The magnetic properties of noble‐metal nanoparticles are a puzzling phenomenon, tentatively often explained as a size effect or a ligand effect. Many experimental studies performed to date have ...attempted to vary these readily available parameters without reaching a definitive conclusion. In an attempt at better understanding the role of core crystallinity on these magnetic properties, we have compared the behavior of silver nanoparticles, which were either single‐crystalline or multi‐twinned, of almost identical sizes and with the same ligand coating. Our results indicate that single‐crystalline nanoparticles tend to behave as classical paramagnetic materials, whereas multi‐twinned ones exhibit a combination of para‐ and ferro‐magnetic behaviors. Our hypothesis is that lattice defects within the core bear magnetic moments which couple through conduction electrons, with dipolar interactions also playing a local and macroscopic role.
Magnetism: Another Idiosyncrasy of Boron? Vignolo, Maurizio; Bovone, Gianmarco; Capra, Marco ...
European journal of inorganic chemistry,
April 8, 2021, Letnik:
2021, Številka:
13
Journal Article
Recenzirano
Odprti dostop
We have studied the magnetic properties of various Boron particles obtained by different methods and have found evidence of soft ferromagnetism in all. While our study cannot unequivocally exclude ...that Boron is at the origin of the magnetism, we suggest that various impurities which are either the result of the synthetic process or come from the intentional doping of the Boron particles are indeed responsible for the observed magnetic properties. The phenomenon bears similarities with what is observed in magnetic oxides such as MgO or ZnO.
Magnetometry measurements on Boron particles reveal that they exhibit soft ferromagnetism at room temperature. The magnetic properties are provisonally ascribed to structure defects or embedded impurities such as oxygen and carbon.
•Neutron and proton irradiation of gold nanoparticles.•Lattice defects are at the origin of nanoparticles magnetism.•Irradiation create lattices defects in the cores.
The origin of the unexpected ...magnetic properties of nanoparticles made of gold, silver, or other diamagnetic metals remains obscure despite a large body of experimental and theoretical studies. Whereas many studies have endeavoured at finding correlations between magnetism and nanoparticle size or ligand coating, none so far has attempted at investigating the role of core crystallinity. We have irradiated gold nanoparticles with energetic neutrons or protons with the aim of nucleating lattice defects in the crystalline cores. Comparison of the magnetic behaviours before and after irradiation demonstrates clearly that the presence of defects in the crystalline lattice of the nanoparticles cores contributes efficiently to their magnetism.
Recent advances on the organization and characterization of Mn12 single molecule magnets (SMMs) on a surface or in 3D are reviewed. By using nonconventional techniques such as X‐ray magnetic circular ...dichroism (XMCD) and scanning tunneling microscopy (STM), it is shown that Mn12‐based SMMs deposited on a surface lose their SMM behavior, even though the molecules seem to be structurally undamaged. A new approach is reported to get high‐density information‐storage devices, based on the 3D assembling of SMMs in a liquid crystalline phase. The 3D nanostructure exhibits the anisotropic character of the SMMs, thus opening the way to address micrometric volumes by two photon absorption using the pump‐probe technique. We present recent developments such as µ‐SQUID, magneto‐optical Kerr effect (MOKE), or magneto‐optical circular dichroism (MOCD), which enable the characterization of SMM nanostructures with exceptional sensitivity. Further, the spin‐polarized version of the STM under ultrahigh vacuum is shown to be the key tool for addressing not only single molecule magnets, but also magnetic nano‐objects.
Recent advances on the organization of Mn12 “single molecule magnets” (SMMs) on a surface or in 3D are reviewed. It is shown that μ‐SQUID, the magneto‐optical Kerr effect, or magnetic optical circular dichroism enable the characterization of SMM nanostructures with exceptional sensitivity. Furthermore, the spin‐polarized version of the STM under ultrahigh vacuum is shown to be the key tool for addressing SMMs.
Amphiphilic pillar5arene‐containing 2rotaxanes have been prepared and fully characterized. In the particular case of the 2rotaxane incorporating a 1,4‐diethoxypillar5arene subunit, the structure of ...the compound was confirmed by X‐ray crystal structure analysis. Owing to a good hydrophilic/hydrophobic balance, stable Langmuir films have been obtained for these rotaxanes and the size of the peripheral alkyl chains on the pillar5arene subunit has a dramatic influence on the reversibility during compression–decompression cycles. Indeed, when these are small enough, molecular reorganization of the rotaxane by gliding motions are capable of preventing strong π–π interactions between neighboring macrocycles in the thin film.
A good hydrophilic/hydrophobic balance aided in the formation of stable Langmuir films from amphiphilic pillar5arene‐containing 2rotaxanes. When the pillar5arene component has the appropriate substituents, molecular reorganization of the rotaxane by gliding motions are capable of preventing strong π–π interactions between neighboring macrocycles in the thin film.
Functionalized gold nanoparticles receive much attention for biomedical applications thanks to their improved in vivo circulation time and colloidal stability. This work aimed at developing a simple ...and efficient synthetic route for synthesizing nanoparticles coated with linear polyethyleneimine for use as non‐toxic platforms in non‐viral gene delivery. We show that the reproducible one‐pot synthesis of gold nanoparticles stabilized with a biocompatible linear PEI yields nanodelivery devices offering a low toxicity and very good transfection efficiency.
Linear PEI‐coated gold nanoparticles are easily prepared from AuI and TBAB. The spherical shape and narrow size of the nanoparticles were confirmed by TEM observations. These PEI‐AuNPs display great stability even in the presence of mouse serum and show low toxicity as well as good transfection efficiency.
Gold nanoparticles possessing a positionally ordered 3D liquid crystalline phase in the bulk have been prepared (see figure). Induction of the mesophase results from the synergy between the gold core ...and the non‐mesogenic dendrons. These particles are also ferromagnetic up to 400 K and are able to self‐organize in a 2D hexagonal array on solid substrates, opening perspectives in the field of information storage at the molecular level.
Single molecule magnets (SMM) may be considered for the construction of future integrated nanodevices, provided however that some degree of ordering is imparted to these molecules (surfaces ...nanostructuration). Combining such nanoobjects with liquid-crystalline orderings to control their assembly and to potentially address them individually therefore appears as one promising strategy. Four mesomorphic, mixed-valent MnIII 8MnIV 4O12(L x,y,z‑CB)16(H2O)4 SMM, differing in the number of liquid-crystalline promoters, (L x,y,z‑CB), were synthesized, and their self-organizing and magnetic properties were investigated. The influence of the peripheral modifications, and precisely how supramolecular ordering and magnetic properties may be affected by the evolution of the proto-mesogenic cyanobiphenyl-based ligands substitution pattern, was explored. Small-angle X-ray scattering studies revealed that all of the hybridized clusters self-organize into room-temperature bilayer smectic phases, mandated by the specific mesogenic functionalization and that the polymetallic cores are further organized according to a short-range pseudo-2D lattice with hexagonal and/or square symmetry. All mesomorphous hybridized dodecamanganese complexes still behave as SMM: they exhibit blocking of the magnetization at about 2.6 K as evidenced by the occurrence of frequency-dependent out-of-phase ac susceptibility signals as well as an opening of the hysteresis cycle with coercive fields varying between 0.13 and 0.6 T, depending on the surface ligands topology. Comparison of the magnetic properties within this series reveals intricate correlations between the structural features of the mesomorphous molecule magnet (i.e., symmetry of the ligands substitution patterns, molecular conformation, average intercluster distances, and respective inclination) with respect to the relative proportion of slow- and fast-relaxing species and the absolute values of the coercive fields.
A new dendritic manganese(II) chelate 1 has been evaluated by in vivo (relaxivity) and in vitro (toxicity and relaxivity) experiments as a manganese enhanced magnetic resonance imaging (MEMRI) ...contrast agent. Also, a comparison with its corresponding gadolinium(III) homologue 2 and the commercially available MEMRI agent MnDPDP (Teslascan, Amersham Health) was achieved in order to determine respectively the real influence of the paramagnetic ion in terms of toxicity and relaxivity for this precise treelike structure and the potential of 1 to be a favorable candidate for brain-targeting MRI. Complexes 1 and 2 displayed high hydrosolubility (0.1 M) and revealed no in vitro neuronal toxicity at concentrations as high as 1 mM. Considering manganese(II) complex 1, the in vivo nontoxicity at 20 mM (100% rats survival) is very likely due to a slow diffusion of the compound, meaning a controlled release of the paramagnetic ions. Finally, T 1 relaxivity of 4.2 mM−1.s−1 for 2 and T 2 relaxivity of 17.4 mM−1.s−1 for 1 at 4.7 T were measured and are higher than that of the commercial MRI contrast agents GdDTPA and MnDPDP, respectively.
PDF
