Application of capillary electrophoresis technique for the enantioseparation of bioactive ferrocene-based compounds versus DFT calculated data.

Herein, a series of bioactive ferrocene-modified N-heterocycles with alkyl linkers was prepared in good to quantitative yields starting from easy accessible ferrocene alcohols and heterocycles under acidic or neutral (for imidazole) conditions in racemic forms. The analytical resolution of a number of bioactive racemic ferrocene azoles 1-6 (where azole = imidazole, pyrazole, and benzotriazole derivatives) into enantiomers was first carried out by CE using sulfobuthylether-ß-CD (captisol) as a chiral selector. The analytical approaches to highly enantiomeric-enriched ferrocene derivatives are based on the formation of their inclusion complexes. The best chiral separation was achieved using zone CE in a quartz capillary. The ACE was used to evaluate the stability constants of captisol complexes with enantiomeric forms of two ferrocene derivatives 1, FcCHMe-imidazole, and 6, FcCHMe-benzotriazole. The optimal conditions for the resolution of the studied (R, S)-ferrocene compounds 1, 2, and 6 were predicted on the basis of the performed quantum chemical calculations and then implemented by the electrophoretic method. A high correlation between density functional theory calculation results and experimental electrophoresis data were obtained. Successful enantioseparation of racemic mixtures is of great importance for the characterization and further applications of drug candidates in enantiopure forms and in the development of clinical treatment. The advantages of the CE procedure make it possible to have important practical value and significance for determining the purity and enantiomeric excess of other ferrocene-containing compounds.

On the Risks of Phylogeny-Based Strain Prioritization for Drug Discovery: Streptomyces lunaelactis as a Case Study.

Strain prioritization for drug discovery aims at excluding redundant strains of a collection in order to limit the repetitive identification of the same molecules. In this work, we wanted to estimate what can be unexploited in terms of the amount, diversity, and novelty of compounds if the search is focused on only one single representative strain of a species, taking Streptomyces lunaelactis as a model. For this purpose, we selected 18 S. lunaelactis strains taxonomically clustered with the archetype strain S. lunaelactis MM109T. Genome mining of all S. lunaelactis isolated from the same cave revealed that 54% of the 42 biosynthetic gene clusters (BGCs) are strain specific, and five BGCs are not present in the reference strain MM109T. In addition, even when a BGC is conserved in all strains such as the bag/fev cluster involved in bagremycin and ferroverdin production, the compounds produced highly differ between the strains and previously unreported compounds are not produced by the archetype MM109T. Moreover, metabolomic pattern analysis uncovered important profile heterogeneity, confirming that identical BGC predisposition between two strains does not automatically imply chemical uniformity. In conclusion, trying to avoid strain redundancy based on phylogeny and genome mining information alone can compromise the discovery of new natural products and might prevent the exploitation of the best naturally engineered producers of specific molecules.

C-H Amination via Nitrene Transfer Catalyzed by Mononuclear Non-Heme Iron-Dependent Enzymes.

Expanding the reaction scope of natural metalloenzymes can provide new opportunities for biocatalysis. Mononuclear non-heme iron-dependent enzymes represent a large class of biological catalysts involved in the biosynthesis of natural products and catabolism of xenobiotics, among other processes. Here, we report that several members of this enzyme family, including Rieske dioxygenases as well as α-ketoglutarate-dependent dioxygenases and halogenases, are able to catalyze the intramolecular C-H amination of a sulfonyl azide substrate, thereby exhibiting a promiscuous nitrene transfer reactivity. One of these enzymes, naphthalene dioxygenase (NDO), was further engineered resulting in several active site variants that function as C-H aminases. Furthermore, this enzyme could be applied to execute this non-native transformation on a gram scale in a bioreactor, thus demonstrating its potential for synthetic applications. These studies highlight the functional versatility of non-heme iron-dependent enzymes and pave the way to their further investigation and development as promising biocatalysts for non-native metal-catalyzed transformations.

Potentials and challenges of phosphorus recovery as vivianite from wastewater: A review.

Due to the shortage of phosphorus resources and the limitations of existing phosphorus recovery methods, phosphorus recovery in the form of vivianite has attracted considerable attention with its natural ubiquity, easy accessibility and foreseeable economic value. This review systematically summarizes the chemistry of vivianite, including the characteristics, formation process and influencing factors of the material. Additionally, the potential of phosphorus recovery as vivianite from wastewater has also been comprehensively examined from the prospects of economic value and engineering feasibility. In general, this method is theoretically and practically feasible, and brings some extra benefits in WWTPs. However, the insufficient understanding on vivianite recovery in wastewater/sludge decelerate the development and exploration of such advanced approach. Further researches and cross-field supports would facilitate the improvement of this technique in the future.

Immobilized FhuD2 Siderophore-Binding Protein Enables Purification of Salmycin Sideromycins from Streptomyces violaceus DSM 8286.

Siderophores are a structurally diverse class of natural products common to most bacteria and fungi as iron(III)-chelating ligands. Siderophores, including trihydroxamate ferrioxamines, are used clinically to treat iron overload diseases and show promising activity against many other iron-related human diseases. Here, we present a new method for the isolation of ferrioxamine siderophores from complex mixtures using affinity chromatography based on resin-immobilized FhuD2, a siderophore-binding protein (SBP) from Staphylococcus aureus. The SBP-resin enabled purification of charge positive, charge negative, and neutral ferrioxamine siderophores. Treatment of culture supernatants from Streptomyces violaceus DSM 8286 with SBP-resin provided an analytically pure sample of the salmycins, a mixture of structurally complex glycosylated sideromycins (siderophore-antibiotic conjugates) with potent antibacterial activity toward human pathogenic Staphylococcus aureus (minimum inhibitory concentration (MIC) = 7 nM). Siderophore affinity chromatography could enable the rapid discovery of new siderophore and sideromycin natural products from complex mixtures to aid drug discovery and metabolite identification efforts in a broad range of therapeutic areas.

Identity of cofactor bound to mycothiol conjugate amidase (Mca) influenced by expression and purification conditions.

Mycothiol serves as the primary reducing agent in Mycobacterium species, and is also a cofactor for the detoxification of xenobiotics. Mycothiol conjugate amidase (Mca) is a metalloamidase that catalyzes the cleavage of MS-conjugates to form a mercapturic acid, which is excreted from the mycobacterium, and 1-D-myo-inosityl-2-amino-2-deoxy-α-D-glucopyranoside. Herein we report on the metal cofactor preferences of Mca from Mycobacterium smegmatis and Mycobacterium tuberculosis. Importantly, results from homology models of Mca from M. smegmatis and M. tuberculosis suggest that the metal binding site of Mca is identical to that of the closely related protein N-acetyl-1-D-myo-inosityl-2-amino-2-deoxy-α-D-glucopyranoside deacetylase (MshB). This finding is supported by results from zinc ion affinity measurements that indicate Mca and MshB have comparable K(D)(ZnII) values (~10-20 pM). Furthermore, results from pull-down experiments using Halo-Mca indicate that Mca purifies with (stoichiometric) Fe(2+) when purified under anaerobic conditions, and Zn(2+) when purified under aerobic conditions. Consequently, Mca is likely a Fe(2+)-dependent enzyme under physiological conditions; with Zn(2+)-Mca an experimental artifact that could become biologically relevant under oxidatively stressed conditions. Importantly, these findings suggest that efforts towards the design of Mca inhibitors should include targeting the Fe(2+) form of the enzyme.

Reactivity of biomimetic iron(II)-2-aminophenolate complexes toward dioxygen: mechanistic investigations on the oxidative C-C bond cleavage of substituted 2-aminophenols.

The isolation and characterization of a series of iron(II)-2-aminophenolate complexes [(6-Me3-TPA)Fe(II)(X)](+) (X = 2-amino-4-nitrophenolate (4-NO2-HAP), 1; X = 2-aminophenolate (2-HAP), 2; X = 2-amino-3-methylphenolate (3-Me-HAP), 3; X = 2-amino-4-methylphenolate (4-Me-HAP), 4; X = 2-amino-5-methylphenolate (5-Me-HAP), 5; X = 2-amino-4-tert-butylphenolate (4-(t)Bu-HAP), 6 and X = 2-amino-4,6-di-tert-butylphenolate (4,6-di-(t)Bu-HAP), 7) and an iron(III)-2-amidophenolate complex [(6-Me3-TPA)Fe(III)(4,6-di-(t)Bu-AP)](+) (7(Ox)) supported by a tripodal nitrogen ligand (6-Me3-TPA = tris(6-methyl-2-pyridylmethyl)amine) are reported. Substituted 2-aminophenols were used to prepare the biomimetic iron(II) complexes to understand the effect of electronic and structural properties of aminophenolate rings on the dioxygen reactivity and on the selectivity of C-C bond cleavage reactions. Crystal structures of the cationic parts of 5·ClO4 and 7·BPh4 show six-coordinate iron(II) centers ligated by a neutral tetradentate ligand and a monoanionic 2-aminophenolate in a bidentate fashion. While 1·BPh4 does not react with oxygen, other complexes undergo oxidative transformation in the presence of dioxygen. The reaction of 2·ClO4 with dioxygen affords 2-amino-3H-phenoxazin-3-one, an auto-oxidation product of 2-aminophenol, whereas complexes 3·BPh4, 4·BPh4, 5·ClO4 and 6·ClO4 react with O2 to exhibit C-C bond cleavage of the bound aminophenolates. Complexes 7·ClO4 and 7(Ox)·BPh4 produce a mixture of 4,6-di-tert-butyl-2H-pyran-2-imine and 4,6-di-tert-butyl-2-picolinic acid. Labeling experiments with (18)O2 show the incorporation of one oxygen atom from dioxygen into the cleavage products. The reactivity (and stability) of the intermediate, which directs the course of aromatic ring cleavage reaction, is found to be dependent on the nature of ring substituent. The presence of two tert-butyl groups on the aminophenolate ring in 7·ClO4 makes the complex slow to cleave the C-C bond of 4,6-di-(t)Bu-HAP, whereas 4·BPh4 containing 4-Me-HAP displays fastest reactivity. Density functional theory calculations were conducted on [(6-Me3-TPA)Fe(III)(4-(t)Bu-AP)](+) (6(Ox)) to gain a mechanistic insight into the regioselective C-C bond cleavage reaction. On the basis of the experimental and computational studies, an iron(II)-2-iminobenzosemiquinonate intermediate is proposed to react with dioxygen resulting in the oxidative C-C bond cleavage of the coordinated 2-aminophenolates.

Electrochemically induced oxidative precipitation of Fe(II) for As(III) oxidation and removal in synthetic groundwater.

Mobilization of Arsenic in groundwater is primarily induced by reductive dissolution of As-rich Fe(III) oxyhydroxides under anoxic conditions. Creating a well-controlled artificial environment that favors oxidative precipitation of Fe(II) and subsequent oxidation and uptake of aqueous As can serve as a remediation strategy. We reported a proof of concept study of a novel iron-based dual anode system for As(III) oxidation and removal in synthetic groundwater. An iron anode was used to produce Fe(II) under iron-deficient conditions, and another inert anode was used to generate O2 for oxidative precipitation of Fe(II). For 30 min's treatment, 6.67 µM (500 µg/L) of As(III) was completely oxidized and removed from the solution during the oxidative precipitation process when a total current of 60 mA was equally partitioned between the two anodes. The current on the inert anode determined the rate of O2 generation and was linearly related to the rates of Fe(II) oxidation and of As oxidation and removal, suggesting that the process could be manipulated electrochemically. The composition of Fe precipitates transformed from carbonate green rust to amorphous iron oxyhydroxide as the inert anode current increased. A conceptual model was proposed for the in situ application of the electrochemically induced oxidative precipitation process for As(III) remediation.

A novel electrochemical process for the recovery and recycling of ferric chloride from precipitation sludge.

During wastewater treatment and drinking water production, significant amounts of ferric sludge (comprising ferric oxy-hydroxides and FePO4) are generated that require disposal. This practice has a major impact on the overall treatment cost as a result of both chemical addition and the disposal of the generated chemical sludge. Iron sulfide (FeS) precipitation via sulfide addition to ferric phosphate (FePO4) sludge has been proven as an effective process for phosphate recovery. In turn, iron and sulfide could potentially be recovered from the FeS sludge, and recycled back to the process. In this work, a novel process was investigated at lab scale for the recovery of soluble iron and sulfide from FeS sludge. Soluble iron is regenerated electrochemically at a graphite anode, while sulfide is recovered at the cathode of the same electrochemical cell. Up to 60 ± 18% soluble Fe and 46 ± 11% sulfide were recovered on graphite granules for up-stream reuse. Peak current densities of 9.5 ± 4.2 A m(-2) and minimum power requirements of 2.4 ± 0.5 kWh kg Fe(-1) were reached with real full strength FeS suspensions. Multiple consecutive runs of the electrochemical process were performed, leading to the successful demonstration of an integrated process, comprising FeS formation/separation and ferric/sulfide electrochemical regeneration.

Nonprecious-metal-assisted photochemical hydrogen production from ortho-phenylenediamine.

The combination of o-phenylenediamine (opda), which possesses two proton- and electron-pooling capability, with Fe(II) leads to the photochemical hydrogen-evolution reaction (HER) in THF at room temperature without addition of photosensitizers. From the THF solution, the tris(o-phenylenediamine) iron(II) complex, [Fe(II)(opda)3](ClO4)2 (1), was isolated as a photoactive species, while the deprotonated oxidized species was characterized by X-ray crystallographic analysis, electrospray ionization mass spectrometry, and UV-vis NIR spectra. Furthermore, the HER is photocatalyzed by hydroquinone, which serves as a H(+)/e(-) donor. The present work demonstrates that the use of a metal-bound aromatic amine as a H(+)/e(-) pooler opens an alternative strategy for designing nonprecious-metal-based molecular photochemical H2 production/storage materials.

Ferrous iron removal by limestone and crushed concrete in dynamic flow columns.

In-situ passive reactive barriers containing carbonate minerals show potential for dissolved iron removal from groundwater at landfill sites. The removal of Fe(II) from synthetic groundwater using limestone and crushed concrete (7-10 mm) was evaluated using dynamic flow columns. Solutions of 50 mg/L Fe(II) were passed through duplicate columns of limestone and concrete until breakthrough (250-300 days); water quality was evaluated at distinct column depths throughout the study. Each material was successful in reducing the concentration of Fe(II), with both achieving an average of greater than 99.4% iron removal (<0.3 mg/L effluent concentration) over 288 and 216 pore volumes, resulting in effective removal capacities of 4.06 and 3.80 g Fe/kg reactive material for limestone and crushed concrete, respectively. These values are less than removal capacities achieved from a sequencing batch test (32.9 and 27.9 g Fe/kg limestone and crushed concrete, respectively), a possible result of preferential flow pathways, shorter equilibration time, and formation of surface films on the reactive materials in the columns.

Sediment porewater extraction and analysis combining filter tube samplers and capillary electrophoresis.

Careful extraction and analysis of porewater from sediment cores are critical for the investigation of small-scale biogeochemical processes. Firstly, small sample volumes and high spatial resolution are required. Secondly, several chemical species in the anaerobic porewater are sensitive to oxidation when brought in contact with ambient air. Here we present the combination of a special sampling technique and an analytical method for the porewater extraction of a varved sediment core from Lake Baldegg in central Switzerland, using MicroRhizon samplers and a portable capillary electrophoresis (CE) instrument. MicroRhizon filter tubes of 1 mm diameter and 20 mm length are suitable for fast retrieval of particle-free porewater samples directly from the sediment core. Since the time-span between sampling and analysis is less than 20 seconds, oxygen-sensitive Fe(ii) can be analyzed in one go together with Na(+), K(+), Ca(2+), Mg(2+), NH4(+), and Mn(ii) without splitting, acidification or dilution of the sample. The major inorganic cations and anions of the sediment porewater can be determined in less than 15 minutes. Detection limits are in the sub-micromolar concentration range. The capillary electrophoresis instrument used in this study requires sample volumes of only 20 µL. These remarkable small sample volumes allow the minimization of disturbance of the sediment cores and a high spatial resolution of the sediment profile, even in sediments with low water content. The equipment is inexpensive, easy to handle, fully portable and therefore suitable for environmental on-site applications.

Removal of FePO4 and Fe3(PO4)2 crystals on the surface of passive fillers in Fe0/GAC reactor using the acclimated bacteria.

As past studies presented, there is obvious defect that the fillers in the Fe(0)/GAC reactor begin to be passive after about 60 d continuous running, although the complicated, toxic and refractory ABS resin wastewater can be pretreated efficiently by the Fe(0)/GAC reactor. During the process, the Fe(3)(PO(4))(2) and FePO(4) crystals with high density in the passive film are formed by the reaction between PO(4)(3-) and Fe(2+)/Fe(3+). Meanwhile, they obstruct the formation of macroscopic galvanic cells between Fe(0) and GAC, which will lower the wastewater treatment efficiency of Fe(0)/GAC reactor. In this study, in order to remove the Fe(3)(PO(4))(2) and FePO(4) crystals on the surface of the passive fillers, the bacteria were acclimated in the passive Fe(0)/GAC reactor. According to the results, it can be concluded that the Fe(3)(PO(4))(2) and FePO(4) crystals with high density in the passive film could be decomposed or removed by the joint action between the typical propionic acid type fermentation bacteria and sulfate reducing bacteria (SRB), whereas the PO(4)(3-) ions from the decomposition of the Fe(3)(PO(4))(2) and FePO(4) crystals were released into aqueous solution which would be discharged from the passive Fe(0)/GAC reactor. Furthermore, the remained FeS and sulfur (S) in the passive film also can be decomposed or removed easily by the oxidation of the sulfur-oxidizing bacteria. This study provides some theoretical references for the further study of a cost-effective bio-regeneration technology to solve the passive problems of the fillers in the zero-valent iron (ZVI) or Fe(0)/GAC reactor.

Selective modification of halloysite lumen with octadecylphosphonic acid: new inorganic tubular micelle.

Selective fatty acid hydrophobization of the inner surface of tubule halloysite clay is demonstrated. Aqueous phosphonic acid was found to bind to alumina sites at the tube lumen and did not bind the tube's outer siloxane surface. The bonding was characterized with solid-state nuclear magnetic resonance ((29)Si, (13)C, (31)P NMR), Fourier transform infrared (FTIR), and X-ray photoelectron spectroscopy. NMR and FTIR spectroscopy of selectively modified tubes proved binding of octadecylphosphonic acid within the halloysite lumen through bidentate and tridentate P-O-Al linkage. Selective modification of the halloysite clay lumen creates an inorganic micelle-like architecture with a hydrophobic aliphatic chain core and a hydrophilic silicate shell. An enhanced capacity for adsorption of the modified halloysite toward hydrophobic derivatives of ferrocene was shown. This demonstrates that the different inner and outer surface chemistry of clay nanotubes can be used for selective modification, enabling different applications from water purification to drug immobilization and controlled release.

Optimization of hydrous ferrous sulfate dehydration by microwave heating using response surface methodology.

The work relates to assessing the ability of the microwave for dehydration of large amount of waste hydrous ferrous sulfate generated from the titanium pigment process industry. The popular process optimization tool of response surface methodology with central composite design was adopted to estimate the effect of dehydration. The process variables were chosen to be power input, duration of heating and the bed thickness, while the response variable being the weight loss. An increase in all the three process variables were found to significantly increase the weight loss, while the effect of interaction among the parameters were found to be insignificant. The optimized process conditions that contribute to the maximum weight loss were identified to be a power input of 960 W, duration of heating of 14 min and bed thickness of 5 cm, resulting in a weight loss of 31.44%. The validity of the optimization process was tested with the repeat runs at optimized conditions.

Nano-CuFe2O4 as a magnetically separable and reusable catalyst for the synthesis of diaryl/aryl alkyl sulfides via cross-coupling process under ligand-free conditions.

An efficient protocol was developed for the CuFe(2)O(4) nanopowder-catalyzed aryl-sulfur bond formation between aryl halide and thiol/disulfide. A variety of aryl sulfides were synthesized in impressive yields with good chemoselectivity and functional group tolerance in the presence of a catalytic amount of CuFe(2)O(4), Cs(2)CO(3) as base, in nitrogen atmosphere, under ligand-free conditions, in DMSO as solvent at 100 °C. The catalyst is air-stable, inexpensive, magnetically separable and recyclable up to four cycles.

Removal and recovery of lead (II) ions from contaminated licorice extracts using oxidized multi-walled carbon nanotubes.

A column with oxidized multi-walled carbon nanotubes (MWNTs) has been studied as a sorbent for removing and accumulating lead (II) from contaminated Licorice extracts. Under optimized situation, the adsorption capacity of lead (II) on oxidized MWNTs was 17 mg g(-1) at pH 7.0, and the lead (II) was eluted with 10 ml of 1% hydrochloric acid. Additionally, the effects of adsorptive parameters, including pH of the solution, sample volume, flow rates of the sample, matrix ions, and eluent type were investigated for optimization of the presented procedure. A fluorescence spectrophotometer was employed to determine the contents of lead (II). High-performance liquid chromatography (HPLC) was developed for the quantitative determination of main constituents of Licorice extracts. Oxidized MWNT cartridges were used to remove lead ions from contaminated Licorice extracts, high adsorption capacity, adsorption reversibility of lead (II), and low loss of major constituents. The results suggested that the oxidized MWNT column has the potential to remove heavy metal ions from herbal extracts.

A comparative study on two extraction procedures in speciation of iron in municipal solid waste.

Two extraction reagents, hydrochloric acid (HCl) and acid ammonium oxalate solution (Tamm's reagent), were used to evaluate the redox state of iron in municipal solid waste (MSW) with different deposit ages. Orthogonal experiments were conducted to optimize the extraction conditions for extractable iron speciation (ferric and ferrous) in MSW. The optimal extraction conditions for HCl were determined as follows: the liquid-to-solid ratio was set at 100, and then the samples were extracted at the shaking speed of 200 rpm at 35 degrees C for 60 min by 1.00 M HCl. For Tamm's reagent, the optimal extraction conditions were extracted at the shaking speed of 175 rpm at 30 degrees C for 12 h with the same liquid-to-solid ratio. However, Tamm's reagent extraction is much more laborious and time-consuming. Thus the HC1 extraction might be a better choice for the evaluation of the redox state of iron in MSW. The results also showed that the yield of extractable iron increased with deposited age. About 60-83% of extractable iron was presented as ferrous in the MSW deposited for 1-8 years. This study supplied a tool for investigating the role of iron on the fate of pollutants in the landfill.

Differential magnetic catch and release: analysis and separation of magnetic nanoparticles.

This article reports the purification and separation of magnetic nanoparticle mixtures using differential magnetic catch and release (DMCR). This method applies a variable magnetic flux orthogonal to the flow direction in an open tubular capillary to trap and controllably release magnetic nanoparticles. Magnetic moments of 8, 12, and 17 nm diameter CoFe2O4 nanoparticles are calculated using the applied magnetic flux and experimentally determined force required to trap 50% of the particle sample. Balancing the relative strengths of the drag and magnetic forces enables separation and purification of magnetic CoFe2O4 nanoparticle samples with <20 nm diameters. Samples were characterized by transmission electron microscopy to determine the average size and size dispersity of the sample population. DMCR is further demonstrated to be useful for separation of a magnetic nanoparticle mixture, resulting in samples with narrowed size distributions.

Iron-monosulfide oxidation in natural sediments: resolving microbially mediated S transformations using XANES, electron microscopy, and selective extractions.

Iron-monosulfide oxidation and associated S transformations in a natural sediment were examined by combining selective extractions, electron microscopy and S K-edge X-ray absorption near-edge structure (XANES) spectroscopy, The sediment examined in this study was collected from a waterway receiving acid-sulfate soil drainage. It contained a high acid-volatile sulfide content (1031 micromol g(-1)), reflecting an abundance of iron-monosulfide. The iron-monosulfide speciation in the initial sediment sample was dominated by nanocrystalline mackinawite (tetragonal FeS). At near-neutral pH and an 02 partial pressure of approximately 0.2 atm, the mackinawite was found to oxidize rapidly, with a half-time of 29 +/- 2 min. This oxidation rate did not differ significantly (P < 0.05) between abiotic versus biotic conditions, demonstrating that oxidation of nanocrystalline mackinawite was not microbially mediated. The extraction results suggested that elemental S (S8(0)) was a key intermediate S oxidation product Transmission electron microscopy showed the S8(0) to be amorphous nanoglobules, 100-200 nm in diameter. The quantitative importance of S8(0) was confirmed by linear combination XANES spectroscopy, after accounting for the inherent effect of the nanoscale S8(0) particle-size on the corresponding XANES spectrum. Both the selective extraction and XANES data showed that oxidation of S8(0) to SO4(2-) was mediated by microbial activity. In addition to directly revealing important S transformations, the XANES results support the accuracy of the selective extraction scheme employed here.