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International audience; Monoclinic and cubic europium-doped Gd2O3 structures were selectively synthesized by the glycine–nitrate process by fine control of the synthesis temperature through the crucial fuel/oxidant ratio. The cubic phase is obtained under fuel-rich conditions, whereas stoichiometric conditions induce the simultaneous formation of cubic and monoclinic polymorphs. The samples were subjected to appropriate sintering to obtain highly crystalline and carbon-free materials. The average nanoparticle (NP) size determined by TEM for these nanopowders (23 nm) agrees with the average crystallite sizes obtained from XRD Rietveld analysis; therefore, the particles are monocrystalline. Both electron energy loss spectroscopy (EELS) and photoluminescence studies showed that the europium-doped NPs are highly luminescent, and the Eu3+ ions are homogeneously distributed over the whole material as well as over the two gadolinium crystallographic sites of the cubic phase. These fluorescent NPs exhibit relaxivities that define them as potential T1 contrast agents for further biomedical applications.

International audience; The lanthanide (Ln3+) complexes of three cyclen-based ligands containing three methylphosphonate pendant arms were studied, the ligands being 1,4,7,10-tetraazacyclododecane-1,4,7-triyltris(methylphosphonic acid) (H6do3p), 3-[4,7,10-tris(phosphonomethyl)-1,4,7,10-tetraazacyclododec-1-yl]propanoic acid (H7do3p1pr), and 10-(3-hydroxypropyl)-1,4,7,10-tetraazacyclododecane-1,4,7-triyltris(methylphosphonic acid) (H6do3p1ol). The three macrocyclic ligands form complexes of very high thermodynamic stability with all studied Ln3+ ions. Kinetic studies showed that the acid-assisted dissociation of Ce3+ complexes of these ligands is much faster than for the complex of the related ligand H8dotp [1,4,7,10-tetraazacyclododecane-1,4,7,10-tetrayltetrakis(methylphosphonic acid)]. The number of water molecules coordinated to the Eu3+ and Gd3+ complexes was estimated to be < 1 for the do3p1ol ligand but ca. 1 for the other two ligands, as obtained by time-resolved luminescence spectroscopy and by 1H and 17O relaxometric measurements. The NMR spectroscopic data indicate the existence of a considerable contribution from second-sphere water molecules to the relaxivity of all the Gd3+ complexes studied. The 1H and 31P NMR spectra of the Eu3+, Yb3+ and Lu3+ complexes showed that the propionate arm in the [Ln(do3p1pr)]4- complexes and the propanol arm in the [Ln(do3p1ol)]3- complexes are not bound to the Ln3+ ion. The [Ln(do3p)]3- and [Ln(do3p1pr)]4- complexes have a clear preference for the TSAP (twisted square antiprismatic) isomer, while both SAP (square antiprismatic) and TSAP isomers are present in solutions of the [Ln(do3p1ol)]3- complexes.

The interaction of the negatively charged Ln3+ chelate Ln–DOTP with β- and γ-cyclodextrins bearing ammonium groups at the upper rim (CD+s) was investigated using mass spectrometry and NMR spectroscopic techniques. Mass spectroscopy shows the presence of 1:1 adducts of Ln–DOTP and both β- or γ-CD+. The peak intensities increased upon increasing the pH of the samples from 7 to 9.0, suggesting an increase in the strength of the interaction. Lanthanide induced 1H NMR chemical shifts and relaxation ratesmeasured in aqueous solutions confirmed the presence of these adducts. The strength of the interactions appeared to be dependent on the pH, reflecting the strong electrostatic interactions between the oppositely charged host CD+ and guest Ln–DOTP chelate. Evaluation of the lanthanide induced relaxation rates showed that the Ln–DOTP does not enter the cavity of the CDs, but remains above it with a distance of 10–11 A between the Ln3+ ion and the centre of the CD. Molecular modelling indicated that hydrogen bonds between the functionalized groups participating in the interaction sites contribute to the adduct stabilization. The apparent binding constants at pH 7 and 9 were obtained by using relaxometric measurements at 9 MHz. Fitting the NMRD profiles showed an increase in the number of second-sphere water molecules surrounding the phosphonate pendant arms of the Ln–DOTP chelate upon its interaction with the CDs. A brief description of the PARACEST properties of the supramolecular systems formed by Tm–DOTP and the positively charged CDs is presented. Both CDs display a shift of the saturation transfer peaks of the ammonium functions by the Tm complex, with an accentuated effect observed for the γ-CD derivative.

Five DOTA-like ligands lacking a water molecule in the first coordination sphere of their Gd III complexes, namely the phosphinates H 4 DOTP H , H 4 DOTP hm and H 4 DOTP Et , and the phosphonate monoesters H 4 DOTP OEt and H 4 DOTP OBu , were synthesized with the aim of exploring the influence of the second hydration sphere on the relaxivity of Gd III complexes. The H 4 DOTP H , H 4 DOTP hm and H 4 DOTP OEt ligands and their Ln III complexes were characterized by potentiometry and time-resolved luminescence; the Gd III complexes are thermodynamically much less stable than that of H 4 DOTA, and no water is coordinated in the inner sphere. The crystal structures of the free ligand H 4 DOTP OEt and of the Gd III complexes of H 4 DOTP H and H 4 DOTP OEt were determined by X-ray diffraction. The complexes have the expected octadentate coordination mode with an N 4 O 4 arrangement; no water molecule is bound to the Gd III ion. Information on the structures of the Ln III complexes of all five ligands in aqueous solution were obtained from 1 H and 31 P NMR spectra. The NMR spectra of the [Ln(DOTP hm )]- and [Ln(DOTP Et )]- complexes show that these compounds have a clear preference for a specific arrangement of phosphorus atoms which gives rise to the symmetrical RRRR (or SSSS) isomer. However, many diastereoisomers were observed for all other complexes. Ln III -induced 17 O NMR shift data reveal that the spatial location of the second-sphere water molecules for the two groups of complexes differs. The parameters governing the effect of the second hydration sphere on the relaxivity of the Gd III complexes of all ligands were evaluated by EPR, variable-temperature 17 O NMR spectroscopy and 1 H NMRD re-laxometry. The presence of second-sphere water molecules is clearly confirmed, depending on the character of the pendant arms. As the relaxivity does not depend significantly on the nature of the phosphorus substituents and/or on the isomerism present in solution, the second-sphere water molecules should be located close to the phosphorus-oxygen atoms.

The behaviour of the cyclic trimeric V v complex [V 3 O 3 (μ-0) 3 (dmpp) 3 (H 2 O)](H 2 O) 2 , V 3 L 3 , (L = Hdmpp = 3-hydroxy-1,2-dimethyl-4-pyridinone) was studied in methanol and methanol/water solutions by using 51 V and 1D- and 2D 1 H NMR spectroscopy. Red crystals, isolated from a highly concentrated methanol solution of the trimeric complex, were analysed by X-ray crystallography. The solid-state structure of the compound showed the presence of a new dinuclear V v cluster and allowed for its formulation as a [V 2 O 2 (μ-O)-(dmpp) 2 (OCH 3 ) 2 ] complex, V 2 Y 2 L 2 (Y = OCH 3 ). This complex crystallises in the monoclinic system: P2 1 /c, a = 8.4573(11) A, b = 15.034(2) A and c = 15.849(2) A, β = 105.300(2)°, V = 1943,7(4)A 3 , Z = 2, and R 1 (wR 2 ) = 0.0492(0.1706). The trimer V 3 L 3 complex dissolved in a dry methanol solution fully decomposes, as shown by the 51 V NMR signals at -388, -450 and -551 ppm, which are assigned to a monomer complex [VO(OMe)(dmpp) 2 ] (VYL 2 ), the dimer V 2 Y 2 L 2 and the monomethyl ester of monovanadate, V 1 Y (V 1 = monovanadate; Y = OCH 3 ), respectively. In methanol/water solutions, a new 51 V NMR signal appears at δ = -492 ppm, which is assigned to the [VO 2 (dmpp)(H 2 O) 2 ] (VL) complex. When the percentage of water in the mixture increases, the relative intensities of the V 2 Y 2 L 2 and V 1 Y signals decrease sharply, and a broad signal at -488 ppm appears, corresponding to the original V v trimer complex, which is the only species present in 94 % water. A temperature-dependent 1 H NMR study of a CD 3 OD solution of V 3 L 3 confirmed the presence, at room temperature, of the dinuclear V 2 L 2 complex and the VL 2 species. At temperatures below 0 °C down to -50 °C, the appearance of new signals reflects the presence of isomers for the V 2 Y 2 L 2 and VYL 2 species with different stabilities and symmetries. 2D 1 H homonuclear NMR exchange experiments (EXSY) allowed us to establish the isomeric equilibria that take place in solution, and indicates intramolecular exchange between the two ligands of the major isomer of VYL 2 and intermolecular exchange between the major and minor isomers of species of different nuclearity, V 2 Y 2 L 2 and VYL 2 . However, no evidence was found for intermolecular exchange between the major isomers and between the minor isomers of species of different nuclearity or between isomers of species of the same nuclearity.

The synthesis and characterization of a new class of DTPA bisamide-linked glycoconjugates of different sugars (lactose, Lac, and galactose, Gal) and valencies (di and tetra) and their Ln(III) complexes is reported. The 1H NMR spectra of the Sm(III) and Eu(III) complexes of DTPAGal2, DTPAGal4, and DTPALac2 obtained between 7 and 80 ºC, indicate that most (if not all) of the four possible diastereoisomeric pairs of structures, resulting from the chirality of the three bound DTPA nitrogen atoms, are present in solution, with different relative populations. The dynamic effects of racemization of the central nitrogen on the NMR spectra show that this process is in fast exchange at 60 ºC for the Sm(III) complexes and in slow exchange at 7 ºC for the Eu(III) complexes. The in vitro r1 nuclear magnetic relaxation dispersion (NMRD) of the water protons of the Gd(III)-DTPA bis-amide glycoconjugate containing two lactosyl moieties, Gd(III)-DTPALac2, was studied, yielding the molecular parameters that govern its relaxivity. Its r1 value, at 25 oC and 20 MHz, is 13% higher than that reported for Gd(III) chelates of lower molecular weight DTPA-bisamides, such as DTPA-BMA, consistent with a five times longer tau-R value. The water exchange rate, kex, and the electron spin relaxation parameters of the Gd(III)-DTPALac2 complex are within the usual range for similar Gd(III)-DTPA bisamide chelates., EU COST Action D18 “Lanthanide chemistry for diagnosis and therapy”. Fundação para a Ciência e Tecnologia - POCTI/QUI/47005/2002. FEDER. Swiss National Science Foundation. Swiss Federal Office for Education and Science.

A new trinuclear oxovanadium(V) complex with the anionic dmpp ligand (Hdmpp = 3-hydroxy-1,2-dimethyl-4-pyridinone), [V3O6(dmpp)3(H2O)](H2O)2, was isolated from the reaction of Hdmpp, KOH and sodium metavanadate at pH 4.5. The solid state structure of the [V3O6(H2O)(dmpp)3](H2O)2 complex, investigated by X-ray diffraction methods, was found to contain a cyclic trinuclear metal cluster. This complex crystallises in the monoclinic system: P21/n, a =

Copper(II) mononuclear complexes with the polyazamacrocyclic ligands NOTA (1,4,7-triazacyclononane-N,N′,N″triacetate), DOTA (1,4,7,10-tetraazacyclo-dodecane-N,N′,N″,N″′-tetraacetate), NOTP [1,4,7-triazacyclononane-N,N′,N″-tris(methylenephosphonate)] and DOTP [1,4,7,10tetraazacyclododecane-N,N′,N″,N‴-tetrakis(methylenephosphonate)] were characterised in aqueous solution by electronic absorption spectrophotometry and electron paramagnetic resonance (EPR) spectroscopy. While two isomeric species were detected by EPR spectroscopy in frozen samples of the polycarboxylate complexes, only one complex form was found for the poly(methylenephosphonate) systems. The results obtained are in accordance with a six-coordinate pattern for the metal centre, yielding tetragonally distorted complexes in solution, in agreement with previously reported studies on CuII complexes, both in solution and in the solid state.

The interactions between α-, β-, and γ-CD and the TmIII chelates of the macrocyclic polyaminopolycarboxylates DOTA and NOTA were studied with the use of 1H- and 13C-NMR shift and relaxation rate measurements. Interactions were only observed between Tm(DOTA)- and γ-CD. The structure and the stability of the concerning supramolecular structures was elucidated by fitting of the NMR titration curves to a theoretical model. It appears that an inclusion compound is formed, where the hydrophobic macrocyclic part of the chelate sits in the γ-CD cavity. This inclusion compound binds a second Tm(DOTA)- molecule at the outside lower rim of the CD cone. The binding occurs probably via hydrogen bonds between non-chelated carboxylate oxygen atoms of the concerning Tm(DOTA)- and CH2OH groups of the γ-CD molecule, which are in a favorable position due to opening of the γ-CD cone angle as a result of the inclusion of the first γ-CD. http://dx.doi.org/10.1002/(SICI)1099-0682(19990202)1999:23.0.CO;2-W

The front cover picture shows gives an impression on the breadth of coverage of this Cluster Issue on Metal-Based Magnetic Resonance Imaging Probes. Superimposed on an angiographic MRI image are the zeolite cages for Gd3+ and the mode of action of this probe from the review by J. A. Peters and K. Djanashvili (top) and a depiction of the principle of magnetoluminescent contrast agents for dual MRI and luminescence imaging (V. C. Pierre et al., bottom right). Representative of papers on different approaches to optimize the efficacy of contrast agents are the PARACEST properties of the large Tm-DOTP–cyclodextrin complex of C. F. G. C. Geraldes et al. (bottom left) and the high relaxivity associated with two bis(aqua) complexes of M. Mazzanti et al. (center left). We thank the authors for making their graphics available for use on the cover and Dr. Giorgio Gatti for the time-consuming creation of this attractive picture.