Investigation of Dynamic Behavior of Confined Ionic Liquid [BMIM]+[TCM]- in Silica Material SBA-15 Using NMR.

The molecular dynamics of 1-butyl-3-methyl imidazolium tricyanomethanide ionic liquid [BMIM]+[TCM]- confined in SBA-15 mesoporous silica were examined using 1H NMR spin-lattice (T1) relaxation and diffusion measurements. An extensive temperature range (100 K-400 K) was considered in order to study both the liquid and glassy states. The hydrogen dynamics in the two states and the self-diffusion coefficients of the cation [BMIM]+ above the glass transition temperature were extracted from the experimental data. The results were then compared to the corresponding bulk substance. The effects of confinement on the dynamic properties of the ionic liquid clearly manifest themselves in both temperature regimes. In the high-temperature liquid state, the mobility of the confined cations reduces significantly compared to the bulk; interestingly, confinement drives the ionic liquid to the glassy state at a higher temperature Tg than the bulk ionic liquid, whereas an unusual T1 temperature dependence is observed in the high-temperature regime, assigned to the interaction of the ionic liquid with the silica-OH species.

Self-Diffusion in Confined Water: A Comparison between the Dynamics of Supercooled Water in Hydrophobic Carbon Nanotubes and Hydrophilic Porous Silica.

Confined liquids are model systems for the study of the metastable supercooled state, especially for bulk water, in which the onset of crystallization below 230 K hinders the application of experimental techniques. Nevertheless, in addition to suppressing crystallization, confinement at the nanoscale drastically alters the properties of water. Evidently, the behavior of confined water depends critically on the nature of the confining environment and the interactions of confined water molecules with the confining matrix. A comparative study of the dynamics of water under hydrophobic and hydrophilic confinement could therefore help to clarify the underlying interactions. As we demonstrate in this work using a few representative results from the relevant literature, the accurate assessment of the translational mobility of water molecules, especially in the supercooled state, can unmistakably distinguish between the hydrophilic and hydrophobic nature of the confining environments. Among the numerous experimental methods currently available, we selected nuclear magnetic resonance (NMR) in a field gradient, which directly measures the macroscopic translational self-diffusion coefficient, and quasi-elastic neutron scattering (QENS), which can determine the microscopic translational dynamics of the water molecules. Dielectric relaxation, which probes the re-orientational degrees of freedom, are also discussed.

Crystal and electronic facet analysis of ultrafine Ni2P particles by solid-state NMR nanocrystallography.

Structural and morphological control of crystalline nanoparticles is crucial in the field of heterogeneous catalysis and the development of "reaction specific" catalysts. To achieve this, colloidal chemistry methods are combined with ab initio calculations in order to define the reaction parameters, which drive chemical reactions to the desired crystal nucleation and growth path. Key in this procedure is the experimental verification of the predicted crystal facets and their corresponding electronic structure, which in case of nanostructured materials becomes extremely difficult. Here, by employing 31P solid-state nuclear magnetic resonance aided by advanced density functional theory calculations to obtain and assign the Knight shifts, we succeed in determining the crystal and electronic structure of the terminating surfaces of ultrafine Ni2P nanoparticles at atomic scale resolution. Our work highlights the potential of ssNMR nanocrystallography as a unique tool in the emerging field of facet-engineered nanocatalysts.

The Role of Titanium Dioxide on the Hydration of Portland Cement: A Combined NMR and Ultrasonic Study.

Titanium dioxide (TiO2) is an excellent photocatalytic material that imparts biocidal, self-cleaning and smog-abating functionalities when added to cement-based materials. The presence of TiO2 influences the hydration process of cement and the development of its internal structure. In this article, the hydration process and development of a pore network of cement pastes containing different ratios of TiO2 were studied using two noninvasive techniques (ultrasonic and NMR). Ultrasonic results show that the addition of TiO2 enhances the mechanical properties of cement paste during early-age hydration, while an opposite behavior is observed at later hydration stages. Calorimetry and NMR spin-lattice relaxation time T1 results indicated an enhancement of the early hydration reaction. Two pore size distributions were identified to evolve separately from each other during hydration: small gel pores exhibiting short T1 values and large capillary pores with long T1 values. During early hydration times, TiO2 is shown to accelerate the formation of cement gel and reduce capillary porosity. At late hydration times, TiO2 appears to hamper hydration, presumably by hindering the transfer of water molecules to access unhydrated cement grains. The percolation thresholds were calculated from both NMR and ultrasonic data with a good agreement between both results.

Resolving Dirac electrons with broadband high-resolution NMR.

Detecting the metallic Dirac electronic states on the surface of Topological Insulators (TIs) is critical for the study of important surface quantum properties (SQPs), such as Majorana zero modes, where simultaneous probing of the bulk and edge electron states is required. However, there is a particular shortage of experimental methods, showing at atomic resolution how Dirac electrons extend and interact with the bulk interior of nanoscaled TI systems. Herein, by applying advanced broadband solid-state 125Te nuclear magnetic resonance (NMR) methods on Bi2Te3 nanoplatelets, we succeeded in uncovering the hitherto invisible NMR signals with magnetic shielding that is influenced by the Dirac electrons, and we subsequently showed how the Dirac electrons spread inside the nanoplatelets. In this way, the spin and orbital magnetic susceptibilities induced by the bulk and edge electron states were simultaneously measured at atomic scale resolution, providing a pertinent experimental approach in the study of SQPs.

NMR and EPR Structural Analysis and Stability Study of Inverse Vulcanized Sulfur Copolymers.

Sulfur copolymers with high sulfur content find a broad range of applications from Li-S batteries to catalytic processes, self-healing materials, and the synthesis of nanoparticles. Synthesis of sulfur-containing polymers via the inverse vulcanization technique gained a lot of attention due to the feasibility of the reaction to produce copolymers with high sulfur content (up to 90 wt %). However, the interplay between the cross-linker and the structure of the copolymers has not yet been fully explored. In the present work, the effect of the amount of 1,3-diisopropenyl benzene (DIB) cross-linker on the structural stability of the copolymer was thoroughly investigated. Combining X-ray diffraction and differential scanning calorimetry, we demonstrated the partial depolymerization of sulfur in the copolymer containing low amount of cross-linker (<30 wt % DIB). On the other hand, by applying NMR and electron paramagnetic resonance techniques, we have shown that increasing the cross-linker content above 50 wt % leads to the formation of radicals, which may severely degrade the structural stability of the copolymer. Thus, an optimum amount of cross-linker is essential to obtain a stable copolymer. Moreover, we were able to detect the release of H2S gas during the cross-linking reaction as predicted based on the abstraction of hydrogen by the sulfur radicals and therefore we emphasize the need to take appropriate precautions while implementing the inverse vulcanization reaction.

Novel Synthesis of Ultra-Small Dextran Coated Maghemite Nanoparticles for MRI and CT Contrast Agents via a Low Temperature Co-Precipitation Reaction.

Ultra-small dextran coated maghemite nanoparticles are synthesized via a low temperature modified co-precipitation method. A monoethylene glycol/water solution of 1:1 molar ratios and a fixed apparatus is used at a constant temperature of 5-10 degrees C. The growth of nanoparticles is prohibited due to low temperature synthesis and differs from usual thermal decomposition methods via Ostwald ripening. Strict temperature control and reaction timing of less than 20 minutes are essential to maintain narrow distribution in particle size. These nanoparticles are water-dispersible and biocompatible by capping with polyethylene glycol ligands. The aqueous suspensions are tested for cytotoxic activity on normal human skin fibroblasts. There is no reduction of the cells' viability at any concentration tested, the highest being 1% v/v of the suspension in culture medium, corresponding to the highest concentrations to be administered in vivo. Initial comparison with a T1 MRI contrast agent in sale shows that maghemite nanoparticles exhibit high r1 and r2 relaxivities in MRI tomography and strong contrast in computed tomography, demonstrating that these nanoparticles can be efficient T1, T2 and CT contrast agents.

Attachment of Pseudomonas putida onto differently structured kaolinite minerals: a combined ATR-FTIR and 1H NMR study.

The attachment of Pseudomonas (P.) putida onto well (KGa-1) and poorly (KGa-2) crystallized kaolinite was investigated in this study. Batch experiments were carried out to determine the attachment isotherms of P. putida onto both types of kaolinite particles. The attachment process of P. putida onto KGa-1 and KGa-2 was adequately described by a Langmuir isotherm. Attenuated Total Reflection Fourier Transform Infrared Spectroscopy and Nuclear Magnetic Resonance were employed to study the attachment mechanisms of P. putida. Experimental results indicated that KGa-2 presented higher affinity and attachment capacity than KGa-1. It was shown that electrostatic interactions and clay mineral structural disorders can influence the attachment capacity of clay mineral particles.

Rapid magnetic heating treatment by highly charged maghemite nanoparticles on Wistar rats exocranial glioma tumors at microliter volume.

One of the most significant challenges implementing colloidal magnetic nanoparticles in medicine is the efficient heating of microliter quantities by applying a low frequency alternating magnetic field. The ultimate goal is to accomplish nonsurgically the treatment of millimeter size tumors. Here, we demonstrate the synthesis, characterization, and the in vitro as well as in vivo efficiency of a dextran coated maghemite (gamma-Fe(2)O(3)) ferrofluid with an exceptional response to magnetic heating. The difference to previous synthetic attempts is the high charge of the dextran coating, which according to our study maintains the colloidal stability and good dispersion of the ferrofluid during the magnetic heating stage. Specifically, in vitro 2 mul of the ferrofluid gives an outstanding temperature rise of 33 degrees C within 10 min, while in vivo treatment, by infusing 150 mul of the ferrofluid in animal model (rat) glioma tumors, causes an impressive cancer tissue dissolution.

Synthesis and characterization of multifunctional hyperbranched polyesters as prospective contrast agents for targeted MRI.

Based on a commercially available hyperbranched aliphatic polyester, novel multifunctional gadolinium complexes were prepared bearing protective PEG chains, a folate targeting ligand and EDTA or DTPA chelate moieties. Their relatively high water relaxivity values coupled with biodegradability of the hyperbranched scaffold, folate receptor specificity render these non-toxic dendritic polymers promising candidates for MRI applications.

Novel polycarboxylated EDTA-type cyclodextrins as ligands for lanthanide binding: study of their luminescence, relaxivity properties of Gd(iii) complexes, and PM3 theoretical calculations.

Novel -type cyclodextrin (CD) derivatives, , and , bearing 6, 7 and 8 bis(carboxymethyl)amino (iminodiacetic acid) groups, respectively, were prepared, and their complexation with Eu(iii), Tb(iii) and Gd(iii) ions was studied. Luminescence titrations and mass spectrometry showed formation of multimetal complexes ( 2 to 3, mainly 3 and exactly 4 metal ions), whereas luminescence lifetime measurements revealed the presence of exchangeable water molecules. Semiempirical quantum mechanical calculations, performed by the PM3 method and assessed by DFT calculations on model ligands, indicated efficient multi-metal complexation, in agreement with the experiment. The structures showed coordination of the metal ions in the outer primary side of the CDs via 4 carboxylate O atoms, 2 N atoms and a glucopyranose O atom per metal ion. Coordination of water molecules was also predicted, in accordance with experimental results. Calculated bond lengths and angles were in agreement with literature experimental values of lanthanide complexes. Calculated energies showed that complex stability decreases in the order > > . (1)H NMR molecular relaxivity measurements for the Gd(iii) complexes of , or in water afforded values 4 to 10 times higher than the relaxivity of a commercial contrast agent at 12 MHz, and 6 to 20 times higher at 100 MHz. Solutions of and Gd(iii) complexes in human blood plasma displayed relaxivity values at 100 MHz 7 and 12 times, respectively, higher than the commercial agent. MTT tests of the Gd(iii) complexes using human skin fibroblasts did not show toxicity. Attempts to supramolecularly sensitize the luminescence of the lanthanide complexes using various aromatic CD guests were ineffective, evidently due to large guest-metal distances and inefficient inclusion. The described lanthanide complexes, could be useful as contrast agents in MRI.

Synthesis and characterization of novel natural product-Gd(III) MRI contrast agent conjugates.

Several novel gadolinium chelates conjugated with paclitaxel, colchicine and thyroxine have been prepared as MRI contrast agents targeted to tubulin and thyroxine-binding globulin, respectively.

No aging phenomena in ferrofluids: the influence of coating on interparticle interactions of maghemite nanoparticles.

The influence of coating on interparticle interactions in ferrofluids has been investigated using various techniques such as Mossbauer spectroscopy, magnetometry, transmission electron microscopy, photon correlation spectroscopy, X-ray diffraction, X-ray photoelectron, and resonance micro-Raman spectroscopy. Aging and spin-glass-like behavior was investigated in frozen ferrofluids of various concentrations from dense, initial value of 40 mg of coated nanoparticles per 1 mL of water, to dilute 1:10 (4 mg/mL). The as-prepared nanoparticles, core size 7-8 nm, were subsequently coated with a gummic acid corona of 20 nm thickness, which was observed to prevent agglomeration and to delay aggregation even in dense ferrofluids. The resulting separation of magnetic cores due to the coating eliminated all magnetic interparticle interaction mechanisms, such as exchange and dipoledipole, thus ensuring no aging effects of the magnetic particle system, as manifested in particle agglomeration and precipitation.

Hexanuclear iron(III) salicylaldoximato complexes presenting the [Fe6(mu3-O)2(mu2-OR)2]12+ core: syntheses, crystal structures, and spectroscopic and magnetic characterization.

The use of salicylaldehyde oxime (H2salox) in iron(III) carboxylate chemistry has yielded two new hexanuclear compounds [Fe6(mu3-O)2(O2CPh)10(salox)2(L)2].xMeCN.yH2O [L = MeCONH2, x = 6, y = 0 (1); L = H2O, x = 2, y = 3 (2)]. Compound 1 crystallizes in the triclinic space group P with (at 25 degrees C) a = 13.210(8) A, b = 13.87(1) A, c = 17.04(1) A, alpha = 105.79(2) degrees , beta = 96.72(2) degrees , gamma = 116.69(2) degrees , V = 2578.17(2) A(3), and Z = 1. Compound 2 crystallizes in the monoclinic space group C2/c with (at 25 degrees C) a = 21.81(1) A, b = 17.93(1) A, c = 27.72(1) A, beta = 111.70(2) degrees , V = 10070(10) A(3), and Z = 4. Complexes 1 and 2 contain the [Fe6(mu3-O)2(mu2-OR)2]12+ core and can be considered as two [Fe3(mu3-O)] triangular subunits linked by two mu2-oximato O atoms of the salox2- ligands, which show the less common mu3:eta1:eta2:eta1 coordination mode. The benzoato ligands are coordinated through the usual syn,syn-mu2:eta1:eta1 mode. The terminal MeCONH2 ligand in 1 is the hydrolysis product of the acetonitrile solvent in the presence of the metal ions. Mössbauer spectra from powdered samples of 2 give rise to two well-resolved doublets with an average isomer shift consistent with that of high-spin Fe(III) ions. The two doublets, at an approximate 1:2 ratio, are characterized by different quadrupole splittings and are assigned to the nonequivalent Fe(III) ions of the cluster. Magnetic measurements of 2 in the 2-300 K temperature range reveal antiferromagnetic interactions between the Fe(III) ions, stabilizing an S = 0 ground state. NMR relaxation data have been used to investigate the energy separation between the low-lying states, and the results are in agreement with the susceptibility data.