[Show abstract][Hide abstract] ABSTRACT: Carbon dots (CDs) are fluorescent nanoprobes offering a great potential in biological and medical applications due to their superior biocompatibility compared to metal chalcogenide quantum dots (e.g., CdSe). Key factors determining their cytotoxicity and cellular/intracellular tracking involve chemical nature and charge of surface functional groups. For the first time, we present a comprehensive cytotoxic study including cell cycle analysis of carbon dots differing in surface functionalization, namely pristine CDs (CDs-Pri) with negative charge due to carboxylic groups, polyethyleneglycol modified dots with neutral charge (CDs-PEG), and polyethylenimine coated dots with a positive charge (CDs-PEI). The CDs in vitro toxicity was studied on standard mouse fibroblasts (NIH/3T3). The results suggest that neutral CDs-PEG are the most promising for biological applications as they do not induce any abnormalities in cell morphology, intracellular trafficking, and cell cycle up to concentrations of 300 μg mL−1. Negatively charged CDs-Pri arrested the G2/M phase of the cell cycle, stimulated proliferation and led to higher oxidative stress, however they did not enter the cell nucleus. In contrast, positively charged CDs-PEI are the most cytotoxic, entering into the cell nucleus and inducing the largest changes in G0/G1 phase of cell cycle, even at concentrations of around 100 μg mL−1.
[Show abstract][Hide abstract] ABSTRACT: An iron compound of +6 oxidation state (FeVIO42-, Fe(VI)) is a green molecule for various applications (water oxidation catalyst, organic transformation for synthesis, and water remediation agent). However, its use is hindered because of its inherent decay in aqueous solution. This study presents systematic kinetics investigation of the decay of ferrate(VI) in the presence of inorganic buffering ions (borate, phosphate, and carbonate) at a pH range from 6.0 to 9.0. When the heterogeneous decay of Fe(VI) on ferric products was inhibited by phosphate, detailed kinetic analysis revealed that carbonate anion enhanced the Fe(VI) decay rate, compared to phosphate and borate ions. The order of the Fe(VI) decay rate in neutral solution condition was carbonate > phosphate ≥ borate. In alkaline solution, the decay rates of Fe(VI) were similar for the studied buffering ions. The decay of Fe(VI) in presence of carbonate ion was described by mixed first- and second-order kinetics and the first-order rate constant (k1’) had a linear relationship with the concentration of carbonate ion at a neutral pH (k1’= 0.023 + 3.54 × [carbonate] L mol–1 s–1). The analysis of the Fe(VI) decay intermediates/products (O2●-, H2O2, and O2) suggests similar decay pathways in the presence of different buffering anions. The impact of carbonate ions on the size of the nanoparticles of Fe(III) precipitate, the final reduced form of Fe(VI), was studied using transmission electron microscopy, 57Fe Mössbauer spectroscopy, and magnetization measurements. The results indicate that carbonate ions induce the formation of ultrasmall iron(III) oxyhydroxide nanoparticles ( 5 nm), which apparently contribute to increased decay of Fe(VI) due to their larger specific surface area. The described homogeneous reaction of carbonate with Fe(VI) has important implications in the efficiency of environmental Fe(VI) applications. On the other hand, the observed low reactivity of borate with Fe(VI) demonstrates that borate is the least reactive buffer for studies of Fe(VI) reactivity in neutral solutions.
Full-text · Article · Jan 2016 · Physical Chemistry Chemical Physics
[Show abstract][Hide abstract] ABSTRACT: A nanocatalyst comprising ultra-small Pd/PdO nanoparticles (<5 nm) supported on maghemite was prepared by a co-precipitation protocol using inexpensive raw materials and was deployed successfully in various significant synthetic transformations, namely the Heck–Mizoroki olefination (up to 95%), the Suzuki reaction (60–95%), and the allylic oxidation of alkenes under milder conditions. The chemical nature, morphology, size, and loading of palladium nanoparticles over the magnetic support were studied by TEM/EDX, HAADF-STEM chemical mapping, XPS, AAS, and in-field 57Fe Mössbauer spectroscopy. The cost-effective catalyst could be easily separated from the reaction mixture by using an external magnet and reused four times without any loss of activity; chemical stability and recyclability aspects of the catalyst were investigated.
[Show abstract][Hide abstract] ABSTRACT: A template-free solid-state synthesis of a morphologically controlled and highly organized iron(III)oxide micro–mesoporous Fenton catalyst has been engineered through a simple two-step synthetic procedure. The 3D nanoassembly of hematite nanoparticles (5–7 nm) organized into a rod/flower-like morphology shows the highest rate constant reported to date for the decomposition of H2O2 (1.43 × 10−1 min−1) with superior efficiency for the degradation of aromatic (phenol, benzene, ethylbenzene) and chlorinated (trichloroethylene) pollutants in contaminated water. The morphological arrangement of nanoparticles is therefore considered one of the key variables that drive catalysis.
Full-text · Article · Nov 2015 · Journal of Materials Chemistry A
[Show abstract][Hide abstract] ABSTRACT: Two new mononuclear Fe(II) complexes, [FeL1(NCBH3)2] () and [FeL2(CN)2]·3H2O () (L1 = N,N'-bis(2-pyridylmethyl)-1,2-ethanediamine, L2 = N-(2-pyridylmethyl)-N'-(2-pyridylmethylene)-1,2-ethanediamine) were synthesized from the same starting solution under different atmospheric conditions. Complex was isolated under an N2 atmosphere with an expected molecular structure, namely a tetradentate L1 ligand and two NCBH3(-) co-ligands wrapping an iron(ii) ion. It exhibits a gradual spin crossover centered around 355 K, as confirmed by X-ray crystallography, magnetic, DSC and Mössbauer studies. Complex was isolated in the presence of air. One of the secondary amine groups in L1 undergoes an in situ oxidative dehydrogenation, forming a new monoimine asymmetric ligand L2. Besides, a CN(-) co-ligand is also in situ generated from NCBH3(-) during the reaction. The strong ligand field strength imposed by CN(-) and L2 stabilizes in the LS state. Solvent water molecules in complex are hydrogen bonded into a well-defined 1D water chain. shows a proton conductivity of 8.9 × 10(-5) S cm(-1) at 55 °C and 95% relative humidity.
No preview · Article · Nov 2015 · Dalton Transactions
[Show abstract][Hide abstract] ABSTRACT: The self-assembly process in a solution of a mononuclear iron(II) complex based on the bispyrazolylpyridine scaffold with graphene oxide (GO) micrometer-sheets allows not only the devising of a new hybrid-architecture for GO-based materials suitable for nanomedicine, but also the unveiling of the reactive nature of GO as a drug-carrier. The neat iron complex is found to be highly active in disrupting the cell cycle through DNA binding, with behaviour and efficiency similar to that expressed by ruthenium-complexes as well as antibiotic-drugs such as doxorubicin. On the contrary, in the hybrid material the proclivity of neat GO to produce reactive oxygen species (ROS) became down-regulated by the electron-buffering properties of the loaded iron complex, evidencing the presence of an active electron transfer from the drug to GO. These findings question the use of the neat GO platform as a suitable carrier for metal-based anticancer drugs and highlight the importance of addressing the chemical/physical integrity of the drug being loaded into GO before drawing conclusions on the potential effectiveness of the hybrid material for medical applications.
[Show abstract][Hide abstract] ABSTRACT: Three new two-dimensional (2D) Hofmann-type coordination polymers with general formula [Fe(3-NH2py)2M(CN)4] (3-NH2py = 3-aminopyridine, M = Ni (1), Pd (2), Pt (3)) have been synthesized. Magnetic susceptibility measurements show that they exhibited cooperative spin crossover (SCO) with remarkable hysteretic behaviors. Their hysteresis widths are 25, 37, and 30 K for 1-3, respectively. The single-crystal structure of 1 suggest that the pseudo-octahedral Fe sites are equatorially bridged by [M(CN)4](2-) to form 2D grids and axially coordinated by 3-NH2py ligands. The intermolecular interactions between layers (the offset face-to-face π···π interactions, hydrogen bonds, and weak Namino···Ni(II) contacts) together with the covalent bonds bridged by [M(CN)4](2-) units are responsible to the significant cooperativity.
Full-text · Article · Aug 2015 · Inorganic Chemistry
[Show abstract][Hide abstract] ABSTRACT: Nickel ferrite NiFe2O4 is a typical soft magnetic ferrite with high electrical resistivity used as high frequency magnetic material. Neodymium (Nd3+) doped NiFe2O4 materials were fabricated using solid state reaction. The properties of the obtained material were investigated by X-Ray Diffraction (XRD), Scanning Electron Microscope (SEM), Fourier-Transform Infrared Spectroscopy (FT-IR), magnetic measurements on SQUID and Mössbauer spectroscopy. It was found that the material consists of two different phases: Nd3+ doped NiFe2O4 and NdFeO3. The Nd3+ ions occupy cation sites of the NiFe2O4 inverse spinel structure. NdFeO3 phase occurred when the level of Nd3+ atoms exceed a percolation limit. The presence of both phases was confirmed by SEM observations. The Mössbauer spectra analysis showed two sextets, which can be ascribed to iron atoms in tetrahedral and octahedral positions. From their intensities it is concluded that Nd3+ occupies octahedral sites in the spinel structure of NiFe2O4, which were originally occupied by Ni2+.
Full-text · Article · Jun 2015 · Progress in Natural Science
[Show abstract][Hide abstract] ABSTRACT: Classification, chemistry, and applications of fullerenes, carbon dots, nanotubes, graphene, nanodiamonds, and combined superstructures of a range of carbon nanoallotropes are investigated. The investigations also cover superstructures consisting of combinations of carbon nanoallotropes such as fullerene aggregates, CNTs or graphene thin films, fibers, membranes, and aerogels in addition to describing individual carbon nanoallotropes. The issue of chemical modification of carbon nanoallotropes with division into several sections based on the origins of the chemical reactivity in each case is also investigated.
[Show abstract][Hide abstract] ABSTRACT: This study continues our investigation of high-temperature superconductors of LaFeO(1−x)Fx
As type initiated in our previous paper (J. Supercond. Nov. Magnetism 27, 1825, ), where the high-temperature Kondo effect had been observed in the sample with x = 0.15. We proceed with exploring the properties of the LaFeO 0.88F
0.12As sample, applying the X-ray diffraction (XRD) method, resistivity measurement, and the magnetic and Mössbauer measurements at the temperature range of 4.2-300 K. We observe the emergence of high-temperature Kondo effect at the temperatures between 30 and 50 K. At the same time, as opposed to the case x=0.15, we reveal the transformation of the high-temperature Kondo effect to the high-temperature superconductivity at the temperature near 25 K. The Mössbauer spectra of the sample obtained at different temperatures represent a single line, lying near zero relative velocity and do not exhibit any visible alterations. Concurrently, the application of an external magnetic field of 5 T to the sample at 5 K induces the emergence of a hyperfine magnetic splitting with the effective magnetic field on resonant nuclei H
ef = 45.5 kOe. We suppose that the appearance of a magnetic ordering in the sample occurs due to the alignment of magnetic moments of impurities that confirms our hypothesis about a strong coupling of electron’s spins with the magnetic moments of impurities in iron-containing superconductors.
No preview · Article · May 2015 · Journal of Superconductivity and Novel Magnetism
[Show abstract][Hide abstract] ABSTRACT: To date, iron oxides have been extensively investigated for promising high applicability in various scientific and industrial fields. Generally, several forms can be distinguished with respect to their crystal structure that drives their specific physical (particularly, magnetic) properties. In this work, the pure β-Fe2O3 phase, prepared in a nanoparticle form by solid-state synthetic strategy, was investigated employing 57Fe Mössbauer spectroscopy, magnetization measurements, transmission electron microscopy, X-ray powder diffraction, heat capacity measurements, and cyclic voltammetry. It turns out that below the Néel transition temperature, β-Fe2O3 behaves as a canted antiferromagnet with a small net moment. For further possible utilization in photoelectrochemical applications, the estimation of β-Fe2O3 band gap by cyclic voltammetry was performed amounting to ~2.2 eV.
[Show abstract][Hide abstract] ABSTRACT: In this study, dielectric properties within 8–12 GHz microwave frequencies, inductively coupled plasma-atomic emission spectrometry, Fourier transform infrared spectrometry, synchronized two thermal analyses, and 57 Fe Mössbauer spec-troscopy analysis of chalcedony, agate, and zultanite samples from Turkey are presented. Agate and chalcedony show the same nine vibrational absorption peaks obtained unlike zultanite from FTIR spectra in the 350 cm −1 to 4000 cm −1 range, ε values of chalcedony, agate and zultanite derived at 10.5 GHz were 4.67, 4.41, and 7.34, respectively, ε and ε values of the studied samples at the microwave frequencies are related to the percentage weight of their constituent parts in their chemical compositions. 57 Fe Mössbauer spectroscopy results confirm the existence of iron-containing islands in the crystal structure of zultanite, agate, and chalcedony samples, equipped them with magnetic features typical for magnetic nanopar-ticles including superparamagnetism. The presence of iron-containing islands significantly affects the magnetic, dielectric, and optical properties of studied samples that are not observed for pure minerals without any foreign inclusions.
Full-text · Article · May 2015 · Chinese Physics B
[Show abstract][Hide abstract] ABSTRACT: Potassium ferrite (KFeO2) was synthesized by a new simple thermal process from natural waste ferrihydrite and KNO3 precursors. The synthesized KFeO2 showed considerable instability when it was in contact with water and CO2 of the humid air.
The decomposition of KFeO2 followed first-order kinetics with rate constants as 0.93 × 10–1 h–1 and 1.86 × 10–1 h–1 at relative humidity of 30–35% and 65–70%, respectively. The products of
decomposition, crystalline KHCO3 and nanocrystalline iron(III) oxides in the molar ratio of 2:1, were characterized in detail by X-ray powder diffraction, low-temperature and in-field 57Fe Mössbauer spectroscopy, magnetization (SQUID) measurements, thermal analysis,
and scanning and transmission electron microscopy. Washing and subsequent air drying of the decomposed products of KFeO2 yielded monodisperse superparamagnetic maghemite (γ-Fe2O3) nanoparticles, which turned out to be efficient as magnetic sorbents
for removing Cu2+ in water. A direct addition of solid KFeO2 into water containing Cu2+ ions yielded rapid coagulation of iron(III) oxyhydroxides, which subsequently removed Cu2+ more efficiently compared to its sorption on the pre-formed maghemite
Full-text · Article · Mar 2015 · Science of Advanced Materials
[Show abstract][Hide abstract] ABSTRACT: A new category of iron oxide nanoparticles (surface active maghemite nanoparticles (SAMNs, γ-Fe2O3)) allows the intimate chemical and electrical contact with DNA by direct covalent binding. On these basis, different DNA-nanoparticle architectures are developed and used as platform for studying electrical properties of DNA. The macroscopic 3D nanobioconjugate, constituted of 5% SAMNs, 70% water, and 25% DNA, shows high stability, electrochemical reversibility and, moreover, electrical conductivity (70–80 Ω cm−1). Reversible electron transfer at the interface between nanoparticles and DNA is unequivocally demonstrated by Mössbauer spectroscopy, which shows the appearance of Fe(II) atoms on nanoparticles following nanobioconjugate formation. This represents the first example of permanent electron exchange by DNA, as well as, of DNA conductivity at a macroscopic scale. Finally, the most probable configuration of the binding is tentatively modeled by density functional theory (DFT/UBP86/6-31+G*), showing the occurrence of electron transfer from the organic orbitals of DNA to surface exposed Fe(III) on nanoparticles, as well as the generation of defects (holes) on the DNA bases. The unequivocal demonstration of DNA conduction provides a new perspective in the five decades long debate about electrical properties of this biopolymer, further suggesting novel approaches for DNA exploitation in nanoelectronics.
Full-text · Article · Feb 2015 · Advanced Functional Materials
[Show abstract][Hide abstract] ABSTRACT: Biogenic iron oxides have been collected from a water stream and subsequently magnetically modified using water-based magnetic fluid. Both natural and magnetically modified materials have been characterized in detail using wavelength dispersive X-ray fluorescence spectrometry, X-ray powder diffraction, Mössbauer spectroscopy, electron microscopy and BET surface area measurements. The natural material is composed of 2-line ferrihydrite, forming hollow microtubules—sheaths of Leptothrix ochracea, and detrital components. As a result of the ferrofluid modification, maghemite nanoparticles were identified on the surface of the treated material. The active surface area of the bulk, magnetically-modified sample was 148 m2 g−1. The magnetically modified material was tested as inexpensive magnetically responsive adsorbent for the removal of selected organic xenobiotics, namely organic dyes, from aqueous solutions. The observed maximum adsorption capacities ranged between 34.3 and 97.8 mg of dye per 1 g of adsorbent.
Full-text · Article · Feb 2015 · International journal of Environmental Science and Technology
[Show abstract][Hide abstract] ABSTRACT: The removal efficiency of heavy metal ions (cadmium(II) - Cd(II), cobalt(II) - Co(II), nickel(II) - Ni(II), and copper(II) - Cu(II)) by potassium ferrate(VI) (K2FeO4, Fe(VI)), was studied as a function of added amount of Fe(VI) (or Fe) and varying pH. At pH = 6.6, the effective removal of Co(II), Ni(II), and Cu(II) from water was observed at a low Fe-to-heavy metal ion ratio (Fe/M(II) = 2:1) while a removal efficiency of 70% was for Cd(II) ions at a high Fe/Cd(II) weight ratio of 15:1. The role of ionic radius and metal valence state was explored by conducting similar removal experiments using Al(III) ions. The unique combination of X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), in-field Mössbauer spectroscopy, and magnetization measurements enabled the delineation of several distinct mechanisms for the Fe(VI)-prompted removal of metal ions. Under Fe/M weight ratio of 5:1, Co(II), Ni(II), and Cu(II) were removed by the formation of MFe2O4 spinel phase and partially through their structural incorporation into octahedral positions of γ-Fe2O3 (maghemite) nanoparticles. In comparison, smaller sized Al(III) ions got incorporated easily into the tetrahedral positions of γ-Fe2O3 nanoparticles. In contrast, Cd(II) ions do not create either the spinel ferrite structure or incorporate into the lattice of iron(III) oxide phase due to the distinct electronic structure and ionic radius. Environmentally-friendly removal of heavy metal ions at a much smaller dosage of Fe than those of commonly applied iron-containing coagulants, and the formation of ferrimagnetic species preventing metal ions leaching back into the environment and allowing their magnetic separation are highlighted.
No preview · Article · Jan 2015 · Environmental Science and Technology
[Show abstract][Hide abstract] ABSTRACT: When developing new nanoparticles for bio-applications, it is important to fully characterize the nanoparticle's behavior in biological systems. The most common techniques employed for mapping nanoparticles inside cells include transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM). These techniques entail passing an electron beam through a thin specimen. STEM or TEM imaging is often used for the detection of nanoparticles inside cellular organelles. However, lengthy sample preparation is required (i.e., fixation, dehydration, drying, resin embedding, and cutting). In the present work, a new matrix (FTO glass) for biological samples was used and characterized by field emission scanning electron microscopy (FE-SEM) to generate images comparable to those obtained by TEM. Using FE-SEM, nanoparticle images were acquired inside endo/lysosomes without disruption of the cellular shape. Furthermore, the initial steps of nanoparticle incorporation into the cells were captured. In addition, the conductive FTO glass endowed the sample with high stability under the required accelerating voltage. Owing to these features of the sample, further analyses could be performed (material contrast and energy-dispersive X-ray spectroscopy (EDS)), which confirmed the presence of nanoparticles inside the cells. The results showed that FE-SEM can enable detailed characterization of nanoparticles in endosomes without the need for contrast staining or metal coating of the sample. Images showing the intracellular distribution of nanoparticles together with cellular morphology can give important information on the biocompatibility and demonstrate the potential of nanoparticle utilization in medicine.