1,2-hydroxypyridonates as contrast agents for magnetic resonance imaging: TREN-1,2-HOPO

1,2-Hydroxypyridinones (1,2-HOPO) form very stable lanthanide complexes that may be useful as contrast agents for magnetic resonance imaging (MRI). X-ray diffraction of single crystals established that the solid-state structures of the Eu(III) and the previously reported [Inorg. Chem. 2004, 43, 5452] Gd(III) complex are identical. The recently discovered sensitizing properties of 1,2-HOPO chelates for Eu(III) luminescence [J. Am. Chem. Soc. 2006, 128, 10 067] allow for direct measurement of the number of water molecules coordinated to the metal center. Fluorescence measurements of the Eu(III) complex corroborate that, in solution, two water molecules coordinate the lanthanide (q = 2) as proposed from the analysis of NMRD profiles. In addition, fluorescence measurements have verified the anion binding interactions of lanthanide TREN-1,2-HOPO complexes in solution, studied by relaxivity, revealing only very weak oxalate binding (KA = 82.7 +/- 6.5 M-1). Solution thermodynamic studies of the metal complex and free ligand have been carried out using potentiometry, spectrophotometry, and fluorescence spectroscopy. The metal ion selectivity of TREN-1,2-HOPO supports the feasibility of using 1,2-HOPO ligands for selective lanthanide binding [pGd = 19.3 (2), pZn = 15.2 (2), pCa = 8.8 (3)].     

The 1H And 2H NMR Spectra Of HFeCo3 (CO)12

The detection of the ²H resonance of ²HfeCo₃ (CO)₁₂ led to the detection of the broader ₁H resonance of the ₁H isotopomer. The shift is -21.4 ppm.     

Study of structural and electronic transport properties of Ce-doped LaMnO3

The structural and electronic transport properties of La_1−x Ce _x MnO₃ (x=0.0–1.0) have been studied. All the samples exhibit orthorhombic crystal symmetry and the unit cell volume decreases with Ce doping. They also make a metal-insulator transition (MIT) and transition temperature increases with increase in Ce concentration up to 50% doping. The system La_0.5Ce_0.5MnO₃ also exhibits MIT instead of charge-ordered state as observed in the hole doped systems of the same composition.     

Relaxometric investigations and MRI evaluation of a liposome-loaded pH-responsive gadolinium(III) complex

Accurate measurement of the tissue pH in vivo by MRI may be of clinical value for both diagnosis and selection/monitoring of therapy. To act as pH reporters, MRI contrast agents have to provide responsiveness to pH that does not require prior knowledge of the actual concentration of the contrast agent. This work deals with the use of a paramagnetic gadolinium(III) complex, loaded into liposomes, whose relaxometric properties are affected by the pH of the medium. In this system, the amphiphilic metal complex, which contains a moiety whose protonation changes the coordination properties of the metal chelate, experiences a different intraliposomial distribution depending on the pH conditions. The pH of the solution can be unambiguously identified by exploiting the peculiar characteristics of the resulting NMRD profiles, and a ratiometric pH-responsive method has been set up by comparing the relaxation enhancement at different magnetic field strengths.     

Lanthanide(III) Complexes of Tris(amide) PCTA Derivatives as Potential Bimodal Magnetic Resonance and Optical Imaging Agents

Lanthanide complexes of two tris(amide) derivatives of PCTA were synthesized and characterized. The relaxometric and luminescence properties of their lanthanide complexes were investigated as bimodal magnetic resonance (MR) and optical imaging agents. Luminescence studies show that one of the Tb^III complexes dimerizes in solution at low millimolar concentrations, whereas the other may have a higher than expected coordination number in solution. The corresponding Gd^III complexes display unusually high T₁ relaxivities and enhanced kinetic inertness compared to GdPCTA. These features suggest that these new chelates may be suitable for in vivo applications. The fast water‐exchange rates observed for these complexes make them unsuitable as paramagnetic chemical exchange saturation transfer (PARACEST) agents.     

pH-dependent modulation of relaxivity and luminescence in macrocyclic gadolinium and europium complexes based on reversible intramolecular sulfonamide ligation

A series of macrocyclic Eu, Gd, and Tb complexes has been prepared in which the intramolecular ligation of a beta-arylsulfonamide nitrogen is rendered pH-dependent, giving rise to changes in the hydration state, q, at the lanthanide center. In complexes based on DO3A, variation of the p-substituent in the arylsulfonamide moiety determines the apparent protonation constant log K(MLH) with values of 5.7, 6.4, and 6.7 for the -CF(3), -Me, and -OMe substituents, respectively. Introduction of three beta-carboxyalkyl substituents, alpha to three ring nitrogens, inhibits displacement of the bound water by added protein and also suppresses intermolecular binding by endogenous anions (lactate, HCO(3)(-)). Measurements of the pH dependence of the form and intensity of the Eu complexes revealed that intramolecular carboxylate coordination occurred competitively. This was reduced either by enhancing the electron density at the sulfonamide nitrogen or by enlarging the chelate ring from 7--8. Amplification of the relaxivity changes in the pH range 8--5 occurred on protein binding, and over the pH range 7.4--6.8 a 48% change in relaxivity was defined for [Gd.3a] (298 K, 65.6 MHz) in 50% human serum solution.     

The influence of scanning rate in sequential analysis of fringes produced by a Michelson interferometer

The influence of sequential analysis rate on measurements of Michelson fringes is examined on a theoretical basis, sh whilst considering the special case where the elementary telescope pupils are small in comparison with Fried's parameter (r₀). As a result of this investigation it seems that the principal effect due to an insufficient scanning rate is a degradation of the spectral analysis window employed in the calculation of spatial energy spectra. This effect is related to Fried's parameter and to the wind speed. Taylor's hypothesis is employed in the calculation.The results obtained appear to be consistent with experimental observations.     

One-dimensional stellar and solar speckle interferometry

A new technique called “one-dimensional speckle-interferometry” is analysed. It appears to be a good compromise between standard speckle-interferometry and Michelson interferometry for precise, high resolution astronomical measurements.