Paramagnetic Gd Research Articles

Magnetic Properties of Perovskite GdCrO3

The gadolinium orthochromate GdCrO3 exhibits negative magnetization when magnetization–temperature curves are measured in a field-cooled mode with low applied fields (<∼500 Oe). This compound shows canted-antiferromagnetic order of Cr3+ moments with a Neel temperature (TN) of ∼170 K. With cooling the samples below TN, magnetization exhibits peak values (MMAX) with a positive sign at ∼160 K. Below this temperature, it decreases with decreasing temperature, passes through a zero value (M=0) at T1<∼130 K, and continues to decrease until TMIN (>∼25 K). This behavior is interpreted in connection with the paramagnetic Gd3+ moments whose direction is opposite to that of canted Cr3+ moments. The maximum absolute value of the negative magnetization was much larger than MMAX, i.e., nearly 30 times as large as MMAX with an applied field of 100 Oe. With further cooling, the magnetization increase and cross again M=0 around T2 (>∼10 K).

Spin resolved photoelectron spectroscopy from paramagnetic Gd at the 4d→4f resonance using circularly polarized radiation, a cross comparison with MCD

Spin resolved resonant photoemission from paramagnetic Gd(0001)/W(110) was performed in the 4d --> 4f excitation region using circularly polarized radiation from the new helical undulator UE 56/1 at BESSY II. The general spectral behaviour of the electron spin polarization, including changes of its sign, revealed in the Gd F-7 photoemission peak coincides with the MCD (magnetic circular dichroism) asymmetry from ferromagnetic Gd. This similarity is substantially due to the spin-orbit interaction, which identically determines the (primary) excitation in both processes. (C) 2001 Elsevier Science B.V. All rights reserved.

Photophysics of the triple state of metal complexes of 9-anthracenecarboxylic acid

The triplet-triplet (T-T) absorption spectra and the T-T absorption decay kinetics are measured for solutions of 9-anthracenecarboxylic acid (ACA) and its complexes with metal ions (Cd3+ and Ln3+=Y3+, La3+, Ce3+, Eu3+, Gd3+, and Tb3+) in dimethylsulfoxide (DMSO) by the methods of flashlamp and laser pulse photolysis. The rate constants kT of intracomplex quenching of the triplet state are measured for ACA complexes with ions Gd3+, Ce3+, Tb3+, and Eu3+. Larger values of kT in complexes of ACA with paramagnetic ions Ce3+, Tb3+, and Eu3+, which have low-lying energy levels, compared to the values of kT for complexes with other ligands (pyrene-3-sulfonate, pyrene-1,3,6,8-tetrasulfonate, and benzo[ghi]perylene-1,2-dicarboxylate) were explained by the lower energy of the triplet state of ACA (14400 cm−1). For a complex with a paramagnetic ion Gd3+, which has no low-lying energy levels, the value of kT is close to that measured by us earlier for the inner-sphere complex of pyrene-1,3,6,8-tetrasulfonate with the same ion. These results confirm our earlier assumption about the inner-sphere complexing of ACA with Ln3+ ions in DMSO.

Theories of structural and dynamic properties of ions in discrete solvents. Application to magnetic resonance imaging

Abstract The molecular Ornstein­Zernike (MOZ) formalism used to compute the structure of a liquid solution is briefly presented. Its ability to describe the equilibrium properties of aprotic solvents and of their electrolyte solutions is demonstrated from selected examples. The potential of mean force and the relative motion of ions in water are studied by the powerful method of intermolecular nuclear magnetic relaxation dispersion (NMRD) in paramagnetic solutions. The interest of the ion­ion dynamics in medical magnetic resonance imaging (MRI) is shown by a typical NMRD study involving paramagnetic gadolinium Gd3+ complexes.

Magnetic resonance imaging of the membranous labyrinth during in vivo gadolinium (Gd-DTPA-BMA) uptake in the normal and lesioned cochlea.

MRI with a T1 contrast agent was used to investigate the normal and noise-damaged cochlea. The time course and distribution of the in vivo uptake of the gadodiamide chelate bound paramagnetic Gd ion (GdDTPA-BMA) throughout the membranous labyrinth of normal and impulse noise-damaged guinea pig cochleae were measured by MRI at 4.7T. Simultaneous signal enhancement of the basal, medial and apical scala tympani (ST) and scala vestibuli (SV) was observed within 10 min following i.v. injection, reaching maximum levels at around 100 min. ANOVA and post hoc paired t-tests showed statistically significant differences in the levels and rates of Gd uptake-enhancement between the scalae. The ST revealed the most rapid and extensive enhancement throughout the period of active Gd uptake, while the SV showed comparatively slower and less enhancement, and the intact scala media (SM) indicated insignificant enhancement. The in vivo Gd penetration and enhancement of the membranous SM increased significantly in the noise-damaged cochlea, suggesting lesioning of the cochlear membranes.

Low-temperature 1H nuclear magnetic resonance study of crystal and electronic structures of the nearly stoichiometric yttrium dihydride

Abstract Proton nuclear magnetic resonance absorption spectra and spin-lattice relaxation rates in yttrium dihydride have been measured in the temperature range from 4.2 to 310K at 36.0MHz. The second moment of the resonance line corresponds to the rigid-lattice regime for YH1.99 and its value agrees with the anticipated CaF2 type of structure. The main contribution to the spin-lattice relaxation rate R 1 arises from conduction electrons and is characterized by R le = 2.77 × 10−3s−1 K−1 × T. Evidence of proton self-diffusion was seen in the linewidth and in R 1 for YH1.99+0.1. The onset temperature, about 250 K, of the self-diffusion, is close to the metal-semiconductor transition reported earlier for that hydride. Below that temperature the linewidth becomes temperature independent and the second moment of the line is explained in terms of different structure models. The fit to the temperature dependence of R 1 in the temperature range 70–310K gives R le = 2.1 × 10−3s−1K−1 × T. The relaxation becomes almost temperature independent below 50 K. Various mechanisms for this behaviour are discussed. In addition, the R 1 data for the sample prepared with yttrium of 99.9% purity are presented. In contrast with the previous case, where pure yttrium from the Ames Laboratory was used, R 1 has a large contribution of spin diffusion to the paramagnetic Gd3+ ions.

Ligand hyperfine interactions and the model of the paramagnetic center Gd3+ in α-LiIO3 single crystals

The ligand hyperfine interaction (HFI) of Gd3+ ions in α-LiIO3 single crystals is studied by the method of rf discrete saturation, and the tensor components of ligand HFI are determined. The model of a paramagnetic center is proposed on the basis of the analysis of the obtained results, and the mechanism of lattice distortion is discussed.

Heat capacity and transport studies of the ferromagnetic superconductorRuSr2GdCu2O8

Resistivity, thermoelectric power, and heat capacity are investigated in the ferromagnetic superconductor ${\mathrm{RuSr}}_{2}{\mathrm{GdCu}}_{2}{\mathrm{O}}_{8}$ with and without Zn substitution. The thermodynamic signatures of the ordering of the Ru moments and the paramagnetic Gd moments as well as the onset of superconductivity are all clearly seen and quantified. The materials are shown to exhibit bulk superconductivity which coexists with spatially uniform ferromagnetism. They appear to be typical underdoped superconducting cuprates in which the pseudogap dominates normal-state transport, thermodynamic, and substitutional properties. However, a field-induced increase in ${T}_{c}$ could suggest some degree of triplet pairing.

Thermal behavior of paramagnetic Gd3+ centers in CsSrCl3

The temperature dependence of the order parameters and the axial initial splitting parameter of Gd3+ impurity complexes is measured in the first low-symmetry phase of CsSrCl3, and the relationship between these parameters is found. The parameters of the thermodynamic potential, which takes into account the interaction of the order parameter with strains, are estimated. The nature of the temperature dependence of the axial initial splitting parameter in the cubic phase is explained.

Exchange interactions in nonmagnetic Kondo system Ce xGd 1− xCu 6− yMn y

Electron paramagnetic resonance on paramagnetic Gd 3+ and Mn 2+ impurities is studied in nonmagnetic Kondo system CeCu 6 in the temperature range 1.6–200 K. Parameters of exchange interactions of gadolinium and manganese ions as also that of cerium ions with the conduction electrons and cerium–cerium exchange constant are determined. Temperature dependence of cerium spins fluctuation rate is deduced and the Kondo temperature of cerium ions is estimated.

EPR study of exchange interactions in the nonmagnetic Kondo system La1−x CexCu6

The EPR of paramagnetic impurities Gd3+ and Mn2+ was studied in nonmagnetic Kondo system La1−xCexCu6 containing in the 1.6–200 K range. The exchange interaction parameters of gadolinium and manganese ions with conduction electrons, of cerium ions with conduction electrons and with one another, the Kondo temperature of cerium ions, and the temperature behavior of cerium-ion spin-fluctuation rate have been determined. A pseudogap in the density of states at the Fermi level has been detected in the CeCu6 regular system, which is apparently due to s-f hybridization. This pseudogap can be destroyed by introducing an aluminum impurity, which induces strong conduction-electron scattering. It was also found that RKKY interaction among manganese ions in CeCu6−yMny is considerably stronger than it is in LaCu6−yMny, which implies enhancement of nonlocal spin susceptibility due to an f band contribution to conduction-electron states.

Calcium Is Essential for the Structural Integrity of the Cysteine-Rich, Ligand-Binding Repeat of the Low-Density Lipoprotein Receptor

Seven cysteine-rich repeats form the ligand-binding region of the low-density lipoprotein (LDL) receptor. Each of these repeats is assumed to bind a calcium ion, which is needed for association of the receptor with its ligands, LDL and beta-VLDL. The effects of metal ions on the folding of the reduced N-terminal cysteine-rich repeat have been examined by using reverse-phase high-performance liquid chromatography to follow the formation of fully oxidized isomers with different disulfide connectivities. In the absence of calcium many of the 15 possible isomers formed on oxidation, whereas in its presence the predominant product at equilibrium had the native disulfide bond connectivities. Other metals were far less effective at directing disulfide bond formation: Mn2+ partly mimicked the action of Ca2+, but Ba2+, Sr2+, and Mg2+ had little effect. This metal-ion specificity was also observed in two-dimensional 1H NMR spectral studies; only Ca2+ induced the native three-dimensional fold. The two paramagnetic ions, Gd3+ and Mn2+, and Cd2+ did not promote adoption of a well-defined structure, and the two paramagnetic ions did not displace calcium ions. The location of calcium ion binding sites in the repeat was also explored by NMR spectroscopy. The absence of chemical shift changes for the side chain proton resonances of Asp26, Asp36, and Glu37 from pH 3.9 to 6.8 in the presence of calcium ions and their proximal location in the NMR structures implicated these side chains as calcium ligands. Deuterium exchange NMR experiments also revealed a network of hydrogen bonds that stabilizes the putative calcium-binding loop.

Towards MRI contrast agents of improved efficacy. NMR relaxometric investigations of the binding interaction to HSA of a novel heptadentate macrocyclic triphosphonate Gd(III)-complex

A novel heptacoordinating ligand consisting of a thirteen-membered tetraazamacrocycle containing the pyridine ring and bearing three methylenephosphonate groups (PCTP-[13]) has been synthesized. Its Gd(III) complex displays a remarkably high longitudinal water proton relaxivity (7.7 mM–1 s–1 at 25 °C, 20 MHz and pH 7.5) which has been accounted for in terms of contributions arising from (1) one water molecule bound to the metal ion, (2) hydrogen-bonded water molecules in the second coordination sphere, or (3) water molecules diffusing near the paramagnetic chelate. Variable-temperature 17O-NMR transverse relaxation data indicate that the residence lifetime of the metal-bound water molecule is very short (8.0 ns at 25 °C) with respect to the Gd(III) complexes currently considered as contrast agents for magnetic resonance imaging. Furthermore, GdPCTP-[13] interacts with human serum albumin (HSA), likely through electrostatic forces. By comparing water proton relaxivity data for the GdPCTP-[13]-HSA adduct, measured as a function of temperature and magnetic field strength, with those for the analogous adduct with GdDOTP (a twelve-membered tetraaza macrocyclic tetramethylenephosphonate complex lacking a metal-bound water molecule), it has been possible to propose a general picture accounting for the main determinants of the relaxation enhancement observed when a paramagnetic Gd(III) complex is bound to HSA. Basically, the relaxation enhancement in these systems arises from (1) water molecules in the hydration shell of the macromolecule and protein exchangeable protons which lie close to the interaction site of the paramagnetic complex and (2) the metal bound water molecule(s). As far as the latter contribution is concerned, the interaction with the protein causes an elongation of the residence lifetime of the metal-bound water molecule, which limits, to some extent, the potential relaxivity enhancement expected upon the binding of the paramagnetic complex to HSA.

Synthesis and NMR Studies of Three Pyridine-Containing Triaza Macrocyclic Triacetate Ligands and Their Complexes with Lanthanide Ions.

The synthesis of three triazamacrocycles containing the pyridine moiety and three acetate pendant arms (PCTA) is reported. The three systems differ due to the number of carbon atoms in the macrocyclic ring forming ligands PCTA-[12], -[13], and -[14], endowed with different coordination capabilities toward lanthanide(III) ions. Microscopic protonation sequences for the three ligands have been investigated by (1)H NMR spectroscopy. Complexes of PCTA-[12], -[13], and -[14] with La(III), Gd(III), and Lu(III) have been prepared. Relaxometric measurements on the aqueous solutions of the paramagnetic Gd(III) complexes in the presence of competitive ligands gave the following stability constants: log K(f) = 20.8 for Gd-PCTA-[12], log K(f) = 19.3 for GdPCTA-[13], and log K(f) = 12.5 for GdPCTA-[14]. The measurement of water relaxation rates indicated a tendency to decrease the degree of hydration upon increasing the ring size. The VT (1)H and (13)C-NMR spectra of the diamagnetic La(III) and Lu(III) complexes exhibit a large variability of the solution structures dictated by the matching of the size of the lanthanide ion and the macrocyclic cavity. This results in noticeable differences in their stereochemical nonrigidity, hydration state, and thermodynamic stability. To some extent the changes observed in continuing from the 12-14-membered ring macrocyclic complexes parallels the behaviors shown by the octacoordinated lanthanide(III) complexes with DOTA and TETA. GdPCTA-[12] and -[13] feature promising properties in view of their possible use as contrast agents for magnetic resonance imaging.

Synthesis, characterization and relaxivity of amphiphilic chelates of DTPA derivatives with Gd III, Yb III and Mn II

Some novel amphiphilic ligands were synthesized by the reaction of diethylenetriaminepentaacetic acid (DTPA) dianhydride and octadecylester of tyrosine or phenylalanine. Their paramagnetic Gd III, Yb III and Mn II metal complexes were also synthesized and characterized. The amphipathic metal complexes were inserted into the membrane of liposomal vesicles and the liposomes bearing metal complexes were obtained. The paramagnetic metal labeled liposomes show high spin-lattice relaxivity ( R 1) on the surrounding water protons.

The influence of Gd and Ni impurities on the superconducting transition temperature of UPt 3

The effect of Gd and Ni impurities on the upper superconducting transition temperature of UPt 3 ( T c + = 0.55 K) has been studied by means of resistivity measurements. Surprisingly, we find that paramagnetic Gd impurities suppress T c + at the same rate as non-magnetic Y or Th impurities, yielding further support for non-s-wave pairing. Ni impurities also suppress T c +, but do not dissolve homogeneously in the UPt 3 matrix.

Alkyl capped carbonates of?-cyclodextrin

The synthesis is described of alkyl capped carbonates ofβ-cyclodextrin, obtained from diols activated with carbonyldiimidazole. The reaction preferentially gave monocapped derivatives which were characterized by HPLC, TLC, FT-IR and13C-NMR. These compounds are stable at pH <7, and methyl orange was found to form stronger inclusion compounds with cappedβ-cyclodextrin than with the parentβ-cyclodextrin. Paramagnetic Gd(III) complexes were also studied, but they were found to be included into cappedβ-cyclodextrin as well as intoβ-cyclodextrin.

Temperature Dependence of the Mcxd at the GD Lm Edge

AbstractAn energy dispersive spectrometer is used to measure the temperature dependence of the Magnetic Circular X-ray Dichroism (MCXD) effect at the gadolinium (Gd metal) LIII absorption edge from 94 K to 335 K. In ferromagnetic Gd, the MCXD spectrum consists of the main positive peak with pre- and post-edge features. Only the main positive peak exhibits a temperature dependence similar to that of Gd magnetization. All other features decrease as the temperature increases and vanish slightly above the transition temperature (293 K). Well above the ordering temperature (paramagnetic Gd), the MCXD consists only of the positive peak, with a post-edge background that slowly decays away from it over a range of 90 eV.

Molecular Recognition of R- and T-States of Human Adult Hemoglobin by a Paramagnetic Gd(III) Complex by Means of the Measurement of Solvent Water Proton Relaxation Rate

Molecular Recognition of R- and T-States of Human Adult Hemoglobin by a Paramagnetic Gd(III) Complex by Means of the Measurement of Solvent Water Proton Relaxation Rate

Effects of paramagnetic lanthanide ions on decay process of photogenerated radical pairs in porphyrin-viologen linked compounds at reversed micellar surfaces

Radical pairs were generated in reversed micelles by laser excitation of zinc tetraphenylporphyrin-viologen linked compounds (ZPnV) with a polymethylene spacer (−(CH2)n−; n=4, 6 and 8). The optical transient-absorption and chemically induced dynamic electron polarization (CIDEP) spectra indicated that paramagnetic lanthanide ions invariably accelerated the decay process of the radical pairs at 0.3 T. The typical E/A/E/A spectra for the ZP6V and ZP8V systems were explained as due to S-T0 mixing and electron-spin relaxation between Zeeman-splitted triplet sublevels. In the case of ZP4V, the paramagnetic Gd3+ ion accelerated the radical decay process even at zero-magnetic field, and strong emissive CIDEP spectra evolved with the elapsed time after laser excitation. Appreciable contribution of S-T level crossing in the radical decay process was suggested to account for the novel features of the ZP4V system.