Development of Iron-Based Single Atom Materials for General and Efficient Synthesis of Amines.

Earth abundant metal-based heterogeneous catalysts with highly active and at the same time stable isolated metal sites constitute a key factor for the advancement of sustainable and cost-effective chemical synthesis. In particular, the development of more practical, and durable iron-based materials is of central interest for organic synthesis, especially for the preparation of chemical products related to life science applications. Here, we report the preparation of Fe-single atom catalysts (Fe-SACs) entrapped in N-doped mesoporous carbon support with unprecedented potential in the preparation of different kinds of amines, which represent privileged class of organic compounds and find increasing application in daily life. The optimal Fe-SACs allow for the reductive amination of a broad range of aldehydes and ketones with ammonia and amines to produce diverse primary, secondary, and tertiary amines including N-methylated products as well as drugs, agrochemicals, and other biomolecules (amino acid esters and amides) utilizing green hydrogen.

Single-Atom (Iron-Based) Catalysts: Synthesis and Applications.

Supported single-metal atom catalysts (SACs) are constituted of isolated active metal centers, which are heterogenized on inert supports such as graphene, porous carbon, and metal oxides. Their thermal stability, electronic properties, and catalytic activities can be controlled via interactions between the single-metal atom center and neighboring heteroatoms such as nitrogen, oxygen, and sulfur. Due to the atomic dispersion of the active catalytic centers, the amount of metal required for catalysis can be decreased, thus offering new possibilities to control the selectivity of a given transformation as well as to improve catalyst turnover frequencies and turnover numbers. This review aims to comprehensively summarize the synthesis of Fe-SACs with a focus on anchoring single atoms (SA) on carbon/graphene supports. The characterization of these advanced materials using various spectroscopic techniques and their applications in diverse research areas are described. When applicable, mechanistic investigations conducted to understand the specific behavior of Fe-SACs-based catalysts are highlighted, including the use of theoretical models.

Condensed Clustered Iron Oxides for Ultrahigh Photothermal Conversion and In Vivo Multimodal Imaging.

Magnetic iron oxide nanocrystals (MIONs) are established as potent theranostic nanoplatforms due to their biocompatibility and the multifunctionality of their spin-active atomic framework. Recent insights have also unveiled their attractive near-infrared photothermal properties, which are, however, limited by their low near-infrared absorbance, resulting in noncompetitive photothermal conversion efficiencies (PCEs). Herein, we report on the dramatically improved photothermal conversion of condensed clustered MIONs, reaching an ultrahigh PCE of 71% at 808 nm, surpassing the so-far MION-based photothermal agents and even benchmark near-infrared photothermal nanomaterials. Moreover, their surface passivation is achieved through a simple self-assembly process, securing high colloidal stability and structural integrity in complex biological media. The bifunctional polymeric canopy simultaneously provided binding sites for anchoring additional cargo, such as a strong near-infrared-absorbing and fluorescent dye, enabling in vivo optical and photoacoustic imaging in deep tissues, while the iron oxide core ensures detection by magnetic resonance imaging. In vitro studies also highlighted a synergy-amplified photothermal effect that significantly reduces the viability of A549 cancer cells upon 808 nm laser irradiation. Integration of such-previously elusive-photophysical properties with simple and cost-effective nanoengineering through self-assembly represents a significant step toward sophisticated nanotheranostics, with great potential in the field of nanomedicine.

Carbon Dots Detect Water-to-Ice Phase Transition and Act as Alcohol Sensors via Fluorescence Turn-Off/On Mechanism.

Highly fluorescent carbon nanoparticles called carbon dots (CDs) have been the focus of intense research due to their simple chemical synthesis, nontoxic nature, and broad application potential including optoelectronics, photocatalysis, biomedicine, and energy-related technologies. Although a detailed elucidation of the mechanism of their photoluminescence (PL) remains an unmet challenge, the CDs exhibit robust, reproducible, and environment-sensitive PL signals, enabling us to monitor selected chemical phenomena including phase transitions or detection of ultralow concentrations of molecular species in solution. Herein, we report the PL turn-off/on behavior of aqueous CDs allowing the reversible monitoring of the water-ice phase transition. The bright PL attributable to molecular fluorophores present on the CD surface was quenched by changing the liquid aqueous environment to solid phase (ice). Based on light-induced electron paramagnetic resonance (LEPR) measurements and density functional theory (DFT) calculations, the proposed kinetic model assuming the presence of charge-separated trap states rationalized the observed sensitivity of PL lifetimes to the environment. Importantly, the PL quenching induced by freezing could be suppressed by adding a small amount of alcohols. This was attributed to a high tendency of alcohol to increase its concentration at the CD/solvent interface, as revealed by all-atom molecular dynamics simulations. Based on this behavior, a fluorescence "turn-on" alcohol sensor for exhaled breath condensate (EBC) analysis has been developed. This provided an easy method to detect alcohols among other common interferents in EBC with a low detection limit (100 ppm), which has a potential to become an inexpensive and noninvasive clinically useful diagnostic tool for early stage lung cancer screening.

Hierarchical Porous Graphene-Iron Carbide Hybrid Derived From Functionalized Graphene-Based Metal-Organic Gel as Efficient Electrochemical Dopamine Sensor.

A metal-organic gel (MOG) similar in constitution to MIL-100 (Fe) but containing a lower connectivity ligand (5-aminoisophthalate) was integrated with an isophthalate functionalized graphene (IG). The IG acted as a structure-directing templating agent, which also induced conductivity of the material. The MOG@IG was pyrolyzed at 600°C to obtain MGH-600, a hybrid of Fe/Fe3C/FeOx enveloped by graphene. MGH-600 shows a hierarchical pore structure, with micropores of 1.1 nm and a mesopore distribution between 2 and 6 nm, and Brunauer-Emmett-Teller surface area amounts to 216 m2/g. Furthermore, the MGH-600 composite displays magnetic properties, with bulk saturation magnetization value of 130 emu/g at room temperature. The material coated on glassy carbon electrode can distinguish between molecules with the same oxidation potential, such as dopamine in presence of ascorbic acid and revealed a satisfactory limit of detection and limit of quantification (4.39 × 10-7 and 1.33 × 10-6 M, respectively) for the neurotransmitter dopamine.

Sustainable Synthesis of Nanoscale Zerovalent Iron Particles for Environmental Remediation.

Nanoscale zerovalent iron (nZVI) particles represent an important material for diverse environmental applications because of their exceptional electron-donating properties, which can be exploited for applications such as reduction, catalysis, adsorption, and degradation of a broad range of pollutants. The synthesis and assembly of nZVI by using biological and natural sustainable resources is an attractive option for alleviating environmental contamination worldwide. In this Review, various green synthesis pathways for generating nZVI particles are summarized and compared with conventional chemical and physical methods. In addition to describing the latest environmentally benign methods for the synthesis of nZVI, their properties and interactions with diverse biomolecules are discussed, especially in the context of environmental remediation and catalysis. Future prospects in the field are also considered.

Biologically safe colloidal suspensions of naked iron oxide nanoparticles for in situ antibiotic suppression.

A category of naked maghemite nanoparticles (γ-Fe2O3), named surface active maghemite nanoparticles (SAMNs), is characterized by biological safety, high water colloidal stability and a surface chemistry permitting the binding of ligands. In the present study, the interaction between SAMNs and an antibiotic displaying chelating properties (oxytetracycline, OxyTC) was extensively structurally and magnetically characterized. OxyTC emerged as an ideal probe for providing insights into the colloidal properties of SAMNs. At the same time, SAMNs turned out as an elective tool for water remediation from OxyTC. Therefore, a dilute colloidal suspension of SAMNs was used for the removal of OxyTC in large volume tanks where, to simulate a real in situ application, a population of zebrafish (Danio rerio) was introduced. Interestingly, SAMNs led to the complete removal of the drug without any sign of toxicity for the animal model. Moreover, OxyTC immobilized on SAMNs surface resulted safe for sensitive Escherichia coli bacteria strain. Thus, SAMNs were able to recover the drug and to suppress its antibiotic activity envisaging their feasibility as competitive option for water remediation from OxyTC in more nature related scenarios. The present contribution stimulates the use of novel smart colloidal materials to cope with complex environmental issues.

Electric-field enhanced reactivity and migration of iron nanoparticles with implications for groundwater treatment technologies: Proof of concept.

The extensive use of nanoscale zero-valent iron (nZVI) particles for groundwater treatment has been limited, in part, because of their non-selective reactivity and low mobility in aquatic environments. Herein, we describe and explore progressive changes in the reactivity and migration of aqueous dispersed nZVI particles under an applied DC electric field. Due to the applied electric field with an intensity of about 1 V cm-1, the solution oxidation-reduction potential (ORP) remained as low as -200 mV for at least 32 days, which was in agreement with the persistence of the reduced iron species (mainly Fe(II)), and led to substantially prolonged reactivity of the original nZVI. The treatment of chlorinated ethenes (DCE > PCE > TCE) was markedly faster, individual CHC compounds were eliminated with the same kinetics and no lesser-chlorinated intermediates were accumulated, following thus the direct dechlorination scheme. When nZVI-dispersion flows towards the anode through vertical laboratory columns filled with quartz sand, significant enhancement of nZVI migration was recorded because of lower extent of nanoparticle aggregation and increased repulsion forces between the nanoparticles and the surface of silica dioxide. The results of this study have significant consequences for groundwater remediation, mainly for the treatment of slowly degradable DCE in real CHC contaminated groundwater, where it could improve the reactivity, the longevity and the migration of nZVI particles.

Stealth Iron Oxide Nanoparticles for Organotropic Drug Targeting.

The ability of peculiar iron oxide nanoparticles (IONPs) to evade the immune system was investigated in vivo. The nanomaterial was provided directly into the farming water of zebrafish ( Danio rerio) and the distribution of IONPs and the delivery of oxytetracycline (OTC) was studied evidencing the successful overcoming of the intestinal barrier and the specific and prolonged (28 days) organotropic delivery of OTC to the fish ovary. Noteworthy, no sign of adverse effects was observed. In fish blood, IONPs were able to specifically bind apolipoprotein A1 (Apo A1) and molecular modeling showed the structural analogy between the IONP@Apo A1 nanoconjugate and high-density lipoprotein (HDL). Thus, the preservation of the biological identity of the protein suggests a plausible explanation of the observed overcoming of the intestinal barrier, of the great biocompatibity of the nanomaterial, and of the prolonged drug delivery (benefiting of the lipoprotein transport route). The present study promises novel and unexpected stealth materials in nanomedicine.

Chloroplasts preferentially take up ferric-citrate over iron-nicotianamine complexes in Brassica napus.

MAIN CONCLUSION: Fe uptake machinery of chloroplasts prefers to utilise Fe(III)-citrate over Fe-nicotianamine complexes. Iron uptake in chloroplasts is a process of prime importance. Although a few members of their iron transport machinery were identified, the substrate preference of the system is still unknown. Intact chloroplasts of oilseed rape (Brassica napus) were purified and subjected to iron uptake studies using natural and artificial iron complexes. Fe-nicotianamine (NA) complexes were characterised by 5 K, 5 T Mössbauer spectrometry. Expression of components of the chloroplast Fe uptake machinery was also studied. Fe(III)-NA contained a minor paramagnetic Fe(II) component (ca. 9%), a paramagnetic Fe(III) component exhibiting dimeric or oligomeric structure (ca. 20%), and a Fe(III) complex, likely being a monomeric structure, which undergoes slow electronic relaxation at 5 K (ca. 61%). Fe(II)-NA contained more than one similar chemical Fe(II) environment with no sign of Fe(III) components. Chloroplasts preferred Fe(III)-citrate compared to Fe(III)-NA and Fe(II)-NA, but also to Fe(III)-EDTA and Fe(III)-o,o'EDDHA, and the Km value was lower for Fe(III)-citrate than for the Fe-NA complexes. Only the uptake of Fe(III)-citrate was light-dependent. Regarding the components of the chloroplast Fe uptake system, only genes of the reduction-based Fe uptake system showed high expression. Chloroplasts more effectively utilize Fe(III)-citrate, but hardly Fe-NA complexes in Fe uptake.

In vivo theranostics with near-infrared-emitting carbon dots-highly efficient photothermal therapy based on passive targeting after intravenous administration.

Carbon dots that exhibit near-infrared fluorescence (NIR CDs) are considered emerging nanomaterials for advanced biomedical applications with low toxicity and superior photostability and targeting compared to currently used photoluminescence agents. Despite progress in the synthesis of NIR CDs, there remains a key obstacle to using them as an in vivo theranostic agent. This work demonstrates that the newly developed sulfur and nitrogen codoped NIR CDs are highly efficient in photothermal therapy (PTT) in mouse models (conversion efficiency of 59%) and can be readily visualized by photoluminescence and photoacoustic imaging. The real theranostic potential of NIR CDs is enhanced by their unique biodistribution and targeting. Contrary to all other nanomaterials that have been tested in biomedicine, they are excreted through the body's renal filtration system. Moreover, after intravenous injection, NIR CDs are accumulated in tumor tissue via passive targeting, without any active species such as antibodies. Due to their accumulation in tumor tissue without the need for intratumor injection, high photothermal conversion, excellent optical and photoacoustic imaging performance, and renal excretion, the developed CDs are suitable for transfer to clinical biomedical practice.

Iron and Iron Oxide Nanoparticles Synthesized Using Green Tea Extract: Improved Ecotoxicological Profile and Ability to Degrade Malachite Green.

In recent years, iron-based nanoparticles (FeNPs) have been successfully used in environmental remediation and water treatment. This study examined ecotoxicity of two FeNPs produced by green tea extract (smGT, GTFe) and their ability to degrade malachite green (MG). Their physicochemical properties were assessed using transmission electron microscopy, X-ray powder diffraction, dynamic light scattering, and transmission Mössbauer spectroscopy. Using a battery of ecotoxicological bioassays, we determined toxicity for nine different organisms, including bacteria, cyanobacterium, algae, plants, and crustaceans. GTFe, amorphous complex of Fe(II, III) ions and polyphenols from green tea extract, proved low capacity to degrade MG and was toxic to all tested organisms. Superparamagnetic iron oxide NPs (smGT) derived from GTFe, showed no toxic effect on most of the tested organisms up to a concentration of 1g/L, except for algae and cyanobacterium and removed 93 % MG at concentration 125 mg Fe/L after 60 minutes. The procedure described in this paper generates new superparamagnetic iron oxide NPs from existing and toxic GTFe, which are nontoxic and has degradative potential for organic compounds. These findings suggest low ecotoxicological risks and suitability of this green-synthesized FeNPs for environmental remediation purposes.

An Isolated Molecule of Iron(II) Phthalocyanin Exhibits Quintet Ground-State: A Nexus between Theory and Experiment.

Iron(II) phthalocyanine (FePc) is an important member of the phthalocyanines family with potential applications in the fields of electrocatalysis, magnetic switching, electrochemical sensing, and phototheranostics. Despite the importance of electronic properties of FePc in these applications, a reliable determination of its ground-state is still challenging. Here we present combined state of the art computational methods and experimental approaches, that is, Mössbauer spectroscopy and Superconducting Quantum Interference Device (SQUID) magnetic measurements to identify the ground state of FePc. While the nature of the ground state obtained with density functional theory (DFT) depends on the functional, giving mostly the triplet state, multi-reference complete active space second-order perturbation theory (CASPT2) and density matrix renormalization group (DMRG) methods assign quintet as the FePc ground-state in gas-phase. This has been confirmed by the hyperfine parameters obtained from 57 Fe Mössbauer spectroscopy performed in frozen monochlorobenzene. The use of monochlorobenzene guarantees an isolated nature of the FePc as indicated by a zero Weiss temperature. The results open doors for exploring the ground state of other metal porphyrin molecules and their controlled spin transitions via external stimuli.

Impact of inorganic ions and natural organic matter on arsenates removal by ferrate(VI): Understanding a complex effect of phosphates ions.

Arsenic compounds are carcinogenic to humans and are typically removed from contaminated water using various sorbents. The ionic composition plays a significant role in arsenate removal efficiency during the process of water remediation. Here, we quantify the effects of natural ions (chlorides, nitrates, carbonates, sulfates, and phosphates) and humic acid on the removal of arsenates by ferrate(VI) at pH = 6.6. In the experiments, the initial concentration of arsenates was 10 mg L-1 (as As) and the concentrations of ions varied in the range from 5 to 100 mg L-1 of element in ionic form and humic acid. The achieved results show that only phosphate ions had principle influence on the efficiency of arsenate removal by ferrate(VI). The effect of phosphates was elucidated by applying transmission electron microscopy, energy-dispersive X-ray spectroscopy, and low temperature in-field 57Fe Mössbauer spectroscopy to solid samples, prepared under different weight ratios of ferrate(VI), arsenates, and phosphates. These results show three crucial effects of phosphates on the arsenate removal mechanisms. At low P:As weight ratio (up to 1:1), the incorporation of arsenate ions into the crystalline structure of γ-Fe2O3/γ-FeOOH nanoparticles was found to be suppressed by the presence of phosphates. Thus, arsenates were mainly adsorbed onto the surface of γ-Fe2O3/γ-FeOOH nanoparticles. Further increase in the P:As weight ratio (more than 1:1) resulted in the competition between arsenates and phosphates sorption. With the increased concentration of phosphate ions, the number of arsenates on the surface of γ-Fe2O3/γ-FeOOH nanoparticles was reduced. Finally, the complexation of iron(III) ions with phosphate ions occurred, leading to a decrease in the arsenates removal efficiency, which resulted from a lower content of precipitated γ-Fe2O3/γ-FeOOH nanoparticles. All these aspects need to be considered prior to application of ferrate(VI) for arsenates removal in real natural waters.

Label-free determination of prostate specific membrane antigen in human whole blood at nanomolar levels by magnetically assisted surface enhanced Raman spectroscopy.

Prostate cancer is one of the most common cancers among men and can in its later stages cause serious medical problems. Due to the limited suitability of current diagnostic biochemical markers, new biomarkers for the detection of prostate cancer are highly sought after. An ideal biomarker should serve as a reliable prognostic marker, be applicable for early diagnosis, and be applicable for monitoring of therapeutic response. One potential candidate is glutamate carboxypeptidase II (GCPII), also known as prostate specific membrane antigen (PSMA), which has a promising role for direct imaging. GCPII is considerably over-expressed on cancerous prostatic epithelial cells; its analysis typically follows radiological or spectrophotometric principles. Its role as a biomarker present in blood has been recently investigated and potential correlation between a concentration of GCPII and prostate cancer has been proposed. The wider inclusion of GCPII detection in clinical praxis limits mainly the time and cost per analysis. Here, we present a novel analytical nanosensor applicable to quantification of GCPII in human whole blood consisted of Fe3O4@Ag magnetic nanocomposite surface-functionalized by an artificial antibody (low-molecular-weight GCPII synthetic inhibitor). The nanocomposite allows a simple magnetic isolation of GCPII using external magnetic force and its consecutive determination by magnetically assisted surface enhanced Raman spectroscopy (MA-SERS) with a limit of detection 6 pmol. L-1. This method enables a rapid determination of picomolar concentrations of GCPII in whole human blood of healthy individuals using a standard addition method without a complicated sample pre-treatment.

Assessment of toxicity of selenium and cadmium selenium quantum dots: A review.

This paper reviews the current understanding of the toxicity of selenium (Se) to terrestrial mammalian and aquatic organisms. Adverse biological effects occur in the case of Se deficiencies, associated with this element having essential biological functions and a narrow window between essentiality and toxicity. Several inorganic species of Se (-2, 0, +4, and +6) and organic species (monomethylated and dimethylated) have been reported in aquatic systems. The toxicity of Se in any given sample depends not only on its speciation and concentration, but also on the concomitant presence of other compounds that may have synergistic or antagonistic effects, affecting the target organism as well, usually spanning 2 or 3 orders of magnitude for inorganic Se species. In aquatic ecosystems, indirect toxic effects, linked to the trophic transfer of excess Se, are usually of much more concern than direct Se toxicity. Studies on the toxicity of selenium nanoparticles indicate the greater toxicity of chemically generated selenium nanoparticles relative to selenium oxyanions for fish and fish embryos while oxyanions of selenium have been found to be more highly toxic to rats as compared to nano-Se. Studies on polymer coated Cd/Se quantum dots suggest significant differences in toxicity of weathered vs. non-weathered QD's as well as a significant role for cadmium with respect to toxicity.

Covalently bound DNA on naked iron oxide nanoparticles: Intelligent colloidal nano-vector for cell transfection.

BACKGROUND: Conversely to common coated iron oxide nanoparticles, novel naked surface active maghemite nanoparticles (SAMNs) can covalently bind DNA. Plasmid (pDNA) harboring the coding gene for GFP was directly chemisorbed onto SAMNs, leading to a novel DNA nanovector (SAMN@pDNA). The spontaneous internalization of SAMN@pDNA into cells was compared with an extensively studied fluorescent SAMN derivative (SAMN@RITC). Moreover, the transfection efficiency of SAMN@pDNA was evaluated and explained by computational model. METHODS: SAMN@pDNA was prepared and characterized by spectroscopic and computational methods, and molecular dynamic simulation. The size and hydrodynamic properties of SAMN@pDNA and SAMN@RITC were studied by electron transmission microscopy, light scattering and zeta-potential. The two nanomaterials were tested by confocal scanning microscopy on equine peripheral blood-derived mesenchymal stem cells (ePB-MSCs) and GFP expression by SAMN@pDNA was determined. RESULTS: Nanomaterials characterized by similar hydrodynamic properties were successfully internalized and stored into mesenchymal stem cells. Transfection by SAMN@pDNA occurred and GFP expression was higher than lipofectamine procedure, even in the absence of an external magnetic field. A computational model clarified that transfection efficiency can be ascribed to DNA availability inside cells. CONCLUSIONS: Direct covalent binding of DNA on naked magnetic nanoparticles led to an extremely robust gene delivery tool. Hydrodynamic and chemical-physical properties of SAMN@pDNA were responsible of the successful uptake by cells and of the efficiency of GFP gene transfection. GENERAL SIGNIFICANCE: SAMNs are characterized by colloidal stability, excellent cell uptake, persistence in the host cells, low toxicity and are proposed as novel intelligent DNA nanovectors for efficient cell transfection.

Carbon Dot Nanothermometry: Intracellular Photoluminescence Lifetime Thermal Sensing.

Nanoscale biocompatible photoluminescence (PL) thermometers that can be used to accurately and reliably monitor intracellular temperatures have many potential applications in biology and medicine. Ideally, such nanothermometers should be functional at physiological pH across a wide range of ionic strengths, probe concentrations, and local environments. Here, we show that water-soluble N,S-co-doped carbon dots (CDs) exhibit temperature-dependent photoluminescence lifetimes and can serve as highly sensitive and reliable intracellular nanothermometers. PL intensity measurements indicate that these CDs have many advantages over alternative semiconductor- and CD-based nanoscale temperature sensors. Importantly, their PL lifetimes remain constant over wide ranges of pH values (5-12), CD concentrations (1.5 × 10-5 to 0.5 mg/mL), and environmental ionic strengths (up to 0.7 mol·L-1 NaCl). Moreover, they are biocompatible and nontoxic, as demonstrated by cell viability and flow cytometry analyses using NIH/3T3 and HeLa cell lines. N,S-CD thermal sensors also exhibit good water dispersibility, superior photo- and thermostability, extraordinary environment and concentration independence, high storage stability, and reusability-their PL decay curves at temperatures between 15 and 45 °C remained unchanged over seven sequential experiments. In vitro PL lifetime-based temperature sensing performed with human cervical cancer HeLa cells demonstrated the great potential of these nanosensors in biomedicine. Overall, N,S-doped CDs exhibit excitation-independent emission with strongly temperature-dependent monoexponential decay, making them suitable for both in vitro and in vivo luminescence lifetime thermometry.