A series of cryptands have been prepared and they demonstrate the relationship between oxidative stability of aqueous EuII and ligand properties (see figure). One of these EuII complexes is more stable than FeII in hemoglobin and appears to be the most oxidatively-stable aqueous EuII species known. The high stability of EuII is expected to enable the use of the unique magnetic and optical properties of this ion in vivo.

The relaxivity (contrast-enhancing ability) of EuII-containing cryptates was found to be better than a clinically approved GdIII-based agent at 7 T. These cryptates are among a few examples of paramagnetic substances that show an increase in longitudinal relaxivity, r1, at ultra-high field strength relative to lower field strengths.

Recent advances in the coordination chemistry of Eu2+ are reviewed. Common synthetic routes for generating discrete Eu2+-containing complexes reported since 2000 are summarized, followed by a description of the reactivity of these complexes and their applications in reduction chemistry, polymerization, luminescence, and as contrast agents for magnetic resonance imaging. Rapid development of the coordination chemistry of Eu2+ has led to an upsurge in the utilization of Eu2+-containing complexes in synthetic chemistry, materials science, and medicine.

The kinetic stabilities and relaxivities of a series of Eu2+-containing cryptates have been investigated. Transmetallation studies that monitored the change in the longitudinal relaxation rate of water protons in the presence of Ca2+, Mg2+, and Zn2+ demonstrated that cryptate structure influences stability, and two of the cryptates studied were inert to transmetallation in the presence of these endogenous ions. The efficacy of these cryptates was determined at different magnetic field strengths, temperatures, and pH values. Cryptate relaxivity was found to be higher at ultra-high field strengths (7 and 9.4 T) relative to clinically relevant field strengths (1.4 and 3 T), but the efficiency of these cryptates decreased as temperature increased. In addition, variation in pH did not yield significant changes in the efficacy of the cryptates. These studies establish a foundation of important properties that are necessary to develop effective positive contrast agents for magnetic resonance imaging from Eu2+-containing cryptates.

Silver tetrahedral nanoparticles (NP) were synthesized using the inert gas condensation technique. We performed morphological and optical characterization of the nanoparticles (NPs) using atomic force microscopy (AFM), mass spectroscopy (MS), and UV-visible spectroscopy. The Ag NPs were produced by modified magnetron sputtering, followed by thermalization and condensation in a high pressure zone. Along the synthesis process, the size of the NPs was controlled through the handling of the gas flow (Ar and He), the magnetron power, and the length of the aggregation zone. We optimized the synthesis parameters to obtain a peak on the size distribution of Ag NPs around of 5 nm (as measured with AFM and MS). The AFM measurements show that the particles have tetrahedral shape, with a fair correspondence with a 2925-atoms ideal tetrahedron. We performed a set of Molecular Dynamics (MD) calculations using the Embedded Atom potential model to simulate the dynamics of particles with different shapes, obtaining that, at sizes close to that of the particles produced experimentally, the tetrahedra may be as energetically stable as cuboctahedra of roughly the same size, and that their melting point is below but close to that of the bulk. We also found that both the size and shape of the nanoparticles determine the shift of the UV-visible absorption spectrum. Finally, we observed the formation of atomic islands above the faces of the Ag tetrahedral NPs, in agreement with the results obtained from the MD simulations.