A. Lascialfari

Analysis of pathological events at the onset of brain damage in stroke‐prone rats: A proteomics and magnetic resonance imaging approach

Spontaneously hypertensive stroke‐prone rats (SHRSP) develop brain abnormalities invariably preceded by the accumulation of acute‐phase proteins in body fluids. This study describes the sequence of pathological events, and in particular the involvement of inflammation, at the onset of brain injury in this animal model. In SHRSP subjected to permissive dietary treatment, the appearance of brain damage and of altered permeability of the blood–brain barrier (BBB) was monitored over time by magnetic resonance imaging (MRI) after intravenous injection of gadolinium. The protein content in cerebrospinal fluid and brain extracts was analyzed by two‐dimensional electrophoresis. Gadolinium diffusion showed impairment of the BBB after 42 ± 3 days from the start of salt loading, simultaneously with the detection of brain abnormalities by MRI. Tissue lesions were initially localized at one or more small foci and then spread throughout the brain in the form of fibrinoid necrosis. This type of lesion is characterized by fibrin deposition, in particular around the vessels; loss of tissue texture; and infiltration of macrophages and lymphocytes. High levels of plasma‐derived proteins of molecular mass up to >130 kDa were detected in the cerebrospinal fluid after MRI had revealed brain abnormalities. Plasma proteins extravasated from brain vessels were immunodetected in tissue homogenates from affected areas. The results obtained in this study provide new insights into the pathogenesis of the spontaneous brain damage in SHRSP and in particular on the involvement of the inflammatory cascade. These studies may be useful in evaluating new pharmacological strategies aimed at preventing/treating brain diseases.

Water-Soluble Rhamnose-Coated Fe3O4 Nanoparticles

Water-soluble biocompatible rhamnose-coated Fe(3)O(4) nanoparticles of 4.0 nm are obtained by covalent anchorage of rhamnose on the nanoparticles surface via a phosphate linker. These nanoparticles present superparamagnetic behavior and nuclear relaxivities in the same order of magnitude as Endorem that make them potential magnetic resonance imaging (MRI) contrast agents of a second generation, where the saccharides represent also specific ligands able to target lectins on skin cells.

A missing high-spin molecule in the family of cyanido-bridged heptanuclear heterometal complexes, [(LCuII)6FeIII(CN)6]3+, and its CoIII and CrIII analogues, accompanied in the crystal by a novel octameric water cluster

Three isostructural cyanido-bridged heptanuclear complexes, [{Cu(II)(saldmen)(H₂O)}₆{M(III)(CN)₆}]-(ClO₄)₃·8H₂O (M= Fe(III) 2; Co(III), 3; Cr(III) 4), have been obtained by reacting the dinuclear copper(II) complex, [Cu₂(saldmen)₂(μ-H₂O)(H₂O)₂](ClO₄)₂·2H₂O 1, with K₃[Co(CN)₆], K₄[Fe(CN)₆], and K₃[Cr(CN)₆], respectively (Hsaldmen is the Schiff base resulting from the condensation of salicylaldehyde with N,N-dimethylethylenediamine). A unique octameric water cluster, with bicyclo[2,2,2]octane-like structure, is sandwiched between the heptanuclear cations in 2, 3 and 4. The cryomagnetic investigations of compounds 2 and 4 reveal ferromagnetic couplings of the central Fe(III) or Cr(III) ions with the Cu(II) ions (J(CuFe) = +0.87 cm⁻¹, J(CuCr) = +30.4 cm⁻¹). The intramolecular Cu···Cu exchange interaction in 3, across the diamagnetic cobalt(III) ion, is -0.3 cm⁻¹. The solid-state ¹H-NMR spectra of compounds 2 and 3 have been investigated.

Finite-size effects on the dynamic susceptibility of CoPhOMe single-chain molecular magnets in presence of a static magnetic field

The static and dynamic properties of the single-chain molecular magnet [Co(hfac)2NITPhOMe] are investigated in the framework of the Ising model with Glauber dynamics, in order to take into account both the effect of an applied magnetic field and a finite size of the chains. For static fields of moderate intensity and short chain lengths, the approximation of a mono-exponential decay of the magnetization fluctuations is found to be valid at low temperatures; for strong fields and long chains, a multi-exponential decay should rather be assumed. The effect of an oscillating magnetic field, with intensity much smaller than that of the static one, is included in the theory in order to obtain the dynamic susceptibility �(!). We find that, for an open chain with N spins, �(!) can be written as a weighted sum of N frequency contributions, with a sum rule relating the frequency weights to the static susceptibility of the chain. Very good agreement is found between the theoretical dynamic susceptibility and the ac susceptibility measured in moderate static fields (Hdc ≤ 2 kOe), where the approximation of a single dominating frequency turns out to be valid. For static fields in this range, new data for the relaxation time, � versus Hdc, of the magnetization of CoPhOMe at low temperature are also well reproduced by theory, provided that finite-size effects are included.

Superconducting fluctuations and anomalous diamagnetism in underdopedYBa2Cu3O6+xfrom magnetization and63CuNMR-NQR relaxation measurements

Magnetization and 63Cu NMR-NQR relaxation measurements are used to study the superconducting fluctuations in YBa2Cu3O6+x (YBCO) oriented powders. In optimally doped YBCO the fluctuating negative magnetization M_{fl}(H,T) is rather well described by an anisotropic Ginzburg-Landau (GL) functional and the curves M_{fl}/sqrt{H} cross at Tc. In underdoped YBCO, instead, over a wide temperature range an anomalous diamagnetism is observed, stronger than in the optimally doped compound by about an order of magnitude. The field and temperature dependences of M_{fl} cannot be described either by an anisotropic GL functional or on the basis of scaling arguments. The anomalous diamagnetism is more pronounced in samples with a defined order in the Cu(1)O chains. The 63Cu(2) relaxation rate shows little, if any, field dependence in the vicinity of the transition temperature Tc(H=0). It is argued how the results in the underdoped compounds can be accounted for by the presence of charge inhomogeneities, favoured by chains ordering.

Spin dynamics and energy gap of a Fe dimer from susceptibility and 1H nuclear magnetic resonance

The iron(III) S=5/2 dimer [Fe(OMe)(dbm)2]2 (in short Fe2) has a nonmagnetic S=0 ground state. The separation between the singlet ground state and the first excited (triplet) state is determined from susceptibility measurements to be about 22 K; for a dimer this value is equal to the antiferromagnetic exchange constant J. Proton nuclear magnetic resonance measurements were performed on Fe2. The nuclear spin-lattice relaxation rate (NSLR) was studied as a function of temperature at 31 and 67 MHz and as a function of the resonance frequency (10–67 MHz) at T=295u200aK. At room temperature the 1Hu2009NSLR is independent of frequency contrary to the strong dependence found in planar ring compounds like Fe6 and ferric wheel (Fe10). The temperature dependence of the proton NSLR shows an exponential decrease on lowering the temperature from which we estimate a gap value about double the value obtained from the uniform susceptibility, a result which is unexpected if the NSLR were simply proportional to the concentration of...

Molecular magnets and magnetic nanoparticles: new opportunities for μSR investigations

Abstract The properties of molecular magnets are briefly reviewed, with the aim to provide interesting new fields of application of μSR techniques. Bulk molecular magnets are classified according to the individual centers with unpaired electrons as organic, organic–inorganic, and inorganic molecular magnets. Examples of all of them will be provided, stressing the μSR experiments so far reported, and highlighting in particular the novel physical properties of the molecular magnets. Molecular clusters will be also reported, showing their similarities to magnetic nanoparticles and stressing the advantages they have. In particular it will be shown how these new materials are the ideal testing grounds of theories of macroscopic quantum phenomena in magnets.

NMR in Magnetic Molecular Rings and Clusters

Molecular nanomagnets (MNM) are magnetic molecular clusters con- taining a limited number of transition ions in a highly symmetric configuration and coupled by strong exchange interaction (either ferromagnetic (FM) or more often antiferromagnetic (AFM)). The magnetic intermolecular interaction is very weak and thus the clusters behave as single nanosize units. NMR has proved to be an excellent probe to investigate the static magnetic properties and the spin dynamics of this new fascinating class of magnetic materials. The chapter contains a compre- hensive review of the work performed in the last few years by the present authors with only a brief reference to work performed by other researchers. Most of the NMR measurements were performed on protons but important results were obtained also using other nuclei like 55 Mn, 57 Fe, 7 Li, 23 Na, 63 Cu, 19 F. In some cases the NMR was observed at low temperature in zero external field. Some novel NMR phenom- ena specific of the systems investigated were discovered and explained. For example in the anisotropic ferrimagnetic clusters Mn12 and Fe8, the ground state is a high total spin S = 10 state whereby the crystal field anisotropy generates an energy barrier typical of superparamagnets. It is shown how NMR and relaxation measure- ments can detect the microscopic local spin configuration in the ground state and the dynamics of quantum tunnelling of the magnetization (QMT). Another exam- ple is the case of the AFM rings, Fe10, Fe6 and Cr8, in which the ground state is a singlet, S = 0, separated from the first triplet excited state by an energy gap of about 5-10 K. By applying a magnetic field one can observe level crossing effects. These effects were studied by proton NMR and relaxation measurements vs field at low temperature (1.5-3 K). Finally, the nuclear relaxation rate as a function of temperature in the above mentioned AFM rings displays a field dependent peak at a temperature of the order of the exchange constant J ,w hich can be fi tted with a general scaling law. From these data, the lifetime broadening of the energy levels can be determined.

Multiexponential T2-relaxation analysis in cerebrally damaged rats in the absence and presence of a gadolinium contrast agent

An analysis of the multiexponential relaxation of transverse nuclear magnetization with and without a gadolinium‐based paramagnetic contrast agent in spontaneously hypertensive stroke‐prone rats (SHR‐SP) and in the rat model of ischemia induced by middle cerebral artery occlusion is described. From the multiexponential relaxation, the presence of two T2 relaxation times in the range of 0.03–0.5 s, T2A (shortest) and T2B (longest), with very different relative weights (respectively, A and B), is evidenced. In our models of cerebral damage, the changes in A and B were more evident than those in T2A and T2B. The two T2 values were interpreted as belonging to water molecules in two different compartments; therefore, the difference between the damaged and normal regions revealed by means of standard T2‐weighted images is suggested to be due to a different water distribution in the two compartments, rather than different T2s. The T2 relaxation in the SHR‐SP stroke model is analyzed for the first time using a multiexponential method. The power of a detailed analysis of MRI relaxation times is confirmed by the correspondence between the revealed changes in T2A, T2B, A and B, and the known T2W and DWI results about blood–brain barrier functionality. Magn Reson Med 53:1326–1332, 2005.

Specific heat and μ+SR measurements in Gd(hfac)3NITiPr molecular magnetic chains: Indications for a chiral phase without long-range helical order

Low-temperature specific heat C(T) and zero-field muon spin resonance (μ + SR) measurements were performed in Gd(hfac) 3 NITiPr, a quasi-one-dimensional molecular magnet with competing nearest-neighbor and next-nearest-neighbor intrachain exchange interactions. The specific heat data exhibit a λ peak at T 0 =2.08 ′0.01 K that disappears upon the application of a 5 T magnetic field. Conversely, the μ + SR data do not present any anomaly at T2 K, proving the lack of divergence of the two-spin correlation function as required for usual three-dimensional long-range helical order. Moreover, no muon spin precession can be evinced from the μ + SR asimmetry curves, thus excluding the presence of a long-range-ordered magnetic lattice. These results provide indications for a low-T phase where chiral order is established in absence of long-range helical order.