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We present a comparative study on superparamagnetic uncoated and silica-coated NiFe2O4@SiO2 nanoparticles with identical NiFe2O4 cores and two different silica coating thicknesses, focusing on the surface spin arrangement on NiFe2O4. For the investigation of surface spin dynamics, in addition to the SQUID magnetometry experiments which probe the macroscopic behaviour of particle magnetization, Mossbauer spectroscopy was utilized as being a local technique with superior characteristic measurement time. It was revealed that two common aspects observed in nanoscaled magnetic particles, namely the surface spin canting and interparticle dipolar interactions, are intertwined with respect to their contributions to the total magnetic anisotropy, where the latter is significantly decreased with silica coating thickness and allowed surface effects to manifest itself in Mossbauer spectra. The reduced saturation magnetization of uncoated NiFe2O4 nanoparticles with respect to their bulk counterparts indicated the existence of a magnetically dead layer on NiFe2O4 surface. In opposite to some assumptions in the literature, the Mossbauer spectra confirmed that such reduced magnetization arises from spin disorder, rather than a change in coordination from inverse spinel to the mixed spinel structure. On the other side, emergence of broad sextet peaks at room temperature Mossbauer spectra showed that for NiFe2O4@SiO2 samples, silica coating further enhanced the spin canting on NiFe2O4 surface. Similarly, for NiFe2O4@SiO2 sample, an unusual asymmetric hysteresis loop at spin freezing temperature was observed as a signature of the existence of disordered spins in the SiO2/NiFe2O4 interface. It was shown that the sextet components in Mossbauer spectra can be reproduced with a continuous hyperfine field distribution due to the frustrated local spin arrangement at the surface. The thickness of the magnetically dead disordered surface spin layer was estimated for uncoated NiFe2O4, and average spin canting angle was calculated for NiFe2O4@SiO2 nanoparticles. WOS:000607962400001 2-s2.0-85100149449

Hyaluronic acid (HA) was crosslinked with Gd(III) and Fe(III) ions rendering physically crosslinked HA-metal(III) microgels as magnetic resonance imaging (MRI) enhancing contrast agents. These HA-Gd(III) and HA-Fe(III) microgels are injectable with size range, 50–5000 nm in water. The same isoelectric point, pH 1.2 ± 0.1, was measured for both microgels. HA-Gd(III) and HA-Fe(III) microgels are hemo-compatible biomaterials and can be safely used in intravascular applications up to 1000 μg/mL concentration. Furthermore, no significant toxicity was attained as 95 ± 8 and 81 ± 2% cell viability on L929 fibroblast cells at 100 μg/mL of HA-Gd(III) and HA-Fe(III) microgels were measured. Moreover, HA-Gd(III) microgels were found to afford significant contrast improvement capability in MRI with proton relaxivity, r1 = 2.11 mM−1 s−1, comparable with the values reported for Gd(III) labeled functionalized HA gel systems and commercial Gd based contrast agents.

Superparamagnetic nanosized particles, whose surfaces are functionalized with several site-specific polymers, ligands, peptides and antibodies are used as sorbent materials in the isolation of analytes from a variety of solution matrices by exerting a magnetic force with an application; the so-called magnetic solid phase extraction (MSPE). In the two decades since the first application of MPSE, various experimental strategies have been introduced employing numerous combinations of MNPs (transition metals such as Fe, Ni, Co; metal oxides MFe2O4 with M: Mn, Zn, Ni, Co and metallic alloys like FePt, and CoPt) with very different types of coating materials such as octadecylsilane, layered double hydroxide, β-cyclodextrine, carbonaceous nanomaterials (like graphene, graphene oxide and carbon nanotubes), dendrimers, molecularly imprinted polymers, ionic liquids and metal organic frameworks. In this review, the most common approaches and recent advances in MSPE applications will be summarized within the perspective of how the application efficiency depends on the physico-chemical and surface properties of MNPs.

International audience; Sn‐based alloys are increasingly investigated owing to possible electronic/structural modulations of interest for electrocatalysis and energy storage applications. Here, we report on the use of a chemical system consisting of an ionic liquid (1‐ethyl‐3‐ methylimidazolium bis(trifluoromethanesulfonyl)imide: [EMIm+][TFSI−]) and Sn‐based precursor Sn(TFSI)2 both featuring similar anionic groups. This strategy increases the solubility of the cationic precursor in the IL and avoids the formation of side‐products during the precipitation of Sn‐nanoparticles formed upon reaction with a reducing agent (NaBH4). Using NMR relaxometry, we further established that these nanoparticles are stabilized by specific interactions with the cationic group of the IL. Targeting the composition Cu6Sn5, we further demonstrated that this approach can be used to prepare Sn‐based alloys which could not be prepared using conventional chloride‐based precursors.

1H spin–lattice relaxation studies of water solutions of Bismuth-ethylenediamine-tetraacetic acid (Bi- EDTA), Bismuth-ethylenediamine-tetrakis(methylenephosphonic) acid (Bi-EDTP), Bismuth-1,4,7,10- tetraazacyclododecane-1,4,7,10-tetraacetic acid (Bi-DOTA), Bismuth-1,4,7,10-tetraazacyclodo decane-1,4,7,10-tetrakis(methylenephosphonic acid) (Bi-DOTP) and Bismuth-1,4,7,10-tetraazacyclo dodecane-1,4,7-triacetic acid (Bi-DO3A) have been performed in order to compare Quadrupole Relaxation Enhancement (QRE) effects with Paramagnetic Relaxation Enhancement (PRE) from the perspective of exploiting the first one as a novel contrast mechanism for Magnetic Resonance Imag- ing (MRI). The selected compounds can be considered as 209Bi counterparts of Gd3+ complexes. The relaxation experiments havebeenperformed in a broad frequency range of5 kHz–30 MHz.Therelax- ation contribution associated with QRE has been extracted from the data and compared with PRE. Similarities and differences between the two effects have been discussed.

H-1 spin-lattice relaxation experiments have been performed for triphenylbismuth dissolved in fully deuterated glycerol and tetrahydrofuran. The experiments have been carried out in a broad frequency range, from 10kHz to 40MHz, versus temperature. The data have been analysed in terms of a relaxation model including two relaxation pathways: H-1-H-1 dipole-dipole interactions between intrinsic protons of triphenylbismuth molecule and H-1-H-2 dipole-dipole interactions between the solvent and solute molecules. As a result of the analysis, rotational correlation times of triphenylbismuth molecules in the solutions and relative translational diffusion coefficient between the solvent and solute molecules have been determined. Moreover, the role of the intramolecular H-1-H-1 relaxation contribution has been revealed, depending on the motional parameters, as a result of decomposing the overall relaxation dispersion profile into contributions associated with the H-1-H-1 and H-1-H-2 relaxation pathways. The possibility of accessing the contribution of the relaxation of the intrinsic protons is important from the perspective of exploiting Quadrupole Relaxation Enhancement effects as possible contrast mechanisms for Magnetic Resonance Imaging.

Contrast agents with a strong R-1 dispersion have been shown to be effective in generating target-specific contrast in MRI. The utilization of this R-1 field dependence requires the adaptation of an MRI scanner for fast field-cycling (FFC). Here, we present the first implementation and validation of FFC-MRI at a clinical field strength of 3 T. A field-cycling range of +/- 100 mT around the nominal Bo field was realized by inserting an additional insert coil into an otherwise conventional MRI system. System validation was successfully performed with selected iron oxide magnetic nanoparticles and comparison to FFC-NMR relaxometry measurements. Furthermore, we show proof-of-principle R-1 dispersion imaging and demonstrate the capability of generating R-1 dispersion contrast at high field with suppressed background signal. With the presented ready-to-use hardware setup it is possible to investigate MRI contrast agents with a strong R-1 dispersion at a field strength of 3 T. (C) 2018 Elsevier Inc. All rights reserved.

We demonstrate magnetic resonance imaging (MRI) contrast enhancement and ac-field induced heating abilities of tetramethylammoniumhydroxide (TMAH) coated nickel ferrite (NiFe2O4) nanoparticles and discuss the underlying physical mechanisms. The structural characterization revealed that the NiFe2O4 particles synthesized with a modified co-precipitation method have a very narrow size distribution with a 4.4 nm magnetic core and 15 nm hydrodynamic diameters, with relatively small fraction of agglomerates. The as-prepared particles presented superparamagnetic behavior at room temperature. The in vitro hyperthermia experiments, performed in ac-field conditions under human tolerable limits, showed that the suspensions of the synthesized nanoparticles exhibit a maximum specific absorption rate (SAR) value of 11 W/g. The H-1 nuclear magnetic resonance (NMR) relaxometry measurements indicated the suspensions of NiFe2O4 have a transverse-to-longitudinal relaxivity ratio r(2)/r(1) greater than two, as required for superparamagnetic MRI contrast agents. On the basis of the parameters obtained from the magnetic measurements, by comparing the relevant theoretical models with the experimental results, we found that the presence of agglomerates, and particularly the interactions within the agglomerated nanoparticles, caused a significant increase in the hyperthermia and MRI efficiencies. On the other hand, from an applicative point of view, both the MRI contrast enhancement and the heating capabilities allow the simultaneous use of nickelferrites in diagnostic and therapeutic applications as theranostic agents. (C) 2019 Elsevier Inc. All rights reserved. University of Pisa through Progetti di Ricerca di Ateneo [PRA_2017_25] Prof. Alessandro Lascialfari (University of Pavia, Italy) is gratefully acknowledged for organizing the SQUID and NMRD measurements and for their valuable contributions. We also thank Prof. Tezer Flrat for the preparation of the hyperthermia experiment setup, measurements, and valuable discussions. Financial support from the University of Pisa through Progetti di Ricerca di Ateneo (grant PRA_2017_25). WOS:000469902400020 2-s2.0-85065141943 PubMed: 31075674

Magnetic Resonance Imaging (MRI) is one of the most powerful diagnostic tools providing maps of 1H relaxation times of human body. The method needs, however, a contrast mechanism to enlarge the difference in the relaxation times between healthy and pathological tissues. In this work we discuss the potential of a novel contrast mechanism for MRI, based on Quadrupole Relaxation Enhancement (QRE) and estimate the achievable value of QRE under the most favorable conditions. It has turned out that the theoreticaly possible enhancement factors are smaller than those of typical paramagnetic contrast agents but in turn the field-selectivity of QRE-based agents makes them extremely sensitive to subtle changes of the electric field gradient in the tissue. So far QRE has been observed for solids (in most cases for 14N) as a result of very slow dynamics and anisotropic spin interactions, believed to be necessary for QRE to appear. We show the first evidence that QRE can be achieved in solutions of compounds containing a high spin nucleus (209Bi) as the quadrupole element. The finding of QRE in liquid state is explained in terms of spin relaxation theory based on the stochastic Liouville equation. The results confirm the relaxation theory and motivate further exploration of the potential of QRE for MRI., The original publication can be found at: https://doi.org/10.1063/1.5082177

H-1 spin-lattice nuclear magnetic resonance relaxation experiments have been performed for triphenylbismuth dichloride (C18H15BiCl2) and phenylbismuth dichloride (C6H5BiCl2) in powder. The frequency range of 20-128 MHz has been covered. Due to H-1-Bi-209 dipole-dipole interactions, a rich set of pronounced Quadrupole Relaxation Enhancement (QRE) peaks (quadrupole peaks) has been observed. The QRE patterns for both compounds have been explained in terms of single- and double-quantum transitions of the participating nuclei. The analysis has revealed a complex, quantum-mechanical mechanism of the QRE effects. The mechanism goes far beyond the simple explanation of the existence of three quadrupole peaks for N-14 reported in literature. The analysis has been supported by nuclear quadrupole resonance results that independently provided the Bi-209 quadrupole parameters (amplitude of the quadrupole coupling constant and asymmetry parameter).

1H spin-lattice relaxation studies have been performed for pure [Bi(NO3)3(H2O)3]*18-crown-6 in powder and its solution in dimethyl sulfoxide (DMSO). The experiments have been carried out in the frequency range of 10 kHz–30MHz and the temperature range of 240–277 K; at 277 K the solution is already frozen. The 1Hrelaxation of pure [Bi(NO3)3(H2O)3]*18-crown-6 has been interpreted in terms of three dynamical processes. Quadrupole Relaxation Enhancement effects have been observed in the frozen DMSO solution of [Bi(NO3)3(H2O)3]*18-crown-6. The specific mechanisms of the 1H spin- lattice relaxation enhancement have been discussed distinguishing between effects caused by time independent (residual) and fluctuating 1H-209Bi dipole-dipole interactions.

Polystyrene/graphene nanoplatelets (PS/GNP) and polystyrene/multi-walled carbon nanotube (PS/MWCNT) nanocomposites were prepared through solution mixing processing. The effect of carbon filler (CF) (GNP or MWCNT) doping on the DC/AC electrical conductivity, dielectric characteristics and optical parameters (absorption coefficient, α and band gap energy, Eg) of nanocomposites were investigated and compared for similar doping concentrations. The observed behavior of the DC surface conductivity for PS/CF nanocomposites was explained according to the classical percolation theory, where the percolation thresholds (ϕc) for PS/GNP and PS/MWCNT nanocomposites were determined as 12.0 vol% and 3.81 vol% and the critical exponents (t) were calculated as 2.19 and 2.13, respectively. These results indicate that CFs create three dimensional CF network in PS matrix. The dielectric relaxation properties and the AC conductivity studied by means of Broadband Dielectric Spectroscopy (BDS) measurements, showed that the presence of carbon fillers significantly enhanced the capacitive/charge storage capabilities of the nanocomposites. The optical band gap energies (Eg) of PS/GNP and PS/MWCNT nanocomposites were obtained by using Tauc method. From applicative point of view, with their enhanced dielectric and AC conductivity properties of the PS/GNP and PS/MWCNT nanocomposites have the potential to be used in energy storage and electromagnetic interference (EMI) shielding applications.

We propose a simple method to calculate and predict quadrupole relaxation enhancement (QRE) features in the spin-lattice nuclear magnetic relaxation dispersion (R1-NMRD) profile of protons (1H) in solids. The only requirement is the knowledge of the nuclear quadrupole resonance (NQR) parameters of the quadrupole nuclei in a molecule. These NQR parameters – the quadrupole coupling constant Qcc and the asymmetry parameter η – can be determined by NQR spectroscopy or using quantum chemistry calculations. As there is an increasing interest in using molecules producing high field QRE features as, e.g. for contrast enhancing agents in magnetic resonance imaging, the experimental efforts of seeking for suitable compounds can be reduced by pre-selecting molecules via calculations. Also, the method can be used to extract NQR parameter, and thus structural information, from R1-NMRD profiles showing QRE features. In this article, we describe the calculation procedure and present examples of comparing the result to experimental R1-NMRD data of two different solid 209Bi-aryl compounds.

Nuclear Quadrupole Resonance (NQR) experiments were performed for deuterated and non-deuterated triphenylbismuth (BiPh3) to inquire into 209Bi relaxation mechanisms. The studies are motivated by the idea of exploiting Quadrupole Relaxation Enhancement (QRE) as a novel contrast mechanism for Magnetic Resonance Imaging. From this perspective relaxation features of nuclei possessing quadrupole moment (quadrupole nuclei) are of primary importance for the contrast effect. Spin-spin relaxation rates associated with the NQR lines were described in terms of the Redfield relaxation theory assuming that the relaxation is caused by fluctuations of the electric field gradient tensor at the position of the quadrupole nucleus that are described by an exponential correlation function. The description referred to as a model-free approach is an analogy of the description used for paramagnetic contrast agents. It was demonstrated that for the deuterated compound this approach captures the essential features of 209Bi relaxation, but it should not be applied for non-deuterated compounds as dipolar interactions between neighbouring protons and the quadrupole nucleus considerably contribute to the relaxation of the last one. Thus, the relaxation scenario for species containing quadrupole nuclei is fundamentally different than for paramagnetic contrast agents and this fact has to be taken into account when predicting contrast effects based on QRE.&nbsp

1H spin-lattice relaxation experiments have been performed for triphenylbismuth dissolved in fully deuterated glycerol and tetrahydrofuran. The experiments have been carried out in a broad frequency range, from 10kHz-40MHz, versus temperature. The data have been analyzed in terms of a relaxation model including two relaxation pathways: 1H-1H dipole-dipole interactions between intrinsic protons of triphenylbismuth molecule and 1H-2H dipole-dipole interactions between the solvent and solute molecules. As a result of the analysis, rotational correlation times of triphenylbismuth molecules in the solutions and relative translational diffusion coefficient between the solvent and solute molecules have been determined. Moreover, the role of the intramolecular 1H-1H relaxation contribution has been revealed, depending on the motional parameters, as a result of decomposing the overall relaxation dispersion profile into contributions associated with the 1H-1H and 1H-2H relaxation pathways. The possibility of accessing the contribution of the relaxation of the intrinsic protons is important from the perspective of exploiting Quadrupole Relaxation Enhancement effects as a possible contrast mechanisms for Magnetic Resonance Imaging.

The interaction between water protons and suitable quadrupolar nuclei (QN) can lead to quadrupole relaxation enhancement (QRE) of proton spins, provided the resonance condition between both spin transitions is fulfilled. This effect could be utilized as a frequency selective mechanism in novel, responsive T1 shortening contrast agents (CAs) for magnetic resonance imaging (MRI). In particular, the proposed contrast mechanism depends on the applied external flux density—a property that can be exploited by special field-cycling MRI scanners. For the design of efficient CA molecules, exhibiting narrow and pronounced peaks in the proton T1 relaxation dispersion, the nuclear quadrupole resonance (NQR) properties, as well as the spin dynamics of the system QN−1H, have to be well understood and characterized for the compounds in question. In particular, the energy-level structure of the QN is a central determinant for the static flux densities at which the contrast enhancement appears. The energy levels depend both on the QN and the electronic environment, i.e., the chemical bonding structure in the CA molecule. In this work, the NQR properties of a family of promising organometallic compounds containing 209Bi as QN have been characterized. Important factors like temperature, chemical structure, and chemical environment have been considered by NQR spectroscopy and abinitio quantum chemistry calculations. The investigated Bi-aryl compounds turned out to fulfill several crucial requirements: NQR transition frequency range applicable to clinical 1.5- and 3T MRI systems, low temperature dependency, low toxicity, and tunability in frequency by chemical modification.

Contrast agents with a strong R

Quadrupole relaxation enhancement (QRE) has been suggested as the key mechanism for a novel class of field-selective, potentially responsive magnetic resonance imaging contrast agents. In previous publications, QRE has been confirmed for solid compounds containing Bi-209 as the quadrupolar nucleus (QN). For QRE to be effective in aqueous dispersions, several conditions must be met, i.e. high transition probability of the QN at the H-1 Larmor frequency, water exchange with the bulk and comparatively slow motion of the Bi-carrying particles. In this paper, the potential influence of structural order within the compounds (crystallinity') on QRE was studied by nuclear quadrupole resonance (NQR) spectroscopy in one crystalline and two amorphous preparations of Triphenylbismuth (BiPh3). The amorphous preparations comprised (1) a shock-frozen melt and (2) a granulate of polystyrene which contained homogeneously distributed BiPh3 after common dissolution in THF and subsequent evaporation of the solvent. In contrast to the crystalline powder which exhibits strong, narrow NQR peaks the amorphous preparations did not reveal any NQR signals above the noise floor. From these findings, we conclude that the amorphous state leads to a significant spectral peak broadening and that for efficient QRE in potential contrast agents structures with a high degree of order (near crystalline) are required.

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.

Motivated by the possibility of exploiting species containing high spin quantum number nuclei (referred to as quadrupole nuclei) as novel contrast agents for Magnetic Resonance Imaging, based on Quadrupole Relaxation Enhancement (QRE) effects, H-1 spin-lattice relaxation has been investigated for tris(2-methoxyphenyl) bismuthane and tris(2,6-dimethoxyphenyl) bismuthane in powder. The relaxation experiment has been performed in the magnetic field range of 0.5 T to 3 T (the upper limit corresponds to the field used in many medical scanners). A very rich QRE pattern (several frequency specific H-1 spin-lattice relaxation rate maxima) has been observed for both compounds. Complementary Nuclear Quadrupole Resonance experiments have been performed in order to determine the quadrupole parameters (quadrupole coupling constant and asymmetry parameters) for Bi-209. Knowing the parameters, the QRE pattern has been explained on the basis of a quantum-mechanical picture of the system including single and double-quantum coherences for the participating nuclei (H-1 and Bi-209). In this way the quantum-mechanical origin of the spin transitions leading to the QRE effects has been explained.

Motivated by the possibility of exploiting species containing high spin quantum number nuclei (referred to as quadrupole nuclei) as novel contrast agents for Magnetic Resonance Imaging, based on Quadrupole Relaxation Enhancement (QRE) effects, 1H spin-lattice relaxation has been investigated for tris(2-methoxyphenyl)bismuthane and tris(2,6- dimethoxyphenyl)bismuthane in powder. The relaxation experiment has been performed in the magnetic field range of 0.5 T to 3 T (the upper limit corresponds to the field used in many medical scanners). A very rich QRE pattern (several frequency specific 1H spin-lattice relaxation rate maxima) has been observed for both compounds. Complementary Nuclear Quadrupole Resonance experiments have been performed in order to determine the quadrupole parameters (quadrupole coupling constant and asymmetry parameters) for 209Bi. Knowing the parameters, the QRE pattern has been explained on the basis of a quantummechanical picture of the system including single and double-quantum coherences for the participating nuclei (1H and 209Bi). In this way the quantum-mechanical origin of the spintransitions leading to the QRE effects has been explained.