, but a large excess of olefin is required to achieve the high conversion efficiency. Reactivity and mechanistic comparisons with the previously characterized Fe(TPA)/H(2)O(2) catalyst/oxidant combination (TPA = tris(pyridin-2-ylmethyl)amine) lead us to postulate an Fe(II)/Fe(IV) redox cycle for the Fe(R-DPAH) catalysts in which an Fe(IV)(OH)(2) oxidant carries out the cis-hydroxylation of olefins. This hypothesis is supported by three sets of observations: (a) the absence of a lag phase in the conversion of the H(2)O(2) oxidant into a cis-diol product, thereby excluding the prior oxidation of the Fe(II) catalyst to an Fe(III) derivative as established for the Fe(TPA) catalyst; (b) the incorporation of H(2)(18)O into the cis-diol product, thereby requiring O-O bond cleavage to occur prior to cis-diol formation; and (c) the formation of cis-diol as the major product of cyclohexene oxidation, rather than the epoxide or allylic alcohol products more commonly observed in metal-catalyzed oxidations of cyclohexene, implicating an oxidant less prone to oxo transfer or H-atom abstraction.     

Studies on Fe complexes produced by yeast. IV. Mechanism of Fe transport from an Fe(II)-oligosaccharide complex across the mucosal membrane of the rat intestine

The mechanism of Fe transport across the rat duodenal membrane from an Fe(II)-oligosaccharide complex (designated B1-c) produced in wine by yeast and showing high hematopoietic activity in rats was examined. The Fe uptake from B1-c by brush border membrane (BBM) vesicles isolated from the rat intestine was based mainly on the Fe binding to membrane components which were suggested to be inside the vesicles. Evidence that Fe was transported into the vesicles by a special transport system other than simple diffusion was obtained by observing saturation kinetics under conditions of isotope exchange, and temperature and pH dependence. This Fe uptake was not inhibited by any metal ions tested, including inorganic Fe(II), and the BBM vesicles from the duodenum had a higher Fe uptake than those from the other parts of the small intestine. Furthermore, the BBM vesicles isolated from rats with Fe deficiency showed a significantly increased Fe uptake. The Km value for B1-c uptake was 0.16 mM, lower than the values for FeSO4 and ferrous ascorbate. These results suggest that a special transport system selective for B1-c may be present on the mucosal membrane. B1-c was taken up by the BBM vesicles in the form of Fe-oligosaccharide complex. From the preloaded vesicles, B1-c was released temperature- and pH-dependently.(ABSTRACT TRUNCATED AT 250 WORDS)     

Fe(II)自旋交叉分子材料

自旋交叉配合物具有理想的分子双稳态,可用作新型的热开关、光开关和信息存储器件。本文对近三年来Fe(II)自旋交叉分子材料的重要研究进展进行了综述,主要讨论了转变温度在室温附近的Fe(II)自旋交叉配合物以及具有光致激发自旋态捕获(LIESST)效应和多功能的Fe(II)自旋交叉分子材料,并对Fe(II)自旋交叉分子材料的应用前景作了探讨。     

CATALASE MIMIC WITH Fe (II) METALLOMICELLE

The effect of Fe (II) metallomicelle as a model of catalase, which was formed by adding surfactants (CTAB, SDS, LSS, Brij35) in Fe (II) -trien complex of molar ratios 1: 500 on the decomposition of hydrogen peroxide was investigated at 20°C and 30°C in pH 10 using KI-color and UV Spectrophotometry. A kinetic model for metallomicellar catalysis was proposed. The association constant of the ternary complex K and the rate constant of the decomposition of hydrogen peroxide k3 were obtained. The results indicate that the metallomicelles making up of Fe (II) metal complex and cationic or nonionic surfactants have obvious catalysis on the decomposition of hydrogen peroxide, but the metallomicelles making up of Fe (II) metal complex and anionic or zwitterionic surfactants have inhibition on this reaction.     

Metal chelates in vinyl polymerization. II. Mechanism of initiation by Fe(DPM)3

The nature of the interaction between the unsaturated monomer and the chelate, Fe(DPM)₃, is studied in detail. The interaction is found to occur only in solution. The stoichiometry of interaction and the equilibrium constant are evaluated. With the help of spectral evidence, attempts are made to point out the specific sites of interaction.     

Electronic spectra of low-spin bioctahedral Fe(II)−Fe(III) mixed-valence dimers

Moldavian State University. Translated fromZhurnal Struktumoi Khimii, Vol. 36, No. 1, pp. 185–189, January–February, 1995.     

Predominance-zone diagrams of Fe(III) and Fe(II) sulfate complexes in acidic media. Voltammetric and spectrophotometric studies

A thermodynamic study based on concepts of generalized species and equilibria, was used to understand the distribution of Fe(III) and Fe(II) species in the Fe(III)/Fe(II)/H(2)SO(4)/H(2)O system. The two-dimensional predominance zone diagrams (TDPZ) and Pourbaix type diagrams thus obtained permitted the selection of optimum experimental conditions, to differentiate the chemical species involved in this system. The existence of the different predominant chemical species for Fe(III): Fe(3+), FeSO(+)(4) and Fe(SO(4))(-)(2) was evidenced by spectrophotometrical studies for pSO'(4) values from 4 to 0 units in a buffered solution of pH 0.5. Additionally, voltammetric studies performed on Pt, Au and carbon paste electrodes confirmed that the electron exchange between Fe(III) Fe(II) in H(2)SO(4) media occurs by an inner Helmholtz layer mechanism. It was also possible to show that the representative couples at pSO'(4) = 0 (buffered) are: (a) for pH < 0 FeSO (+)(4)FeHSO (+)(4) and (b) for pH > 1.0: Fe(SO (4)) (-)(2)FeHSO (+)(4). The last couple presents a coupled chemical reaction in the electrochemical mechanism; this reaction is associated with the different coordination numbers of Fe(III) and Fe(II).     

Water-activity and double-layer effects on the Fe(II)/Fe(Hg) reaction

The title subject is studied by electrode-kinetic measurements in acetate buffered potassium chloride and magnesium sulphate solutions of varied concentration at 25°C, using literature data for activity and double-layer properties. The results indicate that the Fe(II)/Fe(Hg) reaction occurs by an essentially symmetric (α near 1/2) ferrous-ion transfer (n=2), that this transfer is second order in water-activity dependence, and that it exhibits a smaller than classically expected double-layer effect. No specific interaction appears for any of the ions of the supporting salts. An e.c. reaction scheme is proposed for the Fe(Hg)/Fe(II) electrode in non-complexing aqueous solution.     

DNA affinity cleaving : Sequence specific cleavage of DNA by Distamycin-EDTA - Fe(II) and EDTA-distamycin Fe(II)

The attachment of EDTA· Fe(II) to distamycin changes the sequence specific DNA binding antibiotic into a sequence specific DNA cleaving molecule. We report the synthesis of EDTA-distamycin (ED) which has the metal chelator, EDTA, tethered to the carboxy terminus of the N-methylpyrrole tripeptide moiety of the antiobiotic, distamycin. EDTA-distamycin- Fe(II) (ED)·FeII at 10^-6M concentration efficiently cleaves pBR322 DNA (10^-5M in base pairs) in the presence of oxygen and dithiothreitol (DTT). Using Maxam-Gilbert sequencing gel analyses, we find that ED· Fe(II) affords DNA cleavage patterns of unequal intensity covering two to four contiguous base pairs adjacent to a five base pair site consisting of adenines (A) and thymines (T). The multiple cleavages at each site might be evidence for a diffusible oxidizing species, perhaps hydroxyl radical. The unequal intensity of cleavage on each side of the A + T site permit assignment of major and minor orientations of the tripeptide binding unit. A comparison of the cleavage specificity of ED· Fe(II) with distamycin-EDTA· Fe(II), (DE· Fe(II)) which has EDTA · Fe(II) attached to the amino terminus of the N-methylpyrrole tripeptide, shows DNA cleavage patterns at the same sites but with intensities of opposite polarity. Maxam-Gilbert sequencing el analysis of the DNA cleavage patterns by ED Fe(II) and DE Fe(II) on both DNA strands of a 381 se pair restriction fragment reveals asymmetric DNA cleavage patterns. Cleavage is shifted to the 3' de of each DNA strand. A model consistent with this cleavage pattern indicates one preferred binding te for ED Fe(II) and DE Fe(II) is 3'-TTTAA-5' with the “amino end” of the tripeptide oriented to e 3' end of the thymine rich strand. p]This “DNA affinity cleavage” method which consists of attaching cleaving functions to DNA binding molecules followed by DNA cleavage pattern analyses using Maxam-Gilbert sequencing gels may be a useful direct method for determining the binding site and orientation of small molecules on native DNA.     

Induction of diastereoselectivity in Fe(II) tris(amino acid-bipyridine) complexes.

A group of iron(II) tris-bipyridine complexes bearing L-amino acids (L-Lys, L-Phe, L-Ser, L-Val) was prepared to investigate the predetermination of chirality of metal complexes by the chiral amino acid subunits. Noncovalent interactions and solvent polarity seemed to be important factors in inducing diastereoselectivity of the metal complexes. These phenomena were explained by (1)H NMR and CD spectroscopic studies and molecular mechanics calculations.     

Diiron carbonyl complexes possessing a {Fe(II)Fe(II)} core: synthesis, characterisation, and electrochemical investigation

Two diferrous complexes, [Fe(2)(μ-SCH(2)CH(3))(3)(CO)(5)I] and [Fe(2)(μ-SCH(2)CH(2)CH(3))(3)(CO)(5)I] were synthesised via reaction of a monoiron carbonyl precursor, [Fe(CO)(4)I(2)], with ethanethiolate and propanethiolate, respectively. The complexes were fully characterised using spectroscopic techniques, for instance, FTIR and NMR. Their crystal structures were determined using single crystal diffraction analysis. Electrochemical reduction of these complexes are temperature-dependent. At room temperature, the diferrous complexes undergo one-electron reduction. The reduction-initiated cleavage of one bound thiolate and one iodide as a radical, takes the oxidation states of the diiron core from {Fe(I)Fe(II)} to {Fe(I)Fe(I)}. This reduction-initiated transformation can be suppressed by lowering the temperature to 195 K, further reduction of the monoanion was observed at a potential very close to that of the first reduction, which is analogous to the mechanism observed for diiron complexes with a core of {Fe(I)Fe(I)}.     

Concatenation of two molecular switches via a Fe(II)/Fe(III) couple

[reaction: see text] Modulation of the fluorescein fluorescence in the presence of spiropyran and ferric ion by light was observed. Such fluorescence modulation was due to the low oxidation potential of complex MC.Fe(2+), which made the electron transfer from MC.Fe(2+) to Flu(+)()(*)() thermodynamically favorable. As a result, the communication between two molecular switches based on fluorescein and spiropyan, respectively, was realized via the reversible Fe(III)/Fe(II) redox couple. The communicating behavior corresponds well to the function of an INHIBIT logic gate.     

Fe(III)-ion-catalysed non-enzymatic transformation of adenosine diphosphate into adenosine triphosphate part II. Evidence of catalytic nature of Fe ions

Non-enzymatic phosphorylation of adenosine diphosphate (ADP) to adenosine triphosphate (ATP) in aqueous solutions using acetyl phosphate has been studied extensively. The reaction proceeds in the presence of Fe(III) ions. Normally, the yield of ATP never exceeds the amount of Fe ions but, when a sufficient amount of Mg(II) ions is added to the reaction system, the yield of ATP increases beyond the amount of Fe ions. This is because the Fe(III) ion is tightly bound to not only ADP but also ATP, the phosphorylation product. When, however, the Fe(III) ion is liberated from ATP by exchanging with an Mg(II) ion, it regains catalytic activity and contributes to the surplus production of ATP. The Fe(II) ion with either a single molecule of 1,10-phenanthroline or 2,2′-bipyridyl exhibits a remarkably high catalytic activity. This suggests that the Fe(II) aquo ion should also be an excellent catalyst.     

Thermal decompositions of formates. Part IV. Thermal dehydrations of Mg(II), Mn(II), Fe(II), Co(II), Ni(II), Cu(II), Zn(II) and Cd(II) formate dihydrates

The thermal dehydrations of formate dihydrates of Mg(II), Mn(II), Fe(II), Co(II), Ni(II), Cu(II), Zn(II) and Cd(II) were studied by means of thermogravimetry, differential thermal analysis and differential scanning calorimetry in air.The reaction orders of dehydration obtained by the dynamic and the static methods were found to be 2/3 for all the salts examined, which indicated that the rate of dehydration was controlled by a chemical process at a phase boundary. This was confirmed by microscopic observation.The values of activation energy, frequency factor and the enthalpy change of dehydration for all salts examined, were 21–30 kcal mole^?1, 10¹⁰-10¹² sec^?1 and 28–31 kcal mole^?1, respectively.The temperature at which the dehydration occurred was regarded as a measure of the strength of the metalOH₂ bond, and this temperature increased with increasing the reciprocal of the radius of the metallic ion.