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We present a study on biosurfactant uptake at the interface of a millimeter-sized drop of squalene in water, by a recently developed differential interferometric technique. The technique allows detecting capillary waves, with amplitudes of the order of 10−9 m, excited on the surface of the drop by an electric field in the order of 5 V/cm. By studying the resonant surface modes of the drop it is possible to assess the interfacial properties as a function of the surfactant concentration in the water bulk. The technique allows to follow the adsorption process at extremely low surfactant concentration, not accessible by other methods, investigating the gas state in the π-A diagrams of 2D amphiphilic monolayers.

We developed a novel method to produce microcellular thermosetting polyurethane foaming by the gas-foaming technique using high-pressure physical blowing agents. In particular, to tackle the inherent difficulties of imposing a rapid pressure quench O(10(-2) s) to a material whose synthesis timing is much larger O(10(2) s), we utilized a two-stage foaming. In the first stage, a rapid pressure quench O(10(-2) s) from the saturation pressure to an intermediate pressure, was imposed to nucleate a large amount of bubbles; in the second stage, the growth of the nucleated bubble is controlled by slowly O(10(2) s) decreasing the pressure to ambient pressure. In this way, by separating the nucleation from the growth stage and by chasing the synthesis reaction with the pressure to avoid excessive stress to the curing polymer, we achieved fine-celled (size diameter of 20 mu m), medium-to-low density (150 kg/m(3)) thermosetting polyurethane foams. (C) 2019 Elsevier B.V. All rights reserved.

We investigated the theranostic properties of magnetosomes (MNs) extracted from magnetotactic bacteria, promising for nanomedicine applications. Besides a physico-chemical characterization, their potentiality as mediators for magnetic fluid hyperthermia and contrast agents for magnetic resonance imaging, both in vitro and in vivo, are here singled out. The MNs, constituted by magnetite nanocrystals arranged in chains, show a superparamagnetic behaviour and a clear evidence of Verwey transition, as signature of magnetite presence. The phospholipid membrane provides a good protection against oxidation and the MNs oxidation state is stable over months. Using an alternate magnetic field, the specific absorption rate was measured, resulting among the highest reported in literature. The MRI contrast efficiency was evaluated by means of the acquisition of complete NMRD profiles. The transverse relaxivity resulted as high as the one of a former commercial contrast agent. The MNs were inoculated into an animal model of tumour and their presence was detected by magnetic resonance images two weeks after the injection in the tumour mass.

We derive a suitable expression for estimating the size of the cooperatively rearranging regions (CRRs) in supercooled polymer melts by fitting data worked out by ordinary relaxation experiments carried out in isothermal conditions. As an example, the average CRR size in poly(n-butyl methacrylate) in proximity to the glass transition temperature is derived from a stress relaxation experiment performed by means of an atomic force microscopy setup. Good agreement is found with results in the literature derived from measurements of temperature fluctuations (the so-called Donth method). The temperature dependence of the CRR size is explored for poly(butadiene); in this case the segmental relaxation function is derived through a novel method for the analysis of the efficiency with which free induction decay echoes are refocused in 1H NMR experiments. It is found that the CRR size increases upon cooling. The results derived from the analysis of the NMR data are found to be in satisfactory agreement with those worked out from broadband dielectric spectroscopy data in the literature. © 2015 Society of Chemical Industry

The way of viewing cancer has advanced considerably in the last few decades because of recent progress on two different topics: the knowledge of the mechanisms and characteristics of cancer and the innovation in imaging agent design. In particular the unique properties of cancer that allow differentiation from normal tissue could be employed in multi-functional nanoparticle imaging development. Genetic alterations, either endogenous or induced through gene therapy, are one class of such characteristics. At the same time proteomic differences such as overexpressed surface receptors are another targetable feature, used for enhanced nanoparticle retention. The here proposed magnetic nanoparticle (with biocompatible coating) was designed to target the human breast MDA-MB-231 tumor induced on a nude mice model. With the aim of developing a theranostic agent, the overexpression of folate protein receptor in breast cancer cells was exploited, decorating with folate an organic nanocarrier loaded with magnetite nanoparticles that acts as a diagnostic MRI (Magnetic Resonance Imaging) contrast agent, and Paclitaxel (PTX) as antitumoral drug. A high uptake of nanoparticles and remarkable effect on in vivo MRI images show the targeting ability of our compound and its prolonged retention in tumor tissues. Due to the presence of PTX, the developed nanocarrier may potentially be used also for therapeutic purposes.

One dimensional 1 H NMR measurements have been performed to probe slow molecular motions in nitrile butadiene rubber (NBR) around its calorimetric glass transition temperature T g . The purpose is to show how software aided data analysis can extract meaningful dynamical data from these measurements. Spin–lattice relaxation time, free induction decay (FID) and magic sandwich echo (MSE) measurements have been carried out at different values of the static field, as a function of temperature. It has been evidenced how the efficiency of the MSE signal in reconstructing the original FID exhibits a sudden minimum at a given temperature, with a slight dependence from the measuring frequency. Computer simulations performed with the software SPINEVOLUTION have shown that the minimum in the efficiency reconstruction of the MSE signal corresponds to the average motional frequency taking a value around the inter-proton coupling. The FID signals have been fitted with a truncated form of a newly derived exact correlation function for the transverse magnetization of a dipolar interacting spin pair, which allows one to avoid the restriction of the stationary and Gaussian approximations. A direct estimate of the conformational dynamics on approaching the T g is obtained, and the results are in agreement with the analysis performed via the MSE reconstruction efficiency. The occurrence of a wide distribution of correlation frequencies for the chains motion, with a Vogel–Fulcher type temperature dependence, is addressed. A route for a fruitful study of the dynamics accompanying the glass transition by a variety of NMR measurements is thus proposed.

Magnetic nanoparticles are promising systems for biomedical applications and in particular for Magnetic Fluid Hyperthermia, a promising therapy that utilizes the heat released by such systems to damage tumor cells. We present an experimental study of the physical properties that influences the capability of heat release, i.e. the Specific Loss Power, SLP, of three biocompatible ferrofluid samples having a magnetic core of maghemite with different core diameter d= 10.2, 14.6 and 19.7 nm. The SLP was measured as a function of frequency f and intensity of the applied alternating magnetic field H, and it turned out to depend on the core diameter, as expected. The results allowed us to highlight experimentally that the physical mechanism responsible for the heating is size-dependent and to establish, at applied constant frequency, the phenomenological functional relationship SLP=cH^x, with 2

Extremely low-frequency electromagnetic fields (ELF-EMFs) applied in magnetotherapy have frequency lower than 100 Hz and magnetic field intensity ranging from 0.1 to 20 mT. For many years, the use of magnetotherapy in clinics has been increasing because of its beneficial effects in many processes, e.g., skin diseases, inflammation and bone disorders. However, the understanding of the microscopic mechanisms governing such processes is still lacking and the results of the studies on the effects of ELF-EMFs are controversial because effects derive from different conditions and from intrinsic responsiveness of different cell types.In the present study, we studied the biological effects of 1.5 h exposure of human dermal fibroblasts to EMFs with frequencies of 5 and 50 Hz and intensity between 0.25 and 1.6 mT. Our data showed that the magnetic treatment did not produce changes in cell viability, but gave evidence of a sizeable decrease in proliferation at 24 h after treatment. In addition, immunofluorescence experiments displayed an increase in tubulin expression that could foreshadow changes in cell motility or morphology. The decrease in proliferation with unchanged viability and increase in tubulin expression could be consistent with the triggering of a transdifferentiation process after the exposure to ELF-EMFs.

We report a systematic experimental study of the evolution of the magnetic and relaxometric properties as a function of metal (Co, Ni) doping in iron oxide nanoparticles. A set of five samples, having the same size and ranging from stoichiometric cobalt ferrite (CoFe2O4) to stoichiometric nickel ferrite (NiFe2O4) with intermediate doping steps, was ad hoc synthesized. Using both DC and AC susceptibility measurements, the evolution of the magnetic anisotropy depending on the doping is qualitatively discussed. In particular, we observed that the height of the magnetic anisotropy barrier is directly proportional to the amount of Co, while the Ni has an opposite effect. By Nuclear Magnetic Resonance Dispersion (NMR-D) experiments, the experimental longitudinal r(1) and transverse r(2) relaxivity profiles were obtained, and the heuristic theory of Roch et al. was used to analyze the data of both r(1) and, for the first time, r(2). While the experimental and fitting results obtained from r(1) profiles were satisfying and confirmed the anisotropy trend, the model applied to r(2) hardly explains the experimental findings. (C) 2016 AIP Publishing LLC.

OBJECT: Use of polyethylenimines (PEIs) of different molecular weight and selected carboxylated-PEI derivatives (PEI-COOH) in the synthesis and stabilization of iron oxide nanoparticles, to obtain possible multifunctional contrast agents. MATERIALS AND METHODS: Oxidation of Fe(II) at slightly elevated pH and temperature resulted in the formation of highly soluble and stable nanocomposites of iron oxides and polymer. Composites were characterized and studied by atomic force microscopy (AFM), transmission electron microscopy (TEM), X-ray diffractometry, AC and DC magnetometry, NMR relaxometry and magnetic resonance imaging (MRI). RESULTS: From AFM the dimensions of the aggregates were found to be in the ~150-250 nm size region; the mean diameter of the magnetic core of the compounds named PEI-25, PEI-500 and PEI-COOH60 resulted d approximately 20 +/- 5 nm for PEI-25, d approximately 9.5 +/- 1.0 nm for PEI-500 and d approximately 6.8 +/- 1.0 nm for PEI-COOH60. In PEI-COOH60 TEM and X-ray diffractometry revealed small assemblies of mineral magnetic cores with clear indications that the main constituents are maghemite and/or magnetite as confirmed by AC and DC SQUID magnetometry. For PEI-COOH60, the study of NMR-dispersion profiles revealed r (1) and r (2) relaxivities comparable to superparamagnetic iron-oxide commercial compounds in the whole investigated frequency range 7 < or = nu < or = 212 MHz. CONCLUSION: PEI-25 was studied as possible MRI contrast agent (CA) to map the cerebral blood volume (CBV) and cerebral blood flow (CBF) in an animal model obtaining promising results. The reported compounds may be further functionalized to afford novel multifunctional systems for biomedical applications.

We present NMR and μ+SR study of spin dynamics in one-dimensional and quasi-one-dimensional molecular magnets of recent synthesis. In particular, we focus on the so called Gd(hfac)3NIT-R and CoPhOMe magnetic chains families. For Gd-R helimagnets we show some differences between “weakly frustrated systems” and “fully frustrated systems”. The different behaviour is due to the different radical inserted in the chains (R = Me, Ph for “weakly frustrated systems” and R = iPr, Et for “fully frustrated systems”). The existence of different phase transitions, particularly to 3D long-range magnetic order in Gd-Ph and to chiral order in Gd-iPr, is remarked together with a comparison between results obtained from macroscopic and microscopic investigating techniques. As regards CoPhOMe slowly relaxing chain, the 1H NMR measurements confirm the freezing of the spins at low temperature, which prevents the 3D long-range order, and display the presence of two relaxation mechanisms related to distinct contributions to the local spin relaxation.

We report experimental and theoretical results on the concentration dependence of the micellar size of GM1 and GM1acetyl gangliosides, five-sugar-headed anionic glycolipids. Contrary to one of the mainstays of colloid science, that the aggregation number of amphiphile aggregates grows with concentration, an anomalous region is found at intermediate concentrations, where a sharp decrease of the aggregation number occurs. Experiments were performed by small-angle X-ray and neutron scattering (SAXS and SANS). Two models are discussed, reproducing the observed behavior of either GM1acetyl or GM1. The first one is a conventional picture of interacting micelles where a reduction in the molecular surface area, leading to an increase of the aggregate dimension, is paid to reduce intermicellar interactions: it foresees a monotonous increase of the aggregation number with concentration. The second one accounts for a conformational bistability of the bulky headgroups of GM1, modifying the amphiphilic molecular surface area and protrusion from the aggregate surface, and contributing to the inter- and intramicellar interaction balance. Energy minimization leads to a complex behavior of the aggregation number, which is consistent with the anomalous behavior of GM1.

On the basis of a method to describe the relaxation dynamics in an ensemble of spin pairs, an analytical expression is derived for the magic sandwich echo refocusing efficiency of 1H-NMR signals from systems where dipolar interaction dominates. At the sake of illustration the method is applied to the analysis of the α-relaxation in poly(butadiene). The Vogel-Fulcher-Tammann behaviour of the central relaxation rates, derived by fitting the refocusing efficiency as a function of the temperature, follows very well independent measurements performed with stimulated echo 2H-NMR experiments. Comparison with literature data worked out by broad band dielectric spectroscopy also shows very good agreement. In the framework of an Havriliak-Negami representation of the distribution of correlation times, information about width and asymmetry of the frequency profile is also provided by the analysis. This novel method is believed to represent a suitable path to extract basic information on the motional distribution in a variety of similar systems.

A simple and effi cient method for synthesizing a range of hybrid nanocomposites based on a core of silica nanospheres (160, 330, and 660 nm in diameter) covered by an outer shell of superparamagnetic nanoparticles, either iron oxide or heterodimeric FePt-iron oxide nanocrystals, is presented. The magnetic and ultrasound characterization of the resulting nanocomposites shows that they have great potential as contrast agents for dual-mode imaging purposes, combining magnetic resonance imaging (MRI) and ultrasonography (US).

The divergences, on cooling, of NMR-NQR relaxation rates and muon spin rotation in underdoped cuprates, until now interpreted in terms of glassy spin freezing of magnetic moments resulting from charge inhomogeneities, are critically reconsidered. The relaxation data are analyzed in the light of the lack of dependence from an external magnetic field, of the strength of the effective field driving the divergences and of the stretched exponential character of the recovery processes. By resorting also to the theoretical conclusions of the extended t-J model including the intersite Coulomb interactions, it is argued that the divergences of the relaxation rates, rather than arising from magnetic moments could be related to sliding motions of vortex-antivortex orbital currents coexisting with d-wave superconducting state.

We report a broadband H-1 NMR study of the spin dynamics of coated maghemite and goldmaghemite hybrid nanostructures with two different geometries, namely dimers and coreshells. All the samples have a superparamagnetic behavior, displaying a blocking temperature (T-B similar to 80 K (maghemite), similar to 105 K (dimer), similar to 150 K (coreshell)), and the magnetization reversal time follows the VogelFulcher law. We observed three different anomalies in H-1 NMR T(1)1 versus T that decrease in amplitude when increasing the applied magnetic field. We suggest that the anomalies are related to three distinct system dynamics: molecular rotations of the organic groups (240 < T < 270 K), superparamagnetic spin blockage (100 < T < 150 K), and surfacecore spin dynamics (T < 25 K). By fitting the T(1)1 data with a heuristic model, we achieved a good agreement with magnetic relaxation data and literature values for methyl group rotation frequencies.

The spin dynamics of the molecular magnetic chain [Dy(hfac)(3){NIT(C6H4OPh)}] were investigated by means of the Muon Spin Relaxation (mu+SR) technique. This system consists of a magnetic lattice of alternating Dy(III) ions and radical spins, and exhibits single-chain-magnet behavior. The magnetic properties of [Dy(hfac)(3){NIT(C6H4OPh)}] have been studied by measuring the magnetization vs. temperature at different applied magnetic fields (H - 5, 3500, and 16500 Oe) and by performing mu+SR experiments vs. temperature in zero field and in a longitudinal applied magnetic field H - 3500 Oe. The muon asymmetry P(t) was fitted by the sum of three components, two stretched-exponential decays with fast and intermediate relaxation times, and a third slow exponential decay. The temperature dependence of the spin dynamics has been determined by analyzing the muon longitudinal relaxation rate lambda(interm)(T), associated with the intermediate relaxing component. The experimental lambda(interm)(T) data were fitted with a corrected phenomenological Bloembergen-Purcell-Pound law by using a distribution of thermally activated correlation times, which average to tau - tau(0) exp(Delta/k(B)T), corresponding to a distribution of energy barriers Delta. The correlation times can be associated with the spin freezing that occurs when the system condenses in the ground state. (C) 2015 AIP Publishing LLC.

89 Y NMR relaxation has been used to study the spin freezing process in Y 1-x Ca x Ba 2 Cu 3 O 6.1. Substituting Ca 2+ for Y 3+ in the parent antiferromagnetic YBa 2 Cu 3 O 6.1 leads the system in the underdoped superconducting phase. In the normal state of the sample at x=0.15 the spin-lattice relaxation rate, which is not affected by the antiferromagnetic correlation of the Cu 2+ magnetic moments, still evidences a decrease of (1/ T 1 T ) on cooling, indicative of a pseudo-gap opening in the density of states around the Fermi energy. The most relevant result is found in the superconducting phase, where the recovery of the 89 Y NMR signal displays two distinct laws, pointing out different relaxation mechanisms without common spin temperature. One exponential recovery law yields a decay rate which decreases on cooling, as expected in the superconducting phase. The second relaxation process turns out to be described by a stretched exponential, with fast relaxation rates, strongly increasing on cooling, with a characteristic spin fluctuations frequency reaching the 20 MHz range at about 8 K. This observation is interpreted as the direct experimental evidence of the coexistence, at mesoscopic level, of superconductive and spin-glass like phases, the spin freezing process being described by the fast rate of the nuclear relaxation.

The anharmonic vibrational dynamics in nearly stoichiometric ${\mathrm{La}}_{2}{\mathrm{CuO}}_{4+\ensuremath{\delta}}$ is studied by means of anelastic and ${}^{139}\mathrm{La}$ NQR relaxation. In the absorption component of the elastic susceptibility as well as in the nuclear relaxation rate a peak is detected as a function of temperature, and a relaxation time $\ensuremath{\tau}=1.7\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}12}\mathrm{exp}[(2800\phantom{\rule{0ex}{0ex}}\mathrm{K})/T]$ s is derived. The relaxation processes are attributed to tilt motion of the ${\mathrm{CuO}}_{6}$ octahedra in double-well potentials, whose cooperative character increases the effective energy barrier to the observed value. The analysis of the relaxation mechanisms has been carried out by reducing the dynamics of the interacting octahedra to a one-dimensional equation of motion. The solitonlike solutions correspond to parallel walls separating domains of different tilt patterns and give rise to pseudodiffusive modes which appear as a central component in the spectral density of the motion of the octahedra. The tilt waves may be considered to correspond to the dynamical lattice stripes observed in La-based and Bi-based high-${T}_{\mathrm{c}}$ superconductors.

The vibrational dynamics in nearly stoichiometric La 2 CuO 4+δ has been studied by means of anelastic relaxation and by 139 La NQR relaxation. Evidence of dynamical tilting of the octahedra in a double well local potential is obtained with both the experimental techniques. Anelastic relaxation shows a peak at T ~ 150 K for a measuring frequency in the kHz region, while the peak in the NQR relaxation at the quadrupole frequency ν Q ~ 19 MHz occurs at T ~ 330 K. The data are analyzed in terms of a model of pseudo-diffusive cooperative motion. The measured effective barrier is 2800 K, higher than the one of the local potential becuase of the cooperative character of the motion. Upon Sr doping the 139 La relaxation is still dominated by the octahedra tilting waves for T >100 K, while allow temperatures the magnetic relaxation mechanism related to Cu 2+ spin fluctuation dominates. It is argued how the freezing of the tilts (occurring below 100 K in the undoped La 2 CuO 4) might correspond to the formation of static stripes.

Advanced nanostructured materials, such as gold nanoparticles, magnetic nanoparticles, and multifunctional materials, are nowadays used in many state-of-the-art biomedical application. However, although the engineering in this field is very advanced, there remain some fundamental problems involving the interaction mechanisms between nanostructures and cells or tissues. Here we show the potential of (1)H NMR in the investigation of the uptake of two different kinds of nanostructures, that is, maghemite and gold nanoparticles, and of a chemotherapy drug (Temozolomide) in glioblastoma tumor cells. The proposed experimental protocol provides a new way to investigate the general problem of cellular uptake for a variety of biocompatible nanostructures and drugs.

The 19 F NMR linewidth and nuclear spin–lattice relaxation rate T 1 −1 has been measured in the temperature interval 4.2–300 K and at different external magnetic fields in an oriented powder of the superconductor YBa 2 Cu 4 O 8 : F ( T c =81 K). It is observed that below T c both the 19 F linewidth and T 1 −1 are affected by the thermal fluctuations of the flux lines demonstrating the possibility of using 19 F nuclei to probe the flux-line dynamics. An anomalous field dependence of both the linewidth and of T 1 −1 is also reported.

The study of thermal motion of flux lines as evidenced in NMR measurements is reviewed in the light of our recent results on the nuclear spin-lattice and spin-spin relaxation rates in anisotropic HT c SC YBa 2 Cu 4 O 8 and HgBa 2 CuO 4+δ

The spin-lattice relaxation time T1, the spin echo dephasing time T2 and the NMR linewidth δv are used to study the spontaneous fluctuations under thermal excitation of the flux lines (FL) in YBa2Cu4O8. It is shown how the relaxation rate T1-1 is sensitive to the fluctuations of the transverse components of the local field at a frequency around ω = γH0, while T2-1 and δv probe the longitudinal components at frequencies smaller by a factor 103-105. Thus, from a combination of T1 T2 andδv measurements one derives microscopic insights on the degree of correlation in the motion of 2D pancakes belonging to adjacent superconducting planes, on the barriers for the pseudo-diffusion of the FL’s and on their field and temperature dependence. 2D NMR spectroscopy can also be used to evidence the diffusion of the FL’s and a comparison between YBa2Cu3O7 (YBCO123) and YBa2Cu48 (YBCO124) is briefly discussed. Finally for temperatures below Tirr(H the evolution of the amplitude of the63Cu NQR echo after sudden application and/or rotation of a magnetic field is used to investigate the FL flow in the critical state.

Encapsulated Fe3O4 nanoparticles of average diameters d = 12 nm are obtained by coprecipitation, in the presence of 2-methoxyethanol hemiester of poly(maleic anhydride-alt-butyl vinyl ether) 5% grafted with poly(ethylene glycol) (VP-MAG nanoparticles). A complete characterization of nude and encapsulated nanoparticles through structural techniques (namely XRD, TEM, SEM), Raman spectroscopy and magnetic measurements has been performed. These nanoparticles compared with commercial compounds (ENDOREM (R)) present superparamagnetic behavior and nuclear relaxivities that make them promising as magnetic resonance imaging (MRI) contrast agents (CAs). We found that our nanostructures exhibit r(2) relaxivity higher than those of commercial CAs over the whole frequency range. The MRI efficiency of our samples was related to their microstructural and magnetic properties.

Measurements of the $^{89}\mathrm{Y}$ NMR linewidth \ensuremath{\Delta}\ensuremath{\nu} and spin-lattice relaxation rate ${\mathit{T}}_{1}^{\mathrm{\ensuremath{-}}1}$ have been performed in an oriented powder sample of ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{4}$${\mathrm{O}}_{8}$ (${\mathit{T}}_{\mathit{c}}$ = 81 K) for both ${\mathbf{H}}_{0}$\ensuremath{\parallel}c and ${\mathbf{H}}_{0}$\ensuremath{\perp}c at ${\mathit{H}}_{0}$ = 9.4 and 5.9 T. Evidence for the effects of thermal motion of flux lines (FL's) below ${\mathit{T}}_{\mathit{c}}$ is presented and the microscopic correlation times of the FL motion are derived by using a simple model. From the temperature and field dependence of ${\mathit{T}}_{1}^{\mathrm{\ensuremath{-}}1}$ an effective correlation time ${\mathrm{\ensuremath{\tau}}}_{\mathit{e}}$ describing the pseudodiffusion of two-dimensional (2D) pancake vortices is extracted. The effective activation energy of the FL motion is found to be inversely proportional to the magnetic field, supporting the similar conclusion recently obtained in ${\mathrm{HgBa}}_{2}$${\mathrm{CuO}}_{4+\mathrm{\ensuremath{\delta}}}$. From the temperature dependence of \ensuremath{\Delta}\ensuremath{\nu} another correlation time \ensuremath{\tau}, different from ${\mathrm{\ensuremath{\tau}}}_{\mathit{e}}$, is obtained. It is argued that the correlation times derived from \ensuremath{\Delta}\ensuremath{\nu} and ${\mathit{T}}_{1}^{\mathrm{\ensuremath{-}}1}$, respectively, refer to different motional regimes below and above the irreversibility temperature ${\mathit{T}}_{\mathrm{irr}}$. \textcopyright{} 1996 The American Physical Society.

{sup 199}Hg NMR spin-lattice relaxation rates in an aligned powder sample of the anisotropic high-{ital T}{sub {ital c}} superconductor HgBa{sub 2}CuO{sub 4+{delta}} ({ital T}{sub {ital c}}=96 K) show anisotropy in the temperature interval 10{endash}50 K, with an extra contribution present for the external magnetic field parallel to the {ital c} axis. The extra contribution shifts with magnetic field in a way related to the irreversibility temperature {ital T}{sub irr}, indicating that the thermal motion of flux lines (FL{close_quote}s) is the cause of the extra relaxation. A simple model is presented to analyze the relaxation data and to extract values for the correlation time {tau}{sub {ital c}} and the effective activation energy {ital U} of the FL motion. {copyright} {ital 1996 The American Physical Society.}

The molecular nanomagnet [LiFe6(OCH3)12(dbm)6]B(C6H5)4⋅5CH2Cl2 (Fe6:Li in short) is formed by six Fe(III) s=5/2 spins arranged in an almost coplanar ring with antiferromagnetic (AFM) nearest-neighbor coupling constant J/kB∼20 K. We report 7Li nuclear magnetic resonance (NMR) spectra and nuclear spin-lattice relaxation rate (NSLR) measurements as a function of temperature from 1.5 to 50 K with applied field H=1.5 T. No evidence of quadrupole effects was found on the 7Li NMR spectrum within the linewidth resolution (∼25 kHz) ruling against a molecular distortion. The 7Li NSLR is compared with the 1H NSLR results in Fe6:Li and in other AFM rings.

{sup 35}Cl nuclear spin-lattice relaxation rate (NSLR) and magnetic susceptibility ({chi}) measurements are reported for Sr{sub 2}CuO{sub 2}Cl{sub 2} single crystals as functions of temperature and of magnetic field intensity and orientation. From the anisotropy of the {sup 35}Cl NSLR and {chi} we obtained evidence for a crossover of the Cu{sup 2+} spin correlations from Heisenberg to {ital XY}-like at {ital T}{approx}290 K. For H{parallel}{ital c} the 3D antiferromagnetic transition is at {ital T}{sub {ital N}}=257 K and is field independent while for H{parallel}{ital ab} {ital T}{sub {ital N}} increases to 265 K at {ital H}=8.2 T. The field-dependent {ital T}{sub {ital N}} for H{parallel}{ital ab} is explained by a field-induced Ising-like anisotropy in the {ital ab} plane.

The low temperature NMR investigation of Mn(hfac)2NITiPr, a one-dimensional ferrimagnet formed by manganese(II), spin S = 5/2, and nitronyl nitroxide NITiPr, spin S = 1/2, is reported. The main feature observed is a field dependent maximum in the 1H longitudinal relaxation rate. These data are explained assuming nonlinear excitations, like 2π sine-Gordon solitons. The theoretical modelling for solitons in 1D ferrimagnets is outlined. This is the first report of soliton spin dynamics in one-dimensional ferrimagnets.

$^{139}\mathrm{La}$ NQR and zero-field ${\mathrm{\ensuremath{\mu}}}^{+}$SR in antiferromagnetic (AF) ${\mathrm{La}}_{2}$${\mathrm{Cu}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Zn}}_{\mathit{x}}$${\mathrm{O}}_{4}$, for x up to 0.13 and in the temperature range 1.6--350 K, are used to study the effects related to the substitution of magnetic ${\mathrm{Cu}}^{2+}$ S=1/2 with homovalent diamagnetic S=0 ${\mathrm{Zn}}^{2+}$ in ${\mathrm{La}}_{2}$${\mathrm{CuO}}_{4}$. We report measurements both of static magnetic properties, such as N\'eel temperatures ${\mathit{T}}_{\mathit{N}}$, sublattice magnetization and field \ensuremath{\Vert}h\ensuremath{\Vert} at the La nucleus or at the ${\mathrm{\ensuremath{\mu}}}^{+}$ site, as well as of NQR relaxation rates W. These quantities are used to study the effects of Zn doping on the low-energy ${\mathrm{Cu}}^{2+}$ spin excitations. It is found that ${\mathit{T}}_{\mathit{N}}$ decreases with x in a way close to the one expected by diluting quasi-two-dimensional Heisenberg magnets on square lattice, while the sublattice magnetization is slightly affected by Zn doping. Mean-field arguments based on the dilution model for the interplanar interactions allow one to conclude that the in-plane magnetic correlation length is little sensitive to the Zn presence. Up to x\ensuremath{\simeq}0.08 the temperature dependence of the AF field \ensuremath{\Vert}h\ensuremath{\Vert} is close to the one in pure ${\mathrm{La}}_{2}$${\mathrm{CuO}}_{4}$, with a sharp decrease for T\ensuremath{\rightarrow}${\mathit{T}}_{\mathit{N}}^{\mathrm{\ensuremath{-}}}$ indicative of a continuous transition with a small critical exponent \ensuremath{\beta}.For strong doping the low-temperature dependence of \ensuremath{\Vert}h\ensuremath{\Vert} appears to depart from the one in pure ${\mathrm{La}}_{2}$${\mathrm{CuO}}_{4}$. For x\ensuremath{\ge}0.05 both NQR spectra and \ensuremath{\mu}SR reveal the presence of regions where the long-range AF order is suppressed. For temperature above 100 K up to ${\mathit{T}}_{\mathit{N}}$ the $^{139}\mathrm{La}$ relaxation rate W due to the ${\mathrm{Cu}}^{2+}$ spin fluctuations shows only slight corrections with respect to pure ${\mathrm{La}}_{2}$${\mathrm{CuO}}_{4}$ which are possibly related to the disorder in the AF interactions or to finite-size effects. A novel and remarkable effect of Zn doping is the appearance in W, for T\ensuremath{\le}100 K, of large and marked maxima, which are x dependent. This phenomenon is attributed to the cooperative freezing of local magnetic moments induced by Zn on Cu orbitals, interacting via the underlying AF matrix. The maxima in W occur when the fluctuation frequencies of the anomalous spins become of the order of the NQR frequency, thus driving the system to a spin-glass state superimposed to the AF matrix.

The motion of the flux lines (FL) in high temperature superconductors and their relationship with the NMR quantities are reviewed and discussed in the light of recent89Y NMR experiments in YBCO-type compounds. In particular measurements involving the89Y spin echo attenuation induced both by the thermal excitation of the FL’s and by motions driven by DC current and pulsed magnetic fields are presented, with preliminary results and lines of interpretation. Flux line motion as observed with199Hg NMR in HgBa2CuO4+δ high temperature superconductor is discussed.

One dimensional (1)H NMR measurements have been performed to probe slow molecular motions in nitrile butadiene rubber (NBR) around its calorimetric glass transition temperature Tg. The purpose is to show how software aided data analysis can extract meaningful dynamical data from these measurements. Spin-lattice relaxation time, free induction decay (FID) and magic sandwich echo (MSE) measurements have been carried out at different values of the static field, as a function of temperature. It has been evidenced how the efficiency of the MSE signal in reconstructing the original FID exhibits a sudden minimum at a given temperature, with a slight dependence from the measuring frequency. Computer simulations performed with the software SPINEVOLUTION have shown that the minimum in the efficiency reconstruction of the MSE signal corresponds to the average motional frequency taking a value around the inter-proton coupling. The FID signals have been fitted with a truncated form of a newly derived exact correlation function for the transverse magnetization of a dipolar interacting spin pair, which allows one to avoid the restriction of the stationary and Gaussian approximations. A direct estimate of the conformational dynamics on approaching the Tg is obtained, and the results are in agreement with the analysis performed via the MSE reconstruction efficiency. The occurrence of a wide distribution of correlation frequencies for the chains motion, with a Vogel-Fulcher type temperature dependence, is addressed. A route for a fruitful study of the dynamics accompanying the glass transition by a variety of NMR measurements is thus proposed.

Glioblastoma multiforme, the most common type of primary brain tumour, remains an unsolved clinical problem. A great deal of work has been done in an effort to understand the biology and genetics of glioblastoma multiforme, but clinically effective treatments remain elusive. It is well known that malignant gliomas develop resistance to chemo- and radiotherapy. In this review we evaluated the literature data regarding therapeutic progress for the treatment of astrocytic tumours, focusing our attention on new frontiers for glioblastoma. The research studies performed in in vitro and in vivo models show that the application of hyperthermia using magnetic nanoparticles is safe and could be a promising tool in the treatment of glioblastoma patients. Our efforts are focused towards new fields of research, for example nanomedicine and the study of the uptake and cytotoxic effects of magnetic nanoparticles. The improvement of the quality of life of patients, by increasing their survival rate is the best result to be pursued, since these tumours are considered as ineradicable.

We present the magnetic, optical and relaxometric properties of multifunctional Au-Fe3O4 hybrid nanoparticles (HNPs), as possible novel contrast agents (CAs) for magnetic resonance imaging (MRI). The HNPs have been synthesized by wet chemical methods in heterodimer and core-shell geometries and capped with oleylamine. Structural characterization of the samples have been made by X-ray diffraction and transmission electron microscopy, while magnetic properties have been investigated by means of Superconducting Quantum Interference Device-SQUID magnetometry experiments. As required for MRI applications using negative CAs, the samples resulted superparamagnetic at room temperature and well above their blocking temperatures. Optical properties have been investigated by analyzing the optical absorbtion spectra collected in UV-visible region. Relaxometric measurements have been performed on organic suspensions of HNPs and Nuclear Magnetic Resonance (NMR) dispersion curves have been obtained by measuring the longitudinal 1/T-1 and transverse 1/T-2 relaxation rates of solvent protons in the range 10 kHz1300 MHz at room temperature. NMR relaxivities r(1) and r(2) have been compared with ENDOREM (R), one of the commercial superparamagnetic iron oxide based MRI contrast agents. MRI contrast enhancement efficiencies have been investigated also by examining T-2-weighted MR images of suspensions. The experimental results suggest that the nanoparticles' suspensions are good candidates as negative CAs. (C) 2012 Elsevier B.V. All rights reserved.

139La NQR spectra, μSR precessional frequencies and NQR relaxation rates W driven by the Cu2+ spin fluctuations are used to study the static magnetic properties and the low-energy spin excitations upon substitution of Zn2+ (S=0) for Cu2+ (S=1/2) in the antiferromagnetic (AF) phases of La2 Cu1−xZnxO4. It is found that the Neel temperatures TN decrease with x almost linearly, with initial suppression rate close to 4, while the sublttice magnetization is only slightly affected, close to the behaviour expected for a 2D S=1/2 Heisenberg AF in the framework of dilution model. Also the spin wave spectrum appears slightly affected by Zn doping, with moderate effects possibly related to disorder in the AF interactions and/or to finite size. A novel and remarkable effect is observed for T≤100 K. The relaxation rates W show large maxima, with x-dependent Wmax and Tmax. This phenomenon is attributed to the cooperative freezing of local magnetic moments induced by Zn on Cu orbitals. Information on the characteristic fluctuation frequencies and on the spin-glass state superimposed to the AF matrix are thus obtained.

An overview on some works recently carried out by means of pulsed NMR-NQR experiments is given. The choice of the arguments is aimed at providing a flash on the topics and phenomena most tipically studied with the afore-mentioned approach: from the antiferromagnets (AF) precursors of high-temperature superconductors upon charge and spin doping (such as CuO-doped Li, La2CuO4-doped Sr and Zn) to the doping regime leading to superconductivity in LASCO and YBCO with the related issues involving the comparison with the Fermi-liquid behaviour, the possible opening of a pseudo-spin-gap above Tc and the anisotropy and field effect ratios below Tc, the latter also in relation to the s-wave or d-wave orbital coupling. Finally, the topic of the motions of the flux lines in YBCO is addressed, in particular by discussing some experiments based on spin-echo dephasing due to thermal excitations and in the presence of d.c. currents and pulsed magnetic fields.

Glucosidic surfactants play an important role in living matter. An interesting class of them are the gangliosides which have a double-tail hydrophobic part, like phospholipids, and a ramified oligosaccharide chain as polar head. The large hydrophobic moiety ensures very low CMC values, of the order of 10−8 M. Phospholipids have a small head group compared with their hydrophobic part. Therefore they form mainly bilayer-type structures in water. Gangliosides, instead, may form either micelles or bilayers depending on the length and conformation of the oligosaccharide chain. For long chains, micelles are formed with a large aggregation number and a long lifetime (many hours), while vesicles are found for short sugar chains. The presence of a large head group makes vesicle mechanical properties rather peculiar. For instance, the ganglioside GM3, which has the longest sugar chain compatible with bilayer-type structures, forms vesicles spontaneously in solution without supply of external energy. This means that the bending rigidity of the GM3 bilayer is very low, allowing very large thermal undulations. GM3 vesicles, made of a single surfactant, are then found to be in thermodynamic equilibrium with a small amount of large bilayer and multilamellar structures. Frustration of the single-component vesicle system is released if a second amphiphile, of the same type of the ganglioside GM3 but with a larger head group, is added. In this case, spontaneous-curvature readjustements of the two monolayers via demixing can give rise to a spontaneous curvature of the bilayer, energetically favouring vesicles over other structures. It is, in fact, observed experimentally that by adding increasing proportions of GM1 the large aggregates gradually diminish in number, until a pure vesicle solution is obtained for a GM1 to GM3 ratio of 35 to 65.

Micellar solutions of the ganglioside GM1 are studied as a function of temperature in the concentration range 0.003-0.30 g cm-3 in water with light and X-ray scattering. In a narrow temperature range around 50 degrees C, the micelles decrease their aggregation number from 300 to 235. The solution structuring, which is due to the electrostatic interactions among micelles, is found to be strongly affected by the micellar change. For instance, at high concentration the isotropic micellar solution at 25 degrees C transforms into a primitive cubic phase at 60 degrees C.

We report the investigation of new organic complexes containing a magnetic moment (Gd-based molecular nanomagnets), which can serve the double purpose of acting as boron neutron capture therapy (BNCT) agents, and at the same time act as contrast agents to detect the molecule in the tissue by a proton magnetic resonance imaging (MRI). We also explore the possibility of monitoring the concentration of the BNCT agent directly via proton and boron NMR relaxation. The absorption of 10B-enriched molecules inside tumoral liver tissues has been shown by NMR measurements and confirmed by α spectroscopy. A new molecular Gd-tagged nanomagnet and BNCT agent (GdBPA) has been synthesized and characterized measuring its relaxivity R1 between 10 kHz and 66 MHz, and its use as a contrast agent in MRI has been demonstrated. The NMR-based evidence of the absorption of GdBPA into living tumoral cells is also shown.

(10)B molecular compounds suitable for Boron Neutron Capture Therapy (BNCT) are tagged with a Gd(III) paramagnetic ion. The newly synthesized molecule, Gd-BPA, is investigated as contrast agent in Magnetic Resonance Imaging (MRI) with the final aim of mapping the boron distribution in tissues. Preliminary Nuclear Magnetic Resonance (NMR) measurements, which include (1)H and (10)B relaxometry in animal tissues, proton relaxivity of the paramagnetic Gd-BPA molecule in water and its absorption in tumoral living cells, are reported.

A series of maghemite/polymer composite ferrofluids with variable magnetic core size, which show a good efficiency as MRI contrast agents, are presented. These ferrofluids are biocompatible and can be proposed as possible platforms for multifunctional biomedical applications, as they contain anchoring groups for biofunctionalization, can incorporate fluorescent dyes, and have shown low cellular toxicity. The magnetic properties of the ferrofluids have been determined by means of magnetization and ac susceptibility measurements as a function of temperature and frequency. The NMR dispersion profiles show that the low frequency behavior of the longitudinal relaxivity r1 is well described by the heuristic model of 1H nuclear relaxation induced by superparamagnetic nanoparticles proposed by Roch and co-workers. The contrast efficiency parameter, i.e., the nuclear transverse relaxivity r2, for samples with d > 10 nm assumes values comparable with or better than the ones of commercial samples, the best results obtained in particles with the biggest magnetic core, d = 15 nm. The contrast efficiency results are confirmed by in vitro MRI experiments at ν = 8.5 MHz, thus allowing us to propose a set of optimal microstructural parameters for multifunctional ferrofluids to be used in MRI medical diagnosis. Copyright © 2011 Wiley Periodicals, Inc., R. Bustamante would like to thank ICMA-CSIC for the JAE-predoc grant. N.J.O.S. acknowledges FCT for Ciencia 2008 program.

From a combination of NQR, NMR and AFNMR spectra in Cu1-xLixO information on the electric and magnetic electron-nucleus interactions is obtained. In particular, it is argued that Li+ enters the CuO lattice up to x approximately=4%, with a relatively small effect on the Neel temperature TN. 63Cu NQR and AFNMR, and 7Li NMR spin-lattice relaxation measurements are used to study the spin dynamics in the paramagnetic (PA) and in the antiferromagnetic (AF) phase and the effects associated with the creation of holes upon lithium doping. The Li doping modifies in a dramatic way the spin fluctuations in the AF phase. These effects are related to the fluctuations in the local Cu2+ spin configuration due to the diffusional motion of the extra holes in the electronic bands. A satisfactory explanation of the temperature and frequency dependences of Li relaxation rates is given in terms of a correlation time tau h for the hole motion controlled by an energy gap E(x) and quantitative information on tau h and E(x) are thus derived.

[sup 63]Cu nuclear quadrupole resonance (NQR), nuclear antiferromagnetic resonance (AFNMR), and spin-lattice relaxation, as well as [sup 7]Li NMR and relaxation measurements in CuO and in Cu[sub 1[minus][ital x]]Li[sub [ital x]]O, are used to study the spin dynamics in the paramagnetic and in the antiferromagnetic (AF) phase, and in particular the effects induced by lithium doping. It is argued that Li enters in CuO lattice up to a doping [ital x] around 4%; from a comparison of the electric-field gradient (EFG) and of the dipolar field at the nucleus with theoretical estimates, it appears that Li[sup +] is slightly displaced from the Cu lattice site. From NQR, NMR, and AFNMR spectra, information on the Cu hyperfine interaction and the EFG are derived. The Neel temperature [ital T][sub [ital N]] is affected by Li doping to a moderate extent, decreasing from 226 K in CuO to [ital T][sub [ital N]]=183 K for [ital x]=3.7%. The relaxation rates, driven by the time-dependent part of the magnetic electron-nucleus Hamiltonians, indicate that the Cu[sup 2+] spin dynamics is almost unaffected by Li doping for [ital T][much gt][ital T][sub [ital N]] and possibly controlled by valence fluctuations. The Li doping modifies in a dramatic waymore » the spin fluctuations in the AF phase.« less

85,87 Rb NMR spectra and relaxation are reported in the temperature range 4–300 K, for samples of C 60 intercalated with Rb through a direct-reaction technique at the nominal composition Rb 3 C 60 . The NMR spectrum is characteristic of the second-order quadrupole powder distribution of the central line, indicating a local non-cubic symmetry at the Rb site and a very small Knight shift. The relaxation rate is found to follow a T 2 law above 30 K. This result, together with the ratio of the relaxation for the two Rb isotopes, points towards a quadrupole relaxation mechanism by phonons. Two contributions were found in the nuclear magnetization recovery which have been attributed to the Rb nuclei in the tetrahedral site and in the octahedral site, respectively, with the nucleus in the T-site coupled more strongly to the lattice dynamics. No detectable change in the NMR spectrum and/or relaxation rates was found at the superconducting transition located at T c = 27.5 K.

NQR-NMR relaxation measurements in Cu 1-x Li x O and La 2-x Sr x CuO 4 (for x

We study the phonon-induced relaxation dynamics in the heterometallic ${\text{Cr}}_{7}\text{Ni}$ ring. By assuming that spin-phonon coupling occurs through the modulation of local crystal fields, we investigate the decay of time correlations of molecular observables, such as fluctuations of the cluster magnetization. Single-crystal $^{1}\text{H}$ nuclear magnetic resonance measurements have been performed for two orthogonal orientations of the applied magnetic field. The nuclear spin-lattice relaxation rate $1/{T}_{1}$ probes fluctuations of specific molecular observables, thus allowing to determine the magnetoelastic coupling strength and to calculate the magnetization relaxation time as well as phonon-induced level lifetimes. The knowledge of these time scales is crucial to control the spin dynamics of the magnetic cluster in view of the potential technological applications.