Gadolinium(III)-loaded nanoparticulate zeolites as potential high-field MRI contrast agents: relationship between structure and relaxivity

The effects of dealumination, pore size, and calcination on the efficiency (as expressed in the relaxivity) of Gd3+-loaded zeolites for potential application as magnetic resonance imaging (MRI) contrast agents were studied. Partial dealumination of zeolites NaY or NaA by treatment with (NH4)2SiF6 or diluted HCl resulted in materials that, upon loading with Gd3+, had a much higher relaxivity than the corresponding non-dealuminated materials. Analysis of the 1H NMR dispersion profiles of the various zeolites showed that this can be mainly ascribed to an increase of the amount of water inside the zeolite cavities as a result of the destruction of walls between cavities. However, the average residence time of water inside the Gd3+-loaded cavities did not change significantly, which suggests that the windows of the Gd3+-loaded cavities are not affected by the dealumination. Upon calcination, the Gd3+ ions moved to the small sodalite cavities and became less accessible for water, resulting in a decrease in relaxivity. The important role of diffusion for the relaxivity was demonstrated by a comparison of the relaxivity of Gd3+-loaded zeolite NaY and NaA samples. NaA had much lower relaxivities due to the smaller pore sizes. The transversal relaxivities of the Gd3+-doped zeolites are comparable in magnitude to the longitudinal ones at low magnetic fields (<60 MHz). However at higher fields, the transversal relaxivities steeply increased, whereas the longitudinal relaxivities decreased as field strength increased. Therefore, these materials have potential as T1 MRI contrast agents at low field, and as T2 agents at higher fields.     

Shaping, propagation and characterization of ultrafast pulses in optical fibers

The characterization of medium- to low-energy shaped pulses at 1.55 7m through frequency-resolved optical gating (FROG) is illustrated. This capability enables the study of ultrafast pulse propagation through optical fibers. The phase dynamics detected furnishes insight on pulse evolution, specifically on soliton formation - a subject of great importance for telecommunication applications. The combination of shaping and propagation of ultrafast pulses in fibers is examined theoretically using an adaptive pulse-shaping model, based on genetic algorithms, that furnishes optimized pulse shapes for fiber propagation.     

NH3 trapped in nitrogen and rare gas matrices. II. High-resolution spectroscopy of ν2 and calculation of the inversion-translation doubling and proper rotation quadrupling

The high-resolution IR spectrum of the ν₂ absorption band of NH₃ embedded in solid N₂ at 5.5 K exhibits a quadruplet structure. This structure includes the previously mentioned inversion doublet while the additional splitting shows striking nuclear spin species conversion over a very large timescale. The inversion doubling, ? 1.65 cm^?1, is considerably smaller than in rare gas matrices (? 24 cm^?1) and in the gas phase (37 cm^?1). The temperature dependence of the quadruplet frequencies shows in N₂ a larger blue shift than is usually expected and a typical motional narrowing for the doublet structure in the range 8–17 K. The a priori determination of the motions of NH₃ around the equilibrium configurations of the potential surface described in the first paper of this series, shows that the strong coupling between intrinsic inversion and translational space inversion is responsible for the doubling decrease. Such a feature is due to the large equilibrium eccentricity in a N₂ matrix. As this eccentricity is much smaller in rare gas matrices, the coupling is much weaker and the spacing closer to the gas-phase value. The quadruplet structure is due to the vibrational dependence of the hindered proper rotational (spinning) motion in the three-fold wells, characteristically coupled to the nuclear spin species. All numerical predictions are in agreement with experimental measurement.     

Hybrid gadolinium oxide nanoparticles: multimodal contrast agents for in vivo imaging

Luminescent hybrid nanoparticles with a paramagnetic Gd2O3 core were applied as contrast agents for both in vivo fluorescence and magnetic resonance imaging. These hybrid particles were obtained by encapsulating Gd2O3 cores within a polysiloxane shell which carries organic fluorophores and carboxylated PEG covalently tethered to the inorganic network. Longitudinal proton relaxivities of these particles are higher than the positive contrast agents like Gd-DOTA which are commonly used for clinical magnetic resonance imaging. Moreover these particles can be followed up by fluorescence imaging. This study revealed that these particles suited for dual modality imaging freely circulate in the blood vessels without undesirable accumulation in lungs and liver.