Iron Ligand Research Articles

Modulation of iron spin states in highly distorted iron(III) porphyrins: H-bonding interactions and implications in hemoproteins.

A family of five- and six-coordinated Fe-porphyrins which enable us to scrutinize the effects of non-covalent interactions on the out-of-plane displacement of iron and its spin-states and axial ligand orientation in a single distorted macrocyclic environment has been reported. Combined analysis using single-crystal X-ray structure determination and EPR spectral investigation revealed the stabilization of the high-spin state of iron in the five-coordinate complex FeIII(TPPBr8)(OCHMe2), while six-coordinate complexes [FeIII(TPPBr8)(MeOH)2]ClO4, [FeIII(TPPBr8)(H2O)2]ClO4 and [FeIII(TPPBr8)(1-MeIm)2]ClO4 stabilize admixed-high, admixed-intermediate and low-spin states, respectively. The H-bonding interactions between the weak axial H2O/MeOH and perchlorate anion resulted in an elongation of the Fe-O bond which eventually shortened the Fe-N(por) distances leading to the stabilization of the admixed spin state of iron which, otherwise, stabilizes the high-spin (S = 5/2) state only. In addition, the iron atom in [FeIII(TPPBr8)(H2O)2]ClO4 is displaced by 0.02 Å towards one of the water molecules engaged in the H-bonding interactions leading to two different Fe-O (H2O) distances of 2.098(8) and 2.122(9) Å. In contrast, iron in [FeIII(TPPBr8)(MeOH)2]ClO4 sits on the plane of the porphyrin since both the axial methanol units are engaged in similar H-bonding interactions with the ClO4- ion. Moreover, the X-ray structure of low-spin FeII(TPPBr8)(1-MeIm)2 revealed a dihedral angle of 63.0° between two imidazoles which deviates largely from the expected angle of 90° (perpendicular orientations) since the axial imidazole protons are engaged in strong intermolecular C-H⋯π interactions which thereby restrict the axial ligand movement. The complex also displays the shortest Fe-N(1-MeIm) bond along with smallest dihedral angles of 7.8° and 22.4° between the axial imidazole ring and the closest Fe-Np axis due to strong π-interactions between iron and the axial imidazole ligand. Our work highlights the influence of non-covalent interactions on the out-of-plane displacement and spin state of iron and axial ligand orientations which are indeed important steps in the functioning of various hemoproteins.

Macronutrients, iron and humic substances summer cycling over the extended continental shelf of the South Brazil Bight

We surveyed macronutrients and dissolved iron (DFe) concentrations and speciation in a transect over the shelf of the South Brazil Bight (SBB) at Santa Marta Grande Cape (SE Brazil) during a coastal downwelling episode. Driven by dominant NE winds, coastal downwelling is a common feature during the austral summer and force after water convergence, with contribution of internal wave breaking at the shelf edge, upwelling of macronutrients into the nutrient-depleted waters of the southbound Brazil Current at ~100 km from the coastline. As a result, we found a plume of high turbidity that reached the euphotic layer, a deepening of the silicate, nitrate, and phosphate isolines over the shelf and a bulging of the nitrate and phosphate isolines over the shelf edge and the slope. Our first measurements of DFe concentration and speciation in the area revealed that against prior findings in other coastal areas, macronutrients, DFe, and iron ligand cycles were disentangled. Higher DFe concentrations were often found at the surface indicating aerial deposition. Secondary DFe maxima over the sediment-water interface and in the upwelled plume indicated DFe fluxes from the sediment and from resuspended instable colloids. Iron ligand concentrations were higher than DFe concentrations in most stations with a clear land-to-ocean gradient. Subtraction of HS iron ligands revealed that except in upwelled water, the bulk of surface ligands was the result of local biological processes. The analysis of the concentrations of Fe-HS complexes showed that the contribution of HS to DFe was dominant in upwelled waters, significant in waters close to the coast, but nearly negligible in the rest of the studied area. We hypothesize that the injection of iron-humic complexes into the euphotic layer during summer upwelling episodes is the key to understanding the persistent high chlorophyll meanders found over the shelf edge of the SBB coast.

Spontaneous FeIII/FeII redox cycling in single-atom catalysts: Conjugation effect and electron delocalization

The mechanism of spontaneous FeIII/FeII redox cycling in iron-centered single-atom catalysts (I-SACs) is often overlooked. Consequently, pathways for continuous SO4 ·-/HO⋅ generation during peroxymonosulfate (PMS) activation by I-SACs remain unclear. Herein, the evolution of the iron center and ligand in I-SACs was comprehensively investigated. I-SACs could be considered as a coordination complex created by iron and a heteroatom N-doped carbonaceous ligand. The ligand-field theory could well explain the electronic behavior of the complex, whereby electrons delocalized by the conjugation effect of the ligand were confirmed to be responsible for the FeIII/FeII redox cycle. The possible pyridinic ligand in I-SACs was demonstrably weaker than the pyrrolic ligand in FeIII reduction due to its shielding effect on delocalized π orbitals by local lone-pair electrons. The results of this study significantly advance our understanding of the mechanism of spontaneous FeIII/FeII redox cycling and radical generation pathways in the I-SACs/PMS process.

Iron ligands and isotopes in hydrothermal plumes over backarc volcanoes in the Northeast Lau Basin, Southwest Pacific Ocean

Deep-sea hydrothermal venting is an important source of dissolved iron (dFe) to the oceans. Fe isotopes can be used as a potential tool to trace the dispersal of hydrothermal plumes. However, Fe isotope fractionation and its relation with Fe speciation as hydrothermal plumes disperse is still poorly constrained. In this study, we determined the Fe speciation and total and dissolved Fe isotope composition (δ56tFe, δ56dFe) for several hydrothermal plumes from backarc volcanoes in the Northeast Lau Basin. This combined approach provides important insights into the evolution of Fe isotopes in hydrothermal plumes. The results suggest δ56tFe variation in plumes is related to the loss of particulate Fe-sulfides or Fe-oxyhydroxides (FeOOH), both of which are dependant on the H2S concentrations and Fe/H2S in the source hydrothermal fluids. δ56dFe compositions in the hydrothermal plumes increase during plume dispersal/dilution and can be as high as 0.85 ‰, demonstrating that hydrothermal plumes can export dissolved Fe with a significantly heavier δ56dFe than hydrothermal fluids. The reasons may be ascribed to the organic Fe complexes (FeL) and colloidal FeOOH in the dissolved phase. Another interpretation might be associated with the low pH in volcanic arc hydrothermal systems rich in magmatic CO2 and SO2, which decreases the Fe(II) oxidation rate. Further, we demonstrate for the first time that the δ56dFe is positively correlated with the conditional stability constants of FeL (logKʹFeL). A Rayleigh distillation model is presented based on the mass balance of the determined FeL, and colloidal FeOOH in hydrothermal plumes, which can explain the observed Fe isotope compositions in hydrothermal plumes. Our data show how Fe isotopes are transformed within a hydrothermal plume above arc volcanoes and how these may differ from that of the original vent fluids. It adds to our understanding of the processes that have an impact on the Fe speciation and isotope composition in deep-sea hydrothermal plumes.

In-situ oxidation of 5-hydroxymethylfurfural to 5-formylfuran-2-carboxylic acid catalyzed by iron, manganese, copper and salicylic amantadine Schiff base ligands

To synthesize simple and efficient catalysts and their application in catalytic conversion of biomass platform compounds to prepare high value-added chemicals has always been the focus of researchers. In this paper, a catalyst composed of iron, manganese, copper and Schiff base ligand derived from amantadine salicylaldehyde was in-situ constructed to catalyze the selective oxidation of 5-hydroxymethylfurfural (HMF) to prepare 5-formyl-2-furancarboxylic acid (FFCA). The ligands and complexes were characterized by nuclear magnetic resonance (NMR), infrared spectroscopy (FT-IR) and single crystal diffraction, and the reaction conditions such as oxidation reaction time, reaction temperature, molar ratio of MnCl2·4H2O to ligand, oxidant and catalyst dosage, etc, were optimized. Under the optimized conditions, 100% conversion of HMF and the FFCA with a yield of 52.1% can be obtained. Finally, on the basis of the reaction results, the HMF oxidation reaction process catalyzed by Mn metal complexes was analyzed.

Copper nanocomposite decorated two-dimensional metal organic frameworks of metalloporphyrin with peroxidase-mimicking activity

Two-dimensional nanosheets of metalloporphyrin are promising in biomimetic catalysis due to the activity of metalloporphyrin and the ultrathin structure with highly accessible active sites. Many efforts have been devoted to incorporate noble metallic nanoparticles with metalloporphyrinic nanosheets to enhance the catalytic performance. In this paper, a hybrid nanosheet with peroxidase-like activity is constructed by growth of non-precious copper nanocomposites onto nanosheets of metal organic framework (MOF) that have tetrakis-(4-carboxyphenyl)-porphyrin iron (FeTCPP) ligands linked by copper clusters, designated as Cu@Cu-FeTCPP. The copper hydroxide-copper oxide (Cu(OH)2-CuO) heterogeneous composites with nanoparticles, nanoneedles and nanorods structures are uniformly distributed on the surface of metalloporphyrinic nanosheets (Cu-FeTCPP). The synthesized Cu@Cu-FeTCPP nanohybrids shows enhanced peroxidase-mimicking catalytic performance compared to the free copper composites, Cu-FeTCPP nanosheets, and their mixture, because of the synergistic effect between nanosheets and copper nanocomposites. Lower Michaelis−Menten constants Km prove the better affinity of the nanohybrids with substrates than Cu-FeTCPP MOFs, even than HRP. Based on the high peroxidase-like catalytic activity, Cu@Cu-FeTCPP nanohybrids are successfully applied to decolorization of Congo Red and detection of glucose with high efficiency and high sensitivity.

Фотокаталитический нанореактор на основе низкоразмерных структур оксидов титана

Synthesized titanium oxide nanotubes from titanium raw materials are efficient nanoreactors for photocatalysis in comparison with macroanalogues. The dependence of the geometry of titanium oxide structures on the redistribution of the density of electronic states was studied. The presence of natural iron ligands leads to the appearance of midgap states inside the bandgap of titanium oxide.

Distribution and chemical speciation of iron on the outer edge of the Changjiang diluted water plume of the East China Sea

In this study, we investigated the distribution of dissolved iron (DFe) and organic iron-binding ligands (LFe) in the area of contact between the Changjiang diluted water (CDW) plume and the branch of the Kuroshio Current during the early summer. Our objective was to evaluate how the interaction of these water masses affects the iron chemistry in this region. The upper 20 m of the stations on the northwestern sides was characterized by water of relatively low salinity (<33), which was influenced by the CDW. The northward branch of the Kuroshio Current likely flowed below this low-salinity water, at approximately 30–40 m. On the East China Sea continental shelf, low-oxygen water developed in the bottom water and advected horizontally towards the shelf slope on the isopycnic surface. The surface water, influenced by the CDW, contained relatively high concentrations of DFe and humic-like substances of riverine origin. However, the concentration of LFe in this water mass was not significantly different from that in the surrounding water masses. In low-oxygen water, the DFe concentration was high, and the concentration of humic-like substances was lower than that in the water from the upper layers. In addition to the LFe found in the oxygenated water, LFe with weaker affinities for ferric ions were also detected in this low-oxygen water, and the total concentration of LFe (>2 nM) was significantly higher than that in the other water masses. These results suggest that LFe released through biological decomposition of organic matter is more important for iron complexation in this area than humic-like substances. Therefore, it is essential to quantify diapycnal mixing with deep water on the continental shelf and shelf edge to evaluate the Kuroshio branch as a transporter of iron and LFe to the Sea of Japan.

Gauging the donor strength of iron(0) complexesviatheir N-heterocyclic carbene gold(i) adducts

We isolate and characterize the gold(I)-iron(0) adducts [(iPr2-bimy)Au-Fe(CO)3(PMe3)2][BArF4] and [Au-{Fe(CO)3(PMe3)2}2][BArF4] (iPr2-bimy = 1,3-diisopropylbenzimidazolin-2-ylidene, BArF4 = tetrakis(pentafluorophenyl)borate). DFT analysis reveals that the gold-iron interaction in [(iPr2-bimy)Au-Fe(CO)3(PMe3)2][BArF4] is predominantly a σ-donation from iron to gold. We further extend this class of compounds to include [(iPr2-bimy)Au-Fe(CO)3(PR3)2][BArF4] (PR3 = PPh3, PCy3, PCyPh2, PMePh2, PMe2Ph, P(4-C6H4F)3) and [(iPr2-bimy)Au-Fe(CO)4(PPh3)][BArF4] and correlate the iPr2-bimy carbenic 13C NMR signal with the relative donor strength of the iron(0) ligand. This approach allows for a fast and simple approach to gauge relative donor strength of Fe(0) donors.

Organic soluble linear metallo-supramolecular polymer based on iron(II) and terpyridyl ligand with high electrochromic performance

Ionic metallo-supramolecular materials possess excellent electrochromic properties due to the coordination of organic ligands and inorganic metal ion. In this paper, we prepared a linear organic soluble metallo-supramolecular electrochromic material named P-FeTPY which was coordinated with terpyridine as organic ligands and Fe(II) as inorganic metal ion. The polymer P-FeTPY whose ligands were modified with alkyl chains could be dissolved in dichloromethane with a solubility of 20 g/L. This indicates the introduction of long alkyl chains is effective to increase solubility of the ionic metallo-supramolecular polymer. The polymer films were spin-coated on the ITO substrate and their electrochemical and electrochromic properties were investigated. P-FeTPY film showed purplish red color with an absorption band at around 580 nm in neutral state due to the metal-to-ligand charge transfer transition, and became colorless due to the oxidization of central metal ion with around 30% change in transmittance. Cyclic voltammetry test demonstrated that P-FeTPY film which showed a couple of redox peaks at 1.15 V and 0.95 V is electrochemically reversible and stable. After 240 switching cycles, 97% of the optical contrast was retained, indicating excellent stability of P-FeTPY film. This work provides an effective path for producing organic soluble ionic metallo-supramolecular materials, which is solution processible and will greatly benefit the large area production in future industrial applications.

Color-convertible fluorescent nanoprobe for Parkinson’s disease diagnosis

For the fluorescent diagnosis of Parkinson’s disease (PD), molecular probes typically target a single biomarker, which is insufficient because of the limited sensitivity and specificity. Herein, by utilization of the biochemical characteristics with high level of iron and reactive oxygen species (ROS) in PD, an efficient color-convertible fluorescent nanoprobe (TAT-Polyp-QL) was designed and constructed. TAT-Polyp-QL nanoprobe contained a functional iron ligand (L1), a color-convertible fluorescent probe (Q1), and HIV-1 trans-activating transcriptor (TAT) modified hyperbranched polyphosphate (TAT-Polyp), in which TAT was employed as a tool to increase the transport efficiency of the nanoprobe across the blood–brain barrier. Upon meeting high level of iron and ROS in PD, the fluorescent probe Q1 in the TAT-Polyp-QL was oxidized into its sulfoxide derivative, resulting in the blue-shift of fluorescent emission peak from 600 nm to 550 nm and then the fluorescent color conversion from red to green. This unique reaction-based color-convertible fluorescent nanoprobe can be employed for dual-biomarker detection, identifying the emergence of PD in vitro and in vivo with high sensitivity and specificity.

Could root-excreted iron ligands contribute to cadmium and zinc uptake by the hyperaccumulator Noccaea caerulescens?

Could root-excreted iron ligands contribute to cadmium and zinc uptake by the hyperaccumulator Noccaea caerulescens?

Evaluation of Fenton and modified Fenton oxidation coupled with membrane distillation for produced water treatment: Benefits, challenges, and effluent toxicity

Membrane distillation is a promising technology to desalinate hypersaline produced waters. However, the organic content can foul and wet the membrane, while some fractions may pass into the distillate and impair its quality. In this study, the applicability of the traditional Fenton process was investigated and preliminarily optimized as a pre-treatment of a synthetic hypersaline produced water for the following step of membrane distillation. The Fenton process was also compared to a modified Fenton system, whereby safe iron ligands, i.e., ethylenediamine-N,N′-disuccinate and citrate, were used to overcome practical limitations of the traditional reaction. The oxidation pre-treatments achieved up to 55% removal of the dissolved organic carbon and almost complete degradation of the low molecular weight toxic organic contaminants. The pre-treatment steps did not improve the productivity of the membrane distillation process, but they allowed for obtaining a final effluent with significantly higher quality in terms of organic content and reduced Vibrio fischeri inhibition, with half maximal effective concentration (EC50) values up to 25 times those measured for the raw produced water. The addition of iron ligands during the oxidation step simplified the process, but resulted in an effluent of slightly lower quality in terms of toxicity compared to the use of traditional Fenton.

Additive and Counterion Effects in Iron-Catalyzed Reactions Relevant to C-C Bond Formation.

The use of iron catalysts in carbon-carbon bond forming reactions is of interest as an alternative to precious metal catalysts, offering reduced cost, lower toxicity, and different reactivity. While well-defined ligands such as N-heterocyclic carbenes (NHCs) and phosphines can be highly effective in these reactions, additional additives such as N-methylpyrrolidone (NMP), N,N,N',N'-tetramethylethylenediamine (TMEDA), and iron salts that alter speciation can also be employed to achieve high product yields. However, in contrast to well-defined iron ligands, the roles of these additives are often ambiguous, and molecular-level insights into how they achieve effective catalysis are not well-defined. Using a unique physical-inorganic in situ spectroscopic approach, detailed insights into the effect of additives on iron speciation, mechanism, and catalysis can inform further reaction development. In this Perspective, recent advances will be discussed as well as ongoing challenges and potential opportunities in iron-catalyzed reactions.

Structure-Activity Relationship and Mode-Of-Action Studies Highlight 1-(4-Biphenylylmethyl)-1H-imidazole-Derived Small Molecules as Potent CYP121 Inhibitors.

CYP121 of Mycobacterium tuberculosis (Mtb) is an essential target for the development of novel potent drugs against tuberculosis (TB). Besides known antifungal azoles, further compounds of the azole class were recently identified as CYP121 inhibitors with antimycobacterial activity. Herein, we report the screening of a similarity‐oriented library based on the former hit compound, the evaluation of affinity toward CYP121, and activity against M. bovis BCG. The results enabled a comprehensive SAR study, which was extended through the synthesis of promising compounds and led to the identification of favorable features for affinity and/or activity and hit compounds with 2.7‐fold improved potency. Mode of action studies show that the hit compounds inhibit substrate conversion and highlighted CYP121 as the main antimycobacterial target of our compounds. Exemplified complex crystal structures of CYP121 with three inhibitors reveal a common binding site. Engaging in both hydrophobic interactions as well as hydrogen bonding to the sixth iron ligand, our compounds block a solvent channel leading to the active site heme. Additionally, we report the first CYP inhibitors that are able to reduce the intracellular replication of M. bovis BCG in macrophages, emphasizing their potential as future drug candidates against TB.

Electron Transfer and Electrocatalytic Properties of the Immobilized Met80Ala Cytochrome c Variant in Dimethylsulfoxide

AbstractThe electrode‐immobilized Met80Ala variant of yeast iso‐1 cytochrome c in mixed water/dimethylsulfoxide (DMSO) solutions up to 60 % v/v DMSO shows thermodynamic and kinetic parameters of electron exchange and electrocatalytic properties towards O2 reduction fully comparable to those in water. This is the result of moderate protein conformational changes thanks to immobilization that, to a certain extent, preserves protein structure, possibly due to the constraints on protein mobility/flexibility induced by the electrostatic interactions with the electrode‐coating SAM. Upon increasing the DMSO content of the mixed solution beyond 60 %, a much larger perturbation occurs that leads to the progressive loss of the electrocatalytic ability. Therefore, under these conditions, the organic solvent remarkably affects the structure and properties of the protein probably involving major conformational changes or even the replacement of the 6th axial hydroxide ligand of the heme iron with a strong protein ligand, possibly a lysine residue.

Iron- and Cobalt-Catalyzed Asymmetric Hydrofunctionalization of Alkenes and Alkynes.

Transition metal catalyzed asymmetric hydrofunctionalization of readily available unsaturated hydrocarbons presents one of the most straightforward and atom-economic protocols to access valuable optically active products. For decades, noble transition metal catalysts have laid the cornerstone in this field, on account of their superior reactivity and selectivity. In recent years, from an economical and sustainable standpoint, first-row, earth-abundant transition metals have received considerable attention, due to their high natural reserves, affordable costs, and low toxicity. Meanwhile, the earth-abundant metal catalyzed hydrofunctionalization reactions have also gained much interest and been investigated gradually. However, since chiral ligand libraries for earth-abundant transition-metal catalysis are limited to date, the development of highly enantioselective versions remains a significant challenge.This Account summarizes our recent efforts in developing suitable chiral ligands for iron and cobalt catalysts and their applications in the highly enantioselective hydrofunctionalization reactions (hydroboration and hydrosilylation) of alkenes and alkynes. In ligand design, we envisioned that chiral unsymmetric NNN-tridentate (UNT) ligand scaffolds could promote these enantioselective transformations with earth-abundant metals. Therefore, several types of chiral UNT ligands were designed and prepared in our laboratory, utilizing readily available natural amino acids as chiral sources. In the very beginning, chiral oxazoline iminopyridine (OIP) ligands were proposed and investigated through the rational combination of nitrogen-containing ligand scaffolds. After a systematic survey of the ligand effects, the imine moiety in the rigid OIP ligands was replaced by a conformationally more flexible amine unit, leading to the construction of reactive oxazoline aminoisopropylpyridine (OAP) ligands. Subsequently, imidazoline iminopyridine (IIP) and thiazoline iminopyridine (TIP) ligands were prepared by altering the oxygen atom of oxazoline with nitrogen and sulfur linkers, respectively. To further expand the chiral ligand library, other tridentate ligands containing a twisted pincer, anionic, and nonrigid backbone were also designed and synthesized, including iminophenyl oxazolinyl phenylamine (IPOPA) and imidazoline phenyl picolinamide (ImPPA). The efficacy of these chiral UNT ligands for asymmetric induction in iron and cobalt catalysis has been demonstrated through asymmetric hydrofunctionalization of alkenes and asymmetric sequential hydrofunctionalization of alkynes, which exhibit excellent reactivity as well as high chemo-, regio-, and stereoselectivity with broad functional group tolerance. Notably, highly regio- and enantioselective hydrofunctionalization of challenging substrates, such as 1,1-disubstituted aryl alkenes and terminal aliphatic alkenes, was also achieved. Furthermore, the development of asymmetric sequential isomerization/hydroboration of internal alkenes and sequential hydrofunctionalization of alkynes further demonstrates the synthetic power of these catalytic systems. The chiral enantioenriched products obtained by these methodologies could be potentially utilized in organic synthesis, medicinal chemistry, and materials science. We believe that our continuous efforts in this field would be beneficial to the development of asymmetric earth-abundant metal catalysis.

Strigolactones regulate sepal senescence in Arabidopsis.

Flower sepals are critical for flower development and vary greatly in life span depending on their function post-pollination. Very little is known about what controls sepal longevity. Using a sepal senescence mutant screen, we identified two Arabidopsis mutants with delayed senescence directly connecting strigolactones with senescence regulation in a novel floral context that hitherto has not been explored. The mutations were in the strigolactone biosynthetic gene MORE AXILLARY GROWTH1 (MAX1) and in the strigolactone receptor gene DWARF14 (AtD14). The mutation in AtD14 changed the catalytic Ser97 to Phe in the enzyme active site, which is the first mutation of its kind in planta. The lesion in MAX1 was in the haem-iron ligand signature of the cytochrome P450 protein, converting the highly conserved Gly469 to Arg, which was shown in a transient expression assay to substantially inhibit the activity of MAX1. The two mutations highlighted the importance of strigolactone activity for driving to completion senescence initiated both developmentally and in response to carbon-limiting stress, as has been found for the more well-known senescence-associated regulators ethylene and abscisic acid. Analysis of transcript abundance in excised inflorescences during an extended night suggested an intricate relationship among sugar starvation, senescence, and strigolactone biosynthesis and signalling.

Synthesis of novel acyclic and multiple phenyl iron tetraamino ligand catalysts and its catalytic activity for degradation of dye wastewater by H2O2

We need a practical, inexpensive, and green way to reduce the environmental pollutants, especially for dye wastewater. The discharge of industrial wastewater such as organic dyes will cause serious pollution to water bodies, thereby affecting people's lives. In this work, we designed and successfully synthesized four new ligand catalysts. The total outputs of diamide diamino iron ligand compounds A and B are 71.33% and 61.39%, respectively. The total outputs of polyaromatic iron tetraamido macrocyclic ligand (TAML) compounds C and D are 38.49% and 49.11%, respectively. The catalytic effects of four catalysts on the degradation of dye wastewater by hydrogen peroxide oxidation were studied and compared with the second‐generation FeIII‐TAML catalyst. The experimental results showed that acyclic catalyst A and B has good catalytic effect. For methylene blue, methyl orange, rhodamine B three dyes wastewater, under the conditions of 20°C, Ccatalyst A = 0.056–0.28 mM and Chydrogen peroxide = 33 mM, the decolorization rate and chemical oxygen demand (COD) removal rate are 81.53%–97.58% and 52.2%–60.7%, respectively. Under the condition of 20°C, Ccatalyst B = 0.75 mM and Chydrogen peroxide = 33 mM, the decolorization rate and COD removal rate are 48.33%–80.33% and 44.6%–57.8%, respectively.

Chemical speciation of iron in the euphotic zone along the Kuroshio Current

The distributions of dissolved iron (DFe) and organic iron-binding ligands (LFe) in the Kuroshio Current and its neighboring waters were elucidated from four cross-sectional surveys from the eastern coast of Taiwan to Sagami Bay. The Kuroshio surface water was characterized by a high salinity, low concentration of DFe, high concentration of LFe, and low fluorescence of humic-like substances, in comparison to the neighboring waters. The neighboring waters of the Kuroshio can be categorized into two types: the East China Sea water and coastal water. The East China Sea water was found near the Okinawa Trough, and characterized by a steep vertical gradient of DFe concentration, almost as low as that in the Kuroshio within the surface mixed layer, but reached ~0.5 nM below the mixed layer. Coastal water was observed on the southern coast of Japan, and its DFe concentration was high throughout the upper 200 m. The concentration of LFe in the Kuroshio water was significantly higher at 10-m depth than in the deeper layers. This suggests that humic-like substances, which are a major component of LFe in estuarine and deep waters, play a relatively minor role in the Kuroshio surface waters. Mixing with coastal waters can increase the concentration of bioavailable inorganic ferric ions in the Kuroshio surface water in two ways, by increasing the DFe concentration and decreasing the LFe concentration.