Dinuclear Gadolinium Research Articles

High rigid Gd (DO3VA) shows remarkable relaxivity: A novel class of MMI agent engineered for MR analysi

A novel dinuclear gadolinium(III) complex of an amide linked bispolyazatricarboxylate macrocycle (DO3VA) having 2-bromoisovaleric acid pendant arm is reported. The molecular longitudinal relaxivity of the dinuclear complex [Gd2{acamidoet(DO3VA)2}(H2O)2] is 13.23mM–1s–1 which corresponds to a “per Gd” relaxivity of 6.62 mM–1 s–1 (20 MHz, 37 ± 0.1 °C, pH 7). The “per Gd” r1p value is higher than the relaxivity of the clinically approved CAs. The transverse relaxivity (r2p) of [Gd2{acamidoet(DO3VA)2}(H2O)2] is 14.34 mM–1 s–1. The r2p/r1p values of 1.08 indicate that the complex is T1-weighted CAs. The 2-bromoisovaleric acid seems to be an excellent pendant arm for holding Gd(III) metal ion at any pH. The remarkable stability of the complex at various pH and in presence of protein shows that the ligand can be used as functionality in making new CAs for MRI and the amide core is a versatile core molecule for the creation of polynuclear gadolinium(III) chelates and dendrimeric CAs.

Synthesis, structures and magnetic refrigeration properties of four dinuclear gadolinium compounds

Four new Gd2 compounds, [Gd2(L1)2(acac)2(CH3O)2] (1), [Gd2(L1)2(beac)2(OH)2] (2), [Gd2(L2)2(C4H10O3)2(CH3OH)2] (3) and [Gd2(L3)2(acac)2(CH3O)2] (4), were synthesized by solvent evaporation methods and studied by structural analyses and magnetic analyses. Crystallographic studies reveal that these compounds are dinuclear compounds and each center Gd(III) ion is eight-coordinated. The magnetic studies reveal that 1–4 display cryogenic magnetic refrigeration properties with −ΔSMax values of 24.80 J kg−1 K−1 for 1 (T = 3.0 K and ΔH = 7.0 T), 25.45 J kg−1 K−1 for 2 (T = 2.0 K and ΔH = 7.0 T), 21.12 J kg−1 K−1 for 3 (T = 3.0 K and ΔH = 7.0 T), and 31.33 J kg−1 K−1 for 4 (T = 2.0 K and ΔH = 7.0 T).

Synthesis, Characterization, and Biodistribution of a Dinuclear Gadolinium Complex with Improved Properties as a Blood Pool MRI Agent

A dinuclear gadolinium(III) chelate containing two moieties of diethylenetriaminepentaacetic acid (DTPA), covalently conjugated to an analogue of deoxycholic acid, was synthesized and thoroughly characterized. A full relaxometric analysis was carried out, consisting of 1) the acquisition of nuclear magnetic resonance dispersion (NMRD) profiles in various media; 2) the study of binding affinity to serum albumin; 3) the measurement of 17 O transverse relaxation rate versus temperature, and 4) a transmetallation assay. In vivo biodistribution MRI studies at 1 T and blood pharmacokinetics assays were carried out in comparison with Gd-DTPA (Magnevist) and gadocoletic acid trisodium salt (B22956/1), two well-known Gd complexes that share the same chelating cage and the same deoxycholic acid residue of the Gd complex investigated herein ((GdDTPA)2 -Chol). High affinity for plasma protein and, in particular, the availability of more than one binding site, allows the complex to reach a fairly high relaxivity value in plasma (∼20 mm-1 s-1 , 20 MHz, 310 K) as well as to show unexpectedly enhanced properties of blood pooling, with an elimination half-life in rats approximately seven times longer than that of B22956/1.

Synthesis and Characterization of Rare-Earth Metal Complexes Supported by 2-Imino or Amino Appended Indolyl Ligands with Diverse Hapticities: Tunable Selective Catalysis for Isoprene Polymerization

The reaction of 2-(2,6-DippNHCH2)C8H5NH (Dipp = 2,6-iPrC6H3, C8H5NH = indolyl) with 1 equiv of (Me3SiCH2)3Yb(THF)2 at room temperature generated mononuclear ytterbium complex 1 having the indolyl ligands in η1:η1 mode with reduction of Yb3+ to Yb2+ and oxidation of the amino to imino group. In the case of Er and Y, the reactions produced dinuclear complexes 2 and 3 having the indolyl ligands in μ-η2:η2:η1 modes with the central metals. When the rare-earth metal is dysprosium, the reaction afforded mixed ligated dinuclear complex 4a having indolyl ligands in μ-η5:η1:η1 and μ-η6:η1:η1 modes with Dy, and its isomer 4b having the indolyl ligands only in μ-η5:η1:η1 modes with Dy. However, when the rare-earth metal is Gd, the reaction only produced the mixed ligated dinuclear gadolinium complex [(μ-η5:η1:η1)-2-(2,6-DippNCH2)Ind(μ-η6:η1:η1)-2-(2,6-DippNCH2)Ind][Gd(CH2SiMe3)(thf)]2 (5), having indolyl ligands in μ-η5:η1:η1 and μ-η6:η1:η1 modes with Gd. In addition, treatment of 2-(2,6-DippNHCH2)C8H5NH with 1.25 e...

Synthesis and DNA-Binding Studies of a Dinuclear Gadolinium(III)–Platinum(II) Complex

The synthesis and characterisation of a new dinuclear GdIII–PtII complex (1·PF6) containing a functionalised macrocyclic 1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid derivative linked to a PtII-terpy (terpy = 2,2′ : 6′,2″-terpyridine) unit by means of a short thiolato linker are reported. The complex was synthesised in six steps from cyclen by means of a modular synthetic strategy. A preliminary DNA-binding study with calf-thymus DNA (ct-DNA) was performed on 1·PF6 by means of linear dichroism (LD). The observed changes in the DNA LD signal in the presence of the metal complex are fully consistent with an intercalative binding mode. Furthermore, an induced negative LD signal in the ultraviolet absorption region of the complex provides strong evidence of a strong DNA-binding interaction. The in vitro cytotoxicity of 1·PF6 towards a human glioblastoma cell line (T98G) was also determined.

A series of new lanthanoid thioantimonates: a rare example of organic-decorated cationic lanthanoid thioantimonate chains based on asymmetric dinuclear lanthanide complexes

A series of new lanthanoid thioantimonates [Ln(teta)2]SbS4 [teta = triethylenetetramine; Ln = Eu (1), Gd (2), Er (3)], {[Ln(tepa)]2[μ2-SbIIIS3](μ2-OH)}2{[Ln(tepa)]2(μ2-OH)2(SbVS4)2}Cl2 [tepa = tetraethylene-pentamine; Ln = Y(4), Eu(5), Er(6)], and [Gd2(tepa)2(μ2-OH)2(μ2-SbS4)]Cl·0.25H2O (7) were synthesized via reactions of Sb, S and LnCl3 in teta or tepa under solvothermal conditions and were structurally characterized. Compounds 1–3 consist of isolated [Ln(teta)4]3+ cations and tetrahedral [SbS4]3− anions. Compounds 4–6 contain heterometallic mixed amino-thiocluster cations {[Ln(tepa)]2[μ2-SbS3](μ2-OH)}2+, heterometallic anions {[Ln2(tepa)2(μ2-OH)2](SbS4)2}2− and free Cl− ions, which provide a rare example of the coexistence of noncondensed pyramidal [SbIIIS3]3− and tetrahedral [SbVS4]3− anions in a single thioantimonate. 7 consists of a 1-D polymeric cation [Gd2(tepa)2(μ2-OH)2(μ2-SbS4)]+, constructed through the linkage of asymmetric dinuclear gadolinium complex [Gd2(tepa)2(μ2-OH)2]4+ cations, tetrahedral [SbVS4]3− anions and a Cl− ion and water molecule, which represents a rare example of organic-decorated cationic lanthanoid thioantimonate chains based on asymmetric dinuclear lanthanide complexes. The present compounds exhibit semiconducting properties with absorption band edges between 2.00 and 3.03 eV.

Dinuclear gadolinium(III) complexes constructed by monocarboxylate ligands

Dinuclear gadolinium(III) complexes constructed by monocarboxylate ligands

Magnetic Coupling in Dinuclear Gd Complexes

A spin density functional (SDFT) study of carboxylate-bridged and diazenido-bridged dinuclear gadolinium compounds is presented. Calculated magnetic coupling constants for the carboxylate-bridged structures are in good agreement with experimental data, confirming the ability of the broken symmetry approach used in this work to predict magnetic behavior in such compounds. The systematic trend wherein symmetrically bridged complexes are antiferromagnetically coupled and asymmetrically bridged are ferromagnetically coupled is reproduced by the SDFT calculations. The mechanism underlying magnetic coupling in closed- and open-shell dinuclear complexes is described using a perturbative molecular orbital model that focuses the influence of the 4f(7)-5d exchange interaction on molecular orbitals with significant 5d-orbital character for the complex [[[(Me(3)Si)(2)N](2)(thf)Gd](2)(N(2))]. Open-shell electronic configurations facilitate strong ferromagnetic coupling, whereas in closed-shell systems antiferromagnetic coupling is usually preferred.

Synthesis, Characterization, and Pharmacokinetic Evaluation of a Potential MRI Contrast Agent Containing Two Paramagnetic Centers with Albumin Binding Affinity

A dinuclear gadolinium(III) complex of an amphiphilic chelating ligand, containing two diethylenetriamine-N,N,N',N'',N''-pentaacetate (DTPA) moieties bridged by a bisindole derivative with three methoxy groups, has been synthesized and evaluated as a potential magnetic resonance imaging (MRI) contrast agent. Nuclear magnetic relaxation dispersion (NMRD) measurements indicate that at 20 MHz and 37 degrees C the dinuclear gadolinium(III) complex has a much higher relaxivity than [Gd(DTPA)] (6.8 vs 3.9 s(-1) mmol(-1)). The higher relaxivity of the dinuclear gadolinium(III) complex can be related to its reduced motion and larger rotational correlation time relative to [Gd(DTPA)]. In the presence of human serum albumin (HSA) the relaxivity value of the noncovalently bound dinuclear complex increases to 15.2 s(-1) per mmol of Gd3+, due to its relatively strong interaction with this protein. The fitted value of the binding constant to HSA (Ka) was found to be 10(4) M(-1). Because of its interaction with HSA, the dinuclear complex exhibits a longer elimination half-life from the plasma, and a better confinement to the vascular space compared to the commercially available [Gd(DTPA)] contrast agent. Transmetalation of the dinuclear gadolinium(III) complex by zinc(II) has been investigated. Biodistribution studies suggest that the complex is excreted by the renal pathway, and possibly by the hepatobiliary route. In vivo studies indicated that half of the normal dose of the gadolinium(III) complex enhanced the contrast in hepatic tissues around 40 % more effectively than [Gd(DTPA)]. The dinuclear gadolinium(III) complex was tested as a potential necrosis avid contrast agent (NACA), but despite the binding to HSA, it did not exhibit necrosis avidity, implying that binding to albumin is not a key parameter for necrosis-targeting properties.

A high-throughput approach to lanthanide complexes and their rapid screening in the ring opening polymerisation of caprolactone.

Libraries of lanthanide complexes supported by nitrogen and oxygen containing ligands have been synthesised using a high-throughput approach. The complexes were employed in the ring-opening polymerisation of epsilon-caprolactone, in some cases giving polycaprolactone of controlled molecular weight and narrow polydispersity. The libraries, based on twenty-one ligands and eight lanthanide reagents, were developed in order to determine the best combination of lanthanide metal and ligand. They were prepared via transamination reactions of [Ln[N(SiMe(3))(2)](3)] complexes with tetradentate dianionic ligands containing oxygen and nitrogen donors. 1H NMR spectroscopy was used to screen polymerisation activity. The steric demand of the ligand has a significant effect on the polymerisation process, as do the type of nitrogen donor and the size of the central Ln(3+) ion. Ligands containing aryl rings with bulky substituents such as tert-pentyl groups afforded species capable of performing controlled polymerisation of caprolactone, whereas less bulky groups such as methyl were not effective. Yttrium and mid-sized lanthanides such as samarium showed increased activity compared with the larger lanthanides, lanthanum and praseodymium, and the smaller lanthanides like ytterbium. X-ray crystal structures of a sterically demanding chelating amine-bis((2-hydroxyaryl)methyl) ligand and a chloride bridged dinuclear gadolinium complex are reported. The centrosymmetric molecule contains gadolinium in distorted capped trigonal prismatic environments bonded to two amine, two phenolate, one THF and two chloride donors.

Unprecedented ferromagnetic interaction in homobinuclear erbium and gadolinium complexes: structural and magnetic studies.

An intramolecular ferromagnetic interaction (see picture) is evidenced for the first time in a dinuclear gadolinium complex that has four carboxylate bridges. A similar interaction exists in a dinuclear erbium complex, but, as a result of the depopulation of the excited Stark levels, its signature only appears at very low temperature.

Spontaneous Symmetry Breaking in the Formation of a Dinuclear Gadolinium Semiquinonato Complex: Synthesis, High-Field EPR Studies, and Magnetic Properties

Spontaneous Symmetry Breaking in the Formation of a Dinuclear Gadolinium Semiquinonato Complex: Synthesis, High-Field EPR Studies, and Magnetic Properties

Spontaneous symmetry breaking in the formation of a dinuclear gadolinium semiquinonato complex: synthesis, high-field EPR studies, and magnetic properties.

The synthesis and characterisation of an asymmetric dinuclear gadolinium(III) semiquinonato complex, namely [Gd2(HBPz3)2(dtbsq)4] CHCl3 (1; HBPz3 = hydrotris(pyrazolyl)borate, dtbsq = 3,5-di-tert-butyl-O-semiquinone), is reported. The crystal structure of 1 was determined at room temperature. It crystallises in the triclinic system P1, with a = 16.735(5) A, b = 17.705(5) A, c = 19.553(5) A, alpha = 99.680(5) degrees, beta = 109.960(5), gamma = 107.350(5) degrees, Z = 2 and R = 9.96. The structure of 1 consists of a dinuclear asymmetric unit in which the two gadolinium(III) ions have coordination numbers of eight and nine. Three of the dioxolene molecules act as asymmetric bridging ligands, while the fourth molecule behaves as a bidentate ligand towards a single metal ion. The magnetic properties of 1 were investigated by means of susceptibility measurements and high-field electron paramagnetic resonance (HF-EPR) spectroscopy. They revealed an S = 0 ground spin state with excited states of higher spin very close in energy and a small negative zero-field splitting with a transverse anisotropy term for a S = 7 state.