Fe Complexes Research Articles

Iron-Catalyzed Olefin Metathesis: Recent Theoretical and Experimental Advances.

The "metathesis reaction" is a straightforward and often metal-catalyzed chemical reaction that transforms two hydrocarbon molecules to two new hydrocarbons by exchange of molecular fragments. Alkane, alkene and alkyne metathesis have become an important tool in synthetic chemistry and have provided access to complex organic structures. Since the discovery of industrial olefin metathesis in the 1960s, many modifications have been reported; thus, increasing scope and improving reaction selectivity. Olefin metathesis catalysts based on high-valent group six elements or Ru(IV) have been developed and improved through ligand modifications. In addition, significant effort was invested to realize olefin metathesis with a non-toxic, bio-compatible and one of the most abundant elements in the earth's crust; namely, iron. First evidences suggest that low-valent Fe(II) complexes are active in olefin metathesis. Although the latter has not been unambiguously established, this review summarizes the key advances in the field and aims to guide through the challenges.

Fabrication and DFT Calculation of Amine-Functionalized Metal-Organic Framework as a Turn-On Fluorescence Sensor for Fe3+ and Al3+ Ions.

Due to their important role in biological systems, it is urgent to develop a material that can rapidly and sensitively detect the concentration of Fe3+ and Al3+ ions. In this work, a brand-new CdII-based metal-organic framework [Cd(BTBD)2(AIC)]n (JXUST-18, BTBD = 4,7-bis(1H-1,2,4-triazol-1-yl)-2,1,3-benzothiadiazole and H2AIC = 5-aminoisophthalic acid) with a 4-connected sql topology was designed and synthesized. The symmetrical CdII centers are linked by AIC2- ligands with μ3-η1:η1:η1:η1 coordination mode to form a [Cd2(COO)2] secondary building unit (SBU). The contiguous SBUs are further connected by BTBD ligands to form a two-dimensional (2D) layer structure. JXUST-18 can remain stable in aqueous solutions with pH values of 3-12 or in boiling water. Luminescent experiments suggest that JXUST-18 displays more than eightfold fluorescence enhancement in the presence of Fe3+ and Al3+ ions, and the detection limits for Fe3+ and Al3+ ions are 0.196 and 0.184 μM, respectively. Furthermore, the change in luminescence color is uncomplicatedly distinguishable with the naked eye under ultraviolet light at 365 nm. In addition, a series of devices based on JXUST-18 including fluorescence test strips, lamp beads, and composite films were developed to detect metal ions via visual changes in luminescence color. Significantly, JXUST-18 is a rare MOF-based turn-on fluorescence sensor for the detection of Fe3+ ions. The theoretical calculation suggests that the complexation of Fe3+/Al3+ ions and the -NH2 group contributes to fluorescence enhancement.

Structural investigation of Fe(III)-salen complexes as “turn-on” fluorogenic probes for selective detection of pyrophosphate ions

In this work, we revisited the disassembly approach (also known as the Zelder's approach) recently proposed for sensing pyrophosphate (PPi) in water and based on the decomposition of metal-salen complexes. A systematic study devoted to the structural optimization of this novel class of PPi-responsive fluorogenic probes was conducted. Screening of eight different vicinal diamines (i.e., bridge of the salen ligand) combined with the use of 8-formyl-7-hydroxycoumarin (i.e., salicylaldehyde derivative) as the fluorescent reporter, has led to a set of novel and fully characterized coumarin-salen Fe(III) complexes. A series of analytical validations helped us to identify that coumarin-salen Fe(III) complexes derived from ethylenediamine and racemic 1,2-propylenediamine backbones exhibit the best and selective PPi-sensing performances (the limits of detection were estimated as 3.15 × 10−6 M and 2.81 × 10−6 M respectively). The implementation of both fluorescence time-course measurements and RP-HPLC-fluorescence analyses has enabled us to gain further insights into the activation mechanism of the disassembly-based probes. This study therefore demonstrates that the disassembly approach is a valuable strategy to achieve fluorogenic activity-based sensing of anions.

Redox-Responsive MRI Probes Based on First-Row Transition-Metal Complexes.

The presence of multiple oxidation and spin states of first-row transition-metal complexes facilitates the development of switchable MRI probes. Redox-responsive probes capitalize on a change in the magnetic properties of the different oxidation states of the paramagnetic metal ion center upon exposure to biological oxidants and reductants. Transition-metal complexes that are useful for MRI can be categorized according to whether they accelerate water proton relaxation (T1 or T2 agents), induce paramagnetic shifts of 1H or 19F resonances (paraSHIFT agents), or are chemical exchange saturation transfer (CEST) agents. The various oxidation state couples and their properties as MRI probes are summarized with a focus on Co(II)/Co(III) or Fe(II)/Fe(III) complexes as small molecules or as liposomal agents. Solution studies of these MRI probes are reviewed with an emphasis on redox changes upon treatment with oxidants or with enzymes that are physiologically important in inflammation and disease. Finally, we outline the challenges of developing these probes further for in vivo MRI applications.

Asimetrik Schiff Bazı ve Geçiş Metal Komplekslerinin Sentezi ve Karakterizasyonu

Bu çalışmada önce 2-aminobenzilamin ile keton türevi olan 1'-hidroksi-2'-asetonaftonun kondenzasyonundan monoimin bileşiği (H3A) sentezlenmiştir. Elde edilen H3A ile 5-bromosalisilaldehitin kondenzasyonu sonucu asimetrik Schiff bazı (H2L) sentezlenmiştir. Daha sonra sentezlenen H2L bileşiğinin Cu(II), Ni(II), Co(II) ve Fe(III) komplekslerinin sentezi ve karakterizasyonu gerçekleştirilmiştir. Schiff bazı ve metal komplekslerinin yapıları analitik ve spektroskopik yöntemler (UV-Vis, FT-IR, elementel, 13C ve 1H NMR, LC-MS, ICP-AES, manyetik suseptibilite, molar iletkenlik ve TG-DTA) kullanılarak aydınlatılmıştır

Oxidation of l-leucine amino acid initiated by hydroxyl radical: are transition metal ions an enhancement factor?

Hydroxyl radical (HO·) formation initiated by the Fenton-type reactions of Fe and Cu complexes of l-leucine (Leu) amino acid as well as its oxidation reaction by HO· was computationally investigated by using the density functional theory method at the M05-2X/6-311++G(3df,2pd)//M05-2X/6-311++G(d,p) level of theory in the aqueous phase. The results showed that dipole-salt is the main form of Leu in the physiological condition. Leu exhibits high chelating potential towards both Fe(III)/Fe(II) and Cu(II)/Cu(I) ions with the most favourable coordinating positions at two oxygen atoms of the –COO functional group. Furthermore, the Leu-ions complexes show a high risk of HO· formation via Fenton-like reactions, especially when ascorbate anion exists in the environment as a reducing agent. Finally, the oxidation reaction of l-leucine by HO· demonstrated a relatively high overall apparent reaction rate, koverall, being 1.18 × 109 M−1 s−1, in which formal hydrogen transfer reactions of the dipole-salt form occur as the primary mechanism. Consequently, the Leu oxidation by HO· radical can be promoted by the Fenton reaction enhancement of its transition metal complexes.

New Benzimidazole‐Based Fe (III) and Cr (III) Complexes: Characterization, Bioactivity Screening, and Theoretical Implementations Using DFT and Molecular Docking Analysis

Two new Fe (III) and Cr (III) complexes had been synthesized and structurally characterized. The new complexes were based on 2‐methyl‐benzimidazole (MB) and salicylic acid (H2L). Elemental analyses, Fourier transform infrared spectroscopy, UV‐–Vis, mass spectra, conductivity, magnetic, and thermal measurements were used to formulate the compounds structures. The results revealed octahedral geometry for both of Fe (III) and Cr (III) complexes. Structure elucidation of these complexes was also supported by density functional theory (DFT) along with optimized geometrical parameters. Natural bond orbital analysis and molecular electrostatic potential were also investigated. Electronic absorption spectra were theoretically performed using the time‐dependent TD‐DFT/B3LYP in gas phase and acetonitrtile as a solvent. Furthermore, the bio‐mimicking activity as antimicrobial and anti‐inflammatory activity of the understudy compounds was in vitro screened. The results showed that the Fe (III) and Cr (III) complexes exhibited higher pathogenic action than the free ligands. Molecular docking investigation against 3T88 (E. Coli) and 5IKT (Cyclooxygenase‐2) was carried out to provide deep insights into their role in inhibiting the growth of pathogenic microbes.

Structure characterization of Imidazolinone–Fe(II) complex by using multiple analytical and spectroscopic methods

Imazamox, one of imidazolinone herbicides, was found can chelate with Fe(II) in surface water enviroment to form imazamox-Fe(II) complex. By using EDS elemental analysis, HR-ESI-MS and JOB's curves, the complex was characterized as two molecule imazamox coordinated with one ferrous iron, besides, multiple analytical and spectroscopic methods, such as UV-vis, FT-IR, Raman and control experiments were conducted, the function group involved in coordination was determined, and the structure detail of imazamox-Fe(II) complex was proposed as four N atoms from two different imazamox ions (two N atoms from two pyridyl rings and the other two N atoms from two oxo-imidazole rings) and two O atoms from two different carboxylate groups to complete a 6-coordinate mode of Fe(II). Based on the finding, the influence of imidazolinone herbicides on available ferrous iron in soil was also discussed.

Synthesis, characterization, antioxidant and anticancer activities of a new Schiff base and its M(II) complexes derived from 5-fluorouracil

In this study, Schiff base ligand was obtained from the condensation reaction of benzene-1,2-diamine and 5-fluoropyrimidine-2,4(1H,3H)-dione (5-FU). Metal(II) complexes were synthesized with Fe(II), Co(II) and Ni(II) chloride salts. The synthesized ligand and metal complexes were characterized by FT-IR, UV-vis, 1H-13C NMR, elemental analyses, mass spectroscopy, magnetic moments, molar conductivity and thermogravimetric analysis studies. With the help of different techniques reveal Fe(II), Co(II) and Ni(II) complexes have exhibited tetrahedral and octahedral geometry. Ligand acted as bidentate and it binds metal(II) ions through deprotonated-NH, imine-N atom and carbonyl-O atom, respectively. DPPH, ABTS, FRAP, CUPRAC and total antioxidant activity methods were used to determine the antioxidant properties of ligand and metal complexes. According to the results, the synthesized compounds showed very high antioxidant activity compared to 5-FU. The cytotoxicities of the synthesized compounds were performed on MCF-7 (human breast cancer) and L-929 (fibroblast) cell lines using the MTT assay. In addition, the effect of electroporation (EP) on the cytotoxicity of the compounds was investigated. Our results demonstrated that novel Co(II) and Ni(II) complexes show potential as new anticancer agents and ECT may be a viable treatment option for breast cancer.

Pyridine‐oxazoline ligated iron complexes: Synthesis, characterization, and catalytic activity for isoprene polymerization

A series of iron(II) dichloride complexes (Fe1–Fe3) bearing 2‐(pyridin‐2‐yl)‐4,5‐dihydrooxazole (L1), 4‐isopropyl‐2‐(pyridin‐2‐yl)‐4,5‐dihydrooxazole (L2), and 4‐(t‐butyl)‐2‐(pyridin‐2‐yl)‐4,5‐dihydrooxazole (L3) and iron(II) acetylacetonate complex (Fe4) bearing L1 were synthesized and characterized by elemental and spectroscopic analyses. Determined by single‐crystal X‐ray crystallography, complex Fe3 adopts an unusual unsymmetrical binuclear core. Upon activation with methylaluminoxane (MAO), the pyridine‐oxazoline (Py‐ox) ligated iron complexes (Fe1–Fe4) showed excellent activity towards isoprene polymerization. Complex Fe1 displayed the highest activity of 8160 kg (mol·h)−1 with 54% of 3,4‐polyisoprene. The ligand environment and counter anion on iron center all displayed significant effects on polymerization activity and selectivity, which reflected the special performance compared with pyridine‐imine. And we propose the possible mechanism through cis‐η4 mode following the σ bond rotation because of the steric effect of t‐butyl substituent of Fe4 to give high trans‐1,4‐polymers. Furthermore, the effects of reaction parameters on the catalytic activity and selectivity were investigated in detail.

New ternary Fe(III)-8-hydroxyquinoline–reduced Schiff base complexes as selective anticancer drug candidates

Due to the growing prevalence of cancer diseases, new therapeutic options are urgently needed, and drugs based on metal ions other than platinum are alternatives with exciting possibilities. We report the synthesis, characterization and biological effect of mixed-ligand Fe(III)-aminophenolate complexes derived from salicylaldehyde and L-tryptophan with quinoline derivatives as co-ligands, namely 8-hydroxyquinoline (8HQ), [Fe(L)(8HQ)(H2O)] (1) and its 5-cloro derivative (Cl8HQ), [Fe(L)(Cl8HQ)(H2O)] (2). The complex bearing the aminophenolate and lacking the quinoline co-ligand, [Fe(L)(Cl)(H2O)2] (3), was prepared for comparison. The analytical and spectroscopic characterization revealed that 1 and 2 are octahedral Fe(III) complexes with the aminophenolate acting as a dianionic tridentate ligand and 8HQ co-ligands as bidentate chelates. Spectroscopic techniques and molecular docking studies were used to evaluate the ability of these complexes to bind bovine serum albumin (BSA) and calf thymus DNA. Complex 2 [Fe(L)(Cl8HQ)(H2O)] was the one showing higher affinity for both biomolecules. Cell viability was assessed in breast, colorectal and bone human cancer cell lines. 1 and 2 were found to be more active than cisplatin in all cell lines tested. A non-tumoral fibroblast line (L929, mouse non-tumoral fibroblasts) was used to evaluate selectivity. The results evidence that 2 shows much higher selectivity than 1 in all cell lines tested, but particularly in bone cancer cells in which selectivity index (SI) values are 8.0 and 18.8 for 1 and 2, respectively.

Structure elucidation, DNA interaction, potential anticancer, molecular docking activities, and γ‐ray irradiation studies on novel mono‐ and binuclear Fe (II), Ni (II), Co (II), and Hg (II) Schiff base complexes

Bis Schiff baseN,N–((1E,2E)‐ethane 1,2diylidene)bis(azanylylidene)di(isonicotinohydrazide) ligand L was reacted with Fe (III), Ni (II), Co (II), and Hg (II) chlorides to yield complexes (1–6). The structure of the synthesized ligand and metal complexes was well established by various spectroscopic techniques (Fourier‐transform infrared [FT‐IR], UV–Vis., and1H NMR), mass spectrometry, elemental analysis (CHN) and physical studies (thermogravimetric analysis [TGA]/first derivative thermogravimetric analysis [DTG], powder X‐ray diffraction, molar conductance, and magnetic moment). Solid powder samples of the binuclear complexes (3and6) were irradiated at two different irradiation doses (150 and 200 kGy) to yield complexes (3Fand3F*) and (6Fand6F*), respectively. For the γ‐irradiated samples, FT‐IR, UV–Vis., and physical studies (TGA/DTG, X‐ray diffraction, molar conductance, and magnetic moment) were performed using the same methods as for the as‐prepared complexes. In addition, calf thymus ct‐DNA binding results monitored by agarose gel electrophoretic method indicated that the as‐prepared binuclear [Hg2LCl4(OH)2] complex (6) and its γ‐irradiated [Hg2LCl4(OH)2] complex (6F) have the ability to cleave ct‐DNA at a concentration of 30 and 70 μg/ml, respectively. Inhibitory activity against hepatocellular carcinoma cells (HepG‐2) and breast carcinoma cells (MCF‐7) of ligand and as‐prepared complexes (3,6, and6F) was evaluated. The results revealed that metal complexes exhibited enhanced activity in comparison to the free ligand, and the as‐prepared complex (6) shows an IC50value of 5.7 ± 0.2 and 8.72 ± 0.6 μg/ml for the two cell lines, respectively. Docking process for the ligand and complexes (3) and (6) with liver cancer protein (ID: 4FM9) and breast cancer protein (ID: 1H7K) has been evaluated.

High-Performance Material for the Effective Removal of Uranyl Ion from Solution: Computationally Supported Experimental Studies.

Adsorption is a widely used method for pollution removal and for the recovery of valuable species. In recent years, the use of metal–organic compounds among the adsorbents used in adsorption studies has increased. In this study, the performance of the water-insoluble Fe complex as a metal organic framework (MOF-Fe-Ta) of water-soluble tannic acid, which is not used as an adsorbent in uranium recovery and removal, was investigated. For the characterization of the new synthesized material, Fourier transform infrared, scanning electron microscopy, and X-ray diffraction analyses were performed. The changes in the adsorption process based on various parameters were investigated and discussed. The point of zero charges value of the adsorbent was found as 5.52. It was noticed that the adsorption increases as the pH increases. Analyzing the effect of concentration on adsorption, we determined which model explained the adsorption better. The monolayer capacity of the adsorbent determined in light of the Langmuir model was reported as 0.347 mol kg–1. The Freundlich constant, namely the β value obtained in the Freundlich model, which is a measure of surface heterogeneity, was found to be 0.434, and the EDR value, which was found from the Dubinin–Raduskevich model and accepted as a measure of adsorption energy, was 10.3 kJ mol–1. The adsorption was kinetically explained by the pseudo-second-order model and the adsorption rate constant was reported as 0.15 mol–1 kg min–1. The effect of temperature on adsorption was studied; it was emphasized that adsorption was energy consuming, that is, endothermic and ΔH was found as 7.56 kJ mol–1. The entropy of adsorption was positive as 69.3 J mol–1 K–1. As expected, the Gibbs energy of adsorption was negative (−13.1 kJ mol–1 at 25 °C), so adsorption was considered as a spontaneous process. Additionally, the power and mechanism of the interaction between studied adsorbent and adsorbate are explained through density functional theory computations. Computationally obtained data supported the experimental studies.

Synthesis, Characterization, Computational and Biological Activity of Some Schiff Bases and Their Fe, Cu and Zn Complexes

Four new symmetrical Schiff bases derived from 2,2′-diamino-6,6′-dibromo-4,4′-dimethyl-1,1′-biphenyl or 2,2′-diamino-4,4′-dimethyl-1,1′-biphenyl, and 3,5-dichloro- or 5-nitro-salicylaldehyde, were synthesized and reacted with copper-, iron- and zinc-acetate, producing the corresponding complexes. The Schiff bases and their metal complexes were characterized by 1H-, 13C-NMR, IR and UV-Vis spectroscopy and elemental analysis. The structures of one Schiff base and the two zinc complexes were resolved by X-ray structure determination. Density functional theory (DFT) calculations at the B3LYP/6-31G(d) level of the latter compounds were carried out to optimize and examine their molecular geometries. The biomedical applications of the Schiff bases and their complexes were investigated as anticancer or antimicrobial agents.

Mechanistic insights into the efficient activation of peracetic acid by pyrite for the tetracycline abatement

Recently, iron-based heterogenous catalysts have received much attention in the activation of peracetic acid (PAA) for generating reactive radicals to degrade organic pollutants, yet the PAA activation efficiency is compromised by the slow transformation from Fe(III) to Fe(II). Herein, considering the electron-donating ability of reducing sulfur species, a novel advanced oxidation process by combining pyrite and PAA (simplified as pyrite/PAA) for the abatement of tetracycline (TC) is proposed in this study. In the pyrite/PAA process, TC can be completely removed within 30 min under neutral conditions by the synergy of homogeneous and heterogenous Fe(II) species. CH3C(O)OO• is the main radical generated from the pyrite/PAA process responsible for TC abatement. The excellent activation properties of pyrite can be attributed to the superior electron-donating ability of reducing sulfur species to facilitate the reduction of Fe(III). Meanwhile, the complexation of leached Fe2+ with TC favors PAA activation and concomitant TC abatement. In addition, the degradation pathways of TC and the toxicity of the degradation intermediates are analyzed. The pyrite/PAA process shows an excellent TC abatement efficacy in the pH range of 4.0∼10.0. The coexistence of Cl−, HCO3−, and HPO42− exhibits negligible effect on TC abatement, while the HA slightly inhibits the abatement rate of TC. This study highlights the efficient activation of PAA by pyrite and the important role of sulfur in promoting the conversion of Fe(III) to Fe(II) in the pyrite/PAA process.

Structural Characterization and Antimicrobial Studies of Some New Mixed Ligand Complexes of Lomefloxacin and 3‐(Bromoacetyl)coumarin with Some Metals

AbstractThe interaction of Mn(II) (1), Fe(II) (2), Co(II) (3), Ni(II) (4), Cu(II) (5), and Zn(II) (6) with lomefloxacin (LFX) in the existence of 3‐(bromoacetyl)coumarin (BAC) and NaOH in a 1 : 1 : 1 : 1 molar ratio resulted in the formation of unique mixed ligand metal complexes. The ability of two ligands to chelate metal ions was investigated by elemental analysis, molar conductance, effective magnetic moments FT‐IR, ultraviolet‐visible (UV‐Vis), 1H NMR spectra and thermogravimetric analyses (TG‐DTG). FT‐IR spectra of the complexes suggest that LFX reacted with metal ions as bi‐dentate through pyridone oxygen and carboxylate oxygen. BAC also interacts as bi‐dentate through oxygen of α,β‐unsaturated ketone and oxygen of lactone carbonyl of coumarin. These chelates are electrolytes, according to conductivity experiments, with a 1 : 1 ratio for Mn(II), Fe(II), and Zn(II) and a 1 : 2 ratio for Co(II), Ni(II), and Cu(II). Electronic and magnetic data revealed an octahedral shape for all compounds. The thermodynamic parameters of thermal breakdown processes such as Ea, ΔH*, ΔS* and ΔG* were determined from TG and DTG curves using Coats‐Redfern (CR) and Horowitz‐Metzeger (HM) techniques for LFX, BAC and their metal complexes. The structural geometry of the complexes is confirmed by molecular modeling studies. The findings show that the complexes are soft with regard to ligands, with values ranging from 0.058 eV for Fe(II) complex to 0.090 eV for Zn(II) complex and 11.11 to 17.24 eV for LFX and BAC, respectively, and 0.121, 8.26 eV and 0.111, 9.009 eV for LFX and BAC. The ligands and their complexes were tested in vitro for antibacterial activity against a variety of bacterial and fungal strains, and the results revealed that the complexes had significantly higher potency than the parent drug.

Spectrophotometric and biological studies for the interaction of rifaximin with Co, Cu, Fe and vitamin C

The interaction of Rifaximin with Iron, Copper, Cobalt and Vitamin C was studied by Uv-Vis. spectrophotometric technique at different pH and time intervals. The maximum absorbance bands for Co, Fe and Cu rifaximin complexes were 446 nm, 397 nm and 241 nm respectively. The molar ratio method was used to the most stable stoichiometries for the prepared complexes. The yellow color that formed from the interaction of rifaximin with vitamin C, allowed its determination spectrophotometry. The antimicrobial activities of Iron, Copper and Cobalt complexes with Rifaximin against standard human pathogenic Staphylococcus aureus (Gram-positive) and Escherichia coli (Gram negative) using agar diffusion method were studied. Iron and Cobalt complexes were found to exhibit higher zone of inhibition against the tested pathogens while copper inhibit completely the effect of Rifaximin. The biological study for Rifaximin - Vitamin C mixture, vitamin C decreased the effect of the antibiotic on staphylococcus, and this inhibition effect increased on E-coli.

Theoretical approach for Fe(II/III) and its chlorophyll-related complexes as sensitizers in dye-sensitized solar cells

Dye is the key to the efficiency of harvesting solar energy in dye-sensitized solar cells (DSSCs). The dye performances such as light absorption, electron injection, and electron regeneration depend on the dye molecule structure. To predict it, one needs to compute the optimized molecule geometry, HOMO level, LUMO level, electron density distribution, energy gaps, and dipole moment in the ground and excited state. Chlorophyll-related chlorin and porphyrin, as well as their κ2O,O’ complexes with Fe(II/III), were investigated with density functional theory (DFT) and time-dependent density functional theory (TD-DFT) computations using the B3LYP method and def2-TZVP basis set. NPA charges also were calculated to know the valence of the metal cations exactly. In general, the calculations show that the metal cations introduced occupied d orbitals with lower oxidation potentials than the chlorophyll ligand orbitals, which are responsible for the emergence of additional absorption bands. The states result in effective band broadening and the redshift of spectrum absorbance that is expected to improve DSSC performance.
 Another requirement that has to be possessed is the ability of electron regeneration, electron injection, and dipole moment. The Fe(II) complex has fulfilled these requirements, but not the Fe(III) complex due to having a low electron injection capability. However, this work has shown that Fe(III) complex exhibits a non-innocence ligand. It results in trivalent to divalent state change, in the appearance of a ligand radical cation, an extra hole, and a broader absorption spectrum. It also can affect its other electronic properties, such as electron injection capability. Thus, it can be considered an attractive candidate for the sensitizer in DSSCs

Complexation of 16-membered P4N2 macrocycles with Fe(II) ion as tool for stabilization of their RPSPSPRP stereoisomers

The novel mononuclear Fe(II) complexes of 16-membered P4N2 ligands were synthesized, where octahedral Fe(II) ion is coordinated by four phosphorus atoms of the ligand in equatorial positions and nitrogen atoms of two acetonitrile co-ligands in apical positions. The tetraphosphine ligands demonstrate the RPSPSPRP-configuration regardless of the configuration of the starting stereoisomer of the macrocycles, so that the complexation with iron(II) salts drives up the fixation of this configuration of 1,9-di(R)-1,9-diaza-3,7,11,15-tetraphenyl-3,7,11,15-tetraphosphacyclohexadecanes, which in turn is favorable for the binding of octahedral metal cations.

Low-Molecular-Weight Fe(III) Complexes for MRI Contrast Agents.

Fe(III) complexes have again attracted much attention for application as MRI contrast agents in recent years due to their high thermodynamic stability, low long-term toxicity, and large relaxivity at a higher magnetic field. This mini-review covers the recent progress on low-molecular-weight Fe(III) complexes, which have been considered as one of the promising alternatives to clinically used Gd(III)-based contrast agents. Two kinds of complexes including mononuclear Fe(III) complexes and multinuclear Fe(III) complexes are summarized in sequence, with a specific highlight of the structural relationships between the complexes and their relaxivity and thermodynamic stability. In additional, the future perspectives for the design of low-molecular-weight Fe(III) complexes for MRI contrast agents are suggested.