Photoluminescence and magnetic properties of isostructural europium(III), gadolinium(III) and terbium(III) oxamate-based coordination polymers.

Developing and investigating advanced multifunctional materials with magnetic properties as candidates for assembling spin qubits for quantum computing is imperative. A new polytopic ligand based on oxamate and aniline was used to promote the synthesis of three neutral homometallic lanthanide-coordinated polymers. New complexes with the formula {Ln(phox)3(DMSO)2(H2O)}n, where Ln = Eu3+ (1), Gd3+ (2), and Tb3+ (3) [phox = N-(phenyl)oxamate and DMSO = dimethylsulfoxide], were synthesized and well characterized by spectroscopic methods as well as X-ray crystallographic analysis. All crystalline structures comprise neutral zigzag chains. The lanthanide ions are linked by three phox ligands, in which two oxygen atoms from two different ligands are responsible for connecting the trivalent lanthanide ions, and one phox ligand completes the coordination sphere in a bis-bidentate mode, together with two DMSO molecules and one water coordination molecule. The coordination sphere of lanthanide ions consisted of spherical capped square antiprism (CSAPR-9) symmetry. The magnetic properties of 1-3 were investigated in the 2-300 K temperature range. The dynamic (ac) magnetic properties of 2 reveal a frequency dependence involving the phonon bottleneck mechanism below 33 K under nonzero applied dc magnetic fields, resulting in an example of a field-induced single-molecule magnet. Solid-state photophysical measurements for Eu3+ (1) and Tb3+ (3) complexes indicate that the N-(phenyl)oxamate ligands are very efficient in sensitizing the lanthanide(III) ions in the visible region of the electromagnetic spectrum. Compounds 1 and 3 exhibited an emission in the red and green regions, respectively. Experimental results and theoretical calculations using the Sparkle/RM1 method support a quantum efficiency of ∼72% for 1, suggesting its potential as a candidate for light conversion molecular devices (LCMDs).

Control of Anisotropy and Magnetic Hyperthermia Effect by Addition of Cobalt on Magnetite Nanoparticles.

Magnetic hyperthermia (MH) has emerged as a promising technology with diverse applications in medical and technological fields, leveraging the remote induction of temperature elevation through an alternating magnetic field. While Fe3O4 nanoparticles with an average size around 12-25 nm are commonly employed in MH systems, this study introduces a strategy to produce smaller particles (less than or equal to 10 nm) with enhanced heating efficiency, as measured by specific power absorption (SPA). We conducted an exhaustive and detailed investigation into the morphological and magnetic properties of CoxFe3-xO4 nanoparticles, aiming to optimize their MH response. By varying the Co content, we successfully tuned the effective magnetic anisotropy while maintaining saturation magnetization nearly constant. The MH analysis indicates that these nanoparticles predominantly heat through the Néel mechanism, demonstrating robust reproducibility across different concentrations, viscosity mediums, and ac field conditions. Notably, we identified an optimal anisotropy or Co concentration that maximizes SPA, crucial for developing magnetic systems requiring particles with specific sizes. This work contributes to advancing the understanding and application of MH, particularly in tailoring nanoparticle properties for targeted and efficient heat generation in various contexts.

Crystal structure and cryomagnetic study of a mononuclear erbium(III) oxamate inclusion complex.

The synthesis, crystal structure and magnetic properties of an oxamate-containing erbium(III) complex, namely, tetrabutylammonium aqua[N-(2,4,6-trimethylphenyl)oxamato]erbium(III)-dimethyl sulfoxide-water (1/3/1.5), (C16H36N)[Er(C11H12NO3)4(H2O)]·3C2H6OS·1.5H2O or n-Bu4N[Er(Htmpa)4(H2O)]·3DMSO·1.5H2O (1), are reported. The crystal structure of 1 reveals the occurrence of an erbium(III) ion, which is surrounded by four N-phenyl-substituted oxamate ligands and one water molecule in a nine-coordinated environment, together with one tetrabutylammonium cation acting as a counter-ion, and one water and three dimethyl sulfoxide (DMSO) molecules of crystallization. Variable-temperature static (dc) and dynamic (ac) magnetic measurements were carried out for this mononuclear complex, revealing that it behaves as a field-induced single-ion magnet (SIM) below 5.0 K.

Iron Oxide Nanoparticles in a Dynamic Flux: Magnetic Hyperthermia Effect on Flowing Heavy Crude Oil.

An essential part for crude oil extraction is flow assurance, being critical to maintain a financially sustainable flow while getting the petroleum to the surface. When not well managed, it can develop into a significant issue for the O&G industry. By heating the fluids, problems with flow assurance, including paraffin deposition, asphaltene, and methane hydrate, can be reduced. Also, as the temperature rises, a liquid's viscosity decreases. Research focusing on the application of magnetic nanoparticles (NPs) in the oil industry is very recent. When magnetic nanofluids are exposed to an alternating magnetic field, the viscosity decreases by several orders of magnitude as a result of the fluid's temperature rising due to a phenomenon known as magnetic hyperthermia. This work focuses on the use of magnetic NPs (9 nm) in heavy crude oil (API 19.0). The frequency and strength of the magnetic field, as well as the characteristics of the fluid and the NPs intrinsic properties all affect the heating efficiency. For all of the experimental settings in this work, the flowloop's temperature increased, reaching a maximum of ΔT = 16.3 °C, using 1% wt NPs at the maximum available frequency of the equipment (533 kHz) and the highest field intensity for this frequency (14 kA/m), with a flow rate of 1.2 g/s. This increase in temperature causes a decrease of nearly 45% on the heavy crude oil viscosity, and if properly implemented, could substantially increase oil flow in the field during production.

Observation of magnetic vortex configuration in non-stoichiometric Fe3O4 nanospheres.

Theoretical and micromagnetic simulation studies of magnetic nanospheres with vortex configurations suggest that such nanostructured materials have technological advantages over conventional nanosystems for applications based on high-power-rate absorption and subsequent emission. However, full experimental evidence of magnetic vortex configurations in spheres of submicrometer size is still lacking. Here, we report the microwave irradiation fabrication of Fe3O4 nanospheres and establish their magnetic vortex configuration based on experimental results, theoretical analysis, and micromagnetic simulations. Detailed magnetic and electrical measurements, together with Mössbauer spectroscopy data, provide evidence of a loss of stoichiometry in vortex nanospheres owing to the presence of a surface oxide layer, defects, and a higher concentration of cation vacancies. The results indicate that the magnetic vortex spin configuration can be established in bulk spherical magnetite materials. This study provides crucial information that can aid the synthesis of magnetic nanospheres with magnetically tailored properties; consequently, they may be promising candidates for future technological applications based on three-dimensional magnetic vortex structures.

In vitro and in vivo acute toxicity of a novel citrate-coated magnetite nanoparticle.

Magnetic nanoparticles (MNps) have become powerful tools for multiple biomedical applications such as hyperthermia drivers, magnetic resonance imaging (MRI) vectors, as well as drug-delivery systems. However, their toxic effects on human health have not yet been fully elucidated, especially in view of their great diversity of surface modifications and functionalizations. Citrate-coating of MNps often results in increased hydrophilicity, which may positively impact their performance as drug-delivery systems. Nonetheless, the consequences on the intrinsic toxicity of such MNps are unpredictable. Herein, novel magnetite (Fe3O4) nanoparticles covered with citrate were synthesized and their potential intrinsic acute toxic effects were investigated using in vitro and in vivo models. The proposed synthetic pathway turned out to be simple, quick, inexpensive, and reproducible. Concerning toxicity risk assessment, these citrate-coated iron oxide nanoparticles (IONps) did not affect the in vitro viability of different cell lines (HaCaT and HepG2). Moreover, the in vivo acute dose assay (OECD test guideline #425) showed no alterations in clinical parameters, relevant biochemical variables, or morphological aspects of vital organs (such as brain, liver, lung and kidney). Iron concentrations were slightly increased in the liver, as shown by Graphite Furnace Atomic Absorption Spectrometry and Perls Prussian Blue Staining assays, but this finding was considered non-adverse, given the absence of accompanying functional/clinical repercussions. In conclusion, this study reports on the development of a simple, fast and reproducible method to obtain citrate-coated IONps with promising safety features, which may be used as a drug nanodelivery system in the short run. (263 words).

Hybrid magneto-luminescent iron oxide nanocubes functionalized with europium complexes: synthesis, hemolytic properties and protein corona formation.

The use of hybrid nanostructures based on magneto-luminescent properties is a promising strategy for nano-bio applications and theranostics platforms. In this work, we carried out the synthesis and functionalization of iron oxide nanocubes (IONCs) to obtain multifunctional hybrid nanostructures towards biomedical applications. The IONCs were functionalized with tetraethylorthosilicate, thenoyltrifluoroacetone-propyl-triethoxysilane and europium(iii)-dibenzoylmethane complexes to obtain the materials termed as IOCNCs@SiO2, IONCs@SiO2TTA, IONCs@SiO2TTA-Eu and IONCs@SiO2-TTA-Eu-DBM, respectively. Then, the biological interactions of these nanostructures with red blood cells - RBCs (hemolysis) and human blood plasma (protein corona formation) were evaluated. The XPS spectrocopy and EDS chemical mapping analysis showed that each domain is homogeneously occupied in the hybrid material, with the magnetic core at the center and the luminescent domain on the surface of the hybrid nanomaterial with a core@shell like structure. Futhermore, after each functionalization step, the nanomaterial surface charge drastically changed, with critical impact on RBC lysis and corona formation. While IONCs@SiO2 and IONCs@SiO2-TTA-Eu-DBM showed hemolytic properties in a dose-dependent manner, the IONCs@SiO2TTA-Eu did not present any hemolytic effect up to 300 µg mL-1. Protein corona results showed a pattern of selective adsorption of proteins with each surface of the synthesized hybrid materials. However, as a general result, a suppression of hemolysis after protein corona formation in all tests was verified. Finally, this study provides a solid background for further applications of these hybrid magneto-luminescent materials containing new surface functionalities in the emerging field of medical nanobiotechnology.

Control of Multiferroic properties in BiFeO3 nanoparticles.

BiFeO3 (BFO) nanoparticles (NPs) were synthesized using the sol-gel method at different calcination temperatures from 400 °C to 600 °C. XRD studies have confirmed that all BFO NPs show distorted rhombohedral crystals that match the R3c space group. We found evidence of local structural strain that develops with increasing particle size as suggested by TEM and Raman spectroscopy measurements. Magnetic measurements suggest that NPs have two distinct regimes: a ferromagnetic-like one at low temperatures and a superparamagnetic-like one at room temperature. The crossover temperature increases with NPs size, suggesting a size-dependent blocking magnetic regime. Similarly, local piezoelectric measurements at room temperature in single NP have confirmed a ferroelectric order with a NP size-dependent d33 coefficient. An analysis of both the ferroelectric and the magnetic results suggest that ferromagnetism and ferroelectricity coexist at room temperature in NPs. Our results lead to the possibility of tailoring the ferroic order in multifunctional materials by means of NP size.

Synthesis and magnetic properties of cobalt-iron/cobalt-ferrite soft/hard magnetic core/shell nanowires.

A straightforward method for the synthesis of CoFe2.7/CoFe2O4 core/shell nanowires is described. The proposed method starts with a conventional pulsed electrodeposition procedure on alumina nanoporous template. The obtained CoFe2.7 nanowires are released from the template and allowed to oxidize at room conditions over several weeks. The effects of partial oxidation on the structural and magnetic properties were studied by x-ray spectrometry, magnetometry, and scanning and transmission electron microscopy. The results indicate that the final nanowires are composed of 5 nm iron-cobalt alloy nanoparticles. Releasing the nanowires at room conditions promoted surface oxidation of the nanoparticles and created a CoFe2O4 shell spinel-like structure. The shell avoids internal oxidation and promotes the formation of bi-magnetic soft/hard magnetic core/shell nanowires. The magnetic properties of both the initial single-phase CoFe2.7 nanowires and the final core/shell nanowires, reveal that the changes in the properties from the array are due to the oxidation more than effects associated with released processes (disorder and agglomeration).

Compact Ag@Fe3O4 core-shell nanoparticles by means of single-step thermal decomposition reaction.

A temperature pause introduced in a simple single-step thermal decomposition of iron, with the presence of silver seeds formed in the same reaction mixture, gives rise to novel compact heterostructures: brick-like Ag@Fe3O4 core-shell nanoparticles. This novel method is relatively easy to implement, and could contribute to overcome the challenge of obtaining a multifunctional heteroparticle in which a noble metal is surrounded by magnetite. Structural analyses of the samples show 4 nm silver nanoparticles wrapped within compact cubic external structures of Fe oxide, with curious rectangular shape. The magnetic properties indicate a near superparamagnetic like behavior with a weak hysteresis at room temperature. The value of the anisotropy involved makes these particles candidates to potential applications in nanomedicine.

Iron oxide nanosized clusters embedded in porous nanorods: a new colloidal design to enhance capabilities of MRI contrast agents.

Development of nanosized materials to enhance the image contrast between the normal and diseased tissue and/or to indicate the status of organ functions or blood flow is essential in nuclear magnetic resonance imaging (MRI). Here we describe a contrast agent based on a new iron oxide design (superparamagnetic iron oxide clusters embedded in antiferromagnetic iron oxide porous nanorods). We show as a proof-of-concept that aqueous colloidal suspensions containing these particles show enhanced-proton relaxivities (i.e., enhanced MRI contrast capabilities). A remarkable feature of this new design is that large scale production is possible since aqueous-based routes are used, and porosity and iron oxide superparamagnetic clusters are directly developed from a single phase. We have also proved with the help of a simple model that the physical basis behind the increase in relaxivities lies on both the increase of dipolar field (interactions within iron oxide clusters) and the decrease of proton-cluster distance (porosity favors the close contact between protons and clusters). Finally, a list of possible steps to follow to enhance capabilities of this contrast agent is also included (partial coating with noble metals to add extra sensing capacity and chemical functionality, to increase the amount of doping while simultaneously carrying out cytotoxicity studies, or to find conditions to further decrease the size of the nanorods and to enhance their stability).

Interplay between crystallization and particle growth during the isothermal annealing of colloidal iron oxide nanoparticles.

The relationship between crystallization and growth of colloidal iron oxide nanoparticles during isothermal annealing was addressed in this work. The structural, morphological and chemical modifications of the nanoparticles during thermal treatments were followed by combination of electron microscopy, X-ray diffraction and spectroscopic methods. The initially monodisperse spherical nanoparticles with amorphous and partially oxidized structure evolved during the treatments, depending on the temperature and treatment time. Core-void-shell nanoparticles or single crystal nanoparticles and hollow polycrystalline nanoparticles, both with well defined Fe(3)O(4) oxide phase, are formed depending on the conditions. This evolution was interpreted as a result of the Kirkendall effect associated to mass redistribution and fragmentation of the nanoparticles, bringing new information about the effect of post-synthesis treatments on the crystallinity and morphology of colloidal nanoparticles.

Chemical synthesis and structural characterization of highly disordered N colloidal nanoparticles.

This work focuses on synthetic methods to produce monodisperse Ni colloidal nanoparticles (NPs), in the 4-16 nm size range, and their structural characterization. Narrow size distribution nanoparticles were obtained by high-temperature reduction of a nickel salt and the production of tunable sizes of the Ni NPs was improved compared to other methods previously described. The as-synthesized nanoparticles exhibited spherical shape and highly disordered structure, as it could be assigned by X-ray diffraction (XRD) and high resolution transmission electron microscopy (HRTEM). Annealing at high temperature in organic solvent resulted in an increase of nanoparticle atomic ordering; in this case, the XRD pattern showed an fcc-like structure. Complementary data obtained by X-ray absorption spectroscopy confirmed the complex structure of these nanoparticles. Temperature dependence of the magnetic susceptibility of these highly disordered Ni NPs showed the magnetic behavior cannot be described by the conventional superparamagnetic theory, claiming the importance of the internal structure in the magnetic behavior of such nanomaterials.