Size dependence of the surface spin disorder and surface anisotropy constant in ferrite nanoparticles.

The magnetic properties of nanoscale magnets are greatly influenced by surface anisotropy. So far, its quantification is based on the examination of the blocking temperature shift within a series of nanoparticles of varying sizes. In this scenario, the surface anisotropy is assumed to be a particle size-independent quantity. However, there is no solid experimental proof to support this simplified picture. On the contrary, our work unravels the size-dependent magnetic morphology and surface anisotropy in highly uniform magnetic nanoparticles using small-angle polarized neutron scattering. We observed that the surface anisotropy constant does not depend on the nanoparticle's size in the range of 3-9 nm. Furthermore, our results demonstrate that the surface spins are less prone to polarization with increasing nanoparticle size. Our study thus proves the size dependence of the surface spin disorder and the surface anisotropy constant in fine nanomagnets. These findings open new routes in materials based on a controlled surface spin disorder, which is essential for future applications of nanomagnets in biomedicine and magnonics.

Thermal Traits of MNPs under High-Frequency Magnetic Fields: Disentangling the Effect of Size and Coating.

We investigated the heating abilities of magnetic nanoparticles (MNPs) in a high-frequency magnetic field (MF) as a function of surface coating and size. The cobalt ferrite MNPs were obtained by a hydrothermal method in a water-oleic acid-ethanol system, yielding MNPs with mean diameter of about 5 nm, functionalized with the oleic acid. By applying another cycle of hydrothermal synthesis, we obtained MNPs with about one nm larger diameter. In the next step, the oleic acid was exchanged for 11-maleimidoundecanoic acid or 11-(furfurylureido)undecanoic acid. For the heating experiments, all samples were dispersed in the same solvent (dichloroethane) in the same concentration and the heating performance was studied in a broad interval of MF frequencies (346-782 kHz). The obtained results enabled us to disentangle the impact of the hydrodynamic, structural, and magnetic parameters on the overall heating capabilities. We also demonstrated that the specific power absorption does not show a monotonous trend within the series in the investigated interval of temperatures, pointing to temperature-dependent competition of the Brownian and Néel contributions in heat release.

Understanding Magnetization Dynamics of a Magnetic Nanoparticle with a Disordered Shell Using Micromagnetic Simulations.

Spin disorder effects influence magnetization dynamics and equilibrium magnetic properties of real nanoparticles (NPs). In this work, we use micromagnetic simulations to try to better understand these effects, in particular, on how the magnetization reversal is projected in the character of the hysteresis loops at different temperatures. In our simulation study, we consider a prototype NP adopting a magnetic core-shell model, with magnetically coherent core and somewhat disordered shell, as it is one of the common spin architectures in real NPs. The size of the core is fixed to 5.5 nm in diameter and the shell thickness ranges from 0.5 nm to 3 nm. As a starting point in the simulations, we used typical experimental values obtained for a cobalt ferrite NP of a comparable size investigated previously. The simulations enabled us to study systematically the macrospin dynamics of the prototype NP and to address the interplay between the magnetic anisotropies of the core and the shell, respectively. We also demonstrate how the computational time step, run time, damping parameter, and thermal field influence the simulation results. In agreement with experimental studies, we observed that the direction and magnitude of the shell anisotropy influences the effective magnetic size of the core in the applied magnetic field. We conclude that micromagnetic simulations, in spite of being designed for much larger scales are a useful toolbox for understanding the magnetization processes within a single domain NP with an ordered spin structure in the core and partially disordered spins in the shell.

Thermoreversible magnetic nanochains.

The reversible organization of nanomagnets into highly anisotropic assemblies is of considerable interest for many applications, including theragnostic strategies in vivo. The current preparation strategies lead to structures that are not stable without the permanent presence of an applied magnetic field (MF); otherwise, irreversible assemblies are produced with moderate shape anisotropy at nanoscales. Here, we present a new approach based on the thermoreversible Diels-Alder reaction in the presence of an external MF that enables the assembly of single-domain nanomagnets into narrow chains with lengths of several micrometers. The MF-assisted click chemistry approach included (i) the synthesis of nanoparticles through a modified hydrothermal method, (ii) their functionalization via ligand exchange, (iii) the MF-assisted formation of chains, and (iv) the linkage of the nanomagnets in the presence of the magnetic field. Moreover, the chains can be again disassembled at elevated temperatures through a retro-Diels-Alder reaction. We thus demonstrated for the first time that MF-assisted click chemistry is a convenient method for large-scale preparation of highly anisotropic assemblies of nanosized magnets that can be reversibly decomposed by thermal treatment.

Algoritmo para el diagnóstico bioquímico de la hiperglicinemia no cetósica en Cuba / Biochemical diagnosis of non-ketotic hyperglycinemia in Cuba

La hipergilicinemia no cetósica es un error innato del metabolismo originado por un déficit en la actividad del sistema de clivaje de la glicina. Se caracteriza por acumulación de glicina en tejidos, sangre, líquido cefalorraquídeo y orina. Los síntomas clínicos característicos son convulsiones y daño al sistema nervioso central. Existen tres variantes: la clásica, las atípicas y la transitoria. El diagnóstico bioquímico consiste en la cuantificación de glicina en plasma y líquido cefalorraquídeo, así como el análisis simultáneo de ácidos orgánicos en orina. En los casos positivos se realiza el estudio molecular y/o diagnóstico enzimático. Este trabajo se desarrolló con los objetivos de implementar un protocolo para el diagnóstico bioquímico de la hiperglicinemia no cetósica en Cuba y describir los hallazgos clínicos y bioquímicos en los pacientes con sospecha clínica de la enfermedad. Se realizó un estudio descriptivo, transversal en 139 pacientes con sospecha clínica de un EIM de los aminoácidos en el 2014. En los pacientes con resultados positivos de una hiperglicinuria y perfil normal de ácidos orgánicos se cuantificó glicina en suero y líquido cefalorraquídeo por HPLC. Dos pacientes, con cuadros convulsivos refractarios al tratamiento, presentaron niveles elevados de glicina en orina y suero, con un perfil normal de ácidos orgánicos en orina. En ambos pacientes la relación de glicina líquido cefalorraquídeo/suero fue positiva. Debido al cuadro clínico y la edad de aparición de los síntomas se diagnostica una hiperglicinemia no cetósica neonatal clásica y una variante infantil…(AU)

Criterios clínicos, riesgo y manejo de trombosis venosa profunda (TVP)

Como trombosis venosa profunda (TVP) reconocemos el proceso de coagulación intravenosa de la sangre, con dificultad en su retorno, que se traduce a la progresión del coágulo en el interior de las venas y con la posibilidad de su desprendimiento, desplazamiento y fijación del trombo en el árbol arterial pulmonar, embolismo pulmonar (EP); si tomamos en consideración, que las TVP no tienen una manifestación clínica local y el riesgo de embolismo pulmonar con una alta mortalidad, de ahí la importancia de un diagnóstico precoz, para esto es necesario categorizar el riesgo de TVP y su respectivo manejo, parámetros que presentamos en esta revisión bibliográfica.