Superparamagnetic properties of hemozoin

We report that hemozoin nanocrystals demonstrate superparamagnetic properties, with direct measurements of the synthetic hemozoin magnetization. The results show that the magnetic permeability constant varies from mu = 4585 (at -20 degrees C) to 3843 (+20 degrees C), with the values corresponding to a superparamagnetic system. Similar results were obtained from the analysis of the diffusion separation of natural hemozoin nanocrystals in the magnetic field gradient, with mu = 6783 exceeding the value obtained in direct measurements by the factor of 1.8. This difference is interpreted in terms of structural differences between the synthetic and natural hemozoin. The ab initio analysis of the hemozoin elementary cell showed that the Fe3+ ion is in the high-spin state (S = 5/2), while the exchange interaction between Fe3+ electron-spin states was much stronger than k(B)T at room temperature. Thus, the spin dynamics of the neighboring Fe3+ ions are strongly correlated, lending support to the superparamagnetism

Refraction law and Fermat principle: a project using the ant colony optimization algorithm for undergraduate students in physics

info:eu-repo/semantics/publishe

Electron Paramagnetic Resonance Imaging of Melanin in Honey Bee.

Honey bees play a crucial role in the nature by pollinating wild flowers. Over the past years, there has been an increasing concern regarding the honey bee colony decline. Pesticides or environmental effects targeting the biochemistry of insect chitin and cuticle coating may be in part responsible for honey bee pathologies. We here propose the use of electron paramagnetic resonance imaging (EPRI) as a tool to image the melanin-chitin complexes as part of the exoskeleton of the honey bee. EPRI at 9.65 GHz was applied on intact freeze-dried bees. The imaging data were collected on the melanin peak. High-resolution images revealed that this compound is extensively distributed in the periphery of the animal, data consistent with the localization in the cuticle of the bee. While EPR of melanin has been so far explored in the context of melanoma characterization, it may offer new opportunities in research on honey bees and other insects

Fluorinated Mesoporous Silica Nanoparticles for Binuclear Probes in ¹H and ¹⁹F Magnetic Resonance Imaging.

The development of molecular and cellular magnetic resonance imaging (MRI) procedures has always represented a challenge because of the fact that conventional MRI contrast agents are not directly detected in vivo; in proton MRI (e.g., with the nucleus <sup>1</sup> H), their local concentration is measured through the effect they exert on the signal of hydrogen protons present in their immediate vicinity. Because the contrast effects generated by conventional MRI probes superpose to and can often impede the anatomical information contained in <sup>1</sup> H MRI images, new probes based on a nucleus other than <sup>1</sup> H, are being developed. In this study, we report on the development of fluorinated mesoporous silica nanoparticles (MSNs), which could represent an interesting dual probe that allows two MRI modes: <sup>1</sup> H for high-resolution anatomical information and <sup>19</sup> F for the detection of MSNs used as drug delivery agents. MSNs were synthesized and covalently functionalized either with fluorosilane (FMSNs) or polyfluorosiloxane (polyFMSNs) to enable their detection in <sup>19</sup> F MRI. Then, gadolinium chelates were grafted on the particles to enhance their detectability in <sup>1</sup> H MRI. The physicochemical, textural, and relaxometric properties ( <sup>1</sup> H and <sup>19</sup> F relaxation times) of the nanoparticles were measured and compared. The <sup>19</sup> F relaxation properties were found to be dependent on the concentration of fluorine; they were also highly sensitive to the presence of gadolinium. The shortest relaxation times were obtained with polyFMSNs. At clinical magnetic field strengths, high <sup>1</sup> H relaxivities and low relaxometric ratios (r <sub>2</sub> /r <sub>1</sub> = 1.45; 2.2 for nanoparticles entrapped in hydrogel) were found for both nanoparticle systems. Finally, the visibility of both systems was confirmed in <sup>1</sup> H, and the detectability of polyFMSNs was confirmed in <sup>19</sup> F MRI. This physicochemical and relaxometric study opens the door to the applications of fluorinated silica nanoparticles as theranostic materials allowing dual MRI ( <sup>1</sup> H and <sup>19</sup> F)

Physico-chemical and NMR relaxometric characterization of gadolinium hydroxide and dysprosium oxide nanoparticles

Gadolinium hydroxide and dysprosium oxide nanoparticles, which constitute a new interesting class of magnetic nanoparticles, are characterized by different methods, using x-ray diffraction, magnetometry and NMR relaxometry at multiple fields. The rod-like particles are first shown to have a simple paramagnetic behavior, like the bulk compound, without any influence of the nanometric size of the particles. Because of their paramagnetic moment, these particles considerably shorten water relaxation times, especially the transverse relaxation time at high fields. The relaxation induced by gadolinium hydroxide particles is due to a proton exchange between the particle surface and bulk water, while the transverse relaxation caused by dysprosium oxide particles is governed by the diffusion of water protons around the magnetized particles. 1/T(2) increases linearly with the magnetic field for gadolinium hydroxide particles while a quadratic increase is observed for dysprosium oxide nanoparticles. The relaxation results are compared with those from previous studies and interpreted using different theories for the relaxation induced by magnetic particles

Looking for biogenic magnetite in brain ferritin using NMR relaxometry

Mammalian cellular iron is stored inside the multisubunit protein ferritin. normally taking the structure of a ferrihydrite-like mineral core. It has been suggested that biogenic magnetite, which has been detected in the brain and may be related to neurodegenerative diseases such as Alzheimer's and Parkinson's diseases, could initially form in ferritin. Indeed, as ferritin is present in the brain, the ferrihydrite core could be a precursor for biogenic magnetite formation 19 particularly in cases where the normal functioning of the ferritin protein is disrupted. In this work, NMR relaxometry was used to detect magnetite inside samples of ferritin extracted from normal and Alzheimer-diseased brains. The method was first calibrated with different fractions of horse spleen ferritin and synthetic magnetite particles. The relaxometry results suggest that the proportion of iron contained in brain ferritin in the form of well-crystallized magnetite instead of ferrihydrite must be < 1%, which is much less than that reported for 'magnetite-like' phase in recent transmission electron microscopy studies of similar samples. Consequently, the magnetization of this 'magnetite-like' phase must be very low compared with that of magnetite. Copyright (c) 2005 John Wiley & Sons, Ltd

NMR relaxation induced by iron oxide particles : testing theoretical models

Superparamagnetic iron oxide particles find their main application as contrast agents for cellular and molecular magnetic resonance imaging. The contrast they bring is due to the shortening of the transverse relaxation time T 2 of water protons. In order to understand their influence on proton relaxation, different theoretical relaxation models have been developed, each of them presenting a certain validity domain, which depends on the particle characteristics and proton dynamics. The validation of these models is crucial since they allow for predicting the ideal particle characteristics for obtaining the best contrast but also because the fitting of T 1 experimental data by the theory constitutes an interesting tool for the characterization of the nanoparticles. In this work, T 2 of suspensions of iron oxide particles in different solvents and at different temperatures, corresponding to different proton diffusion properties, were measured and were compared to the three main theoretical models (the motional averaging regime, the static dephasing regime, and the partial refocusing model) with good qualitative agreement. However, a real quantitative agreement was not observed, probably because of the complexity of these nanoparticulate systems. The Roch theory, developed in the motional averaging regime (MAR), was also successfully used to fit T 1 nuclear magnetic relaxation dispersion (NMRD) profiles, even outside the MAR validity range, and provided a good estimate of the particle size. On the other hand, the simultaneous fitting of T 1 and T 2 NMRD profiles by the theory was impossible, and this occurrence constitutes a clear limitation of the Roch model. Finally, the theory was shown to satisfactorily fit the deuterium T 1 NMRD profile of superparamagnetic particle suspensions in heavy water