In situ magnetic separation and immobilization of dibenzothiophene-desulfurizing bacteria

In situ cell separation and immobilization of bacterial cells for biodesulfurization were developed by using superparamagnetic Fe₃O₄ nanoparticles (NPs). The Fe₃O₄ NPs were synthesized by coprecipitation followed by modification with ammonium oleate. The surface-modified NPs were monodispersed and the particle size was about 13 nm with 50.8 emu/g saturation magnetization. After adding the magnetic fluids to the culture broth, Rhodococcus erythropolis LSSE8-1 cells were immobilized by adsorption and then separated with an externally magnetic field. The maximum amount of cell mass adsorbed was about 530 g dry cell weight/g particles to LSSE8-1 cells. Analysis showed that the nanoparticles were strongly absorbed to the surface and coated the cells. Compared to free cells, the coated cells not only had the same desulfurizing activity but could also be easily separated from fermentation broth by magnetic force. Based on the adsorption isotherms and Zeta potential analysis, it was believed that oleate-modified Fe₃O₄ NPs adsorbed bacterial cells mainly because of the nano-size effect and hydrophobic interaction.     

The development of an electrochemical immunosensor using a thiol aromatic aldehyde and PAMAM-functionalized Fe3O4@Au nanoparticles

In this work, a novel thiol aromatic aldehyde was synthesized. It can be used as a substrate to directly immobilize antibodies on a gold electrode, for which no additional chemical cross-linker is required. It was also applied as a linker to prepare Fe₃O₄@Au/PAMAM/Ab₂–horseradish peroxidase bioconjugates, which introduced multiple enzymes onto a sensing interface owing to the high surface-to-volume ratio of Fe₃O₄@Au nanoparticles and many functional groups of the poly(amidoamine) dendrimer (PAMAM). The introduced multiple enzymes greatly improved the detection signal. Under optimal conditions, the proposed electrochemical immunosensor exhibited desirable performance for detection of IgG in the range 0.005–50 ng ml⁻¹ with a detection limit of 3 pg ml⁻¹ based on a signal-to-noise ratio of 3. It has great potential application in the area of clinical analysis.     

In situ preparation of magnetic Fe3O4-chitosan nanoparticles for lipase immobilization by cross-linking and oxidation in aqueous solution

A new and simple method has been proposed to prepare magnetic Fe₃O₄-chitosan (CS) nanoparticles by cross-linking with sodium tripolyphosphate (TPP), precipitation with NaOH and oxidation with O₂ in hydrochloric acid aqueous phase containing CS and Fe(OH)₂, and these magnetic CS nanoparticles were used to immobilize lipase. The effects on the sequence of adding NaOH and TPP, the reaction temperature, and the ratio of CS/Fe(OH)₂ were studied. TEM showed that the diameter of composite nanoparticles was about 80 nm, and that the magnetic Fe₃O₄ nanoparticles with a diameter of 20 nm were evenly dispersed in the CS materials. Magnetic measurement revealed that the saturated magnetisation of the Fe₃O₄-CS nanoparticles could reach 35.54 emu/g. The adsorption capacity of lipase onto nanoparticles could reach 129 mg/g; and the maximal enzyme activity was 20.02 μmol min⁻¹ mg⁻¹ (protein), and activity retention was as high as 55.6% at a certain loading amount.     

Optimum conditions for lipase immobilization on chitosan-coated Fe3O4 nanoparticles

Magnetic Fe₃O₄-chitosan nanoparticles are prepared by the coagulation of an aqueous solution of chitosan with Fe₃O₄ nanoparticles. The characterization of Fe₃O₄-chitosan is analyzed by FTIR, FESEM, and SQUID magnetometry. The Fe₃O₄-chitosan nanoparticles are used for the covalent immobilization of lipase from Candida rugosa using N-(3-dimethylaminopropyl)-N′-ethylcarbodiimide (EDC) and N-hydroxysuccinimide (NHS) as coupling agents. The response surface methodology (RSM) was employed to search the optimal immobilization conditions and understand the significance of the factors affecting the immobilized lipase activity. Based on the ridge max analysis, the optimum immobilization conditions were immobilization time 2.14 h, pH 6.37, and enzyme/support ratio 0.73 (w/w); the highest activity obtained was 20 U/g Fe₃O₄-chitosan. After twenty repeated uses, the immobilized lipase retains over 83% of its original activity. The immobilized lipase shows better operational stability, including wider thermal and pH ranges, and remains stable after 13 days of storage at 25 °C.     

Thermal deamination kinetics of the nickel-containing chabazite-like aluminophosphate, Ni(NH2-CH2-CH2-NH2)2(AlPO4)6(OH)2, deposition of nanocrystalline NiO particles

Thermogravimetrical analysis has been used to study the kinetics of thermal deamination of bis(ethylenediamine)nickel(II)-containing aluminophosphate (Ni-CHA) which is a precursor of nickel(II)-containing chabazite-like AlPO₄-34. The deamination occurs as a single-step kinetic process which is best described by the contracting cylinder model. The obtained activation energy of 200 kJ/mol is mainly a reflection of the strong Ni-N coordination bond. The thermal decomposition of Ni-CHA results in the deposition of crystalline NiO particles homogeneously dispersed in the AlPO₄-34 lattice. Average particle size was found to be about 5 nm. The study confirms that the thermal decomposition of amine complexes of Ni(II) encapsulated inside the microporous aluminophosphate host can be a suitable method for obtaining fine nano-oxide particles.     

A nanocomposite/crude extract enzyme-based xanthine biosensor

A novel amperometric biosensor for xanthine was developed based on covalent immobilization of crude xanthine oxidase (XOD) extracted from bovine milk onto a hybrid nanocomposite film via glutaraldehyde. Toward the preparation of the film, a stable colloids solution of core–shell Fe₃O₄/polyaniline nanoparticles (PANI/Fe₃O₄ NPs) was dispersed in solution containing chitosan (CHT) and H₂PtCl₆ and electrodeposited over the surface of a carbon paste electrode (CPE) in one step. Scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectrophotometry, cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS) were used for characterization of the electrode surface. The developed biosensor (XOD/CHT/Pt NPs/PANI/Fe₃O₄/CPE) was employed for determination of xanthine based on amperometric detection of hydrogen peroxide (H₂O₂) reduction at –0.35 V (vs. Ag/AgCl). The biosensor exhibited a fast response time to xanthine within 8 s and a linear working concentration range from 0.2 to 36.0 μM (R² = 0.997) with a detection limit of 0.1 μM (signal/noise [S/N] = 3). The sensitivity of the biosensor was 13.58 μA μM⁻¹ cm⁻². The apparent Michaelis–Menten (K_m) value for xanthine was found to be 4.7 μM. The fabricated biosensor was successfully applied for measurement of fish and chicken meat freshness, which was in agreement with the standard method at the 95% confidence level.     

Study on the heterogeneous degradation of chitosan with H2O2 catalyzed by a new supermolecular assembly crystal: [C6H8N2]6H3[PW12O40]·2H2O

A new supermolecular assembly crystal, [C₆H₈N₂]₆H₃[PW₁₂O₄₀]·2H₂O (DMB-PWA), was synthesized with phosphotungstic acid (PWA) and 1,2-diaminobenzene (DMB) under hydrothermal conditions and was characterized by Fourier-transform infrared spectra (FTIR) and single-crystal X-ray diffraction analysis. DMB-PWA could effectively catalyze oxidative degradation of chitosan with H₂O₂ in the heterogeneous phase. The optimum degradation conditions were determined by orthogonal tests as follows: amount of chitosan 1.00 g, 30% (wt %); H₂O₂, 3.0 mL; dosage of catalyst, 0.06 g; reaction temperature, 85 °C; and reaction time, 30 min. The water-soluble chitosan with a viscosity-average molecular weight (M_v) of 4900 was obtained under the optimum degradation conditions and was characterized by FTIR, ultraviolet-visible diffuse reflection spectra (UV-vis DRS), and X-ray powder diffraction analysis.     

Deposition of iron titanate/titania ceramic composite thin films from a single molecular precursor

A heterobimetallic single molecular precursor, [Fe₂Ti₄(μ-O)₆(TFA)₈(THF)₆] (1) [TFA = trifluoroacetate, THF = tetrahydrofuran], was synthesized by the simple reaction of [Fe₃O(OAc)₆(H₂O)₃]NO₃·4H₂O [OAc = acetato] with tetrakis(2-ethoxyethanalato)titanium(IV) in the presence of trifluoroacetic acid in THF. The synthesized precursor was analyzed by melting point, CHN analysis, FTIR, single crystal X-ray diffraction and thermogravimetric analysis. Complex (1) crystallizes in the orthorhombic space group Pca2₁ with cell dimensions a = 19.2114(14), b = 20.4804(15) and c = 17.2504(12) Å, and the complex undergoes thermal decomposition at 490 °C to give a residual mass corresponding to an Fe₂TiO₅-TiO₂ composite mixture. The synthesized precursor was utilized for deposition of Fe₂TiO₅-TiO₂ composite thin films by aerosol-assisted chemical vapor deposition (AACVD) on glass substrates at 500 °C using argon as the carrier gas. Scanning electron microscopy (SEM), energy dispersive X-ray (EDX) and X-ray powder diffraction (XRD) analyses of the thin films suggest the formation of good quality crystalline thin films of an Fe₂TiO₅-TiO₂ composite with an average grain size of 0.105-0.120 μm.     

Synthesis and characterization of cobalt oxide nanoparticles by thermal treatment process

The simple preparation of Co₃O₄ nanoparticles from a solid organometallic molecular precursor N-N′-bis(salicylaldehyde)-1,2-phenylenediimino cobalt(II); Co(salophen) has been achieved via two simple steps: firstly, the Co(salophen) precursor was precipitated from the reaction of cobalt(II) acetate and N-N′-bis(salicylaldehyde)-1,2-phenylenediimino; H₂salophen; in propanol under nitrogen condition; then, cubic phase Co₃O₄ nanoparticles with the size of mostly 30-50 nm could be produced by thermal treatment of the Co(salophen) in air at 773 K for 5 h. The as-synthesized products were characterized by powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and scanning electronic microscopy (SEM). These results confirm that the resulting oxide was pure single-crystalline Co₃O₄ nanoparticles. The optical property test indicates that the absorption peak of the nanoparticles shifts towards short wavelength, and the blue shift phenomenon might be ascribed to the quantum effect. The hysteresis loops of the obtained samples reveal the ferromagnetic behaviors the enhanced coercivity (H_c) and decreased saturation magnetization (M_s) in contrast to their respective bulk materials.     

Bis(O2S2 macrocycle) complexes of palladium(II)

Two isomeric dibenzo-O₂S₂ macrocycles L¹ and L² have been synthesised and their coordination chemistry towards palladium(II) has been investigated. Two-step approaches via reactions of 1:1-type complexes, [cis-Cl₂LPd] (1a: L = L¹, 1b: L = L²), with different O₂S₂ macrocycle systems (L¹ and L²) have led to the isolation of the following bis(O₂S₂ macrocycle) palladium(II) complexes in the solid state: [Pd(L¹)₂](ClO₄)₂ (2a) and a mixture of [Pd(L¹)₂](ClO₄)₂ (2a) + [Pd(L²)₂](ClO₄)₂ (2b).     

Characterization of magnetic guar gum-grafted carbon nanotubes and the adsorption of the dyes

The hydrophobicity of carbon nanotubes (CNTs) limits their extensive application. The hydrophilicity and biocompatibility of CNTs can be improved by modifying them with biopolymers. As a natural biopolymer, guar gum (GG) was covalently grafted on the surfaces of multiwall carbon nanotube (MWCNT) to obtain GG-MWCNT composite. Then iron oxide nanoparticles were synthesized on the GG-MWCNT to prepare the magnetic GG-MWCNT-Fe₃O₄. The obtained nanocomposites were characterized by Fourier transform infrared spectroscopy, thermogravimetric analysis, transmission electron microscopy, ultraviolet-visible (UV-vis) spectroscopy and X-ray diffraction. GG-MWCNT was composed of about 21.6 wt% GG components, which enhanced the dispersion of GG-MWCNT in aqueous solution and also acted as a template for growth of iron oxide nanoparticles. GG-MWCNT-Fe₃O₄ exhibited superparamagnetic with a saturation magnetization (13.3 emu g⁻¹), and good adsorption on neutral red and methylene blue. GG-MWCNT-Fe₃O₄ could be easily separated from the aqueous solution in a magnetic field.     

Germanium tetra(tertiary butoxide): Synthesis, structure and its utility as a precursor for the preparation of europium doped germanium oxide nanoparticles

Germanium tetra(tertiary butoxide), [Ge(O^tBu)₄], has been prepared by the reaction of GeCl₄ with KOBu^t in benzene. It is a monomeric crystalline solid having a distorted tetrahedral configuration, defined by the coordination of four OBu^t groups around germanium atom. The TG analysis showed that the compound is thermally stable and volatilizes at around 130 °C. Europium doped and un-doped germanium oxide nanoparticles were prepared based on the urea hydrolysis of Ge(O^tBu)₄/Eu(OOCCH₃)₃ in ethylene glycol medium at 150 °C followed by heating the resulting product at 750 °C. The nanoparticles were characterized by XRD, TEM and PL measurements. The europium doped nanoparticles, which were nearly monodispersed (∼30 nm), showed luminescence and the Eu³⁺ ions were occupying the surface of the GeO₂ nanoparticles.     

Colorimetric estimation of human glucose level using γ-Fe2O3 nanoparticles: An easily recoverable effective mimic peroxidase

This article reports simple, green and efficient synthesis of γ-Fe₂O₃ nanoparticles (NPs) (maghemite) through single-source precursor approach for colorimetric estimation of human glucose level. The γ-Fe₂O₃ NPs, having cubic morphology with an average particle size of 30 nm, exhibited effective peroxidase-like activity through the catalytic oxidation of peroxidase substrate 3,3′,5,5′-tetramethylbenzidine (TMB) in the presence of H₂O₂ producing a blue-colored solution. On the basis of this colored-reaction, we have developed a simple, cheap, highly sensitive and selective colorimetric method for estimation of glucose using γ-Fe₂O₃/TMB/glucose–glucose oxidase (GOx) system in the linear range from 1 to 80 μM with detection limit of 0.21 μM. The proposed glucose sensor displays faster response, good stability, reproducibility and anti-interference ability. Based on this simple reaction process, human blood and urine glucose level can be monitored conveniently.     

Role of Phe113 at the distal side of the heme domain of an oxygen-sensor (Ec DOS) in the characterization of the heme environment

The heme-based oxygen-sensor enzyme from Escherichia coli (Ec DOS) is a heme-regulated phosphodiesterase with activity on cyclic-di-GMP and is composed of an N-terminal heme-bound sensor domain with the PAS structure and a C-terminal functional domain. The activity of Ec DOS is substantially enhanced by the binding of O₂ to the Fe(II)-protoporphyrin IX complex [Fe(II) complex] in the sensor domain. The binding of O₂ to the Fe(II) complex changes the structure of the sensor domain, and this altered structure becomes a signal that is transduced to the functional domain to trigger catalysis. The first step in intra-molecular signal transduction is the binding of O₂ to the Fe(II) complex, and detailed elucidation of this molecular mechanism is thus worthy of exploration. The X-ray crystal structure reveals that Phe113 is located close to the O₂ molecule bound to the Fe(II) complex in the sensor domain. Here, we found that the O₂ association rate constants (>200 × 10⁻³ μM⁻¹ s⁻¹: F113L; 26 × 10⁻³ μM⁻¹ s⁻¹: F113Y) of the Fe(II) complexes of Phe113 mutants were markedly different from that (51 × 10⁻³ μM⁻¹ s⁻¹) of the wild-type enzyme, and auto-oxidation rates (0.00068 min⁻¹: F113L; 0.039 min⁻¹: F113Y) of the Phe113 mutants also differed greatly from that (0.0062 min⁻¹) of the wild-type enzyme. We thus suggest that Phe113, residing near the O₂ molecule, has a critical role in optimizing the Fe(II)-O₂ complex for effective regulation of catalysis by the oxygen-sensor enzyme. Interactions of CO and cyanide anion with the mutant proteins were also studied.     

Kinetic studies of the reduction of hexaaquacobalt(III) perchlorate by a cobaloxime, [Co(dmgBF2)2(H2O)2]

The reaction of with Co(dmgBF₂)₂(H₂O)₂ in 1.0 M HClO₄/LiClO₄ was found to be first-order in both reactants and the [H⁺] dependence of the second-order rate constant is given by k_2obs = b/[H⁺], b at 25 °C is 9.23 ± 0.14 × 10² s⁻¹. The [H⁺] dependence at lower temperatures shows some saturation effect that allowed an estimate of the hydrolysis constant for as K_a = 9.5 × 10⁻³ M at 10 and 15 °C. Marcus theory and the known self-exchange rate constant for Co(OH₂)₅OH^2+/+ were used to estimate an electron self-exchange rate constant of k₂₂ = 1.7 × 10⁻⁴ M⁻¹ s⁻¹ for .     

The sedimentation properties of ferritins. New insights and analysis of methods of nanoparticle preparation

Background

Ferritin exhibits complex behavior in the ultracentrifuge due to variability in iron core size among molecules. A comprehensive study was undertaken to develop procedures for obtaining more uniform cores and assessing their homogeneity.

Methods

Analytical ultracentrifugation was used to measure the mineral core size distributions obtained by adding iron under high- and low-flux conditions to horse spleen (apoHoSF) and human H-chain (apoHuHF) apoferritins.

Results

More uniform core sizes are obtained with the homopolymer human H-chain ferritin than with the heteropolymer horse spleen HoSF protein in which subpopulations of HoSF molecules with varying iron content are observed. A binomial probability distribution of H- and L-subunits among protein shells qualitatively accounts for the observed subpopulations. The addition of Fe²⁺ to apoHuHF produces iron core particle size diameters from 3.8 ± 0.3 to 6.2 ± 0.3 nm. Diameters from 3.4 ± 0.6 to 6.5 ± 0.6 nm are obtained with natural HoSF after sucrose gradient fractionation. The change in the sedimentation coefficient as iron accumulates in ferritin suggests that the protein shell contracts ∼ 10% to a more compact structure, a finding consistent with published electron micrographs. The physicochemical parameters for apoHoSF (15%/85% H/L subunits) are M = 484,120 g/mol, ν? = 0.735 mL/g, s_20,w = 17.0 S and D_20,w = 3.21 × 10⁻⁷ cm²/s; and for apoHuHF M = 506,266 g/mol, ν? = 0.724 mL/g, s_20,w = 18.3 S and D_20,w = 3.18 × 10⁻⁷ cm²/s.

Significance

The methods presented here should prove useful in the synthesis of size controlled nanoparticles of other minerals.     

A simple and rapid harvesting method for microalgae by in situ magnetic separation

A simple and rapid harvesting method by in situ magnetic separation with naked Fe₃O₄ nanoparticles has been developed for the microalgal recovery of Botryococcus braunii and Chlorella ellipsoidea. After adding the magnetic particles to the microalgal culture broth, the microalgal cells were adsorbed and then separated by an external magnetic field. The maximal recovery efficiency reached more than 98% for both microalgae at a stirring speed of 120 r/min within 1 min, and the maximal adsorption capacity of these Fe₃O₄ nanoparticles reached 55.9 mg-dry biomass/mg-particles for B. braunii and 5.83 mg-dry biomass/mg-particles for C. ellipsoidea. Appropriate pH value and high nanoparticle dose were favorable to the microalgae recovery, and the adsorption mechanism between the naked Fe₃O₄ nanoparticles and the microalgal cells was mainly due to the electrostatic attraction. The developed in situ magnetic separation technology provides a great potential for saving time and energy associated with improving microalgal harvesting.     

Synthesis and characterization of three group 10 complexes containing nido-carborane diphosphine: [MCl(PPh3){7,8-(PPh2)2-7,8-C2B9H10}] (M = Ni, Pd, Pt)

Three group 10 complexes containing nido-carborane diphosphine, [NiCl(PPh₃){7,8-(PPh₂)₂-7,8-C₂B₉H₁₀}] (1), [PdCl(PPh₃){7,8-(PPh₂)₂-7,8-C₂B₉H₁₀}] · 1.25CH₂Cl₂ (2) and [PtCl(PPh₃){7,8-(PPh₂)₂-7,8-C₂B₉H₁₀}] · 2.5CH₂Cl₂ (3) have been synthesized by the reactions of [M(PPh₃)₂Cl₂] (M = Ni, Pd, Pt) with closo carborane diphosphine 1,2-(PPh₂)₂-1,2-C₂B₁₀H₁₀ in ethanol. For complex 3, it could also be obtained under solvothermal condition. All three complexes were characterized by elemental analysis, FT-IR, ¹H and ¹³C NMR spectroscopy and X-ray structure determination. Single crystal structures show that their structures are similar to each other. In each complex, the nido [7,8-(PPh₂)₂-7,8-C₂B₉H₁₀]⁻, which resulted from the degradation of the initial closo ligand 1,2-(PPh₂)₂-1,2-C₂B₁₀H₁₀ during the reaction process, was coordinated bidentately through the P atoms to M(II) ion, and this resulted in a stable five-membered chelating ring between the bis-diphosphine ligand and the metal. The coordination mode of the metal can be described as a slightly distorted square-planar, in which the remaining two positions were occupied by one Cl⁻ and one PPh₃ group.     

Binding and direct electrochemistry of OmcA, an outer-membrane cytochrome from an iron reducing bacterium, with oxide electrodes: A candidate biofuel cell system

Dissimilatory iron-reducing bacteria transfer electrons to solid ferric respiratory electron acceptors. Outer-membrane cytochromes expressed by these organisms are of interest in both microbial fuel cells and biofuel cells. We use optical waveguide lightmode spectroscopy (OWLS) to show that OmcA, an 85 kDa decaheme outer-membrane c-type cytochrome from Shewanella oneidensis MR-1, adsorbs to isostructural Al₂O₃ and Fe₂O₃ in similar amounts. Adsorption is ionic-strength and pH dependent (peak adsorption at pH 6.5-7.0). The thickness of the OmcA layer on Al₂O₃ at pH 7.0 [5.8 ± 1.1 (2σ) nm] from OWLS is similar, within error, to that observed using atomic force microscopy (4.8 ± 2 nm). The highest adsorption density observed was 334 ng cm⁻² (2.4 × 10¹² molecules cm⁻²), corresponding to a monolayer of 9.9 nm diameter spheres or submonolayer coverage by smaller molecules. Direct electrochemistry of OmcA on Fe₂O₃ electrodes was observed using cyclic voltammetry, with cathodic peak potentials of −380 to −320 mV versus Ag/AgCl. Variations in the cathodic peak positions are speculatively attributed to redox-linked conformation change or changes in molecular orientation. OmcA can exchange electrons with ITO electrodes at higher current densities than with Fe₂O₃. Overall, OmcA can bind to and exchange electrons with several oxides, and thus its utility in fuel cells is not restricted to Fe₂O₃.     

Hydrogen-bonding assemblies constructed from metalloligand building blocks and H2O

New hydrogen-bonding assemblies were synthesized from the reaction of a metalloligand, [Cu(2,4-pydca)₂]²⁻ (L^Cu) (2,4-pydca = 2,4-pyridinedicarboxylate), with a Fe^II ion or an imidazole in an aqueous medium and crystallographically characterized. The obtained compounds, [Fe(H₂O)₆][Cu(2,4-pydca)₂] (1) and [Cu(2,4-pydca)(imidazole)₂] · 2H₂O (2), have metalloligand dimer units, [Cu₂(2,4-pydca)₄]⁴⁻ and [Cu₂(2,4-pydca)₂(imidazole)₄], respectively, each of which assembles by π-π (1) and hydrogen-bonding (2) interactions to form 1-D metalloligand arrays. The 1-D metalloligand arrays are linked by rich hydrogen-bonding interactions via H₂O molecules.