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International audience; Given their potential in a better characterization and diagnosis of major pathologies like cancer or chronic inflammation, redox-activated Magnetic Resonance Imaging (MRI) probes have recently attracted much interest from chemists. Such redox responsive probes are capable of reporting on specific biomarkers that are related to tissue redox potential disruption or hypoxia. Lately, this research area has experienced remarkable development, including redox-responsive metal complexes and nanoparticles. Here we critically review the progress with a specific focus on metal-based probes and some nanoparticle examples. We demonstrate, via representative cases, the different molecular mechanisms that can generate a redox-modulated MRI response. They can be based on the redox activity of either the ligand or the metal center, provided the different oxidation states of the metal ion are endowed with different magnetic properties. A particular emphasis is given to recent advances and to the imaging probes that have attained in vivo validation. In overall, we aim to provide the reader with a comprehensive view of how intracellular or extracellular redox buffer systems can be assessed by using MRI contrast agents based on lanthanide or transition metal ions using T1-weighted, T2-weighted, paraCEST 1H or 19F MRI.

International audience; For the development of redox responsive MRI probes based on the MnIII/MnII couple, stable complexation of both reduced and oxidized forms of the metal ion and appropriate tuning of the redox potential in the biologically relevant range are key elements. The water soluble fluorinated Mn-porphyrin derivative Mn-3 satisfies both requirements. In aqueous solutions, it can reversibly switch between MnIII/MnII oxidation states. In the presence of ascorbic acid or beta-mercaptoethanol, the MnIII form undergoes reduction, which is slowly but fully reversed in the presence of air oxygen. A UV-Vis kinetic study of MnIII/MnII reduction under oxygen-free conditions yielded second-order rate constants, k2, of 46.1 M-1 s-1 and 13.8 M-1 s-1 for the reaction with ascorbic acid and beta-mercaptoethanol, respectively. This could correspond, in the absence of oxygen, to a half-life of a few minutes in blood plasma and a few seconds in circulating immune cells where ascorbic acid reaches 20-40 muM and a few mM concentrations, respectively. In contrast to expectations based on the redox potential, reduction with glutathione or cysteine does not occur. It is prevented by the coordination of the glutathione carboxylate group(s) to MnIII in the axial position, as was evidenced by NMR data. Therefore, MnIII-3 acts as an ascorbate specific turn-on MRI probe, which in turn can be re-oxidized by oxygen. The relaxivity increase from the oxidized to the reduced form is considerably improved at medium frequencies (up to 80 MHz) with respect to the previously studied Mn-TPPS4 analogues; at 20 MHz, it amounts to 150%. No in vitro cytotoxicity is detectable for Mn-3 in the typical MRI concentration range. Finally, 19F NMR resonances of MnIII-3 are relatively sharp which could open further opportunities to exploit such complexes as paramagnetic 19F NMR probes.

The NMR relaxivities of the decatungstolanthanoate core-shell nanoparticles, prepared by encapsulating [Ln(W5O18)2]9− polyoxometalates (LnPOM) within amorphous silica shells (K9[Ln(W5O18)2]@SiO2), were studied along the Ln series. The relaxivity of GdPOM is slightly higher than for Gd-DTPA due to second-sphere relaxation effects, but the values for the other paramagnetic LnPOMs are much smaller due to the short T1e values of their Ln3+-ions. The NPs have core-shell spherical structures, with LnPOM-containing cores with 9.5–28 nm diameters, and 4.0–11.0 nm thick amorphous silica shells. In water suspensions, the NPs have negative zeta potentials (−32.5 to −40.0 mV) and time-dependent hydrodynamic diameters (31–195 nm) reflecting the formation of aggregates. The relaxivities of GdPOM@SiO2 NPs suspensions (r1=10.97 (mM Gd)−1 s−1, r2=12.02 (mM Gd)−1 s−1, 0.47 T, 25 °C) are considerably larger than for the GdPOM solutions, indicating that their silica shell is significantly porous to water. This increase is limited by the agglomeration of the complexes in the NPs core, limiting their access to water to those at the core surface. Replacing half of the Gd3+ ions by Eu3+ decreases the NPs r1 and r2 relaxivities at 0.47 T to 20 % and 35 % of their initial values, which are still considerable, but does not affect the efficient luminescence properties of the Eu3+ centers. This indicates that the mixed NPs have potential as dual modality MRI/optical imaging contrast agents.

Partial symmetry, i.e., the presence of more than one molecule in the asymmetric unit of a crystal, is a relatively rare phenomenon in small-molecule crystallography, but is quite common in protein crystallography, where it is typically known as non-crystallographic symmetry (NCS). Several papers in literature propose molecular determinants such as crystal contacts, thermal factors, or TLS parameters as an explanation for the phenomenon of intrinsic asymmetry among molecules that are in principle equivalent. Nevertheless, are all of the above determinants the cause or are they rather the effect? In the general frame of the NCS often observed in crystals of biomolecules, this paper deals with nickel(II)-substituted human carbonic anhydrase(II) (hCAII) and its SAD structure determination at the nickel edge. The structure revealed two non-equivalent molecules in the asymmetric unit, the presence of a secondary nickel-binding site at the N-terminus of both molecules (which had never been found before in the nickel-substituted enzyme) and two different coordination geometries of the active site nickel (hexa-coordinated in one molecule and mainly penta-coordinated in the other). The above-mentioned standard molecular crystallographic determinants of this asymmetry are analyzed and presented in detail for this particular case. From these considerations, we speculate on the existence of a fundamental, although yet unknown, common cause for the partial symmetry that is so often encountered in X-ray structures of biomolecules.

Mn(III) porphyrins have great potential as Gd-free MRI contrast agents because both the cation and the ligand have interesting properties. The redox properties of the Mn(III)-ion can be exploited for the preparation of reactive oxygen species for therapy. Moreover, the porphyrin ligand allows these complexes to have a high affinity for tumor tissues. The inherent properties of the porphyrin ligands make these systems attractive for photothermal, photodynamic, and sonodynamic therapies. Therefore, these systems are attractive for the development of theranostics for MRI-guided therapy. For the magnetic field strengths at which most clinical MRI machines operate at present (0.5–1.5 T), the longitudinal relativity of low-molecular-weight complexes is even higher than that of the classical Gd-based contrast agents. This review gives an overview of the developments in the field of Mn(III) porphyrin contrast agents during the last 30 years.

The number of scientific reports on the field of imaging in biomedical sciences is rising massively, with the emergence of “noninvasive” in vivo imaging technologies, of which Magnetic Resonance Imaging (MRI) is considered to be among the top techniques in modern Medical Imaging. These techniques manage to detect events at molecular and cellular levels, providing a faster diagnostic evaluation to oncology patients and consequently hastening drug development processes. Of the many contrast agents developed by Organic Chemists during the last decades, tetrapyrrolic macrocycles like porphyrins and related compounds, like phthalocyanines, represent some of the oldest, most widely studied chemical structures in biomedical applications. These macrocyclic structures display intrinsic affinity for tumor localization, and their well-described photosensitizing and photophysical features allured many scientists toward their potential use as contrast agents in a variety of in vivo imaging technologies, namely in the MRI technique. Furthermore, a special emphasis is put on the development of multimodal contrast agents, which may be the future of Medical Imaging. This review intends to give an insight on developments on MRI technologies involving tetrapyrrolic-based contrast agents for cancer detection. It is a Chemist’s view, regarding the synthesis of the crucial contrast agents, selecting influential milestones over the last few decades on this field, along with pertinent reflections pointing to future guidelines.

International audience; Aggregation of misfolded proteins and progressive polymerization of otherwise soluble proteins is a common hallmark of a wide range of highly debilitating and increasingly prevalent diseases, including amyotrophic lateral sclerosis, cerebral amyloid angiopathy, type II diabetes and Parkinson's, Huntington's and Alzheimer's diseases. There is a growing interest in creating imaging agents to detect such aggregates in various imaging modalities, including PET, SPECT and MRI. We present here an overview of recent efforts from the perspective of early diagnosis of amyloid diseases, with a major focus on Aβ detection and metal complexes bearing PiB units.

[Abstract] In the periodical system, the lanthanides (the 15 elements in the periodic table between barium and hafnium) are unique in the sense that their trivalent cations have their valence electrons hidden behind the 5s and 5p electrons. They show a gradual decrease in ionic radius with increasing atomic number (also known as the lanthanide contraction). The resulting steric effects determine to a large extent the geometries of complexes of these ions. Here, we discuss these effects, particularly upon the properties of the complexes in aqueous solution, for selected families of Ln3+-complexes of oxycarboxylate and aminocarboxylate ligands. The physical properties of the cations are very different, which is very useful for the elucidation of the configuration, conformation and the dynamics of the complexes by X-ray techniques, NMR spectroscopy, and optical techniques. Often the structural analysis is assisted by computational methods.

International audience; Superparamagnetic maghemite core–porous silica shell nanoparticles, γ-Fe2O3@SiO2 (FS), with 50 nm diameter and a 10 nm core, impregnated with paramagnetic complexes b-Ln ([Ln(btfa)3(H2O)2]) (where btfa = 4,4,4-trifluoro-l-phenyl-1,3-butanedione and Ln = Gd, Eu, and Gd/Eu), performing as promising trimodal T1–T2 MRI and optical imaging contrast agents, are reported. These nanosystems exhibit a high dispersion stability in water and no observable cytotoxic effects, witnessed by intracellular ATP levels. The structure and superparamagnetic properties of the maghemite core nanocrystals are preserved upon imbedding the b-Ln complexes in the shell. Hela cells efficiently and swiftly internalize the NPs into the cytosol, with no observable cytotoxicity below a concentration of 62.5 μg mL–1. These nanosystems perform better than the free b-Gd complex as T1 (positive) contrast agents in cellular pellets, while their performance as T2 (negative) contrast agents is similar to the FS. Embedding of the b-Eu complex in the silica pores endows the nanoparticles with strong luminescence properties. The impregnation of gadolinium and europium complexes in a 1:1 ratio afforded a trimodal nanoplatform performing as a luminescent probe and a double T1 and T2 MRI contrast agent even more efficient than b-Gd used on its own, as observed in cell-labeled imaging experiments and MRI cell pellets.

A series of Mn(II) aminophosphonate complexes were successfully synthesized and intercalated into the hydroxy double salt [Zn5(OH)8]Cl2·yH2O. Complex incorporation led to an increase in the interlayer spacing from 7.8 to 10–12 A. Infrared spectroscopy showed the presence of the characteristic vibration peaks of the Mn(II) complexes in the intercalates' spectra, indicating successful incorporation. The complex-loaded composites had somewhat lower proton relaxivities than the pure complexes. Nevertheless, these intercalates may have use as MRI contrast agents for patients with poor kidney function, where traditional Gd(III)-based contrast agents cause severe renal failure.

A semi-empirical equation to estimate the hydration number of Mn(II) complexes was derived from a database of 49 previously published 1H longitudinal Nuclear Magnetic Relaxation Dispersion profiles. This equation has the longitudinal 1H relaxivity and the molecular weight of the Mn(II) complex under consideration as parameters.

Three triaza macrocyclic ligands, H6NOTP (1,4,7-triazacyclononane-N,N′,N″-trimethylene phosphonic acid), H4NO2AP (1,4,7-triazacyclononane-N-methylenephosphonic acid-N′,N″-dimethylenecarboxylic acid), and H5NOA2P (1,4,7-triazacyclononane-N,N′-bis(methylenephosphonic acid)-N″-methylene carboxylic acid), and their gallium(III) chelates were studied in view of their potential interest as scintigraphic and PET (Positron Emission Tomography) imaging agents. A 1H, 31P and 71Ga multinuclear NMR study gave an insight on the structure, internal dynamics and stability of the chelates in aqueous solution. In particular, the analysis of 71Ga NMR spectra gave information on the symmetry of the Ga3+ coordination sphere and the stability of the chelates towards hydrolysis. The 31P NMR spectra afforded information on the protonation of the non-coordinated oxygen atoms from the pendant phosphonate groups and on the number of species in solution. The 1H NMR spectra allowed the analysis of the structure and the number of species in solution. 31P and 1H NMR titrations combined with potentiometry afforded the measurement of the protonation constants (log KHi) and the microscopic protonation scheme of the triaza macrocyclic ligands. The remarkably high thermodynamic stability constant (log KGaL =34.44 (0.04) and stepwise protonation constants of Ga (NOA2P)2− were determined by potentiometry and 69Ga and 31P NMR titrations. Biodistribution and gamma imaging studies have been performed on Wistar rats using the radiolabeled 67Ga(NO2AP)− and 67Ga (NOA2P)2−chelates, having both demonstrated to have renal excretion. The correlation of the molecular properties of the chelates with their pharmacokinetic properties has been analysed., The authors thank the financial support from the Fundação para a Ciência e Tecnologia (F.C.T., Portugal, projects RREQ/481/QUI/2006 and RECI/QEQ-QFI/0168/2012), the Rede Nacional de RMN (RNRMN), the Hungarian Scientific Research Fund (OTKA grants K-109029 and K-120224), the János Bolyai Research Scholarship (Gy.T.) of the Hungarian Academy of Sciences and the EU COST Action TD1004 “Theragnostics Imaging and Therapy”. The research was also supported by the EU and co-financed by the European Regional Development Fund (FEDER) under the projects CENTRO-07-CT62-FEDER) and GINOP-2.3.2-15-2016-00008., info:eu-repo/semantics/publishedVersion

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.

The availability of commercial 68Ge/68Ga cyclotron-independent 68Ga3+ generators is making Positron Emission Tomography (PET) accessible to most hospitals, which is generating a surge of interest in the design and synthesis of bi-functional chelators for Ga3+. In this work we introduce the NO2A-N-(α-amino)propionic acid family of chelators based on the triazacyclononane scaffold. Complexation of the parent NO2A-N-(α-amino)propionic acid chelator and of a low molecular weight (model) amide conjugate with Ga3+ was studied by 1H and 71Ga NMR. The Ga3+ chelate of the amide conjugate shows pH-independent N3O3 coordination in the pH range 3–10 involving the carboxylate group of the pendant propionate arm in a 6 member chelate. For the Ga[NO2A-N-(α-amino)propionate] chelate, a reversible pH-triggered switch from Ga3+ coordination to the carboxylate group to coordination to the amine group of the propionate arm was observed upon pH increase/decrease in the pH range 4–6. This phenomenon can conceivably constitute the basis of a physiological pH sensor. Both complexes are stable in the physiological range. The [67Ga][NO2A-N-(α-benzoylamido)propionate] chelate was found to be stable in human serum. Biodistribution studies of the 67Ga3+-labeled pyrene butyric acid conjugate NO2A-N-(α-pyrenebutanamido)propionic acid revealed that, despite its high lipophilicity and concentration-dependent aggregation properties, the chelate follows mainly renal elimination with very low liver/spleen accumulation and no activity deposition in bones after 24 hours. Facile synthesis of amide conjugates of the NO2A-N-(α-amino)propionic acid chelator, serum stability of the Ga3+ chelates and fast renal elimination warrant further evaluation of this novel class of chelators for PET applications.

International audience; We have conjugated the tetraazacyclododecane-tetraacetate (DOTA) chelator to Pittsburgh compound B (PiB) forming negatively charged lanthanide complexes, Ln(L4), with targeting capabilities towards aggregated amyloid peptides. The amphiphilic Gd(L4) chelate undergoes micellar aggregation in aqueous solution, with a critical micellar concentration of 0.68 mM, lower than those for the neutral complexes of similar structure. A variable temperature (17)O NMR and NMRD study allowed the assessment of the water exchange rate, k ex (298) = 9.7 × 10(6) s(-1), about the double of GdDOTA, and for the description of the rotational dynamics for both the monomeric and the micellar forms of Gd(L4). With respect to the analogous neutral complexes, the negative charge induces a significant rigidity of the micelles formed, which is reflected by slower and more restricted local motion of the Gd(3+) centers as evidenced by higher relaxivities at 20-60 MHz. Surface Plasmon Resonance results indicate that the charge does not affect significantly the binding strength to Aβ1-40 [K d = 194 ± 11 μM for La(L4)], but it does enhance the affinity constant to human serum albumin [K a = 6530 ± 68 M(-1) for Gd(L4)], as compared to neutral counterparts. Protein-based NMR points to interaction of Gd(L4) with Aβ1-40 in the monomer state as well, in contrast to neutral complexes interacting only with the aggregated form. Circular dichroism spectroscopy monitored time- and temperature-dependent changes of the Aβ1-40 secondary structure, indicating that Gd(L4) stabilizes the random coil relative to the α-helix and β-sheet. TEM images confirm that the Gd(L4) complex reduces the formation of aggregated fibrils.

International audience; Water soluble phthalocyanines bearing either four PEG500 or four choline substituents in the macrocyclic structure, as well as their Zn(II) and Mn(III) complexes were synthesized. The metal-free and Zn(II) complexes present relatively high fluorescence quantum yields (up to 0.30), while the Mn(III) complexes show no fluorescence as a consequence of rapid non-radiative deactivation of the Mn(III) phthalocyanine excited states through low-lying metal based or charge-transfer states. The effect of DMSO on the aggregation of the phthalocyanines was studied. It was not possible to obtain the Mn(II) complexes by reduction of the corresponding Mn(III) complexes due to the presence of electron donating substituents at the periphery of the phthalocyanines. The (1)H NMRD plots of the PEG500 and choline substituted Mn(III)-phthalocyanine complexes are typical of self-aggregated Mn(III) systems with r1 relaxivities of 4.0 and 5.7mM(-1)s(-1) at 20MHz and 25 degrees C. The Mn(III)-phthalocyanine-PEG4 complex shows no significant cytotoxicity to HeLa cell cultures after 2h of incubation up to 2mM concentration. After 24h of cell exposure to the compound, significant toxicity was observed for all the concentrations tested with IC50 of 1.105mM.

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.

The gallium(III) complex of a new tripodal 3-hydroxy-4-pyridinone (3,4-HP) chelator has been studied in terms of its physico-chemical and in vivo properties aimed at potential application as probe for nuclear imaging. In particular, based on spectrophotometric titrations, the hexa-coordinated (1:1) gallium complex appeared as the major species in a wide physiological acid-neutral pH range and its high stability (pGa = 27.5) should avoid drug-induced toxicity resulting from Ga(III) accumulation in tissues due to processes of transmetallation with endogenenous ligands or demetallation. A multinuclear ( 1 H and 71 Ga) NMR study gave some insights into the structure and dynamics of the gallium(III) chelate in solution, which are consistent with the tris-(3,4-HP) coordination and an eventual pseudo-octahedral geometry. Biodistribution and scintigraphic studies of the 67 Ga(III) labelled chelate, performed in Wistar rats, confirmed the in vivo stability of the radiolabelled complex, its non interaction with blood proteins and its quick renal clearance. These results indicate good perspectives for potential application of extrafunctionalized analogues in radiodiagnostic techniques.

Radiogalium chelates are important for diagnostic imaging in nuclear medicine (PET and ƴ-scintigraphy). Micelles are adequate colloidal vehicles for the delivery of therapeutic and diagnostic agents to organs and tissues. In this paper we describe the synthesis and in vitro and in vivo studies of a series of micelles-forming Ga(III) chelates targeted for the liver. The amphiphilic ligands are based on NOTA (NOTA = 1,4,7-triazacyclonoane-N,N’N’’-triacetic acid) and bear a α-alkyl chain in one of the pendant acetate arms (the size of the chain changes from four to fourteen carbon atoms). A multinuclear NMR study (1H, 13C, 27Al and 71Ga) gave some insights into the structure and dynamics of the metal chelates in solution, consistent with their rigidity and octahedral or pseudo-octahedral geometry. The critical micellar concentration of the chelates was determined using a fluorescence method and 27Al NMR spectroscopy (Al(III) was used as a surrogate of Ga(III)), both showing similar results and suggesting that the chelates of NOTAC6 form pre-micellar aggregates. The logP (octanol-water) determination showed enhancement of the lipophilic character of the Ga(III) chelates with the increase of the number of carbons in the α-alkyl chain. Biodistribution and Ƴ-scintigraphic studies of the 67Ga(III) labeled chelates were performed on Wistar rats, showing higher liver uptake for [67Ga](NOTAC8) in comparison to [67Ga](NOTAC6), consistent with a longer α-alkyl chain and a higher lipophilicity. After 24 hours both chelates were completely cleared off from the tissues and organs with no deposition in the bones and liver/spleen. [67Ga](NOTAC8) showed high kinetic stability in blood serum., Fundação para a Ciência e a Tecnologia (FCT)

Aqueous suspensions of metal organic frameworks (MOF) containing different Ln(3+) ions, consisting of a series of layered Ln(3+) networks formulated as [Ln(H(2)cmp)(H(2)O)] (where H(5)cmp is (carboxymethyl)iminodi(methylphosphonic acid), with a relatively wide size distribution (400 nm to 1 microm) were studied by relaxometry. The water (1)H longitudinal (r(1)) and transverse (r(2)) relaxivities were obtained for aqueous suspensions of these materials with different lanthanide ions. The values of r(1) are very small and varied only slightly with the effective magnetic moment (mu(eff)) of the lanthanide ions, while r(2) values are larger and proportional to the value of mu(eff)(2). The dependence of R(2) on tau(CP) (the time interval between two consecutive refocusing pulses in the train of 180 degrees pulses applied in a CPMG pulse sequence) was evaluated. The value of R(2) initially increases with tau(CP) and then saturates at higher tau(CP) at a value that is about 3 to 5 times lower than R(2p)*. This can be explained by the static dephasing regime (SDR) theory, in which the diffusion effect is taken into account and where the condition tau(D)Delta omega(r(p))(-1) holds (tau(D) = r(p)(2)/D, where D is the diffusion coefficient, r(p) is the radius of the particle, and Delta omega(r(p)) is the Larmor frequency shift at the particle's surface). Separation of the particles into two fractions with different particle sizes led to a significant enhancement of the r(2) relaxivity of the smaller particles with a narrow size distribution. Magnetometric measurements performed with the particles containing Dy(III), Ho(III), and Gd(III) showed a typical paramagnetic behavior from 4 to 100 K, used to determine the Curie constants.

The behaviour of three vanadium(V) systems, namely the pyridinone (V(V)-dmpp), the salicylaldehyde (V(V)-salDPA) and the pyrimidinone (V(V)-MHCPE) complexes, is studied in aqueous solutions, under aerobic and physiological conditions using (51)V NMR, EPR and UV-Visible (UV-Vis) spectroscopies. The speciations for the V(V)-dmpp and V(V)-salDPA have been previously reported. In this work, the system V(V)-MHCPE is studied by pH-potentiometry and (51)V NMR. The results indicate that, at pH ca. 7, the main species present are (V(V)O(2))L(2) and (V(V)O(2))LH(-1) (L=MHCPE(-)) and hydrolysis products, similar to those observed in aqueous solutions of V(V)-dmpp. The latter species is protonated as the pH decreases, originating (V(V)O(2))L and (V(V)O(2))LH. All the V(V)-species studied are stable in aqueous media with different compositions and at physiological pH, including the cell culture medium. The compounds were screened for their potential cytotoxic activity in two different cell lines. The toxic effects were found to be incubation time and concentration dependent and specific for each compound and type of cells. The HeLa tumor cells seem to be more sensitive to drug effects than the 3T3-L1 fibroblasts. According to the IC(50) values and the results on reversibility to drug effects, the V(V)-species resulting from the V(V)-MHCPE system show higher toxicity in the tumor cells than in non-tumor cells, which may indicate potential antitumor activity.

A bifunctional ligand, DO3A-py(NO-C) (DO3A-py(NO-C) = 10-[(4-carboxy-1-oxidopyridin-2-yl)methyl]-1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid), was attached to different generations (G0, G1, G2, and G4) of ethylenediamine-cored PAMAM dendrimers (PAMAM = polyamidoamine). The gadolinium(III) complex of this ligand possesses one molecule of water in its first coordination sphere and has a unique combination of a short water residence lifetime (tau(M) = 34 ns), a neutral overall charge, and a possibility for rigid attachment to molecules bearing primary amino groups. These favorable properties predestine the ligand for constructions of highly efficient nanosized contrast agents for magnetic resonance imaging (MRI). The coupling reaction between the carboxylic group on the pyridine-N-oxide moiety of the protected ligand molecule and primary amines in the dendrimers was achieved by an active ester method under nonaqueous conditions using the coupling agent TBTU. This reaction afforded conjugates with high loadings (80-100% of the theoretically available primary amines) and of high purity. The gadolinium(III) complexes of the conjugates were studied by variable-temperature 17O NMR and 1H NMRD measurements. The water residence lifetime (tau(M) = 55 ns) found in the largest conjugate G4-[Gd(H2O)(do3a-py(NO-C))]57, though somewhat longer compared to the "monomeric" complex, is still short enough not to limit the relaxivity. Surprisingly, compared with analogous conjugates with negatively charged chelates, the prepared uncharged compounds displayed much faster global rotational correlation times (tau(g)) and lower relaxivities. This phenomenon can be explained on the basis of Coulomb interactions. The motion of the charged chelates is restrained due to interactions with their counterions and the chelates themselves, while the uncharged chelates are not affected. Comparison of the PAMAM-based conjugates bearing uncharged and (1-)-charged chelates based on relaxometric data, 1H DOSY spectra, and SAXS measurements reveals that tau(g) reflects the rotational motion of large segments (dendrons) of the conjugates rather than that of the whole macromolecule.

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.

Complexes of Gd3+have found widespread application as contrast agents in magnetic resonance imaging (MRI)1,2 in which they are administered in relatively high doses, typically 0.1– 0.5 mmol kg−1. Numerous Gd3+ complexes have been approved for clinical use and, without exception, the ligand systems employed are octadentate polyamino-polycarboxylates that render the resulting complex either neutral or negatively charged.1,2 These complexes have high thermodynamic stability constants and are considered inert to dissociation under physiological conditions3; they are therefore excreted intact, usually through the renal system,3,4 within several hours of injection. All clinically approved agents also have in common a single coordinated water molecule. This water molecule, which is in relatively rapid exchange with the bulk solvent, contributes significantly to the relaxivity of the contrast agent. Relaxivity, the increase in water proton relaxation rate per unit concentration of contrast agent, is the measure of the effectiveness of the agent. One of the most successful contrast agents is the Gd3+ complex of DOTA (H4DOTA = 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid), a ligand based on the tetraazamacrocycle cyclen. The tetraamide derivatives of DOTA (generic structure shown in Fig. 1) form complexes with lanthanide ions that are structurally analogous to those of DOTA.5 However, unless ionizable groups, such as carboxylates or phosphonates, are incorporated into the ligand, the resulting Ln3+ complexes will be tri-cationic in nature. It is now an accepted feature of these complexes that the exchange kinetics of the coordinated water molecule is much slower than that in the corresponding polyamino-polycarboxylate complexes.5–9 The slow water exchange kinetics of these DOTA-tetraamide complexes was found to limit their relaxivities,5–9 and hence their potential as MRI contrast agents. However, this perceived shortcoming has since been found to be a favorable attribute. The Gd3+ complex of a DOTA-tetraamide ligand that has methylene phosphonate amide substituents, Gd1 (see Appendix), was found to act as a pH-sensing contrast agent.10 The mechanism of action of this agent involves the pH-dependent acceleration of water proton exchange between the coordinated and bulk water by the pendant phosphonate groups.10 This gives rise to low relaxivity when exchange is slow and higher relaxivity under the faster change regimen. The pH range over which this complex exhibits its change in relaxivity is ideal for measuring change in pH in vivo and pH maps of kidneys and tumors in mice have been acquired using this agent.11–13 FIGURE 1 The structure of some DOTA-tetraamide complexes. “Ln” is a generic symbol for a lanthanide ion. DOTA-tetraamide complexes have also shown the potential for generating contrast in MR imaging through chemical exchange saturation transfer (CEST). These paramagnetic CEST agents, often referred to as PARACEST agents,14,15 offer some potential advantages over conventional Gd3+-based contrast agents. In the complexes of Ln3+ ions that induce large hyperfine shifts, such as Eu3+, Tm3+, Dy3+ and Nd3+, the protons of the slowly exchanging coordinated water molecule are shifted far away from the bulk water and hence can easily be saturated by use of a frequency-selective presaturation pulse without directly saturating the solvent water signal itself. Subsequent exchange of these protons with those of the bulk transfers the saturation to the solvent water, thereby reducing its signal intensity and resulting in negative image contrast. The CEST properties of an agent are assessed by recording a CEST spectrum in which the solvent water signal intensity, as a percentage of its initial intensity (MS/M0 %), is plotted against the frequency offset of the presaturation pulse.14 Eu3+ is commonly employed as the basis of PARACEST agents because it has been reported to have the slowest water exchange kinetics of all Ln3+ ions in this type of complex.16 The CEST spectra of Eu2 show a peak at ~+50 ppm characteristic of CEST arising from the water molecule coordinated to Eu3+ (Fig. 2). The more intense peak at 0 ppm is the result of direct saturation of the solvent water protons. The Ln3+ complexes of 4 and 5 have also been extensively studied and found to have favorable CEST properties.9,17–23 In contrast, the exchange kinetics of the coordinated water molecule protons in Ln1 complexes are too rapid for a CEST effect to be observed for Eu1. Fitting the CEST spectra of Eu2 to the Bloch equations modified for exchange24 afforded a value of τM = 67 ± 6 μs (τM = 1/kex) longer than that of Ln1 but shorter than those of Eu3 (τM = 1.3 milliseconds).25 FIGURE 2 The CEST spectrum of a 50 mM solution of Eu2 recorded at 7 T, pH 7, 23°C, and B1 = 450 Hz, 320 Hz, 230 Hz, 160 Hz and 110 Hz, irr. time = 2 s. The solid lines are fits to the experimental data. This new method of generating image contrast offers several advantages over conventional agents, particularly in the development of targeted agents (in which motion artifacts can be reduced by interleaving images acquired with and without saturation)26 and responsive agents (in which ratio-metric detection can be used to eliminate the question of contrast agent concentration).27 However, if this class of compounds is to be used for in vivo applications then developing an understanding of how these compounds are tolerated by the body and their fate postinjection is imperative. As a first step toward this understanding, we have undertaken some in vivo investigations of a number of DOTA-tetraamide complexes (see Appendix) that differ in overall charge (see structures in Fig. 1).

The ion exchange intercalation of two Gd-based magnetic resonance imaging contrast agents into hydroxy double salts (HDSs) is reported. The presence of Gd(3+) diethylenetriaminepentaacetate and Gd(3+) diethylenetriaminepenta(methylenephosphonate) complexes in the HDS lattice after intercalation was confirmed by microwave plasma-atomic emission spectroscopy. The structural aspects of the HDS-Gd composites were studied by X-ray diffraction, with the intercalates having an interlayer spacing of 14.5-18.6 Å. Infrared spectroscopy confirmed the presence of characteristic vibration peaks associated with the Gd(3+) complexes in the intercalation compounds. The proton relaxivities of the Gd(3+) complex-loaded composites were 2 to 5-fold higher in longitudinal relaxivity, and up to 10-fold higher in transverse relaxivity, compared to solutions of the pure complexes. These data demonstrate that the new composites reported here are potentially potent MRI contrast agents.

et al., The relaxivity displayed by Gd3+ chelates immobilized onto gold nanoparticles is the result of the complex interplay between the nanoparticle size, the water exchange rate and the chelate structure. In this work we study the effect of the length of ω-thioalkyl linkers, anchoring fast water exchanging Gd3+ chelates onto gold nanoparticles, on the relaxivity of the immobilized chelates. Gold nanoparticles functionalized with Gd3+ chelates of mercaptoundecanoyl and lipoyl amide conjugates of the DO3A-N-(α-amino)propionate chelator were prepared and studied as potential CA for MRI. High relaxivities per chelate, of the order of magnitude 28-38 mM-1 s-1 (30 MHz, 25 °C), were attained thanks to simultaneous optimization of the rotational correlation time and of the water exchange rate. Fast local rotational motions of the immobilized chelates around connecting linkers (internal flexibility) still limit the attainable relaxivity. The degree of internal flexibility of the immobilized chelates seems not to be correlated with the length of the connecting linkers. Biodistribution and MRI studies in mice suggest that the in vivo behavior of the gold nanoparticles was determined mainly by size. Small nanoparticles (HD = 3.9 nm) undergo fast renal clearance and avoidance of the RES organs while larger nanoparticles (HD = 4.8 nm) undergo predominantly hepatobiliary excretion. High relaxivities, allied to chelate and nanoparticle stability and fast renal clearance in vivo suggest that functionalized gold nanoparticles hold great potential for further investigation as MRI contrast agents. This study contributes to a better understanding of the effect of linker length on the relaxivity of gold nanoparticles functionalized with Gd3+ complexes. It is a relevant contribution towards >design rules> for nanostructures functionalized with Gd3+ chelates as Contrast Agents for MRI and multimodal imaging., This work was financially supported by Fundação para a Ciência e a Tecnologia, Portugal: PhD grant SFRH/BD/63994/2009 to Miguel Ferreira and Sabbatical Grant SFRH/BSAB/1328/2013 to José Martins at Bath University, UK; and Rede Nacional de NMR (REDE/1517/RMN/2005) for the acquisition of the Varian VNMRS 600 NMR spectrometer in Coimbra. T.B.R. was supported by a Marie Curie Fellowship (FP/- PEOPLE-2009-IEF 254380) and an EMBO Fellowship (ALTF1145-2009). Financial support from Ministerio de Ciencia e Innovación, Spain, projects SAF2011-23622 (S.C.) and CTQ2010-20960-C02-02 (P.L.-L.), and Comunidad de Madrid, Spain, project S2010/BMD-2349 (S.C. and P.L.-L), is also acknowledged. B. Mousavi and L. Helm acknowledge financial support by the Swiss National Science Foundation.

A series of allyl complexes of the general formula [Cp'Mo(eta(3)-C3H5)(CO)(2)], where Cp' = Cp, CpMe, Cp*, Ind, IndMe, IndMe2, Flu, and three tungsten analogues, has been prepared and characterized by H-1, C-13, and Mo-95 NMR, cyclic voltammetry, and the structure of [IndMo(eta(3)-C3H5)(CO)(2)] was determined by Xray single crystal analysis. Two conformers, corresponding to the two extreme orientations of the allyl ligand (endo and exo), have been identified in solution by H-1 and Mo-95 NMR for all the complexes, except for [FluMo(eta(3)-C3F15)(CO)(2)], which only presents an exo conformation in solution. A Mo-95 NMR investigation also shows the influence of electron donor capability of the Cp' ligands on the Mo-95 chemical shifts of the Mo center. He I and He II photoelectron spectra probe the electron richness of the metal center and the electronic structure of the complexes. Cyclic voltammetry studies show one oxidation process, which is only reversible for the Cp derivatives. DFT calculations provided a reliable way to determine ionization energies, and reflected very well the trends of the other properties, from the Mo-95 NMR chemical shifts, to vibration frequencies, and oxidation potentials. (1) 2015 Elsevier BY. All rights reserved.

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 uptake of the oxidation products of two oxovanadium(IV) compounds, [N,N'-ethylenebis(pyridoxylaminato)]oxovanadium(IV), VIVO(Rpyr2en), and bis-[3-hydroxy-1,2-dimethyl-4-pyridinonato]oxovanadium(IV), VIVO(dmpp)2, by human erythrocytes was studied using 51V and 1H NMR and EPR spectroscopy. VIVO(Rpyr2en) in aerobic aqueous solution is oxidized to its VV counterpart and the neutral form slowly enters the cells by passive diffusion. In aerobic conditions, VIVO(dmpp)2 originates VV complexes of 1:1 and 1:2 stoichiometry. The neutral 1:1 species is taken up by erythrocytes through passive diffusion in a temperature-dependent process; its depletion from the extracellular medium promotes the dissociation of the negatively charged 1:2 species, and the protonation of the negatively charged 1:1 species. The identity of these complexes is not maintained inside the cells, and the intracellular EPR spectra suggest N2O2 or NO3 intracellular coordinating environments. The oxidative stress induced by the oxovanadium compounds in erythrocytes was not significant at 1 mM concentration, but was increased by both vanadate and oxidized VIVO(dmpp)2 at 5 mM. Only 1 mM oxidized VIVO(dmpp)2 significantly stimulated erythrocytes glucose intake (0.75 ± 0.13 against 0.37 ± 0.17 mM/h found for the control, pÂ

Phenylalanine hydroxylase (PAH) is a tetrahydrobiopterin (BH4)-dependent enzyme that catalyzes the hydroxylation of l-Phe to l-Tyr. The non-heme iron in the enzyme (Fe(III) as isolated) is 6-coordinated to a 2-His-1-carboxylate motif and three water molecules (wat1, wat2 and wat3). Tyr325 is at the second coordination sphere, hydrogen-bonded to water (wat1). We prepared and expressed mutants with Leu, Ala, Ser and Phe at this position. Only Y325L and the conservative mutation Y325F resulted in stable enzymes, but the mutant Y325F has been found to be post-translationally hydroxylated and to revert back to wild-type PAH [S.D. Kinzie, M. Thevis, K. Ngo, J. Whitelegge, J.A. Loo, M.M. Abu-Omar, J. Am. Chem. Soc. 125 (2003) 4710-4711], being inadequate to investigate the early inferred functional role of Tyr325. On the other hand, compared to wild-type PAH, Y325L shows reduced specific activity, decreased coupling efficiency and decreased iron content. The mutant also reveals a very high affinity for l-Phe and BH4 and does not manifest positive cooperativity for the substrate. All together, our results support that the mutation Y325L causes the removal or increased delocalization of the iron-ligated wat1 and, in turn, a less tight binding of the metal. Tyr325 thus appears to have an important role ensuring stoichiometric binding of iron, correct geometry of the complexes with substrate and cofactor and, consequently, a right coupling efficiency of the PAH reaction. In addition, the residue appears to be important for the correct cooperative regulation by l-Phe. http://www.sciencedirect.com/science/article/B6TGG-4G24X8N-2/1/c2de94cf547830652188dae1c1f6ed94

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.

The ligand H5dotasa (=(alphaRS)-alpha-(carboxymethyl)-1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid) is a H4dota-like macrocyclic ligand with a carboxymethyl CH2COOH substituent at the C(alpha) atom of one of the four acetate pendant arms of H4dota (=1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid), present as a racemic mixture of (alphaR) and (alphaS) enantiomers. The protonation constants of the ligand were determined by potentiometry, giving values close to those of H4dota except for the extra pK3 value of 5.35 assigned to protonation of the extra carboxylate group in the alpha-substituted (=succinic acid) pendant arm. The 1H-NMR spectra of H5dotasa at different pH values are too complex to allow the determination of its microscopic protonation scheme, due to the presence of multiple isomeric structures in solution. The thermodynamic stability constant of its Gd3+ chelate was determined by a potentiometric method, and the value obtained, log KML=27.2 (0.2), is higher than for the [Gd(dota)(OH2)]- complex. The solution structure of the asymmetric Ln3+ chelates of dotasa was studied by 1H-NMR spectroscopy, indicating the presence of four isomers, corresponding to the combination of the antiprismatic (M) and twisted antiprismatic (m) helicities of the pendant arms and to the (alphaR) and (alphaS) configurations at the substituted pendant arm. The m/M isomer ratio decreases along the lanthanide series, with the m isomer decreasing from 90% at La to ca. 50% from Eu-Lu. This shows that the expected m isomer population of the [Gd(dotasa)(OH2)]2- complex is higher than for the unsubstituted [Gd(dota)(OH2)]- (ca. 15%) but lower than for a Gd3+ chelate of an alpha,alphaprime,alphaPrime,alphaprimeprimeprime-tetrasubstituted (RRRR)-configurated dota (ca. 70%). Thus the stabilization of the m isomer by C' monosubstitution at the dota acetate pendant arm in [Gd(dotasa)(OH2)]2- is responsible for its increased H2O-exchange rate and higher relaxivity.

Li+ is the most effective drug used to treat bipolar disorder; however, its exact mechanism of action has yet to be elucidated. One hypothesis is that Li+ competes with Mg2+ for the Mg2+ binding sites on guanine-nucleotide binding proteins (G-proteins). Using 7Li T1 relaxation measurements and fluorescence spectroscopy with the Mg2+ fluorophore furaptra, we detected Li+/Mg2+ competition in three preparations: the purified G-protein transducin (Gt), stripped rod outer segment membranes (SROS), and SROS with purified Gt reattached (ROS-T). When purified ROS-T, SROS or transducin were titrated with Li+ in the presence of fixed amounts of Mg2+, the apparent Li+ binding constant decreased due to Li+/Mg2+ competition. Whereas for SROS the competition mechanism was monophasic, for Gt, the competition was biphasic, suggesting that in Gt, Li+/Mg2+ competition occurred with different affinities for Mg2+ in two types of Mg2+ binding sites. Moreover, as [Li+] increased, the fluorescence excitation spectra of both ROS-T and Gt were blue shifted, indicating an increase in free [Mg2+] compatible with Li+ displacement of Mg2+ from two low affinity Mg2+ binding sites of Gt. Gt release from ROS-T membrane was also inhibited by Li+ addition. In summary, we found evidence of Li+/Mg2+ competition in Gt-containing preparations. http://www.sciencedirect.com/science/article/B6TGG-4BJ2538-2/1/c5cc8bd5992b6629aba06705e0861119

A critical analysis of the lanthanide induced paramagnetic shift (LIS) data for several series of Ln3+ complexes of C3 symmetry in terms of structural changes, crystal-field effects and/or variation of hyperfine constants along the lanthanide series was undertaken using a combination of the two-nuclei and three-nuclei techniques together with the classical one-nucleus technique. The crystal-field independent two-nuclei technique to study the isostructurality of a series of lanthanide complexes, is usefully complemented by the three nuclei shift ratio method, which is based exclusively on the experimental shift data, requiring no knowledge of B02, 〈Sz〉 or Cj values. However, this later method cannot provide quantitative values for Fi and Gi. The combined use of the three methods was found to be a powerful analytical tool of the solution structure of lanthanide complexes. Isostructurality of whole series of complexes, either with no change of the Fi, Gi and B02 parameters (L5 and L6), or with changes of the Fi and B02 parameters (L7 and L8), is clearly defined by the combination of the two first methods. In these cases, the three-nuclei method sometimes fully supports such an isostructurality (L6, L8), but in other cases, due to the high structural sensitivity of its α and β parameters, it is able to detect small, unnoticed, structural changes in the complexes of L5 and L7. Clear structural changes, involving the Fi, Gi and B02 parameters, are observed for the series of complexes of (L9), where the three methods agree, involving hydration and carboxylate coordination changes. More subtle structural changes, involving the internal dynamics of the bound ligands, are proposed in other cases (L1–L4). These could also result from a magnification, by the present graphical analysis, of the breaks expected from the gradual structural changes along the series due to the lanthanide contraction.

The redox behavior of the potential oral insulin mimetic compound bis[3-hydroxy-1,2-dimethyl-4-pyridinonate]oxovanadium(IV), VO(dmpp) 2 , was studied in aqueous solution, under aerobic conditions and at different pH values and metal-to-ligand ratios, as well as the speciation of its V(V) oxidation products. Dissolution of this compound in water originates a violet solution with pH 4.7, which is partially oxidized to two V(V) species, VO 2 L and [VO 2 L 2 ] − , detected through their 51 V NMR signals at −485 and −504 ppm. However, the VO(dmpp) 2 compound still remains to some extent in solution, as confirmed by EPR Spectroscopy. High pH values favor the oxidation of the V(IV) complex in solution, whereas at low pH the V(IV) species are predominant. Aqueous solutions containing vanadate–Hdmpp mixtures spontaneously yield V(IV) species, reflecting the reducing capacity of the ligand. This reduction process is favored by ligand excess and low pH. For a ligand excess of fivefold or higher, the [VO 2 L 2 ] − complex, the only species present in solution, produces, at pH 2 (H 2 O)] and [VO(H 2 O) 5 ] 2+ , as detected by EPR. At higher vanadate–hdmpp ratios [VO(dmpp)(H 2 O) 2 ] + is also produced. The V(V) species formed in solution were studied through a parallel 51 V and 1 H NMR study of the vanadate–Hdmpp system, as a function of metal/ligand ratio and pH. The p K a values of the two main mononuclear V(V) octahedral complexes, VO 2 L and [VO 2 L 2 ] − (L=dmpp), were determined from the pH dependence of their 51 V and 1 H NMR chemical shifts. For VO 2 L, p K a values of 5.88±0.03 and 3.30±0.07 were assigned, respectively, to protonation of [VO 2 (dmpp)(OH)(H 2 O)] − at the coordinated hydroxo ligand and at the ligand nitrogen atom. For [VO 2 L 2 ] − , the three p K a values obtained, 3.96±0.06, 5.62±0.03, and 2.9±0.4, were attributed, respectively, to protonation of [VO 2 (dmpp) 2 ] − at the nitrogen atom of one of the ligands, at one oxygen of the VO 2 + core, and at its resulting VOH group, with formation of the VO 3+ core. The stability constants of these two complexes (log K 1 =10.48±0.05; log K 2 =5.25±0.04; log β 2 =15.73±0.05) were obtained from 51 V NMR data, at pH 8.2, ionic strength 0.1 M, by changing the metal/ligand ratio at constant metal concentration.

Analysis of the LIS data for several series of Ln3+ complexes of C4 symmetry in terms of structural changes, crystal-field effects and/or variation of hyperfine constants along the lanthanide series was undertaken using a combination of the two-nuclei and three-nuclei techniques together with the classical onenucleus technique. Isostructurality of whole series of complexes, with changes of the Fi, and B02 parameters, was clearly defined for the complexes of L by the combination of the two first methods. Small changes, involving the three Fi, Gi and B02 parameters, are observed for the series of complexes of L-L4, using the three data plotting methods. Some of the plots according to the two- and three-nuclei methods are accidentally linear, without necessarily implying isostructurality of the complexes, as they involve parameters, which may be insensitive to any small structural changes occurring in these systems. These parameter variations could result from a magnification, by the present graphical analysis, of the breaks expected from the gradual structural changes along the series due to the lanthanide contraction. The α and β parameters of the three-nuclei method are not diagnostic of the type of structures the complexes have in solution, due to their very indirect dependence on the geometric factors.

The linear graphical analysis of the LIS NMR data available for the axially symmetric complexes [Ln(DOTA)]- (M and m isomers), [Ln(DOTP)]5- (pH 10.0, 7.0 and 3) and [Ln(DOTEA)]3+ using the classical crystal field dependent method and a crystal field independent method were compared. As the second method provides ratios of geometric structural terms G rather than G values, the effect of lanthanide contraction was reduced. Thus, the large breaks in plots observed for all nuclei of those systems using the classical method are still present in the plots of the second method, only in a few of the nuclei and much reduced. This shows that the large breaks at the middle of the lanthanide series present in plots of the classical method as well as the anomalies often present for those plots for the Tm and Yb ions are mostly due to changes of the crystal field coefficient A2Â 0 along the lanthanide series, while both the hyperfine coupling constants and the ratios of geometric terms also change as a result of the lanthanide contraction, leading to small breaks at the middle of the lanthanide series. Analysis of the proton shifts of [Ln(DOTP)] complexes at pH 10, 7 and 3 indicates that protonation of the complexes results in a decrease on the crystal field coefficient. The dipolar shift ratios and absolute shifts obtained were also interpreted in terms of the structural models for those complexes in solution and their available X-ray crystal structures. http://www.sciencedirect.com/science/article/B6TG5-45S49G7-1/1/7fee3ca7ba8b89327bec4ab48419d290

Two DTPA derivatives, a mono-amide derivative containing an iodinated synthon, DTPA-IOPsp (L1) and the ligand DTPA(BOM)3 (BOM=benzyloxymethyl) (L2), radiolabelled with 153Sm3+ and 111In3+, were studied as potential hepatospecific gamma scintigraphic agents. In vivo studies with Wistar rats show that the main excretory pathway for all the chelates studied is the hepatobiliary system. The complexes of L2 show even greater hepatobiliary specificity than L1, perhaps as a consequence of longer blood circulation times due to their strong affinity towards HSA. The 153Sm3+ chelates are also more hepatospecific than the corresponding 111In3+ chelates. The La3+ and In3+ chelates of L1 and L2 show some structural and dynamic differences in aqueous solution, as studied by 1H NMR spectroscopy. While only two nona-coordinated isomers were observed for the La3+ complexes with both ligands, its number is much larger in the In3+ complexes, with both octa- and hepta-coordinated species (with unbound side arms), as well as structural isomers for each coordination number. http://www.sciencedirect.com/science/article/B6TGG-45HFJNC-1/1/26df0708dbb11a2e6f7218c1115fd80b

International audience; We report the synthesis of a cyclen-based ligand (4,10-bis[(1-oxidopyridin-2-yl)methyl]-1,4,7,10-tetraazacyclododecane-1,7-diacetic acid=L1) containing two acetate and two 2-methylpyridine N-oxide arms anchored on the nitrogen atoms of the cyclen platform, which has been designed for stable complexation of lanthanide(III) ions in aqueous solution. Relaxometric studies suggest that the thermodynamic stability and kinetic inertness of the Gd(III) complex may be sufficient for biological applications. A detailed structural study of the complexes by (1) H NMR spectroscopy and DFT calculations indicates that they adopt an anti-Δ(λλλλ) conformation in aqueous solution, that is, an anti-square antiprismatic (anti-SAP) isomeric form, as demonstrated by analysis of the (1) H NMR paramagnetic shifts induced by Yb(III) . The water-exchange rate of the Gd(III) complex is ${k{{298\hfill \atop {\rm ex}\hfill}}}$=6.7×10(6) s(-1) , about a quarter of that for the mono-oxidopyridine analogue, but still about 50 % higher than the ${k{{298\hfill \atop {\rm ex}\hfill}}}$ of GdDOTA (DOTA=1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid). The 2-methylpyridine N-oxide chromophores can be used to sensitize a wide range of Ln(III) ions emitting in both the visible (Eu(III) and Tb(III) ) and NIR (Pr(III) , Nd(III) , Ho(III) , Yb(III) ) spectral regions. The emission quantum yield determined for the Yb(III) complex (${Q{{{\rm L}\hfill \atop {\rm Yb}\hfill}}}$=7.3(1)×10(-3) ) is among the highest ever reported for complexes of this metal ion in aqueous solution. The sensitization ability of the ligand, together with the spectroscopic and relaxometric properties of its complexes, constitute a useful step forward on the way to efficient dual probes for optical imaging (OI) and MRI.

In an effort towards the visualization of b-amyloid (Ab) plaques by T1-weighted magnetic resonance imaging for detection of Alzheimer’s disease, we report the synthesis and characterization of stable, noncharged Gd3? complexes of three different 1,4,7,10- tetraazacyclododecane-1,4,7-triacetic acid monoamide derivatives conjugated to Pittsburgh compound B, a wellestablished marker of Ab plaques. The ligands L1, L2, and L3 differ in the nature and size of the spacer linking the macrocyclic chelator and the Pittsburgh compound B targeting moiety, which affects their lipophilicity, the octanol– water partition coefficients of the complexes ranging from -0.15 to 0.32. Given their amphiphilic behavior, the complexes form micelles in aqueous solution (critical micellar concentration 1.00–1.49 mM). The parameters determining the relaxivity, including the water exchange rate and the rotational correlation times, were assessed for the monomeric and the micellar form by a combined 17O NMR and 1H nuclear magnetic relaxation dispersion (NMRD) study. They are largely influenced by the aggregation state and the hydrophobic character of the linkers. The analysis of the rotational dynamics for the aggregated state in terms of local and global motions using the Lipari– Szabo approach indicates highly flexible, large aggregates. On binding of the complexes to human serum albumin or to the amyloid peptide Ab1–40 in solution, they undergo a fourfold and a twofold relaxivity increase, respectively (40 MHz). Proton relaxation enhancement studies confirmed moderate interaction of Gd(L1) and Gd(L3) with human serum albumin, with KA values ranging between 250 and 910 M-1. This work was financially supported by Fundação para a Ciência e a Tecnologia, Portugal (PhD grant SFRH/BD/ 46370/2008 to AFM) and Rede Nacional de RMN (project REDE/ 1517/RMN/2005) for the acquisition of the Varian VNMRS 600 NMR spectrometer in Coimbra and the French-Portuguese PESSOA project. This work was carried out in the frame of the European Actions TD1004 ‘‘Theragnostics Imaging and Therapy’’ and TD1007 ‘‘PET-MRI’’.

We have proposed recently that the DO3A-N-alfa-(amino)propionate chelator and its amide conjugates are leads to targeted, high relaxivity, safe Contrast Agents for Magnetic Resonance Imaging. In this work we illustrate further the expeditious nature and robustness of the synthetic methodologies developed by preparing the DO3A-N-(alfa-pyrenebutanamido)propionate chelator. Its Gd3+ chelate retains the optimized water exchange, high stability and inertness of the parent complex. The pyrene moiety imparts concentration-dependent self-assembly properties and aggregation-sensitive fluorescence emission to the Gd3+ complex. The Gd3+ complex displays pyrene-centred fluorescence whilst the Yb3+ and Nd3+ complexes exhibit sensitized lanthanide-centred near-infrared luminescence. The aggregated form of the complex displays high relaxivity (32 mM-1s-1, 20 MHz, 25 ºC) thanks to simultaneous optimization of the rotational correlation time and of the water exchange rate. The relaxivity is however still limited by chelate flexibility. This report demonstrates that the DO3A-N-(alfa-amino)propionate chelator is a valuable platform for constructing high relaxivity CA using simple design principles and robust chemistries accessible to most chemistry labs., This work was financially supported by Fundação para a Ciência e Tecnologia, Portugal: PEst-C/QUI/UI0686/2013; FCOMP-01-0124-FEDER-037302; PTDC/QUI/70063/2006; grant SFRH/BD/63994/2009 to Miguel Ferreira and sabbatical grant SFRH/BSAB/1328/2013 to J. A. Martins; Rede Nacional de RMN (REDE/1517/RMN/2005) for the acquisition of the Varian VNMRS 600 NMR spectrometer at the University of Coimbra and the Bruker Avance-3 400 Plus at the University of Minho in Braga. The work in France was supported by La Ligue contre le Cancer. S. Petoud acknowledges support from the Institut National de la Santé́ et de la Recherche Médicale (INSERM). This work was carried out in the framework of the COST Actions D38 “Metal Based Systems for Molecular Imaging”, TD1004 “Theragnostic Imaging” and CM1006 “EUFEN: European F-Element Network”.

A representative set of vanadium(IV and V) compounds in varying coordination environments has been tested in the concentration range 1 to 10(-6) mM, using transformed mice fibroblasts (cell line SV 3T3), with respect to their short-term cell toxicity (up to 36 hours) and their ability to stimulate glucose uptake by cells. These insulin-mimetic tests have also been carried out with non-transformed human fibroblasts (cell line F-26). The compounds under investigation comprise established insulin-mimetic species such as vanadate ([H2VO4](-)), [VO(acetylacetonate)(2)], [VO2(dipicolinate)](-) and [VO(maltolate)(2)], and new systems and coordination compounds containing OO, ON, OS, NS and ONS donor atom sets. A vitality test assay, measuring the reduction equivalents released in the mitochondrial respiratory chain by intracellular glucose degradation, is introduced and the results are counter-checked with H-3-labelled glucose. Most compounds are toxic at the 1 mM concentration level, and most compounds are essentially non-toxic and about as effective as or more potent than insulin at concentrations of 0.01 mM and below. V-V compounds tend to be less toxic than V-IV compounds, and complexes containing thio functional ligands are somewhat more toxic than others. Generally, ON ligation is superior in insulin-mimetic efficacy to OO or O/NS coordination, irrespective of the vanadium oxidation state. There is, however, no striking correlation between the nature of the ligand systems and the insulin-mimetic potency in these cell culture tests, encompassing 41 vanadium compounds, the results on 22 of which are reported in detail here. The syntheses and characteristics of various new compounds are provided together with selected speciation results. The crystal and molecular structures of {[VO(naph-tris)](2)} [where naph-tris is the Schiff base formed between o-hydroxynaphthaldehyde and tris(hydroxymethyl)amine] are reported. Electronic supplementary material to this paper can be obtained by using the Springer Link server located at http://dx.doi.org/10.1007/s00775-001-0311-5 (1). Journal of Biological Inorganic Chemistry

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) complexes with a series of bibracchial lariat ethers are described. Independently of the nature of the counterion present (nitrate or perchlorate), the lariat ether N,N'-bis(2-aminobenzyl)-1,10-diaza-15-crown-5 (L1) always forms mononuclear complexes, whereas the lariat ethers N,N'-bis(2-aminobenzyl)-4,13-diaza-18-crown-6 (L2) and N,N'-bis(2-salicylaldiminobenzyl)-4,13-diaza-18-crown-6 (L3) only give binuclear compounds. The X-ray crystal structure of [CuL1](ClO4)2 shows a seven-coordinated copper(II) ion in a distorted (axially compressed) pentagonal-bipyramidal geometry. The X-ray crystal structure of [Cu2(L3-2H)](ClO4)2 confirms the binuclear nature of the compound with both metal ions having identical coordination environments and each one placed out of the crown hole but efficiently encapsulated by the corresponding pendant arm; each copper(II) ion is five-coordinated with an intermediate geometry between trigonal-bipyramidal and square-pyramidal ([tau]=0.40). The EPR spectra in frozen solution samples are in accordance with a stable coordinate pattern for the metal centre of ligand L1, yielding a rhombic distorted complex with axial compression in solution, in agreement with the X-ray crystal structure of [CuL1](ClO4)2. For the binuclear complexes of L2 and L3, the Cu(II) centres in solution can be distorted from their tetragonally elongated structures via interaction with ethanol and/or the nitrate counterion, leading to more than one species. http://www.sciencedirect.com/science/article/B6TG5-433PCM9-T/1/7815e8fe94b2b6b2129e76252c3517d0

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.

Li+ influx by bovine chromaffin cells, obtained from bovine adrenal medulla, was studied in intact cell suspensions using 7Li NMR spectroscopy with the shift reagent [Tm(HDOTP)]4-. The influx rate constants, ki, were determined in the absence and in the presence of two Na+ membrane transport inhibitors. The values obtained indicate that both voltage sensitive Na+ channels and (Na+/K+)-ATPase play an important role in Li+ uptake by these cells. 7Li NMR T1 and T2 relaxation times for intracellular Li+ in bovine chromaffin cells provided a T1/T2 ratio of 305, showing that Li+ is highly, immobilized due to strong binding to intracellular structures. Using fluorescence spectroscopy and the Mg2+ fluorescent probe, furaptra, the free intracellular Mg2+ concentration in the bovine chromaffin cells incubated with 15 mM LiCl was found to increase by about mM after the intracellular Li+ concentration reached a steady state. Therefore, once inside the cell, Li+ is able to displace Mg2+ from its binding sites.