Developing High Field MRI Contrast Agents by Tuning the Rotational Dynamics: Bisaqua GdAAZTA-based Dendrimers

Monomeric and dimeric AAZTA-based bifunctional chelators (AAZTA=6-amino-6-methylperhydro-1,4-diazepine tetraacetic acid) were attached to different generations (G0, G1 and G2) of ethylenediamine-cored PAMAM dendrimers (PAMAM=polyamidoamine) to obtain a series of six dendrimeric systems with 4 to 32 chelates at the periphery. These Gd^III-loaded dendrimers have molecular weight ranging from 3.5 to 25 kDa, thus allowing a systematic investigation on the changes in relaxivity (r₁) with the variation of the rotational dynamics following the increase in molecular size. Variable-temperature ¹⁷O NMR (on the dimeric building block Gd₂ L2 ) and ¹H Nuclear Magnetic Relaxation Dispersion measurements at different temperatures indicate that the water exchange lifetime (τ_M∼90 ns) of the two inner sphere water molecules does not represent a limiting factor to the relaxivity of the systems. The r₁ values at 1.5 T (60 MHz) and 298 K increases from 10.2 mM⁻¹ s⁻¹ for the monomer Gd L1 to 31.4 mM⁻¹ s⁻¹ for the dendrimer Gd₃₂ G2-32 (+308 %). However, the relaxivity (per Gd) does not show a linear dependence on the molecular mass, but rather the enhancement tends to attenuate markedly for larger systems. This effect has been attributed to the growing decrease in correlation between local rotational motions and global molecular tumbling.     

Polymeric gadolinium chelate–containing magnetic resonance signal‐enhancing coating materials: Synthesis,characterization, and properties

The present investigation deals with studies on novel magnetic resonance signal‐enhancing coating materials. The polyaminocarboxylate complexes of Gd³⁺ as side chains were prepared by the conjugation of N‐(2‐hydroxyethyl)ethylenediaminetriacetic acid (HEDTA) with poly(styrene‐maleic acid) copolymer (SMA). The complexation of the Gd³⁺ ion to the conjugates was carried out by adding GdCl₃ to the solution of the polymer ligands. The resulting Gd³⁺‐containing polymer complexes were characterized by GPC, FTIR, NMR, and inductively coupled plasma–Auger electron spectroscopy, which confirmed that HEDTA was covalently attached to SMA and Gd³⁺‐containing polymer complexes were formed. The PP catheters were coated with the Gd³⁺‐containing polymer complexes and characterized by XPS. The result confirms that the Gd³⁺ complexes were coated on the surface of PP catheters. In the relaxation test, the relaxation rates of the water proton in the vicinity of the coated PP catheter surface increase significantly, suggesting that Gd³⁺‐containing polymer complex coating materials show great MR enhancement of water proton, and potentialities in making catheters used for endovascular interventions or therapy, visible by MRI. The influence of protein on the relaxation rates of coated PP catheter shows that the protein adsorption on the catheter surface influences the enhancement of the MR signal for the coating materials of Gd³⁺‐containing polymer complex. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 1358–1364, 2003     

Sandwich type organic-inorganic hybrid of 3d–4f heterometallic containing germanotungstates [{Cu2(1,10-phen)2(μ-CH3COO)2}Ln(α-GeW11O39)2]11 −: Syntheses,crystal structures,magnetic and photoluminescence properties

Alkali salts of organic-inorganic hybrid 3d-4f heterometallic containing derivatives of sandwich type germanotungstates: [{Cu₂(1,10-phen)₂(μ-CH₃COO)₂}Ln(α-GeW₁₁O₃₉)₂]^11 − [Ln = Pr^III (1a), Nd^III (2a), Sm^III (3a), Eu^III (4a), Gd^III (5a); 1,10-phen = 1.10-phenanthroline] have been prepared in the aqueous potassium acetate buffer (pH 4.7) solution. All these compounds were synthesized following by one pot reaction procedure under mild reaction conditions. All compounds were isolated as mixed alkali sodium/potassium salts from the solution and used for further structural characterization by single crystal XRD, powder-XRD, FT-IR, liquid UV/vis, solid state photoluminescence spectroscopy and thermo-gravimetric analysis. FT-IR spectra and powder-XRD pattern suggest that all compounds (1a–5a) are isomorphous. Further single crystal XRD analysis shows that all these compounds exhibit sandwich-type [Ln(α-GeW₁₁O₃₉)₂]^13 − structural feature in the polyoxoanions as the fundamental building block units, and the copper complexes coordinated with 1,10-phen and acetate ligands are coordinated to the terminal oxygen of the polyanion. The compounds 1a, 3a and 4a show good photoluminescence properties at room temperature. The compound 5a shows weak ferromagnetic behavior.     

Empirical Correlation of Minimum Burning Pressures of Ammonium Nitrate Emulsions

Experimental minimum burning pressures (MBP) of emulsions with solution phase containing ammonium nitrate/water, ammonium nitrate/sodium nitrate/water, and ammonium nitrate/sodium nitrate/sodium perchlorate/water are investigated. A correlation is proposed to relate the MBP’s with the combustion temperatures. The formulations containing sodium nitrate or sodium perchlorate have much lower MBP’s and can be accounted for by an activation energy of 150.7 kJ mol⁻¹ obtained from literature for ingredients having catalyzing effects on the reaction of ammonium nitrate, e.g. sodium nitrate. The ammonium nitrate/water formulations have a higher activation energy of 173.4 kJ mol⁻¹ deduced from an analysis of the data. The MBP vs. combustion temperature plot is linearized by a multiplication factor to the MBP that includes the activation energy of the corresponding system. This allows the MBP to be predicted from combustion temperatures determined from the formulations and the corresponding activation energy.     

Gold‐cyanide biosorption with L‐cysteine

L ‐Cysteine increased gold‐cyanide biosorption by protonated Bacillus subtilis, Penicillium chrysogenum and Sargassum fluitans biomass. At pH 2, the maximum Au uptakes were 20.5 µmol g⁻¹, 14.2 µmol g⁻¹ and 4.7 µmol g⁻¹ of Au, respectively, approximately 148–250% of the biosorption performance in the absence of cysteine. Au biosorption mainly involved anionic AuCN₂⁻ species adsorbed by ionizable functional groups on cysteine‐loaded biomass carrying a positive charge when protonated [(biomass–cysteine–H⁺)–(AuCN₂⁻)]. Deposited gold could be eluted from Au‐loaded biomass at pH 3–5. The elution efficiencies were higher than 92% at pH 5.0 with the Solid‐to‐Liquid ratio, S/L, = 4. Increasing solution ionic strength (NaNO)₃ decreased Au uptake. FTIR analyses indicated that the main functional groups involved in gold biosorption in the presence of L ‐cysteine are probably N‐, S‐ and O‐containing groups. The present results confirm that certain waste microbial biomaterials are capable of effectively removing and concentrating gold from solutions containing residual cyanide if applied under appropriate conditions. © 2000 Society of Chemical Industry     

Spectroscopic properties of an engineered maltose binding protein

The maltose binding protein (MBP) has been site specifically labelled with a nitrobenzoxadiazole (NBD) group following mutation of a serine to a cysteine residue at position 337. The resulting protein shows a large ligand (maltose or beta-cyclodextrin) dependent increase in its steady-state fluorescence intensity. Analysis of the static (intensity and anisotropy) and dynamic (lifetime distributions) fluorescence of the NBD label as well as the tryptophan residues in both ligand-bound and ligand-free states of this molecule reveals complex multi-component decays that are interpreted in terms of a ligand-induced solvent shielding mechanism. In the context of the known crystal structures of the various forms of the maltose-binding protein (MBP), ligand- dependent changes in both the fluorescence parameters as well as the circular dichroism spectra of the NBD group are interpreted by a twisted intramolecular charge-transfer (TICT) mechanism, wherein ligand binding locks the NBD group into a conformation that prevents efficient relaxation of the excited state.      

White Light Emitting Eu<Superscript>III</Superscript> and Tb<Superscript>III</Superscript> Doped Lanthanide Coordination Polymers Based on in Situ Formed Nitrilotriacetic Anion

Three 2D lanthanide coordination polymers of in situ formed nitrilotriacetic anion (NTA^3?) have been hydrothermally synthesized with N-(2-carbamoylmethyl) iminodiacetic acid (H₂ADA) as starting material. The photoluminescence properties as well as the energy-transfer behavior of the resulted coordination polymers are studied in detail and the investigations reveal that both Eu^III and Tb^III complexes show intense emissions characteristic of Eu^III and Tb^III ion under irradiation of 399 nm. Considering the blue-emission of compound Gd^III and the intense emission of Eu^III and Tb^III compounds, we afforded Eu^III and Tb^III doped white light emitting materials by the different combination of the doped Eu^III and Tb^III concentrations.     

Synthesis, crystal structure and magnetic properties of a new three-dimensional porous framework: [Gd2(BDA)3(DMF)2(H2O)4] · 2DMF

The open framework compound of [Gd₂(BDA)₃(DMF)₂(H₂O)₄] · 2DMF (1), prepared by heating GdCl₃ with 2,2′-bipyridyl-4,4′-dicarboxylatic acid (BDA) in mixed solvent, is constructed from BDA linking up polymeric [GdO₅(DMF)(H₂O)₂]_n tethers. The 1D channels are filled with coordinated and uncoordinated DMF molecules hydrogen bonding to terminal aqua ligands. The study of the temperature dependent magnetic susceptibilities revealed that there are ferromagnetic interactions between intra-chain Gd^III atoms and weak antiferromagnetic interactions between inter-chain Gd^III atoms.     

Electrocatalytic oxidation of thiocyanate, l-cysteine and 2-mercaptoethanol by self-assembled monolayer of cobalt tetraethoxy thiophene phthalocyanine

Catalytic activity of a self-assembled monolayer (SAM) of cobalt tetra ethoxythiophene phthalocyanine (CoTEThPc-SAM) complex towards oxidation of thiocyanate (SCN⁻), l-cysteine (CYS) and 2-mercaptoethanol (2-ME) is reported. The oxidation of thiocyanate occurs via a two electron transfer, whereas l-cysteine and 2-ME require 1 electron. The oxidation of thiocyanate is catalysed by ring based processes, while l-cysteine is catalysed by both Co^III/Co^II process and by ring based processes. 2-ME is catalysed by Co^III/Co^II process. The oxidation of thiocyanate on CoTEThPc was performed in acid media instead of basic media commonly employed. The reaction order was found to be unity for all the analytes, showing that only one molecule of analyte interacts with one molecule of the catalyst during the rate determining step.     

The functional role of selenocysteine (Sec) in the catalysis mechanism of large thioredoxin reductases: proposition of a swapping catalytic triad including a Sec-His-Glu state

Thioredoxin reductases catalyse the reduction of thioredoxin disulfide and some other oxidised cell constituents. They are homodimeric proteins containing one FAD and accepting one NADPH per subunit as essential cofactors. Some of these reductases contain a selenocysteine at the C terminus. Based on the X-ray structure of rat thioredoxin reductase, homology models of human thioredoxin reductase were created and subsequently docked to thioredoxin to model the active complex. The formation of a new type of a catalytic triad between selenocysteine, histidine and a glutamate could be detected in the protein structure. By means of DFT (B3LYP, lacv3p**) calculations, we could show that the formation of such a triad is essential to support the proton transfer from selenol to a histidine to stabilise a selenolate anion, which is able to interact with the disulfide of thioredoxin and catalyses the reductive disulfide opening. Whereas a simple proton transfer from selenocysteine to histidine is thermodynamically disfavoured by some 18 kcal mol(-1), it becomes favoured when the carboxylic acid group of a glutamate stabilises the formed imidazole cation. An identical process with a cysteine instead of selenocysteine will require 4 kcal mol(-1) more energy, which corresponds to a calculated equilibrium shift of approximately 1000:1 or a 10(3) rate acceleration: a value close to the experimental one of about 10(2) times. These results give new insights into the catalytic mechanism of thioredoxin reductase and, for the first time, explain the advantage of the incorporation of a selenocysteine instead of a cysteine residue in a protein.     

Phase transitions and upconversion luminescence in oxyfluoride glass ceramics containing Ba4Gd3F17 nanocrystals

Novel transparent Er³⁺ doped oxyfluoride glass-ceramics containing Ba₄Gd₃F₁₇ nanocrystals were prepared by melt quenching followed by heat treatment of as-prepared glasses. The phase composition and microstructure were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Intense upconversion luminescence (UCL) was detected. Longer characteristic decay times and splitting of the luminescence bands compared to the precursor glass indicated the incorporation of erbium ions in the crystalline phase. The spectroscopic properties of glass ceramics were compared with single phase cubic and rhombohedral Ba₄Gd₃F₁₇ ceramics. The unit cell parameters and atomic positions in the rhombohedral phase were calculated using Rietveld refinement. The local environment of Er³⁺ and the phonon energy of both polymorphs were analyzed using luminescence and Raman spectroscopy. In the glass ceramics, a phase transition from distorted metastable fluorite to ordered rhombohedral Ba₄Gd₃F₁₇ was observed and resulted in the enhancement of the efficiency of UCL.     

Improved photocatalytic activity of Bi4TaO8Cl by Gd3+ doping

Bi₄TaO₈Cl and Bi₄TaO₈Cl:Gd³⁺ photocatalysts were synthesized by the solvothermal technique. The phase, microstructure, optical properties, and photocatalytic activities were investigated. Both Bi₄TaO₈Cl and Bi₄TaO₈Cl:Gd³⁺ have the singly orthorhombic phase and the flower-like hierarchical structure. The Bi₄TaO₈Cl:Gd³⁺ has higher photocatalytic activity of MB than that of Bi₄TaO₈Cl under visible light irradiation. The higher photocatalytic activity of Bi₄TaO₈Cl:Gd³⁺ is induced by its lower band gap energy, the higher efficiency charge separation, and transfer process, as well as the photogenerated charge carriers with a longer time, which are confirmed by the longer absorption band edge, lower emission intensity, and higher photocurrent under visible light irradiation. The trapping experiments and electron spin resonance results suggest that ˙O₂⁻ is the predominant active species for the photocatalysis of MB by Bi₄TaO₈Cl and Bi₄TaO₈Cl:Gd³⁺ under visible light irradiation.     

Preparation of Gd2Zr2O7 nanoceramics from two-step thermal treatment and the aqueous durability analysis

Gd₂Zr₂O₇ ceramics demonstrate important prospect in the immobilization of high-level radioactive wastes (HLWs). In this study, Gd₂Zr₂O₇ nanoceramics were fabricated using two-step method, where Gd₂Zr₂O₇ nanopowder was firstly synthesized by solvothermal method and Gd₂Zr₂O₇ nanoceramics were subsequently sintered via self-propagating chemical furnace plus quick pressing (SCF/QP). The characterization results display that the Gd₂Zr₂O₇ nanocrystalline ceramics with average grain size of 78 nm and bulk density of 5.53 g cm⁻³ were successfully prepared. The results of MCC-1 static leaching experiments show that the normalized release rate (LR_i) of Gd is 2.2 × 10⁻² g m⁻²•d⁻¹ on the first day and converges to 1.2 × 10⁻³ g m⁻²•d⁻¹ after 42 days. Zr shows superior chemical stability as the 21 days LR_Zr value is as low as 2.7 × 10⁻⁶ g m⁻²•d⁻¹, which becomes constant as the leaching duration prolongs.     

Mixed conductivity of garnet phases based on gadolinium ferrite

Incorporation of Pr and Ca into the garnet lattice of Gd₃Fe₅O_12±δ was found to increase the electronic conductivity, and to decrease the thermal expansion coefficients and oxygen ion transference numbers. The ionic conductivity of Gd_2.2Pr_0.8Fe₅O_12±δ ceramics is similar to that of undoped gadolinium ferrite, whilst Gd_2.5Ca_0.5Fe₅O_12-δ exhibits slightly higher ionic transport, suggesting an enhanced vacancy contribution. The activation energies for ionic conduction in Gd₃Fe₅O₁₂-based materials vary in the narrow range 211–224 kJ/mol. Due to a significantly lower activation energy for the total conductivity (24–81 kJ/mol), the oxygen ion transference numbers in air increase with temperature, from 4 × 10⁻⁵ – 5×10⁻³. Steady-state oxygen permeation fluxes through dense garnet membranes are limited by bulk ambipolar conductivity. The thermal expansion coefficients of the ferrite ceramics (100–1000 °C) were found linear and in the range 10.36–10.86 × 10⁻⁶ K⁻¹.     

Two organic–inorganic hybrid materials based on the penta-nuclear {MMn4} (M = W and Mo) heterometallic clusters and Schiff-base ligands

Two organic–inorganic hybrid compounds with the formula {[Mn^III(Salen)(H₂O)]₄MoO₄}·Cl₂·16H₂O (1) and {[Mn^III(Salen)(H₂O)]₄WO₄}·(CH₃COO)₂·11H₂O (2) (Salen = Di-[2-hydroxyl-3-methoxyl-benzaldehyde] ethylenediamine) have been synthesized and structurally characterized by IR, UV–vis spectroscopy, TG analysis and single crystal X-ray diffraction. Structural analysis revealed that compounds 1 and 2 consist of a [MoO₄]^2 − or [WO₄]^2 − building unit and four {[Mn^III(Salen)(H₂O)]⁺ metal–organic moieties, respectively. In the crystal structure, the [MoO₄]^2 − or [WO₄]^2 − tetrahedra coordinated with four Mn^III ions, resulting in the penta-nuclear heterometallic tetrahedra cluster compounds, which were rarely observed in the Mn-Salen system. Magnetic study revealed that there was antiferromagnetic coupling in the two compounds.     

Chemical copolymerization of aniline with o‐chloroaniline: thermal stability by spectral studies

Poly(aniline‐co‐o‐chloroaniline) salts were synthesized by chemical copolymerization of aniline with o‐chloroaniline using three different acids. The polymer salt samples were heat treated at four different temperatures (150, 200, 275 and 375 °C) and the thermal stability of the polymer salts were studied by conductivity, electron paramagnetic resonance (EPR), infrared (IR) and electronic absorption spectral measurements. The conductivity of the copolymers could be controlled in a broad range from 10 S cm⁻¹ for homopolymer of aniline to 10⁻⁴ S cm⁻¹ for those of o‐chloroaniline. No structural changes took place up to 200 °C and this was confirmed from EPR, IR and electronic absorption spectra. No definite correlation exists between conductivity and spin concentration. © 2000 Society of Chemical Industry     

A novel Gd3+ and Yb3+ co-doped ceria-sulphate composite electrolyte for intermediate-temperature fuel cells

In this study, Yb³⁺ and Gd³⁺ co-doped CeO₂ and the corresponding (Li/K)₂SO₄ composite electrolyte were prepared. The structures and morphologies of Ce_0.8Yb_0.1Gd_0.1O_2-α and Ce_0.8Yb_0.1Gd_0.1O_2-α-Li₂SO₄–K₂SO₄ were investigated using X-ray diffraction (XRD), Raman spectroscopy, and scanning electron microscopy (SEM). The conductivity of Ce_0.8Yb_0.1Gd_0.1O_2-α (1550 °C) as a function of time during humidification in a nitrogen atmosphere at 700 °C was investigated. The log(σT) vs. 1000T⁻¹ plots, logσ vs. log(pO₂) curves, and fuel cell performances of Ce_0.8Yb_0.1Gd_0.1O_2-α (1550 °C) and Ce_0.8Yb_0.1Gd_0.1O_2-α-Li₂SO₄–K₂SO₄ (1550 °C) were investigated. At 700 °C, Ce_0.8Yb_0.1Gd_0.1O_2-α-Li₂SO₄–K₂SO₄ (1550 °C) showed a power density of 197 mW cm⁻², which is five times higher than that of Ce_0.8Yb_0.1Gd_0.1O_2-α (1550 °C).     

Facile synthesis of gadolinium (III) chelates functionalized carbon quantum dots for fluorescence and magnetic resonance dual-modal bioimaging

Multi-modal imaging probes through synergistically combining two or more imaging modalities into single nanoparticle, offer possibilities to address multiple issues such as resolution, sensitivity, and tissue penetration. In this study, we report a facile strategy to synthesize a dual-modal fluorescence/magnetic resonance (MR) imaging nanoprobe with bright fluorescence and significantly improved relaxivity, where Gd³⁺ ions are simply chelated onto the outer surface of the cyclic DTPA dianhydride (cDTPAA) functionalized carbon quantum dots (CQDs). Transmission electron microscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and zeta potential measurements validated the successful preparation of CQD–DTPA–Gd. The surface conjugation of CQDs with cDTPAA and further Gd³⁺ chelation does not perturb core optical properties of CQDs, and the thus prepared CQD–DTPA–Gd contain minimum Gd³⁺ content (8.06%, w/w), while exhibiting significantly improved longitudinal relaxivity (56.72 mM⁻¹ s⁻¹). Excellent water solubility, good cell-membrane permeability and negligible cytotoxicity make CQD–DTPA–Gd an ideal dual-modal fluorescence/MR imaging probe, suggesting its potential and significance in practical bioimaging applications and medical translation in the future.     

Two-equivalent electrochemical reduction of a cyano-complex [Tl(CN)2] and the novel di-nuclear compound [(CN)5Pt−Tl]

Extending our recent insights in two-electron transfer microscopic mechanisms for a Tl^III/Tl^I redox system [D.E. Khoshtariya, et al., Inorg. Chem. 41 (2002) 1728], the electrochemical response of glassy carbon electrode in acidified solutions of Tl^III (ClO₄)₃ containing different concentrations of sodium cyanide has been extensively studied for the first time by use of cyclic voltammetry and the CVSIM curve simulation PC program. The complex [Tl^III(CN)₂]⁺ has been thoroughly identified electrochemically and shown to display a single well-defined reduction wave (which has no anodic counterpart), ascribed to the two-equivalent process yielding [Tl^I(aq)]⁺. This behavior is similar to that of [Tl^III(aq)]³⁺ ion in the absence of sodium cyanide, disclosed in the previous work, and is compatible with the quasi-simultaneous yet sequential two-electron transfer pattern (with two reduction waves merged in one), implying the rate-determining first electron transfer step (resulting in the formation of a covalently interacting di-thallium complex as a metastable intermediate), and the fast second electron transfer step. Some preliminary studies of the two-equivalent reduction of directly metal-metal bonded stable compound [(CN)₅Pt^II-Tl^III]⁰ has been also performed displaying two reduction waves compatible with a true sequential pattern.     

Structure,thermal properties and hot corrosion behaviors of Gd2Hf2O7 as a potential thermal barrier coating material

In this work, Gd₂Hf₂O₇ ceramics were synthesized and investigated as a potential thermal barrier coating (TBC) material. The phase composition, microstructure and associated thermal properties of Gd₂Hf₂O₇ ceramics were characterized systematically. Results show that the thermal conductivity of Gd₂Hf₂O₇ ceramics is 1.40 Wm⁻¹K⁻¹ at 1200 °C, ~25% lower than that of 8 wt% yttria partially stabilized zirconia (8YSZ). Gd₂Hf₂O₇ ceramics also present large thermal expansion coefficients, which decrease from 12.0 × 10⁻⁶ K⁻¹ to 11.3 × 10⁻⁶ K⁻¹ (300–1200 °C). Besides, the hot corrosion behaviors of Gd₂Hf₂O₇ ceramics exposed to V₂O₅ and Na₂SO₄ + V₂O₅ salts at temperatures of 900–1200 °C were discussed in great detail. We pay much attention on the corrosion process, corrosion mechanism and corrosion damage of Gd₂Hf₂O₇ ceramics subjected to molten V₂O₅ and Na₂SO₄ + V₂O₅ salts at different temperatures.