The current status of fundamental physics that govern nanoparticle magnetism is reviewed. Emphasis is placed on studies of the particles’ intrinsic spin structure as influenced by surface and ...finite-size effects. Theories of dynamic spin fluctuation and spin reversal processes for uniaxial, isolated magnetic nanoparticles are presented, as applied primarily to the interpretation of magnetization and Mössbauer spectroscopic measurements. Monte Carlo simulation studies that corroborate experimental findings and advance elucidation of core vs. surface contributions to magnetic behavior are also presented. In addition, applications to nano and bio technology and future research directions in core/shell, matrix embedded and interacting magnetic nanoparticles are also addressed.
Quantum dots (QDs) and magnetic nanoparticles (MPs) are of interest for biological imaging, drug targeting, and bioconjugation because of their unique optoelectronic and magnetic properties, ...respectively. To provide for water solubility and biocompatibility, QDs and MPs were encapsulated within a silica shell using a reverse microemulsion synthesis. The resulting SiO2/MP−QD nanocomposite particles present a unique combination of magnetic and optical properties. Their nonporous silica shell allows them to be surface modified for bioconjugation in various biomedical applications.
Background: Mössbauer and magnetization measurements, singly or in combination, extract detailed information on the microscopic or internal magnetism of iron-based materials and their macroscopic or ...bulk magnetization. The combination of the two techniques affords a powerful investigatory probe into spin relaxation processes of nanosize magnetic systems. The ferritin core constitutes a paradigm of such nano-magnetic system where Mössbauer and magnetization studies have been broadly combined in order to elucidate its composition, the initial steps of iron nucleation and biomineralization, particle growth and core-size distribution. In vivo produced and in vitro reconstituted wild-type and variant ferritins have been extensively studied in order to elucidate structure/function correlations and ferritin’s role in iron overloading or neurodegenerative disorders.
Scope of Review: Studies on the initial stages of iron biomineralization, biomimetic synthetic analogues and ferrous ion retention within the ferritin core are presented. The dynamical magnetic properties of ferritin by Mössbauer and magnetization measurements are critically reviewed. The focus is on experiments that reveal the internal magnetic structure of the ferritin core. Novel magnetic measurements on individual ferritin molecules via AFM and nanoSQUID investigations are also mentioned.
Major Conclusions: A complex two-phase spin system is revealed due to finite-size effects and non-compensated spins at the surface of the anti-ferromagnetic ferritin core. Below the blocking temperature surface spins participate in relaxation processes much faster than those associated with collective magnetic excitations of interior spins.
General Significance: The studies reviewed contribute uniquely to the elucidation of the spin-structure and spin-dynamics of anti-ferromagnetic nanolattices and their possible applications to nano/bio-technology.
Graphene oxide (GO) offers interesting physicochemical and biological properties for biomedicine due to its versatility, biocompatibility, small size, large surface area, and its ability to interact ...with biological cells and tissues. GO is a two-dimensional material of exceptional strength, unique optical, physical, mechanical, and electronic properties. Ease of functionalization and high antibacterial activity are two major properties identified with GO. Due to its excellent aqueous processability, amphiphilicity, surface functionalization capability, surface enhanced Raman scattering (SERS), and fluorescence quenching ability, GO chemically exfoliated from oxidized graphite is considered a promising material for biological applications. In addition, due to π-π* transitions, a low energy is required for electron movement, a property important in Biosensor and Bioimaging applications of GO. In this article, we present an overview of current advances in GO applications in biomedicine and discuss future perspectives. We conclude that GO is going to play a vital role in Biomedical applications in the near future.
As-prepared, single-crystalline bismuth ferrite nanoparticles show strong size-dependent magnetic properties that correlate with: (a) increased suppression of the known spiral spin structure (period ...length of ∼62 nm) with decreasing nanoparticle size and (b) uncompensated spins and strain anisotropies at the surface. Zero-field-cooled and field-cooled magnetization curves exhibit spin-glass freezing behavior due to a complex interplay between finite size effects, interparticle interactions, and a random distribution of anisotropy axes in our nanoparticle assemblies.
Fe3O4–Ag heterodimer nanocomposites of tunable sizes are synthesized with high yield under mild conditions, without the loss of high magnetic moment. A ligand‐exchange scheme is devised utilizing the ...bifunctionality of the heterodimer system to render the nanocomposite soluble in aqueous solutions. Cells labeled with the heterodimer nanoparticles can be magnetically manipulated and imaged with two‐photon fluorescence microscopy.
N−H Bond Formation at a Diiron Bridging Nitride Zhang, Shaoguang; Cui, Peng; Liu, Tianchang ...
Angewandte Chemie (International ed.),
August 24, 2020, Letnik:
59, Številka:
35
Journal Article
Recenzirano
Odprti dostop
Despite their connection to ammonia synthesis, little is known about the ability of iron‐bound, bridging nitrides to form N−H bonds. Herein we report a linear diiron bridging nitride complex ...supported by a redox‐active macrocycle. The unique ability of the ligand scaffold to adapt to the geometric preference of the bridging species was found to facilitate the formation of N−H bonds via proton‐coupled electron transfer to generate a μ‐amide product. The structurally analogous μ‐silyl‐ and μ‐borylamide complexes were shown to form from the net insertion of the nitride into the E−H bonds (E=B, Si). Protonation of the parent bridging amide produced ammonia in high yield, and treatment of the nitride with PhSH was found to liberate NH3 in high yield through a reaction that engages the redox‐activity of the ligand during PCET.
A diiron bridging nitride complex supported by a geometrically flexible, redox‐active macrocycle was synthesized and characterized by X‐ray crystallography and Mössbauer spectroscopy. Treatment of the electrophilic nitride with PhSH afforded NH3 in high yield through a reaction that engages the redox‐activity of the ligand during proton‐coupled electron transfer followed by protonolysis.
The extracellular matrix (ECM) is a macromolecular network that can provide biochemical and structural support for cell adhesion and formation. It regulates cell behavior by influencing biochemical ...and physical cues. It is a dynamic structure whose components are modified, degraded, or deposited during connective tissue development, giving tissues strength and structural integrity. The physical properties of the natural ECM environment control the design of naturally or synthetically derived biomaterials to guide cell function in tissue engineering. Tissue engineering is an important field that explores physical cues of the ECM to produce new viable tissue for medical applications, such as in organ transplant and organ recovery. Understanding how the ECM exerts physical effects on cell behavior, when cells are seeded in synthetic ECM scaffolds, is of utmost importance. Herein we review recent findings in this area that report on cell behaviors in a variety of ECMs with different physical properties, i.e., topology, geometry, dimensionality, stiffness, and tension.
The physical properties of the natural extracellular matrix (ECM) control the design of naturally or synthetically derived biomaterials to guide cell function in tissue engineering. It is important to understand how the ECM exerts physical effects on cell behavior when cells are seeded in synthetic ECM scaffolds. We review recent reports on cell behavior in a variety of ECMs with different physical properties like topology, geometry, dimensionality, stiffness and tension.
We have investigated the structural, magnetic, and electronic properties of nonstoichiometric iron oxide nanocrystals prepared by decomposition of iron(II) and iron(0) precursors in the presence of ...organic solvents and capping groups. The highly uniform, crystalline, and monodisperse nanocrystals that were produced enabled a full structural and compositional survey by electron microscopy and X-ray diffraction. The complex and metastable behavior of nonstoichiometric iron oxide (wüstite) at the nanoscale was studied by a combination of Mössbauer spectroscopy and magnetic characterization. Deposition from hydrocarbon solvents with subsequent self-assembly of iron oxide nanocrystals into superlattices allowed the preparation of continuous thin films suitable for electronic transport measurements.
We investigate the size- and composition-dependent ac magnetic permeability of superparamagnetic iron oxide nanocrystals for radio frequency (RF) applications. The nanocrystals are obtained through ...high-temperature decomposition synthesis, and their stoichiometry is determined by Mössbauer spectroscopy. Two sets of oxides are studied: (a) as-synthesized magnetite-rich and (b) aged maghemite nanocrystals. All nanocrystalline samples are confirmed to be in the superparamagnetic state at room temperature by SQUID magnetometry. Through the one-turn inductor method, the ac magnetic properties of the nanocrystalline oxides are characterized. In magnetite-rich iron oxide nanocrystals, size-dependent magnetic permeability is not observed, while maghemite iron oxide nanocrystals show clear size dependence. The inductance, resistance, and quality factor of hand-wound inductors with a superparamagnetic composite core are measured. The superparamagnetic nanocrystals are successfully embedded into hand-wound inductors to function as inductor cores.
