Magnetoresistance and collective Coulomb blockade in super-lattices of ferromagnetic CoFe nanoparticles

We report on transport properties of millimetric super-lattices of CoFe nanoparticles surrounded by organic ligands. R(T)s follow R(T) = R_0.exp(T/T_0)^0.5 with T_0 ranging from 13 to 256 K. At low temperature I(V)s follow I=K[(V-V_T)/V_T]^ksi with ksi ranging 3.5 to 5.2. I(V) superpose on a universal curve when shifted by a voltage proportional to the temperature. Between 1.8 and 10 K a high-field magnetoresistance with large amplitude and a strong voltage-dependence is observed. Its amplitude only depends on the magnetic field/temperature ratio. Its origin is attributed to the presence of paramagnetic states present at the surface or between the nanoparticles. Below 1.8 K, this high-field magnetoresistance abruptly disappears and inverse tunnelling magnetoresistance is observed, the amplitude of which does not exceed 1%. At this low temperature, some samples display in their I(V) characteristics abrupt and hysteretic transitions between the Coulomb blockade regime and the conductive regime. The increase of the current during these transitions can be as high as a factor 30. The electrical noise increases when the sample is near the transition. The application of a magnetic field decreases the voltage at which these transitions occur so magnetic-field induced transitions are also observed. Depending on the applied voltage, the temperature and the amplitude of the magnetic field, the magnetic-field induced transitions are either reversible or irreversible. These abrupt and hysteretic transitions are also observed in resistance-temperature measurements. They could be the soliton avalanches predicted by Sverdlov et al. [Phys. Rev. B 64, 041302 (R), 2001] or could also be interpreted as a true phase transition between a Coulomb glass phase to a liquid phase of electrons

High-field and low field magnetoresistance of CoFe nanoparticles elaborated by organometallic chemistry

We report on magnetotransport measurements on CoFe nanoparticles surrounded by an insulating organic layer. Samples were obtained by evaporating a solution of nanoparticles on a patterned substrate. Typical behaviour of Coulomb blockade in array of nanoparticles is observed. High and low field magnetoresistance have been evidenced. Below 10 K, a large high-field magnetoresistance is measured, reaching up to 500 %. Its amplitude decreases strongly with increasing voltage. At 1.6 K, this high-field magnetoresistance vanishes and an inverse low field tunnelling magnetoresistance is observed.Comment: 12 pages, with 3 figures, references and figure captions. Proceeding of the 52nd MMM conferenc

Etudes de stabilité de médicaments anticancéreux injectables (apports analytiques et pharmaceutiques)

La prise en charge des patients atteints de cancer fait intervenir le pharmacien hospitalier dans la préparation des médicaments anticancéreux injectables. Afin de limiter les coûts de cette prise en charge médicamenteuse, une des alternatives consiste à optimiser leur préparation en prenant en compte la stabilité physico-chimique des anticancéreux : 1-en utilisant les reliquats générés lors de la préparation. 2- en évaluant la possibilité de fabriquer à l avance les préparations d anticancéreux. L absence de données de stabilité de ces médicaments nous a conduits à l évaluer sur le pemetrexed et le methotrexate afin de répondre à cette double problématique et d étudier le gain de coût associé.Nous avons démontré, au cours de ce travail, la stabilité des reliquats de pemetrexed-Alimta® pendant14 jours permettant ainsi leur réutilisation. Nous avons également montré la stabilité de solutions de méthotrexate conditionnées en seringues pendant 28 jours.Une des conséquences de ces études est la réalisation d économie pour la sécurité sociale par l optimisation de la gestion des reliquats d anticancéreux. Cette économie représente environ 10 % du budget annuel des anticancéreux injectables soit 750 kEUR. Nous avons montré au cours de ce travail l apport de la chimie analytique et organique ainsi que l apport de la pharmacie dans la mise en place et l exploitation des études de stabilité sur les médicaments anticancéreux injectables.Hospital pharmacists are involved in the management of cancer patients through preparation of intravenous anticancer drugs. To limit the costs of the chemotherapies, an alternative is to optimize their preparation by considering the physicochemical stability of anticancer drugs. This can be done by using the leftovers generated during the preparation and by preparing in advance the devices to be used for administration. The lack of data on the stability of anticancer drugs has led us to evaluate pemetrexed and methotrexate with the aim of answering both the above issues. In parallel, we studied the associated cost savings.In this thesis, we have demonstrated the stability of leftovers of pemetrexed-Alimta® for 14 days allowing their use for subsequent preparations. We also showed the stability of solutions of methotrexate packaged in syringes for 28 days.One consequence of these studies is its translation in cost-savings for our Healthcare Funding Organization by managing leftover anticancer drugs. These cost-savings (about 750 kEUR) represent about 10 % of the total annual expenditure of anticancer drugs. Our work illustrates the contribution of analytical and organic chemistry and the role pharmacists can have in improving costs by performing stability studies of anticancer drugs.TOURS-Bibl.électronique (372610011) / SudocSudocFranceF

High-Performance Liquid Chromatography Assay for Moxifloxacin in Brain Tissue and Plasma: Validation in a Pharmacokinetic Study in a Murine Model of Cerebral Listeriosis

Moxifloxacin is a broad-spectrum antibacterial 8-methoxy-fluoroquinolone. In order to evaluate the pharmacokinetic properties of moxifloxacin in mouse plasma and brain tissue, we developed a high-performance liquid chromatography (HPLC) method. This study was based on single-drug delivery, intravenously dosed in a central listeriosis murine model. The method employed a reversed-phase Lichrospher RP-18 with a precolumn (250 × 4.6 mm) and a mobile phase composed of a mixture of acetonitrile, methanol, and citric buffer (pH = 3.5) with sodium dodecyl sulfate and tetrabutylammonium bromide. Fluorescence detection was performed at an excitation wavelength of 290 nm and an emission wavelength of 550 nm. The relative standard deviation of intra- and inter-day assays was <10%. This validated method led to a short retention time (8.0 min) for moxifloxacin. The standard curves were linear from 5–250 μg/L in plasma and from 0.1–2.5 μg/g of brain tissue. The limits of quantification were 5 μg/L in plasma and 0.1 μg/g in brain tissue. The method enabled the detection of systemic antimicrobial in plasma and in CNS in Listeria-infected mice. Injected moxifloxacin passed through the encephalic barrier within a 30 to 60 min after injection time frame. Moxifloxacin pharmacokinetics are modeled in an infected model compared to control mice

Urinary Elimination of Coproporphyrins Is Dependent on ABCC2 Polymorphisms and Represents a Potential Biomarker of MRP2 Activity in Humans

MRP2 encoded by ABCC2 gene is involved in the secretion of numerous drugs and endogenous substrates. Patients with Dubin-Johnson syndrome due to mutation in ABCC2 gene have elevated urinary coproporphyrin ratio (UCP I/(I + III)). Here we investigated whether this ratio could serve as a biomarker of MRP2 function. Phenotype-genotype relationships were studied in 74 healthy subjects by measuring individual UCP I/(I + III) ratio obtained on 24-hour urine and by analyzing five common SNPs in ABCC2 gene. The UCP I/(I + III) ratio varied from 14.7% to 46.0% in our population. Subjects with 3972TT genotype had a higher ratio (P = .04) than those carrying the C allele. This higher UCP I/(I + III) ratio was correlated with a higher level of isomer I excretion. This study provides a proof of concept that UCP I/(I + III) ratio can be used as a biomarker of MRP2 function in clinical studies as it provides quantitative information about the in vivo activity of MRP2 in a given patient

Transport in Magnetic Nanoparticles Super-Lattices : Coulomb Blockade, Hysteresis and Magnetic Field Induced Switching

We report on magnetotransport measurements on millimetric super-lattices of Co-Fe nanoparticles surrounded by an organic layer. At low temperature, the transition between the Coulomb blockade and the conductive regime becomes abrupt and hysteretic. The transition between both regime can be induced by a magnetic field, leading to a novel mechanism of magnetoresistance. Between 1.8 and 10 K, high-field magnetoresistance due to magnetic disorder at the surface of the particles is also observed. Below 1.8 K, this magnetoresistance abruptly collapses and a low-field magnetoresistance is observed.Comment: 9 pages (text, figures, figures legends and references). 3 figures reference 33 added : "arXiv:0710.1750v1

3000 % high-field magnetoresistance in super-lattices of CoFe nanoparticles

We report on magnetotransport measurements on millimetre-large super-lattices of CoFe nanoparticles surrounded by an organic layer. Electrical properties are typical of Coulomb blockade in three dimensional arrays of nanoparticles. A large high-field magnetoresistance, reaching up to 3000 %, is measured between 1.8 and 10 K. This exceeds by two orders of magnitude magnetoresistance values generally measured in arrays of 3d metals ferromagnetic nanoparticles. The magnetoresistance amplitude scales with the magnetic field / temperature ratio and displays an unusual exponential dependency with the applied voltage. The magnetoresistance abruptly disappears below 1.8 K. We propose that the magnetoresistance is due to some individual paramagnetic moments localized between the metallic core of the nanoparticles, the origin of which is discussed.Comment: 9 pages (text, references, figures and legends

Stability studies of anticancer drugs : analytical and pharmaceutical contribution

La prise en charge des patients atteints de cancer fait intervenir le pharmacien hospitalier dans la préparation des médicaments anticancéreux injectables. Afin de limiter les coûts de cette prise en charge médicamenteuse, une des alternatives consiste à optimiser leur préparation en prenant en compte la stabilité physico-chimique des anticancéreux : 1-en utilisant les reliquats générés lors de la préparation. 2- en évaluant la possibilité de fabriquer à l’avance les préparations d’anticancéreux. L’absence de données de stabilité de ces médicaments nous a conduits à l’évaluer sur le pemetrexed et le methotrexate afin de répondre à cette double problématique et d’étudier le gain de coût associé.Nous avons démontré, au cours de ce travail, la stabilité des reliquats de pemetrexed-Alimta® pendant14 jours permettant ainsi leur réutilisation. Nous avons également montré la stabilité de solutions de méthotrexate conditionnées en seringues pendant 28 jours.Une des conséquences de ces études est la réalisation d’économie pour la sécurité sociale par l’optimisation de la gestion des reliquats d’anticancéreux. Cette économie représente environ 10 % du budget annuel des anticancéreux injectables soit 750 k€. Nous avons montré au cours de ce travail l’apport de la chimie analytique et organique ainsi que l’apport de la pharmacie dans la mise en place et l’exploitation des études de stabilité sur les médicaments anticancéreux injectables.Hospital pharmacists are involved in the management of cancer patients through preparation of intravenous anticancer drugs. To limit the costs of the chemotherapies, an alternative is to optimize their preparation by considering the physicochemical stability of anticancer drugs. This can be done by using the leftovers generated during the preparation and by preparing in advance the devices to be used for administration. The lack of data on the stability of anticancer drugs has led us to evaluate pemetrexed and methotrexate with the aim of answering both the above issues. In parallel, we studied the associated cost savings.In this thesis, we have demonstrated the stability of leftovers of pemetrexed-Alimta® for 14 days allowing their use for subsequent preparations. We also showed the stability of solutions of methotrexate packaged in syringes for 28 days.One consequence of these studies is its translation in cost-savings for our Healthcare Funding Organization by managing leftover anticancer drugs. These cost-savings (about 750 k€) represent about 10 % of the total annual expenditure of anticancer drugs. Our work illustrates the contribution of analytical and organic chemistry and the role pharmacists can have in improving costs by performing stability studies of anticancer drugs

Etude pharmacocinétique de la moxifloxacine chez la souris atteinte de listériose neuroméningée

PARIS-BIUP (751062107) / SudocSudocFranceF