Magnetochemistry, Volume 6, Issue 1 (March 2020) – 16 articles

In order to protect their environmental niche, most bacteria secret antimicrobial substances designed to target specific bacterial strains that are often closely related to the producer strain. Bacteriocins, small, ribosomally synthesised antimicrobial peptides, comprise a class of such substances and can either inhibit (bacteriostatic) or kill (bactericidal) target cells. Glycocins are a class of bacteriocin that are post-translationally modified by one or more carbohydrate moieties that are either β-O-linked to either a serine or threonine and/or β-S-linked to a cysteine. The solution nuclear magnetic resonance structure (NMR) of the glycocin ASM1 (produced by Lactobacillus plantarum A-1), an orthologue of GccF, has been determined. In both structures, the disulfide bonds are essential for activity and restrict the mobility of the N-acetyl-glucosamine (GlcNAc) attached to Ser-18 (O-linked), compared to the much more flexible GlcNAc moiety on Cys-43 (S-linked). Interestingly, despite 88% sequence identity, the helical structure of ASM1 is less pronounced which appears to be consistent with the far ultra-violet circular dichroism (UV CD) spectra. Full article

In recent years, many efforts have been made to develop advanced metal oxide semiconductor nanomaterials with exotic magnetic properties for modern applications w.r.t traditional analogues. Dilute magnetic semiconductor oxides (DMSOs) are promising candidates for superior control over the charge and spin degrees of freedom. DMSOs are transparent, wide band gap materials with induced ferromagnetism in doping, with a minor percentage of magnetic 3d cation to create a long-range antiferromagnetic order. Although significant efforts have been carried out to achieve DMSO with ferromagnetic properties above room temperature, it is a great challenge that still exists. However, TiO₂, SnO₂, ZnO and In₂O₃ with wide band gaps of 3.2, 3.6, 3.2 and 2.92 eV, respectively, can host a broad range of dopants to generate various compositions. Interestingly, a reduction in the size of these binary oxides can induce ferromagnetism, even at room temperature, due to the grain boundary, presence of defects and oxygen vacancies. The present review provides a panorama of the structural analysis and magnetic properties of DMSOs based on binary metal oxides nanomaterials with various ferromagnetic or paramagnetic dopants, e.g., Co, V, Fe and Ni, which exhibit enhanced ferromagnetic behaviors at room temperature. Full article

Doping rare-earth ions into spinel ferrites can alter their electrical and magnetic properties. The present study delineates the structure–property relationship of the effect of rare-earth terbium doping in NiFe₂O₄ ferrite. X-ray diffraction analysis (XRD) showed unit cell lattice expansion with increased Tb³⁺ content. The Fourier transform infrared spectroscopy (FTIR) results indicate preferential occupancy of Tb³⁺ at the octahedral B site. The magnetic parameters derived from room temperature hysteresis loops where both the saturation magnetization, Ms, and coercivity, Hc, value decreased with the Tb³⁺ substitution and reached a minimum value of Ms ~30.6 emu/g at x = 0.1 and Hc ~102 Oe at x = 0.075. The temperature-dependent magnetocrystalline anisotropy derived from the magnetic isotherm was observed to be the highest for x = 0.1 at 5 K with the value K1 ~1.09 × 10⁶ J/m³. The Tb³⁺ doping also resulted in the Curie temperature reduction from 938 K at x = 0.0 to 899 K at x = 0.1. Full article

Drug formulations and suitable methods for their detection play a very crucial role in the development of therapeutics towards degenerative neurological diseases. For diseases such as Alzheimer’s disease, magnetic resonance imaging (MRI) is a non-invasive clinical technique suitable for early diagnosis. In this review, we will discuss the different experimental conditions which can push MRI as the technique of choice and the gold standard for early diagnosis of Alzheimer’s disease. Here, we describe and compare various techniques for administration of nanoparticles targeted to the brain and suitable formulations of nanoparticles for use as magnetically active therapeutic probes in drug delivery targeting the brain. We explore different physiological pathways involved in the transport of such nanoparticles for successful entry in the brain. In our lab, we have used different formulations of iron oxide nanoparticles (IONPs) and protein nanocages as contrast agents in anatomical MRI of an Alzheimer’s disease (AD) brain. We compare these coatings and their benefits to provide the best contrast in addition to biocompatibility properties to be used as sustainable drug-release systems. In the later sections, the contrast enhancement techniques in MRI studies are discussed. Examples of contrast-enhanced imaging using advanced pulse sequences are discussed with the main focus on important studies in the field of neurological diseases. In addition, T1 contrast agents such as gadolinium chelates are compared with the T2 contrast agents mainly made of superparamagnetic inorganic metal nanoparticles. Full article

The incorporation of the natural amino acid L-proline in the synthesis to vanadium-chromium Prussian blue derivatives results in materials exhibiting magnetic ordering including chiral magnetic centers. Although the amorphous nature of these materials makes difficult to assess the structural features of these proline-containing compounds, magnetic and spectroscopic data confirms their multifunctionality. They exhibit high-temperature magnetic ordering (T_c < 255 K) and a circular dichroic signal, representing the molecule-based chiral magnets with the highest ordering temperatures reported to date. In addition, the presence of chiral L-proline (or D-proline) has additional benefits, including higher redox stability and the appearance of magnetic hysteresis. The latter was not observed in the parent compounds, the series of room temperature molecule-based magnets V[Cr(CN)₆]_x. Full article

Relaxivity r₂ and thus the contrast efficacy of superparamagnetic nanoparticles (NPs) can be enhanced via either NP’s magnetic properties or coating optimization. Numerous reports can be found about the investigation of the optimal iron oxide nanoparticles (IO NPs) size, shape, crystallinity and composition that yield high saturation magnetization (m_s) values and, consequently, high r₂ values. Although the use of an appropriate coating can boost up the NPs MRI contrast agent efficiency, this topic has been largely understudied. Therefore, in this review, the factors affording r₂ enhancement of spherical magnetic NPs are discussed. Based on the literature, the requirements for an optimal surface coating that may increase r₂ values and ensure stability and biocompatibility of NPs are listed. One of the best candidates that fulfil these requirements are liposomes with embedded magnetic NPs, so-called magneto-liposomes. The analysis of the literature elucidated the most appropriate phospholipid compositions for the relaxivity enhancement and for magneto-liposomes in vivo stability. Finally, the future directions in the development of NP-based contrast agents are given. For example, most of the synthetic NPs are recognized and eliminated as a foreign substance by the immune system. To overcome this issue, a design of a biomimetic, cell-membrane-based nanocarrier for contrast agents is proposed. Disguised with cell membranes, NPs or other active components can act as autogenous cells and thus ensure the inherent biocompatibility. Full article

A possibility of the intramolecular ferromagnetic (FM) interaction in pyrazole-bridged dinuclear Mn(II), Fe(II), Co(II), and Ni(II) complexes is examined by density functional theory (DFT) calculations. When azide is used for additional bridging ligand, the complexes indicate the strong antiferromagnetic (AFM) interaction, while the AFM interaction becomes very weak when acetate ligand is used. In the acetate-bridged complexes, an energy split of the frontier orbitals suggests the orbital counter-complementarity effect between the d_xy orbital pair, which contributes to the FM interaction; however, a significant overlap of other d-orbital pairs also suggests an existence of the AFM interaction. From those results, the orbital counter-complementarity effect is considered to be canceled out by the overlap of other d-orbital pairs. Full article

The effects of substitution of Zr and Ga on the structural and magnetic properties of Dy₂Fe₁₇ intermetallic compound were investigated in this study. The Rietveld analysis confirmed that the crystalline system was a Th₂Ni₁₇ structure. Lattice parameters a (Å) and c (Å), unit cell volume (ų), and bonding distance (Å) were calculated using Rietveld analysis. The unit cell volume of Dy₂Fe_17−xZr_x and Dy₂Fe₁₆Ga_1−xZr_x increased linearly with Zr and Ga substitution. The Curie temperature (Tc) of Dy₂Fe_17−xZr_x and Dy₂Fe₁₆Ga_1−xZr_x was found to be Zr content-dependent. The maximum Curie temperatures were observed at 510 K (x = 0.75 Zr content) for Dy₂Fe_17−xZr_x and 505.1 K (x = 0.5 Zr content) for Dy₂Fe₁₆Ga_1−xZr_x, which are 102 K and 97 K higher than the value found for Dy₂Fe₁₇, respectively. The room-temperature Mössbauer analysis showed a decrease in the average hyperfine field and increases in the isomer shift with Zr doping. The overall improvement in Curie temperature with the substitution strategy of Zr–Ga substitution in 2:17 intermetallic compounds could find potential use of these magnetic compounds in high-temperature applications. Full article

One major goal in medical imaging is the elaboration of more efficient contrast agents (CAs). Those agents need to be optimized for the detection of affected tissues such as cancers or tumors while decreasing the injected quantity of agents. The paramagnetic contrast agents containing fluorine atoms can be used for both proton and fluorine magnetic resonance imaging (MRI), and they open the possibility of simultaneously mapping the anatomy using ¹H MRI and accurately locating the agents using ¹⁹F MRI. One of the challenges in this domain is to synthesize molecules containing several chemically equivalent fluorine atoms with relatively short relaxation times to allow the recording of ¹⁹F MR images in good conditions. With that aim, we propose to prepare a CA containing a paramagnetic center and nine chemically equivalent fluorine atoms using a cycloaddition reaction between two building blocks. These fluorinated contrast agents are characterized by ¹⁹F NMR, showing differences in the fluorine relaxation times T₁ and T₂ depending on the lanthanide ion. To complement the experimental results, molecular dynamics simulations are performed to shed light on the 3D-structure of the molecules in order to estimate the distance between the lanthanide ion and the fluorine atoms. Full article

The 1884 suggestion of Pierre Curie (1859–1906) that the type of dissymmetry shown by collinear electric and magnetic fields may induce an enantiomeric excess, in a chemical reaction that would otherwise produce a racemic mixture, is explored in the context of fundamental symmetry arguments. Curie’s arrangement exhibits false chirality (time-noninvariant enantiomorphism), and so it may not induce absolute enantioselection (ae) in a process that has reached thermodynamic equilibrium, since it does not lift the degeneracy of chiral enantiomers. However, it may do so in far-from-equilibrium processes via a breakdown in microscopic reversibility analogous to that observed in elementary particle processes under the influence of CP violation, the associated force possessing false chirality with respect to CP enantiomorphism. In contrast, an influence like circularly polarized light exhibiting true chirality (time-invariant enantiomorphism) lifts the degeneracy of enantiomers, and so may induce ae in all circumstances. Although to date, ae has not been observed under the influence of Curie’s arrangement of collinear electric and magnetic fields, it is argued that two different experiments have now demonstrated ae under a falsely chiral influence in systems far from equilibrium, namely in a spinning sample under a gravitational field, and in the separation of enantiomers at a ferromagnetic surface. Full article

Nanotechnology offers the possibility of operating on the same scale length at which biological processes occur, allowing to interfere, manipulate or study cellular events in disease or healthy conditions. The development of hybrid nanostructured materials with a high degree of chemical control and complex engineered surface including biological targeting moieties, allows to specifically bind to a single type of molecule for specific detection, signaling or inactivation processes. Magnetite nanostructures with designed composition and properties are the ones that gather most of the designs as theragnostic agents for their versatility, biocompatibility, facile production and good magnetic performance for remote in vitro and in vivo for biomedical applications. Their superparamagnetic behavior below a critical size of 30 nm has allowed the development of magnetic resonance imaging contrast agents or magnetic hyperthermia nanoprobes approved for clinical uses, establishing an inflection point in the field of magnetite based theragnostic agents. Full article

The field of nanomedicine has recently emerged as a product of the expansion of a range of nanotechnologies into biomedical science, pharmacology and clinical practice. Due to the unique properties of nanoparticles and the related nanostructures, their applications to medical diagnostics, imaging, controlled drug and gene delivery, monitoring of therapeutic outcomes, and aiding in medical interventions, provide a new perspective for challenging problems in such demanding issues as those involved in the treatment of cancer or debilitating neurological diseases. In this review, we evaluate the role and contributions that the applications of magnetic nanoparticles (MNPs) have made to various aspects of nanomedicine, including the newest magnetic particle imaging (MPI) technology allowing for outstanding spatial and temporal resolution that enables targeted contrast enhancement and real-time assistance during medical interventions. We also evaluate the applications of MNPs to the development of targeted drug delivery systems with magnetic field guidance/focusing and controlled drug release that mitigate chemotherapeutic drugs’ side effects and damage to healthy cells. These systems enable tackling of multiple drug resistance which develops in cancer cells during chemotherapeutic treatment. Furthermore, the progress in development of ROS- and heat-generating magnetic nanocarriers and magneto-mechanical cancer cell destruction, induced by an external magnetic field, is also discussed. The crucial roles of MNPs in the development of biosensors and microfluidic paper array devices (µPADs) for the detection of cancer biomarkers and circulating tumor cells (CTCs) are also assessed. Future challenges concerning the role and contributions of MNPs to the progress in nanomedicine have been outlined. Full article

Iron oxide nanoparticles are the basic components of the most promising magneto-responsive systems for nanomedicine, ranging from drug delivery and imaging to hyperthermia cancer treatment, as well as to rapid point-of-care diagnostic systems with magnetic nanoparticles. Advanced synthesis procedures of single- and multi-core iron-oxide nanoparticles with high magnetic moment and well-defined size and shape, being designed to simultaneously fulfill multiple biomedical functionalities, have been thoroughly evaluated. The review summarizes recent results in manufacturing novel magnetic nanoparticle systems, as well as the use of proper characterization methods that are relevant to the magneto-responsive nature, size range, surface chemistry, structuring behavior, and exploitation conditions of magnetic nanosystems. These refer to particle size, size distribution and aggregation characteristics, zeta potential/surface charge, surface coating, functionalization and catalytic activity, morphology (shape, surface area, surface topology, crystallinity), solubility and stability (e.g., solubility in biological fluids, stability on storage), as well as to DC and AC magnetic properties, particle agglomerates formation, and flow behavior under applied magnetic field (magnetorheology). Full article

Magnetoelectrochemistry is a branch of electrochemistry where magnetic fields play a vital role in the oxidation and reduction process of the molecules. When it comes to spin-dependent electrochemistry (SDE), becomes a new paradigm. This work presents electrochemical response during the “chiral imprinting” on working electrodes and the effects of potentiostatic and galvanostatic methods. We explore the use of the SDE concept, which is implemented for chiral-ferromagnetic (CFM) hybrid working electrodes, and we compare various electrochemical parameters affecting the quality of deposition. We electrochemically co-deposited nickel (Ni) with a chiral compound (tartaric acid) in its enantiopure forms (L and D), which allows us to obtain a chiral co-deposited nickel-tartaric acid (Ni-LTA or Ni-DTA) working electrode. Full article