Catechol derivatives-coated Fe3O4 and gamma-Fe2O3 nanoparticles as potential MRI contrast agents.

Superparamagnetic iron oxide nanoparticles, Fe(3)O(4) and gamma-Fe(2)O(3), were produced by the so-called polyol process. In order to stabilize the particles in a physiological environment as potential contrast agents for Magnetic Resonance Imaging (MRI), the as-prepared particles were successfully transferred to an aqueous medium through ligand exchange chemistry of the adsorbed polyol species with the dopamine or the catechaldehyde. The ligands were able to participate in bidentate binding to the nanoparticles surface and to improve the stability of aqueous suspensions of the nanoparticles. Analysis was performed by various techniques including X-ray diffraction, transmission electron microscopy, infrared spectroscopy and thermal analysis. The results of magnetic measurements and initial in vitro magnetic resonance imaging essays are presented for the pre- and post-surface modified nanoparticles, respectively and discussed in relation with their structure and microstructure.

Infrared and polarized Raman spectra of a noncentrosymmetric compound "sodium samarium fluorosilicate" NaSmSiO4.0.25NaF.

Chemical preparation, infrared and Raman spectra of sodium samarium fluorosilicate, NaSmSiO(4).0.25NaF are presented. The spectra are analyzed with regard to the symmetry, and the numbers of the SiO(4)(4-) internal vibrational modes observed in the Raman and infrared spectra are consistent with the predictions.

Vibrational study of Li6P6O18.3H2O and ab initio calculations in P6O18 and P6O18.3H2O.

The infrared and polarized Raman spectra of the trigonal Li(6)P(6)O(18).3H(2)O crystal are reported. The results are analysed using several group theory approaches, in terms of internal and external modes of the highly symmetric P(6)O(18) cyclophosphoric ring and water molecules. Equilibrium geometries and vibrational spectra of P(6)O(18) units, free and in interaction with water molecules (P(6)O(18).3H(2)O) have been determined by ab initio calculations using the basis set 6-31+G(d) of Hartree Fock method. Experimental frequencies and polarisation conditions are remarkably consistent with ab initio calculations. A detailed description of the normal modes of vibration of these systems is presented.

Correlation between 31P chemical shift tensor and local structure in lithium cyclohexaphosphates Li6P6O18 x 3H2O and Li6P6O18.

To understand the surprising behavior between the variations of the P'-P-P" angles and the correlated variations of the O'-P-O" ones, two lithium cyclohexaphosphate compounds Li6P6O18 x 3H2O and Li6P6O18 are studied by solid state nuclear magnetic resonance (NMR) spectroscopy. The two compounds exhibit the same [P6O18]6- ring anions but with 3m or 1 internal symmetry, respectively. Such symmetries induce local distortions that are exhibited by NMR spectroscopy. One-dimensional (1D) NMR gives information on structural sites of 7Li and 31P ions and the crystallographic non-equivalencies are observed. Nevertheless, in the anhydrous compound, X-ray diffraction and NMR results do not completely agree and some discrepancy exists between the number of sites observed with the first technique and the number of lines exhibited in the NMR spectra either for 7Li or 31P nuclei. This problem is elucidated by using 2D double quantum NMR spectroscopy coupled with theoretical considerations. We find that the 31P chemical shift tensor is dependent on the deviations of the O-P-O angles from those in the regular tetrahedron. Within the same empirical model, we suggest that the surprising behavior between the variations of the P'-P-P" and the ones of the O'-P-O" is related to the overall charge on the PO4 group. We also find the positions of the isotropic lines for 7Li essentially depend on the site co-ordination of this nuclei.