Nuclear Magnetic Resonance Dispersion Research Articles

Dynamics of the ionic liquid 1-butyl-3-methylimidazolium bis(trifluoromethylsulphonyl)imide studied by nuclear magnetic resonance dispersion and diffusion.

The dynamics of the imidazolium based room temperature ionic liquid Bmim Tf2N was investigated by means of nuclear magnetic resonance relaxation dispersion (NMRD) and nuclear magnetic resonance pulsed field gradient (NMR-PFG) diffusion experiments on the bulk liquid in a wide range of temperatures. Relaxation and diffusion properties were determined for anions and cations individually, giving evidence of heterogeneities in the dynamics of the ionic liquid. The relevant NMR relaxation mechanisms are the inter- and intramolecular dipolar interactions between the molecular ions reflecting the molecular translational and rotational diffusion. Rotational and translational correlation times could be obtained and showed different dependences on temperature. The experimental diffusion values follow the Vogel-Fulcher-Tammann (VFT) relation above a transition temperature Tc∼ 1.26 Tg, below which a deviation was observed. Differential scanning calorimetry experiments show a transition at the same temperature.

Multifunctional rare-Earth vanadate nanoparticles: luminescent labels, oxidant sensors, and MRI contrast agents.

Collecting information on multiple pathophysiological parameters is essential for understanding complex pathologies, especially given the large interindividual variability. We report here multifunctional nanoparticles which are luminescent probes, oxidant sensors, and contrast agents in magnetic resonance imaging (MRI). Eu(3+) ions in an yttrium vanadate matrix have been demonstrated to emit strong, nonblinking, and stable luminescence. Time- and space-resolved optical oxidant detection is feasible after reversible photoreduction of Eu(3+) to Eu(2+) and reoxidation by oxidants, such as H2O2, leading to a modulation of the luminescence emission. The incorporation of paramagnetic Gd(3+) confers in addition proton relaxation enhancing properties to the system. We synthesized and characterized nanoparticles of either 5 or 30 nm diameter with compositions of GdVO4 and Gd0.6Eu0.4VO4. These particles retain the luminescence and oxidant detection properties of YVO4:Eu. Moreover, the proton relaxivity of GdVO4 and Gd0.6Eu0.4VO4 nanoparticles of 5 nm diameter is higher than that of the commercial Gd(3+) chelate compound Dotarem at 20 MHz. Nuclear magnetic resonance dispersion spectroscopy showed a relaxivity increase above 10 MHz. Complexometric titration indicated that rare-earth leaching is negligible. The 5 nm nanoparticles injected in mice were observed with MRI to concentrate in the liver and the bladder after 30 min. Thus, these multifunctional rare-earth vanadate nanoparticles pave the way for simultaneous optical and magnetic resonance detection, in particular, for in vivo localization evolution and reactive oxygen species detection in a broad range of physiological and pathophysiological conditions.

Bifunctional chelates optimized for molecular MRI.

Important requirements for exogenous dyes or contrast agents in magnetic resonance imaging (MRI) include an effective concentration of paramagnetic or superparamagnetic ions at the target to be imaged. We report the concise synthesis and characterization of several new enantiopure bifunctional derivatives of (α1R,α4R,α7R,α10R)-α1,α4,α7,α10-tetramethyl-1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTMA) (and their 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) analogues as controls) that can be covalently attached to a contrast agent delivery system using either click or peptide coupling chemistry. Gd complexes of these derivatives can be attached to delivery systems while maintaining optimal water residence time for increased molecular imaging sensitivity. Long chain biotin (LC-biotin) derivatives of the Eu(III) and Gd(III) chelates associated with avidin are used to demonstrate higher efficiencies. Variable-temperature relaxometry, 17O NMR, and nuclear magnetic resonance dispersion (NMRD) spectroscopy used on the complexes and biotin–avidin adducts measure the influence of water residence time and rotational correlation time on constrained and unconstrained systems. The Gd(III)-DOTMA derivative has a shorter water residence time than the Gd(III)-DOTA derivative. Compared to the constrained Gd(III)-DOTA derivatives, the rotationally constrained Gd(III)-DOTMA derivative has ∼40% higher relaxivity at 37 °C, which could increase its sensitivity as an MRI agent as well as reduce the dose of the targeting agent.

Gadolinium-loaded polychelating amphiphilic polymer as an enhanced MRI contrast agent for human multiple myeloma and non Hodgkin's lymphoma (human Burkitt's lymphoma)

Liposomes, loaded with gadolinium (Gd) ions using different membrane-incorporated chelating lipids and functionalized with monoclonal anti-CD138 (syndecan-1) antibody were prepared. Nuclear Magnetic Resonance Dispersion (NMRD) analysis showed that use of the polychelating amphiphilic polymer (PAP) increases both the Gd content and the spin–lattice relaxivity of the Gd-loaded-PAP–liposomes as compared to Gd–DTPA–BSA equivalents. The potential application of contrast syndecan-1– and Rituximab–liposomes, for application as a novel minimally invasive diagnostic agent for multiple myeloma and non Hodgkin's lymphoma was investigated.

Screening of the Relaxivity of Gadolinium‐Loaded Periodic Mesoporous Silica Functionalized by Means of Soft Metalorganic Silylamide Grafting

AbstractSoft metalorganic grafting of periodic mesoporous silica (PMS) materials is introduced as a method for obtaining nanostructured GdIII‐loaded silica particles with relatively high 1H relaxivity. The silylamide complex Gd[N(SiHMe2)2]3(THF)2 was grafted onto MCM‐41, SBA‐15, and SBA‐1, thereby providing PMSs of distinct symmetry as well as pore size and configuration. The materials were characterized by infrared spectroscopy, elemental analysis, powder X‐ray diffraction (PXRD), N2 physisorption, and scanning as well as transmission electron microscopy (SEM/TEM). Relaxivities up to 15.8 mM–1 s–1 were determined at high magnetic field strength (400 MHz). The nuclear magnetic resonance dispersion (NMRD) data of a calcined Gd[N(SiHMe2)2]3(THF)2@SBA‐1 material had a shape typical for slow‐tumbling systems, with a maximum at approximately 50 MHz. Temperature‐dependence studies of the relaxivity (r1) indicated that the grafted materials were characterized by an efficient water exchange. To maintain a high relaxivity, a low (1 wt.‐%) GdIII loading and a hydrophilic surface had to be provided. Varying the topology of the silica support only resulted in small variations in r1 of the hybrid materials.

High Relaxivities and Strong Vascular Signal Enhancement for NaGdF4 Nanoparticles Designed for Dual MR/Optical Imaging

Near-infrared (NIR)-to-NIR upconverting NaY(Gd)F4 :Tm(3+) ,Yb(3+) paramagnetic nanoparticles (NPs) are efficiently detected by NIR imaging techniques. As they contain Gd(3+) ions, they also provide efficient "positive" contrast in magnetic resonance imaging (MRI). Water-dispersible small (≈25 nm, "S-") and ultrasmall (<5 nm diam., "US-") NaY(Gd)F4 :Tm(3+) ,Yb(3+) NPs are synthesized by thermal decomposition and capped with citrate. The surface of citrate-coated US-NPs shows sodium depletion and high Gd elemental ratios, as confirmed by a comparative X-ray photoelectron spectroscopy (XPS)/neutron absorption analysis study. US-NaGd0.745 F4 :Tm0.005 ,Yb0.25 NPs have hydrodynamic diameters close to that measured by TEM, with the lowest relaxometric ratios (r2 /r1 = 1.18) reported for NaGdF4 nanoparticle suspensions (r1 = 3.37 mM(-1) s(-1) at 1.4 T and 37 °C). Strong relaxivity peaks in the range of 20 (0.47 T) - 300 MHz (7.05 T) are revealed in nuclear magnetic resonance dispersion profiles, with high r2 /r1 ratios at increasing field strengths for S-NPs. This indicates the superiority of US-NPs over S-NPs for achieving high positive contrast at clinical MRI field strengths. I.-v. injected citrate-coated US-NPs evidence long blood retention times (>90 min) in mice. Biodistribution studies (48 h, 8 d) show elimination through the reticuloendothelial and urinary systems, similarly to other citrate-capped US-NP systems. In summary, upconverting NaY(Gd)F4 :Tm(3+) ,Yb(3+) nanoparticles have promising luminescent, relaxometric and blood-retention properties for dual MRI/optical imaging.

The magnetic, relaxometric, and optical properties of gadolinium-catalyzed single walled carbon nanotubes

We report the magnetic behavior, relaxometry, phantom magnetic resonance imaging (MRI), and near-infrared (NIR) photoluminescence spectroscopy of gadolinium (Gd) catalyzed single-walled carbon nanotubes (Gd-SWCNTs). Gd-SWCNTs are paramagnetic with an effective magnetic moment of 7.29 μB . Gd-SWCNT solutions show high r1 and r2 relaxivities at very low (0.01 MHz) to clinically relevant (61 MHz) magnetic fields (r1 ≥ 130 mM-1 s-1, r2 ≥ 160 mM-1 s-1). Analysis of nuclear magnetic resonance dispersion profiles using Solomon, Bloembergen, and Morgan equations suggests that multiple structural and dynamic parameters such as rotational correlation time [Formula: see text], rate of water exchange [Formula: see text], and the number of fast-exchanging water molecules within the inner sphere q may be responsible for the increase in r1 and r2 relaxivity. The T1 weighted MRI signal intensity (gradient echo sequence; repetition time (TR) = 66 ms, echo time (TE) = 3 ms, flop angle = 108°) of Gd-SWCNT phantom solution is 14 times greater than the Gd-based clinical MRI contrast agent Magnevist. Additionally, these nanotubes exhibit near infrared fluorescence with distinct E11 transitions of several semiconducting SWCNTs. Taken together, these results demonstrate that Gd-SWCNTs have potential as a novel, highly efficacious, multimodal MRI-NIR optical imaging contrast agent.

Relaxometric properties of gadolinium-grafted mesoporous SBA-15 silica materials with varying pore size

Gadolinium loaded mesoporous silicas are interesting for MRI contrast agent application due to high r1 relaxivities. Here, gadolinium grafted mesoporous SBA-15 materials with varying pore diameters are investigated by field dependence profiling, temperature studies and high field r1 (11.7T, 500MHz) measurements. SBA-15 hybrid materials with varying pore diameters are prepared via pseudo surface organometallic chemistry (pseudo-SOMC) of Gd[N(SiHMe2)2]3(THF)2 and their Nuclear Magnetic Resonance Dispersion (NMRD) profiles (range 4–80MHz, pore diameters 5.4, 6.5 and 7.7nm) are presented. The profiles have the shape of a slowly tumbling system, with a maximum at relatively high field strength (30–50MHz) and are characterized by increasing r1 with increasing pore size and decreasing temperature. The same trends are observed at 500MHz, where r1 increases from 6.5 to 14.1mM−1s−1 when the pore diameter increases from 5.4 to 9.1nm. Modeling of the NMRD profiles proposes that the Gd-modified SBA-15s have as much as five inner-sphere water molecules (q=5), a relatively slow global (τg=100μs) and fast local rotation (τR=0.08ns) and an efficient water accessibility to the metal center (τm=1.15ns). A model originally developed for zeolites is used to describe the water dynamics in the SBA-15 silicas, and implies that the observed trend with pore size is due to a combination of an increasing number of free water molecules per Gd3+ (x) and a decreasing residence lifetime of water inside the pores (τp).

Scaling laws at the nanosize: the effect of particle size and shape on the magnetism and relaxivity of iron oxide nanoparticle contrast agents

The magnetic properties of iron oxide nanoparticles govern their relaxivities and efficacy as contrast agents for MRI. These properties are in turn determined by their composition, size and morphology. Herein we present a systematic study of the effect of particle size and shape of magnetite nanocrystals synthesized by thermal decompositions of iron salts on both their magnetism and their longitudinal and transverse relaxivities, r1 and r2, respectively. Faceted nanoparticles demonstrate superior magnetism and relaxivities than spherical nanoparticles of similar size. For faceted nanoparticles, but not for spherical ones, r1 and r2 further increase with increasing particle size up to a size of 18 nm. This observation is in accordance with increasing saturation magnetization for nanoparticles increasing in size up to 12 nm, above which a plateau is observed. The NMRD (Nuclear Magnetic Resonance Dispersion) profiles of MIONs (Magnetic Iron Oxide Nanoparticles) display an increase in longitudinal relaxivity with decreasing magnetic field strength with a plateau below 1 MHz. The transverse relaxivity shows no dependence on the magnetic field strength between 20 MHz and 500 MHz. These observations translate to phantom MR images: in T1-weighted SWIFT (SWeep imaging with Fourier Transform) images MIONs have a positive contrast with little dependence on particle size, whereas in T2-weighted gradient-echo images MIONs create a negative contrast which increases in magnitude with increasing particle size. Altogether, these results will enable the development of particulate MRI contrast agents with enhanced efficacy for biomedical and clinical applications.

Polymer cross-linking: a nanogel approach to enhancing the relaxivity of MRI contrast agents.

Polymer cross-linking was explored as an approach for increasing the relaxivity of macromolecular contrast agents for magnetic resonance imaging. Poly(ethylene glycol) methyl ether methacrylate, N-(2-aminoethyl)methacrylamide hydrochloride, and the cross-linker ethylene glycol dimethacrylate were copolymerized under free radical conditions. By tuning the cross-linker content and reaction concentration, it was possible to obtain 10 nm nanogels in a single synthetic step. The pendant amine moieties were functionalized with an isothiocyanate derivative of diethylenetriaminepentaacetic acid (DTPA) and Gd(iii) was chelated. In comparison with a linear control polymer prepared under the same conditions in the absence of the cross-linking agent, the nanogel contrast agent did exhibit enhanced relaxivity with an r1 of 20.8 ± 0.2 at 20 MHz and 17.5 ± 0.4 at 60 MHz (corresponding to the clinical field strength of 1.5 T). The nuclear magnetic resonance dispersion profile was modeled to demonstrate that the enhanced relaxivity was a result of the nanogel agent's increased rotational correlation time, that is proposed to result from the constraint on motion imparted by the cross-linking. T1 weighted imaging in mice showed enhanced contrast and vascular circulation for the nanogel relative to Gd(iii)-DTPA (Magnevist) demonstrating the future promise of these new agents.

Synthesis of pseudopolyrotaxanes-coated Superparamagnetic Iron Oxide Nanoparticles as new MRI contrast agent

Superparamagnetic Iron Oxide Nanoparticles (SPIONs) were synthesized and coated with pseudopolyrotaxanes (PPRs) and proposed as a novel hybrid nanostructure for medical imaging and drug delivery. PPRs were prepared by addition of α-cyclodextrin rings to functionalized polyethylene glycol (PEG) chain with hydrophobic triazine end-groups. Non-covalent interactions between SPIONs and PPRs led to the assembly of SPIONs@PRs hybrid nanomaterials. Measurements of the 1H Nuclear Magnetic Resonance (NMR) relaxation times T1 and T2 allowed us to determine the NMR dispersion profiles. Comparison between our SPIONs@PRs hybrid nano-compound and the commercial SPION compound, Endorem®, showed a higher transverse relaxivity for SPIONs@PRs. In vitro MRI experiments showed that our SPIONs@PRs produces better negative contrast compared to Endorem® and can be considered as a novel MRI contrast agent.

Role of the Iron Axial Ligands of Heme Carrier HasA in Heme Uptake and Release

The hemophore protein HasA from Serratia marcescens cycles between two states as follows: the heme-bound holoprotein, which functions as a carrier of the metal cofactor toward the membrane receptor HasR, and the heme-free apoprotein fishing for new porphyrin to be taken up after the heme has been delivered to HasR. Holo- and apo-forms differ for the conformation of the two loops L1 and L2, which provide the axial ligands of the iron through His(32) and Tyr(75), respectively. In the apo-form, loop L1 protrudes toward the solvent far away from loop L2; in the holoprotein, closing of the loops on the heme occurs upon establishment of the two axial coordination bonds. We have established that the two variants obtained via single point mutations of either axial ligand (namely H32A and Y75A) are both in the closed conformation. The presence of the heme and one out of two axial ligands is sufficient to establish a link between L1 and L2, thanks to the presence of coordinating solvent molecules. The latter are stabilized in the iron coordination environment by H-bond interactions with surrounding protein residues. The presence of such a water molecule in both variants is revealed here through a set of different spectroscopic techniques. Previous studies had shown that heme release and uptake processes occur via intermediate states characterized by a Tyr(75)-iron-bound form with open conformation of loop L1. Here, we demonstrate that these states do not naturally occur in the free protein but can only be driven by the interaction with the partner proteins.

Physicochemical Characterization, and Relaxometry Studies of Micro-Graphite Oxide, Graphene Nanoplatelets, and Nanoribbons

The chemistry of high-performance magnetic resonance imaging contrast agents remains an active area of research. In this work, we demonstrate that the potassium permanganate-based oxidative chemical procedures used to synthesize graphite oxide or graphene nanoparticles leads to the confinement (intercalation) of trace amounts of Mn2+ ions between the graphene sheets, and that these manganese intercalated graphitic and graphene structures show disparate structural, chemical and magnetic properties, and high relaxivity (up to 2 order) and distinctly different nuclear magnetic resonance dispersion profiles compared to paramagnetic chelate compounds. The results taken together with other published reports on confinement of paramagnetic metal ions within single-walled carbon nanotubes (a rolled up graphene sheet) show that confinement (encapsulation or intercalation) of paramagnetic metal ions within graphene sheets, and not the size, shape or architecture of the graphitic carbon particles is the key determinant for increasing relaxivity, and thus, identifies nano confinement of paramagnetic ions as novel general strategy to develop paramagnetic metal-ion graphitic-carbon complexes as high relaxivity MRI contrast agents.

Magnetic, optical and relaxometric properties of organically coated gold–magnetite (Au–Fe3O4) hybrid nanoparticles for potential use in biomedical applications

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/T1 and transverse 1/T2 relaxation rates of solvent protons in the range 10kHz/300MHz at room temperature. NMR relaxivities r1 and r2 have been compared with ENDOREM®, one of the commercial superparamagnetic iron oxide based MRI contrast agents. MRI contrast enhancement efficiencies have been investigated also by examining T2-weighted MR images of suspensions. The experimental results suggest that the nanoparticles' suspensions are good candidates as negative CAs.

Nuclear Magnetic Resonance Dispersion of Distributions as a Probe of Aggregation in Crude Oils

We present a new technique—nuclear magnetic resonance dispersion of distributions (NMRDD)—and we demonstrate that it is a particularly sensitive probe of aggregation in asphaltene-rich crude oils. The technique is based on the measurement of the NMR relaxation distributions at different magnetic fields, i.e., at different proton Larmor frequencies. Because the NMR relaxation rates are controlled by molecular fluctuations at the Larmor frequency, these measurements probe the presence of aggregates that tumble at characteristic rates near that frequency. Our experimental results span the Larmor frequencies from 10 kHz to 40 MHz, which is the range relevant for rotation times of asphaltene and resin aggregates in crude oil. The presence of large aggregates is evident by visual inspection of the data, and aggregate sizes for small and medium size aggregates of the order of several nanometers can be extracted without recourse to any specific models of asphaltene interactions. The technique is noninvasive and nondestructive and can be used for monitoring and study of the onset of aggregation at the preflocculation stage in unstable crude oils.

A modular system for the synthesis of multiplexed magnetic resonance probes.

We have developed a modular architecture for preparing high-relaxivity multiplexed probes utilizing click chemistry. Our system incorporates azide bearing Gd(III) chelates and a trialkyne scaffold with a functional group for subsequent modification. In optimizing the relaxivity of this new complex, we undertook a study of the linker length between a chelate and the scaffold to determine its effect on relaxivity. The results show a strong dependence on flexibility between the individual chelates and the scaffold with decreasing linker length leading to significant increases in relaxivity. Nuclear magnetic resonance dispersion (NMRD) spectra were obtained to confirm a 10-fold increase in the rotational correlation time from 0.049 to 0.60 ns at 310 K. We have additionally obtained a crystal structure demonstrating that modification with an azide does not impact the coordination of the lanthanide. The resulting multinuclear center has a 500% increase in per Gd (or ionic) relaxivity at 1.41 T versus small molecule contrast agents and a 170% increase in relaxivity at 9.4 T.

A Pyrophosphate‐Responsive Gadolinium(III) MRI Contrast Agent

This study shows that the relaxivity and optical properties of functionalised lanthanide-DTPA-bis-amide complexes (lanthanide=Gd(3+) and Eu(3+) , DTPA=diethylene triamine pentaacetic acid) can be successfully modulated by addition of specific anions, without direct Ln(3+) /anion coordination. Zinc(II)-dipicolylamine moieties, which are known to bind strongly to phosphates, were introduced in the amide "arms" of these ligands, and the interaction of the resulting Gd-Zn(2) complexes with a range of anions was screened by using indicator displacement assays (IDAs). Considerable selectivity for polyphosphorylated species (such as pyrophosphate and adenosine-5'-triphosphate (ATP)) over a range of other anions (including monophosphorylated anions) was apparent. In addition, we show that pyrophosphate modulates the relaxivity of the gadolinium(III) complex, this modulation being sufficiently large to be observed in imaging experiments. To establish the binding mode of the pyrophosphate and gain insight into the origin of the relaxometric modulation, a series of studies including UV/Vis and emission spectroscopy, luminescence lifetime measurements in H(2) O and D(2) O, (17) O and (31) P NMR spectroscopy and nuclear magnetic resonance dispersion (NMRD) studies were carried out.

Brownian dynamics of water confined in AOT reverse micelles: A field-cycling deuteron NMR relaxometry study

Reversed micelles and water in oil micro-emulsions can be used to solubilize biopolymers and genetic materials allowing analyzing their properties in a confined geometry. Nuclear Magnetic Resonance Dispersion (NMRD) provides a powerful and a noninvasive experimental technique to probe the long-term dynamics of these confined systems. However, the first step is to analyze and understand the slow dynamics of water inside these micro-reactors without any guest molecule. This is the aim of this presentation. Experimental results have been obtained for deuteron 2H NMRD of water confined in reverse micelles of bis (2-ethylhexyl) sodium sulfosuccinate (AOT) dispersed in isooctane C8H18. The water content is expressed as the molar ratio W0 = [Water]/[AOT]. The radius of the spherical reversed micelles, Rm, increases almost linearly with W0. In our case, W0 is chosen in the range 20 ≤ W0 ≤ 50 (35 ≤ Rm ≤ 80 Å). The frequency dependence for the spin-lattice relaxation rate R1(ω) exhibits two regimes, for all W0 values: a plateau at low frequency, proportional to 1/Rm, followed by the beginning of an algebraic decay. These experimental observations are discussed and compared to a numerical simulation of the intermittent Brownian diffusion of a water molecule inside a rotating reverse micelle. The possibility to probe some properties of the confinement, such as the localisation time on the sulfonated palisade and/or the water self-diffusion inside the water pool is emphasised. Les micelles inverses sont des nano-gouttelettes d’eau thermodynamiquement stables qui peuvent être utilisées pour solubiliser des systèmes biologiques et d’étudier leurs propriétés physicochimique en confinement. La dispersion RMN est une technique non invasive, permettant l’étude de la dynamique lente de ces systèmes confinés. Cependant, dans un premier temps nous cherchons à comprendre la dynamique lente de l’eau confinée dans ces micelles inverses. Nous présentons les variations avec le champ magnétique des vitesses de relaxation spin-réseau R1 des deutérons de l’eau confinée dans des micelles inverses formées par le mélange d’un tensioactif bis (2-éthylhexyl) sodium sulfosuccinate (AOT), de l’isooctane et de l’eau. La quantité d’eau solubilisée est exprimée par le rapport des concentrations molaires W0 = [Water]/[AOT]. Le rayon aqueux Rm de ces micelles sphériques varie linéairement avec W0. Dans notre cas, W0 est compris entre 20 et 50 (35 ≤ Rm ≤ 80 Å). Les profils de dispersion RMN R1(ω) passent par deux régimes pour toutes les valeurs de W0: un plateau à basse fréquence, proportionnel à 1/Rm, suivi du début d’une décroissance en loi de puissance. Une simulation numérique de dynamique brownienne de molécules d’eau confinées dans des micelles inverses sphériques en rotation dans l’isooctane est proposée et comparée aux résultats expérimentaux. Cette simulation offre la possibilité d’étudier l’effet de confinement sur la diffusion interne de l’eau et/ou sur le temps de localisation des molécules d’eau sur la palissade sulfonatée.

Relaxometric Studies for Food Characterization: The Case of Balsamic and Traditional Balsamic Vinegars

NMR spectroscopy is a powerful technique for investigating the structure and composition, as well as the physicochemical properties, of foodstuff. NMR-field cycling modality reports about the relaxation times of solvent molecules as a function of the applied magnetic field strength. In the case of aqueous solutions, this methodology is particularly valuable in assessing the interactions of water molecules with paramagnetic and large-size macromolecular systems. (1)H NMR field cycling relaxometry has been used to characterize traditional balsamic vinegars and balsamic vinegars of Modena. It has been found that the longitudinal relaxation time (T(1)) of the water proton resonance is mainly determined by the water molar fraction and the occurrence of dissolved macromolecules and paramagnetic metal ions. Actually, the observed (1)H nuclear magnetic resonance dispersion (NMRD) profiles appear markedly affected by the formation of paramagnetic macromolecular adducts. It has been shown that counterfeit specimens can be identified on the basis of the comparison of their T(1) and T(2) (transverse relaxation time) values with respect to the corresponding values of genuine samples. For the latter ones, a relationship has been found that relates the observed T(1) to the age of the vinegar.

Manipulation of tissue contrast using contrast agents for enhanced MR microscopy in ex vivo mouse brain

Detailed 3D mouse brain images may promote better understanding of phenotypical differences between normal and transgenic/mutant mouse models. Previously, a number of magnetic resonance microscopy (MRM) studies have successfully established brain atlases, revealing genotypic traits of several commonly used mouse strains. In such studies, MR contrast agents, mainly gadolinium (Gd) based, were often used to reduce acquisition time and improve signal-to-noise ratio (SNR). In this paper, we intended to extend the utility of contrast agents for MRM applications. Using Gd-DTPA and MnCl2, we exploited the potential use of MR contrast agents to manipulate image contrast by drawing upon the multiple relaxation mechanisms and tissue-dependent staining properties characteristic of each contrast agent. We quantified r1 and r2 of Gd-DTPA and MnCl2 in both aqueous solution and brain tissue and demonstrated the presence of divergent relaxation mechanisms between solution and tissue for each contrast agent. Further analyses using nuclear magnetic resonance dispersion (NMRD) of Mn2+ in ex vivo tissue strongly suggested macromolecule binding of Mn2+, leading to increased T1 relaxation. Moreover, inductively coupled plasma (ICP) mass spectroscopy revealed that MnCl2 had higher tissue affinity than Gd-DTPA. As a result, multiple regions of the brain stained by the two agents exhibited different image contrasts. Our results show that differential MRM staining can be achieved using multiple MR contrast agents, revealing detailed cytoarchitecture, and may ultimately offer a window for investigating new techniques by which to understand biophysical MR relaxation mechanisms and perhaps to visualize tissue anomalies even at the molecular level.