Use of Conglomerate Mixed Crystals to Deracemize a Stable Racemic-Compound-Forming System.

Deracemization extended to racemic-compound-forming systems is demonstrated. We present here the first results of an alternative for the resolution of systems that exhibit a stable racemic compound but also a closely related conglomerate-forming system. If the couples of enantiomers forming the racemic compound and the enantiomers of the stable conglomerate can syncrystallize in mirror-related partial solid solutions, it is possible to deracemize the racemic mixture of mixed crystals to access to a single handedness. The evidence for this possibility is given in three examples by using temperature-cycling-induced deracemization.

The M de Jussieu's 'mirror of the Incas': an ecuadorian archaeological artefact in the mineralogical collection of René-Just Haüy (1743-1822).

This article reports on a historical investigation carried out on the conical object MIN000-3519 preserved in the mineralogy collections of the Muséum National d'Histoire Naturelle at Paris (France). The mineralogist René-Just Haüy (1743-1822) included this object, cut in a single pyrite (FeS2) crystal, in his working collection with the references 'Sulphured iron, mirror of the Incas, of Peru, M. de Jussieu'. All of the research lines followed lead the author to Joseph de Jussieu (1704-1779) and his shipments of botanical specimens and various other samples from South America. As a member of the Godin-La Condamine-Bouguer geodesic expedition on the equator (1735-1743), he returned to France only after 36 years (1771), ill, exhausted and dispossessed of the scientific product of his Andean collections. This pyrite mirror is important because, in addition to appearing to be the only archaeological object that can be linked to Joseph's peregrinations in America, it resembles other specimens found at sites of the Cañaris culture (500-1500 AD) in Ecuador. Preserved within the de Jussieu family, this object would presumably have been given to Haüy by Joseph's heirs, his nephews Antoine-Laurent (1748-1836) or Laurent-Pierre (1792-1866), with whom he had close ties.

Degradability of superparamagnetic nanoparticles in a model of intracellular environment: follow-up of magnetic, structural and chemical properties.

The unique magnetic properties of iron oxide nanoparticles have paved the way for various biomedical applications, such as magnetic resonance cellular imaging or magnetically induced therapeutic hyperthermia. Living cells interact with nanoparticles by internalizing them within intracellular acidic compartments. Although no acute toxicity of iron oxide nanoparticles has been reported up to now, the mechanisms of nanoparticle degradation by the cellular environment are still unknown. In the organism, the long term integrity and physical state of iron-based nanoparticles are challenged by iron homeostasis. In this study, we monitored the degradation of 7 nm sized maghemite nanoparticles in a medium mimicking the intracellular environment. Magnetic nanoparticles with three distinct surface coatings, currently evaluated as MRI contrast agents, were shown to exhibit different kinetics of dissolution at an acidic pH in the presence of a citrate chelating agent. Our assessment of the physical state of the nanoparticles during degradation revealed that the magnetic properties, size distribution and structure of the remaining nanocrystals were identical to those of the initial suspension. This result suggests a model for nanoparticle degradation with rapidly dissolved nanocrystals and a reservoir of intact nanoparticles.

Nanomagnetism reveals the intracellular clustering of iron oxide nanoparticles in the organism.

There are very few methods to investigate how nanoparticles (NPs) are taken up and processed by cells in the organism in the short and long terms. We propose a nanomagnetism approach, in combination with electron microscopy, to document the magnetic outcome of iron oxide-based P904 NPs injected intravenously into mice. The NP superparamagnetic properties are shown to be modified by cell internalization, due to magnetic interactions between NPs sequestered within intracellular organelles. These modifications of magnetic behaviour are observed in vivo after NP uptake by resident macrophages in spleen and liver or by inflammatory macrophages in adipose tissue as well as in vitro in monocyte-derived macrophages. The dynamical magnetic response of cell-internalized NPs is theoretically and experimentally evidenced as a global signature of their local organization in the intracellular compartments. The clustering of NPs and their magnetism become dependent on the targeted organ, on the dose administrated and on the time elapsed since their injection. Nanomagnetism probes the intracellular clustering of iron-oxide NPs and sheds light on the impact of cellular metabolism on their magnetic responsivity.

Long term in vivo biotransformation of iron oxide nanoparticles.

The long term outcome of nanoparticles in the organism is one of the most important concerns raised by the development of nanotechnology and nanomedicine. Little is known on the way taken by cells to process and degrade nanoparticles over time. In this context, iron oxide superparamagnetic nanoparticles benefit from a privileged status, because they show a very good tolerance profile, allowing their clinical use for MRI diagnosis. It is generally assumed that the specialized metabolism which regulates iron in the organism can also handle iron oxide nanoparticles. However the biotransformation of iron oxide nanoparticles is still not elucidated. Here we propose a multiscale approach to study the fate of nanomagnets in the organism. Ferromagnetic resonance and SQUID magnetization measurements are used to quantify iron oxide nanoparticles and follow the evolution of their magnetic properties. A nanoscale structural analysis by electron microscopy complements the magnetic follow-up of nanoparticles injected to mice. We evidence the biotransformation of superparamagnetic maghemite nanoparticles into poorly-magnetic iron species probably stored into ferritin proteins over a period of three months. A putative mechanism is proposed for the biotransformation of iron-oxide nanoparticles.