1H NMR STUDY OF MIXED-LIGAND LANTHANIDE COMPLEXES. STOICHIOMETRY AND TEMPERATURE SENSITIVITY OF PARAMAGNETIC CHEMICAL SHIFTS OF PRASEODYMIUM β-DIKETONATES AND THEIR COMPOUNDS WITH 18-CROWN-6

Journal of Structural Chemistry - Complexes [(Pr(DPM)3)2], [Pr(DPM)3(18-crown-6)], [(Pr(DPM)3)2(18-crown-6)], [Pr(DPM)(PTA)(18-crown-6)]+ and the temperature sensitivity of paramagnetic...     

Paramagnetic Properties and Complexation Kinetics of Edta With Praseodymium and Holmium(III) Cations in Aqueous Solution

The NMR method is used to study the features of the complexation kinetics of paramagnetic lanthanide cations with EDTA in aqueous media at temperature and pD variation. The acidity of solutions is determined by the potentiometric method with a glass electrode. By the dynamic NMR method it is found that the activation enthalpy of the association between EDTA complexones and Ln cations is ΔH = 71±5 kJ/mol in a temperature range from 290 K to 368 K (at pD = 1.6). The obtained results indicate that Ho and Pr complexes with EDTA are promising compounds as in vivo NMR thermosensors for biology and medicine.     

NMR studies of mixed-ligand lanthanide complexes. Reaction of β-diketonates of the yttrium subgroup with 18-crown-6

Institute of Inorganic Chemistry, Siberian Branch, USSR Academy of Sciences. Translated from Zhurnal Strukturnoi Khimii, Vol. 31, No. 3, pp. 44–47, May–June, May–June, 1990.     

Study of magnetoresistance and conductance of bicrystal grain boundary in La0.67Ba0.33MnO3 thin film

La_0.67Ba_0.33MnO₃ (LBMO) thin film is deposited on a 36.7°C SrTiO₃ bicrystal substrate using laser ablation technique. A microbridge is created across bicrystal grain boundary and its characteristics are compared with a microbridge on the LBMO film having no grain boundary. Presence of grain boundary exhibits substantial magnetoresistance ratio (MRR) in the low field and low temperature region. Bicrystal grain boundary contribution in MRR disappears at temperature T>175 K. At low temperature, I-V characteristic of the microbridge across bicrystal grain boundary is nonlinear. Analysis of temperature dependence of dynamic conductance-voltage characteristics of the bicrystal grain boundary indicates that at low temperatures (T<175 K) carrier transport across the grain boundary in LBMO film is dominated by inelastic tunneling via pairs of manganese atoms and tunneling through disordered oxides. At higher temperatures (T>175 K), magnetic scattering process is dominating. Decrease of bicrystal grain boundary contribution in magnetoresistance with the increase in temperature is due to enhanced spin-flip scattering process.     

NMR applications for a study of converted photochemical processes kinetics

The analytical expression describing dynamics of the nuclear magnetization with the use of double resonance nuclear magnetic resonance of a procedure of transfer of spin saturation under photo-induced chemical exchange is obtained. Three different experimental procedures for the definition of the effective rate constants and the quantum yield of responses are considered.     

Self-injection length in La0.7Ca0.3MnO3-YBa2Cu3O7-δ ferromagnet-superconductor multilayer thin films

We have carried out extensive studies on the self-injection problem in barrierless heterojunctions between La_0.7Ca_0.3MnO₃ (LCMO) and YBa₂Cu₃O_7-δ (YBCO) thin films. The heterojunctions were formed in situ by sequentially growing LCMO and YBCO films on 〈100〉 LaAlO₃ (LAO) substrate using a pulsed laser deposition (PLD) system. YBCO micro-bridges with 64 μm width were patterned both on the LAO (control) and LCMO side of the substrate. Critical current, I _c, was measured at 77 K on both the control side as well as the LCMO side for different YBCO film thickness. It was observed that while the control side showed a J _c of ∼ 2 × 10⁶ A/cm², the LCMO side showed about half the value for the same thickness (1800 ?). The difference in J _c indicates that a certain thickness of YBCO has become ‘effectively’ normal due to self-injection. From the measurement of J _c at two different thicknesses (1800 ? and 1500 ?) of YBCO films both on the LAO as well as the LCMO side, the value of self-injection length (at 77 K) was estimated to be ∼ 900 ?. To the authors’ best knowledge, this is the first time that self-injection length has been quantified. A control experiment carried out with LaNiO₃ deposited by PLD on YBCO did not show any evidence of self-injection.     

Molar extinction coefficients of some carbohydrates in aqueous solutions

Molar extinction coefficients of some carbohydrates viz. l-arabinose (C₅H₁₀O₅), d-glucose (C₆H₁₂O₆), d-mannose (C₆H₁₂O₆), d-galactose (C₆H₁₂O₆), d(-) fructose (C₆H₁₂O₆) and maltose (C₁₂H₂₄O₁₂) in aqueous solutions have been determined at 81, 356, 511, 662, 1173 and 1332 keV by gamma ray transmission method in a narrow beam good geometry set-up. These coefficients have been found to depend upon the photon energy following a 4-parameter polynomial. These extinction coefficients for different sugars having the same molecular formula have same values varying within experimental uncertainty. Within concentration ranges studied, Beer-Lambert law is obeyed very well.     

Lanthanide complexes with polyaminopolycarboxylates as prospective NMR/MRI diagnostic probes: peculiarities of molecular structure,dynamics and paramagnetic properties

Journal of Inclusion Phenomena and Macrocyclic Chemistry - The paramagnetic lanthanide complexes with polyaminopolycarboxylate (PAPC) ligands attract considerable attention from the standpoint of...