Nucleophilic addition to di- and poly-iron arene complex cations

1996 ◽  
Vol 74 (11) ◽  
pp. 2073-2082 ◽  
Author(s):  
Alaa S. Abd-Ei-Aziz ◽  
Debbie A. Armstrong ◽  
Shelly Bernardin ◽  
Harold M. Hutton
Keyword(s):  
Nucleophilic Addition ◽  
Iron Complexes ◽  
Iron Complex ◽  
Cyanide Anion ◽  
Meta Position ◽  
Arene Complex ◽  
Nmr Techniques ◽  
Cyano Groups ◽  
Predominant Effect

Hydride and cyanide addition to a series of di- and polycyclopentadienyliron arene complex cations with etheric bridges is described. Reaction of the di-iron complexes with sodium borohydride resulted in the formation of a number of adducts.p-Methyl- and o,o-dimethylphenoxybenzene cyclopentadienyliron complexes were used as models in this study to allow for the characterization of the analagous di-iron complexes. The use of HH COSY and CH COSY NMR techniques enabled us to identify the isomeric nature of these adducts. The hydride addition results indicated that the etheric substituent had the predominant effect over the methyl group, leading to a higher addition ratio to the meta-, followed by the ortho-, then the para-positions. It was also clear that in the di-iron system, the hydride addition to each complexed arene ring took place independently. The addition of the cyanide anion to di- and poly-iron arene systems was more selective than that of the hydride anion. Reaction of sodium cyanide with p-methyl- or o-methyl-substituted arene complexes led to the formation of one adduct, with the cyanide being added to the meta position to the etheric bridges. However, cyanide addition to the di-iron complex, with a methyl substituent attached at the meta position of each complexed arene, led to the formation of a mixture of adducts. Cyanide addition to the poly-iron system with p-substituted arenes proved to be very selective, allowing for the formation of one adduct. Oxidative demetallation with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) produced the uncomplexed polyaromatic ethers with cyano groups in a very good yield. Key words: cyclopentadienyliron, arene, nucleophilic addition, hydride, cyanide.

Structure and Characterization of Fe(III) Complexes with a Square Planar Ligand and the Effect by the Introduction of External Monodentate Axial Ligands

2006 ◽  
Vol 11-12 ◽  
pp. 335-338
Author(s):  
Takeshi Okumura ◽  
Yasuhiro Funahashi ◽  
Tomohiro Ozawa ◽  
Koichiro Jitsukawa ◽  
Hideki Masuda
Keyword(s):  
Iron Complexes ◽  
Iron Complex ◽  
Oxidation Products ◽  
Heterocyclic Nitrogen ◽  
Axial Ligands ◽  
Square Planar ◽  
Oxidation Reactivity ◽  
Slight Amount ◽  
Amide Protons

A square planar iron complex with H2babp was synthesized and its coordination behaviors with monodentate axial ligands were studied. Cl– or imidazole ligand coordinated at the axial positions of the complex, but pyridine could not be introduced. The heterocyclic nitrogen donors, such as pyridine and imidazole, abstracted the amide protons of the ligand H2babp [1]. The oxidation reactivity was controlled by the presence or absence of amide protons of planar ligand H2babp rather than the axial ligands. The oxidation of cyclohexene by their complexes in the presence of PhIO proceeded catalytically when the iron complexes with protonated H2babp was used, while only a slight amount of oxidation products were obtained when the complexes with deprotonated babp2– were used.

scholarly journals Neutrophil Gelatinase-Associated Lipocalin Expresses Antimicrobial Activity by Interfering with l-Norepinephrine-Mediated Bacterial Iron Acquisition

2010 ◽  
Vol 54 (4) ◽  
pp. 1580-1589 ◽  
Author(s):  
Marcus Miethke ◽  
Arne Skerra
Keyword(s):  
Iron Acquisition ◽  
Primary Source ◽  
Iron Complexes ◽  
Iron Complex ◽  
Immune Defense ◽  
Uptake System ◽  
Iron Chelate ◽  
Neutrophil Gelatinase Associated Lipocalin ◽  
Bacterial Uptake ◽  
Neutrophil Gelatinase

ABSTRACT l-norepinephrine (NE) is a neuroendocrine catecholamine that supports bacterial growth by mobilizing iron from a primary source such as holotransferrin to increase its bioavailability for cellular uptake. Iron complexes of NE resemble those of bacterial siderophores that are scavenged by human neutrophil gelatinase-associated lipocalin (NGAL) as part of the innate immune defense. Here, we show that NGAL binds iron-complexed NE, indicating physiological relevance for both bacterial and human iron metabolism. The fluorescence titration of purified recombinant NGAL with the FeIII·(NE)3 iron complex revealed high affinity for this ligand, with a K D of 50.6 nM. In contrast, the binding protein FeuA of Bacillus subtilis, which is involved in the bacterial uptake of triscatecholate iron complexes, has a K D for FeIII·(NE)3 of 1.6 μM, indicating that NGAL is an efficient competitor. Furthermore, NGAL was shown to inhibit the NE-mediated growth of both E. coli and B. subtilis strains that either are capable or incapable of producing their native siderophores enterobactin and bacillibactin, respectively. These experiments suggest that iron-complexed NE directly serves as an iron source for bacterial uptake systems, and that NGAL can function as an antagonist of this iron acquisition process. Interestingly, a functional FeuABC uptake system was shown to be necessary for NE-mediated growth stimulation as well as its NGAL-dependent inhibition. This study demonstrates for the first time that human NGAL not only neutralizes pathogen-derived virulence factors but also can effectively scavenge an iron-chelate complex abundant in the host.

scholarly journals A Facially Coordinating Tris-Benzimidazole Ligand for Nonheme Iron Enzyme Models

2020 ◽  
Author(s):  
David Lacy ◽  
Parami Gunasekera ◽  
Preshit Abhyankar ◽  
Samantha N. Macmillan
Keyword(s):  
Structural Models ◽  
Iron Complexes ◽  
Nonheme Iron ◽  
Synthesis And Characterization ◽  
Enzyme Models

This work describes the synthesis and characterization of new ligands and iron complexes for mononuclear nonheme iron oxygenase structural models.

scholarly journals Characterization of Halogen Bonded Adducts in Solution by Advanced NMR Techniques

2017 ◽  
Author(s):  
Gianluca Ciancaleoni
Keyword(s):  
Nuclear Overhauser Effect ◽  
Halogen Bonding ◽  
X Ray Crystallography ◽  
Diffusion Nmr ◽  
Overhauser Effect ◽  
Crucial Information ◽  
Nmr Techniques ◽  
Nuclear Overhauser ◽  
And Diffusion

In the last 20 years, a huge amount of experimental results about halogen bonding (XB) has been produced. Most of the systems have been characterized by solid state X-ray crystallography, whereas in solution the only routine technique is the titration (by using 1H and 19F NMR, IR, UV-Vis or Raman spectroscopies, depending on the nature of the system), with the aim of characterizing the strength of the XB interaction. Unfortunately, the titration techniques have many intrinsic limitations and they should be coupled with other, more sophisticated techniques to have an accurate and detailed description of the geometry and stoichiometry of the XB adduct in solution. In this review, it will be shown how crucial information about XB adducts can be obtained by advanced NMR techniques, as Nuclear Overhauser Effect-based Spectroscopies (NOESY, ROESY, HOESY…) and diffusion NMR techniques (PGSE or DOSY).

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